Browsing by Subject "Behavioral Neurobiology"
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Item Cellular and Molecular Mechanisms that Distinguish the Effects of Progestorone and Medroxyprogesterone Acetate on Neuroprotection(2006-07-28) Kaur, Paramjit; Goldfarb, Ronald; Singh, Meharvan; Agarwal, NeerajKaur, Paramjit. Cellular and Molecular Mechanisms That Distinguish the Effects of Progesterone and Medroxyprogesterone Acetate on Neuroprotection., Doctor of Philosophy, (Pharmacology and Neuroscience), July, 2006, 203 pp., 5 illustrations, 20 figures and bibliography. Women have a higher prevalence for Alzheimer’s disease (AD) than men, suggesting that the precipitous decline in gonadal hormone levels following the menopause may contribute to the risk of developing AD. However, principal results from the Women’s Health Initiative concluded that women taking conjugated equine estrogens combined with medroxyprogesterone acetate (MPA, tradename: Prempro) incurred more harmful than beneficial outcomes versus the placebo group (Rossouw et al., 2002). This dissertation was aimed at determining if the discrepancy between basic science reports and these clinical studies could have been due to the synthetic progestin, MPA. I hypothesized that P4 and MPA differed in their ability to protect against the excitotoxic/oxidative insult, glutamate. Further, I proposed that this difference in neuroprotective potential would be reflected in the difference in the ability of these hormones to elicit key effectors of two neuroprotection-associated signaling pathways, the ERK/MAPK and P13-Kinase pathways. Finally, studies were initiated to evaluate the potential importance of BDNF (brain-derived neurotrophic factor) in mediating the protective effects of P4. I used organotypic explants of the cerebral cortex, and found that both P4 and MPA elicit the phosphorylation of ERK and Akt, two signaling pathways implicated in neuroprotection, with maximal phosphorylation occurring at a concentration of 100 nM. Interestingly, P4 protected against glutamate- induced toxicity however, while an equimolar concentration of MPA (100nM) did not. Further, P4 resulted in an increase in BDNF, while MPA did not. Our data bring into question the relevance of using MPA as a component of hormone therapies in postmenopausal women, and instead, argue that the relevant progestin for use in treating brain-related disorders is progesterone. Collectively, the data presented here suggest that P4 is protective via multiple, and potentially related mechanism, and importantly, its neurobiology is different from the clinically used progestin, MPA.Item Characterization of the Serotonin Receptors in the Long Posterior Ciliary Artery of the Bovine Eye(2000-08-01) Landry, Theresa A.; Quist, Eugene; Martin, Michael; Pang, Iok-HouLandry, Theresa A., Characterization of the Serotonin Receptors in the Long Posterior Ciliary Artery of the Bovine Eye. Doctor of Philosophy (Biomedical Science), August 2000, 14 pp., 5 tables, 29 illustrations, bibliography, 104 titles. Vascular disease and vasospasm are implicated in the etiology of glaucoma. The long posterior ciliary (LPCA) is the major blood supply for the ciliary body including the ciliary processes that produce aqueous humor. Information about the pharmacological control of this vessel would be helpful in understanding its normal and pathologic function. Serotonin (5-HT) is a neurotransmitter that effectively constricts the LPCA. The objective of this research is to identify the serotonin receptor subtype responsible for the 5-HT induced vasoconstriction of the LPCA and to characterize the cellular mechanisms that mediate that contraction. Ring segments of the LPCA were dissected from bovine eyes and mounted on tungsten triangles attached to a force transducer. Changes in vascular tension were measured and recorded using a physiography recorder. Dose response curves with 5-HT, 5-HT 1-like agonist, 5-CT, and 5-HT2 agonist, α-methyl-5-HT, indicate that the 5-HT 1-like receptor contributed about 15.13% to the contraction and the 5-HT2 receptor contributed to 61.61%. The EC50 for the three agonists were 283 nM (5-HT), 336 nM (5-CT), and 1.7 μM (α-methyl-5-HT). Inhibition curves with selective antagonists indicate that the IC50 is (5-HT 1-like antagonist) and ketanserin (5-HT2 antagonist). Following incubation of the rings with diltiazem 10 μM or nifedipine 10μM, the response to 5-HT was reduced 65.*% and 61.7% respectively. Incubation in calcium free PB produced similar results. Ryanodine inhibited the 5-HT contraction by 58.1% and caffeine inhibited the response 100%. PKC inhibitors bisindolymaleimide II 1 μM, disindolylamalemide II 10 μM, chelerythrine 25 μM and H-7 5 μM decreased the 5-HT response by19.8%, 55.7%, 31.1% and 61.5% respectively. Incubation of the ring segments with one of three PLC antagonists, 2-NCDC 70 μM, U73122 0.5μM, or neomycin 5 mM, prior to the addition of 1 μM serotonin, significantly reduced the contraction of each vessel, p [less than] 0.0001. The 5-HT-induced vasoconstriction of the LPCA of the bovine eye is mediated through activation of both 5-HT2 and 5-HT 1-like receptors. The contraction is dependent on the mobilization of calcium and is mediated in part through PLC activated intracellular calcium release from IP3 sensitive stores.Item Corticotropin-Releasing Factor and Corticosterone Modulate the Anxiogenic-Like Effects of mCPP(1998-06-01) Jenkins, Jennifer A.; Michael Forster; Robert Luedtke; Patricia GwirtzJenkins, Jennifer A., Corticotropin-Releasing Factor and Corticosterone Modulate the Anxiogenic-Like Effects of mCPP. Doctor of Philosophy (Pharmacology), June 1998, 119 pp., 2 tables, 29 figures, bibliography, 100 titles. The administration of PTZ or mCPP produces anxiety-like behavior as measured by an increase in the percentage of entries into the open arms and the time spent on the open arms of the elevated plus maze (Prunell et al., 1994). Reportedly, PTZ and mCPP substitute for each other in the drug discrimination paradigm (Wallis and Laz, 1998). It is therefore suggested that commonality exists among anxiogenic drugs as perceived by trained animals. Andrews and Stephen (1990) suggested that this overall parallelism is an indication that anxiogenic agents may possess similar properties. Therefore, the question posed is as follows: Is there a common denominator anxiety? The global hypothesis is that the core component of anxiety produced by anxiogenic agents or processes involves stimulation of the HPA axis to release CRF, ACTH and/or CORT. Long Evans rats were trained to discriminate either mCPP (1.4 mg/kg) or PTZ (16mg/kg) from saline in a two-lever choice procedure (FR10) which is food reinforced. Animals were pretreated with CRF, α-helical CRF (a CRF antagonist), two steroid synthesis inhibitors (ketoconazole, KETZ and aminoglutethimide, AMG), CORT or underwent an adrenalectomy prior to behavioral testing in order to test the hypothesis that the release of CRF and/or CORT are components of the discriminate stimulus of the mCPP and/or PTZ. Pretreatment with CRF, KETZ, AMG and an adrenalectomy facilitated mCPP level selection. However in the absence of mCPP neither drug nor adrenalectomy produced drug lever selection. In addition CORT did not alter the mCPP dose response curve. However, CORT replacement therapy returned the does response curve to baseline in adrenalectomized animals. Alpha-helical CRF did not block mCPP discrimination. Unlike mCPP-trained animals, KETZ and AMG decreased PTZ-lever selection in PTZ-trained animals. In addition, CORT enhanced and partially substituted for the discriminative stimulus of PTZ. However, adrenalectomy completely abolished drug lever selection in PTZ animals. To compare the discriminative stimulus effects of mCPP and PTZ, PTZ-trained animals were injected with cumulative doses of mCPP. mCPP-trained animals were injected with cumulative doses of PTZ. mCPP and PTZ minimally substituted for each other. The results suggested that neither CRF nor CORT are components of the discriminative stimulus of mCCP and that the role of the HPA axis in mCPP discrimination maybe be a modulator of the stress response. However, CORT is a component of the discriminative stimulus of PTZ such that CORT is necessary for drug lever selection in PTZ trained animals.Item Discriminative and Negative Reinforcing Properties of the Periaqueductal Gray and the Medial Hypothalamus(1994-12-01) Jung, Marianna E.; Emmett-Oglesby, Michael W.; Yorio, ThomasMarianna Eunsun, Jung, Discriminative and Negative Reinforcing Properties of Electrical brain stimulation of the Periaqueductal Gray and the Medial Hypothalamus. Master of Science [Biomedical Sciences, (Pharmacology)], December, 1994, 123 pp., 24 figures, references, 137 titles. Electrical brain stimulation (EBS) of the periaqueductal gray (PAG) and the medial hypothalamus (MH) is known to serve as a discriminative and a negative reinforcing stimulus (NRS). Using a two-lever food reinforced discrimination paradigm and a switch-off paradigm, the present study investigated the effects of anxiolytic drugs and an anxiogenic drug on these stimulus effects. A prototypic anxiogenic, pentylenetetrazole (PTZ) potentiated both discriminative stimulus and NRS effects, whereas the full benzodiazepine (BZD) agonist diazepam (DZP), the partial BZD agonist abecarnil (ABC) and 5-HT1A agonist buspirone (BUS, chronic regimen) attenuated a NRS effect. A BZD antagonist, flumazenil (FLU) blocked the effects of DZP and ABC on the NRS effects. DZP failed to attenuate the discriminative stimulus effect. Thus, present study extended the use of a switch-off paradigm to detect novel anxiolytic ABC (putative) and BUX as well as an anxiogenic PTZ. In addition, under the condition used in this study, the use of NRS in a switch-off paradigm more reliably detected both anxiolytic drugs and an anxiogenic drug than the use of discriminative stimulus in a two-lever food reinforced paradigm.Item Interactive Effects of Mental and Physical Stress on Cardiovascular Control(1998-08-01) Westerholm, Erin Carpenter; Smith, Michael; Raven, Peter B.; Shi, XiangrongWesterholm, Erin C., Interactive Effects of Mental and Physical Stress on Cardiovascular Control. Master of Science (Biomedical Sciences, Integrative Physiology), August, 1998, 42 pp., 1 table, 13 figures, 35 references. Mental task and exercise often occur together. Physiological responses to each of these stressors have been studied independently, yet the interactive effects of these stressors are unknown. Hypothesis: Combined mental and physical stress will produce a synergistic interaction. Methods: Twelve healthy subjects were studied by measuring cardiovascular responses to five minutes of static left handgrip alone (25-35% of maximal handgrip strength), mental arithmetic alone, and combined stimuli in random order. Sympathetic nerve activity (SNA, microneurography), mean arterial blood pressure (MAP, Finapres), heart rate (HR, ECG), and vascular resistance (Doppler) were measured. Results: Physical and combined stressors significantly changed SNA, MAP, HR, and FVR. SNA responses to handgrip and the combined stimuli exceeded responses to mental arithmetic alone (p [less than] 0.05), yet no significant difference existed between responses to handgrip alone and the combined stimuli (p=0.33). The three stimuli increased heart rate similarity (p [less than] 0.0006). Conclusion: The data refuted the hypothesis: mental task did not synergistically interact or even add to the stress response elicited by handgrip exercise. Thus these data suggest that mental task and static exercise interact in a redundant manner.Item Mechanisms of Chemoreflex Control of Muscle Sympathetic Nerve Activity and Blood Pressure in Humans(2004-05-01) Hardisty, Janelle M.; Smith, Michael; Shi, Xiangrong; Clark, MichaelHardisty, Janelle M., Mechanisms of Chemoreflex Control of Muscle Sympathetic Nerve Activity and Blood Pressure in Humans. Doctor of Philosophy (Integrative Physiology), May 2004. The mechanisms linking obstructive sleep apnea (OSA) and cardiovascular disease are not fully understood; however, studies report patients with OSA exhibit chronic elevations in muscle sympathetic nerve activity (MSNA). This appears to be due to altered chemoreflex control of MSNA, mediated primarily by hypoxia. Yet, a correlation between degree of hypoxia and chemoreflex control of MSNA is unknown. Therefore, it was evaluated whether degree of hypoxia occurring during apnea determines the sympathoexcitatory and blood pressure responses, and whether these responses are augmented in OSA patients. Additionally, it was studied whether altered chemoreflex function in OSA patients is predictive of blood pressure response to apnea. In a clinical setting, the blood pressure response to voluntary apnea was determined to evaluate whether this could be used as a non-invasive measure of chemoreflex gain in OSA. Finally, the effect of hyperoxia on MSNA was studied to determine whether 15 min of hyperoxia, following intermittent hypoxic apnea, reverses the elevation of MSNA and altered chemoreflex control of MSNA. Consistent with the hypotheses, a relationship between MSNA responses, blood pressure response and level of hypoxia were determined. MSNA and peak systolic pressure responses were augmented in OSA subjects (p≤0.05 and p≤0.05, respectively), as well as, chemoreflex gain (p≤0.05). Clinically, peak systolic pressure responses to apnea were augmented in OSA patients (p˂0.001). Finally, basal MSNA and chemoreflex control of MSNA, following hyperoxia, was not different from baseline through 180 min of recovery (p=0.940 and p=0.278, respectively). These data support the hypotheses that chemoreflex gain is predicative of the blood pressure response; and furthermore, the MSNA and blood pressure responses to hypoxic apnea are augmented in OSA. Additionally, peak systolic pressure responses to voluntary apnea are augmented in OSA. Additionally, peak systolic pressure responses to voluntary apnea are augmented in OSA patients and could possibly be used as a marker of chemoreflex gain. Moreover, these data support the hypothesis that hyperoxia can reverse basal sympathoexcitation and augmented chemoreflex control of MSNA, associated with hypoxic apnea, supporting that elevations in MSNA are hypoxia mediated.Item Met-Enkephalin-Arg-Phe (MERF) and Metabolism of MERF Across the Canine Heart Vascular Bed(2000-08-01) Pearlman, Eric Brian; Barbara Barron; Patricia A. Gwirtz; Michael L. SmithPearlman, Eric B., Met-Enkephalin-Arg-Phe (MERF) and Metabolism of MERF Across the Canine Heart Vascular Bed. Master of Science (Biomedical Science), August, 2000, 37 pp., 3 tables, 11 figures, references, 20 titles. Methionine enkephalin arginine phenylalanine (MERF) has been shown to be co-stored with catecholamines in vesicles. The catecholamines appear to decrease the degradation rate of 3H-MERF in vitro. The aim of this study is to investigate the spillover and metabolism of MERF across the canine heart vascular bed. I hypothesize that 3H-MERF is either degraded in the plasma or taken up and degraded by the heart. I further hypothesize that the exogenous catecholamine, isoproterenol, inhibits or reduces the rate of MERF degradation. Mongrel dogs were anesthetized and instrumented to record cardiovascular parameters, infuse 3H-MERF, and obtain blood samples across the heart. Blood samples were taken before and after stopping 3H-MERF infusion to evaluate kinetics, show steady state, and test the effect of treatments. Steady state concentration of 3H-MERF was observed after 30 min of infusion. Chromatography separated intact from degraded 3H-MERF. Three experimental groups were used: control, propranolol plus isoproterenol, and propranolol only. Blockade of β-receptors was necessary to prevent changes in coronary blood flow. Propranolol bolus (0.2 mg/kg) was administered IV at 50 min. 3 μg/min isoproterenol or 0.5 ml/min normal saline was infused starting at 70 min until the end of sample collection. The 3H-MERF venous-arterial (V-A) difference prior to treatment was negative, indicating degradation in the plasma or uptake and degradation by the heart. The 75 min V-A difference was used to calculate the effect of the infusions on the degradation or uptake of the 3H-MERF; this value was unchanged by any treatment. Spillover of 3H-MERF was significantly lower in the propranolol + isoproterenol dogs (p [less than] 0.05) compared to propranolol only treatment at 75 min. Heart rate was significantly lower for the propranolol only group compared to control. Blood pressure and change in coronary flow were unchanged. In conclusion, isoproterenol does not affect the metabolism of 3H-MERF across the canine heart vascular bed. Propranolol, however, does increase the intact 3H-MERF in the plasma, but additional β adrenergic blockade agents need to be investigated to determine the mechanism by which this takes place.Item Sexually Dimorphic Anxiety-Like Interoceptive Discriminative Stimuli(1997-12-01) Jung, Marianna E.; Walls, Cleatus; Downey, H. Fred; Forster, MichaelJung, Marianna E., Sexually Dimorphic Anxiety-Like Interoceptive Discriminative Stimuli. Doctor of Philosophy (Biomedical Sciences), December 1997, 150 pp, introduction, 2 chapters, discussion, bibliography, 109 titles. This study compared gender differences in the anxiogenic stimuli induced by either a GABA-A antagonist, pentylenetetrazol (PTZ) or by a 5-HT1b/2 agonist, m-chlorophenylpiperazine (m-CPP) before and during ethanol withdrawal (EW). Rats were trained to discriminate either PTZ (16mg/kg, IP) or m-CPP (1.2 mg/kg, IP) from saline in a two lever choice task for food reward. Male and female rats were gonadectomized or sham-operated, and ovariectomized (OVX) female rats were tested during replacement treatment with 17β estradiol (2.5 mg, 21 day release, sc). The dose-response for the discrimination of the interoceptive stimulus (IDS) produced by PTZ (0-16 mg/kg) or m-CPP (0 to 1.2 mg/kg) was measured under all hormonal conditions. For m-CPP trained rats, latency to first lever-press response was also tested. Results: sham and estradiol-replaced female rats had higher ED50s for discrimination of the PTZ or m-CPP IDS than intact males or OVX rats. There is a dose-related impairment of operant responding after mCPP injection. Sham and estradiol replaced OVX rats showed an increased delay to the initiation of response after m-CPP injection as compared to sham or castrated male rats or OVX rats that showed no effect at the doses tested. Rats then received a chronic ethanol diet (6.5%) for 10 days. At twelve hours of ethanol withdrawl, they were tested for lever selection after saline injection. Fewer sham female and estradiol-replaced female rats responded on the drug lever during acute EW as compared to sham male, castrated or OVX rats. In general, the anxiogenic drug lever selection of OVX rats resembled that of male rats but was restored toward that of sham female rats by estradiol replacement. Castration did not alter the response of male rats to either PTZ or mCPP. Serum β –estradiol concentrations were determined by radioimmunoassay for sham, OVX, and estradiol-replaced female rats. The concentration was significantly higher in hormone-replaced female rats than in OVX. The estradiol concentration in sham female rats showed a cyclic pattern over 4 consecutive days, but this pattern did not correlate with any difference in IDS. Blood ethanol concentration (BEC) was determined using head space gas chromatography. BEC was higher in intact female rats than in intact male rats after ethanol injection (2 g/kg, ip), but did not differ during EW. Conclusions: females produce less anxiogenic IDS in response to either GABA inhibition or 5-HT1b/2 activation, but are more impaired by m-CPP in their ability to initiate operant responses than male rats. In addition, fewer intact females developed a spontaneous IDS during EW than males which is not the result of lower BEC. Estrogen appears to play a trophic role in altering responsiveness to anxiogenic stimuli.Item The Effect of Late-Life Antioxidant Supplementaion on Brain Function(2007-10-01) Shetty, Ritu A.; Forster, Michael J.; Sumien, Nathalie; Singh, MeharvanShetty, Ritu A., The effect of late-life antioxidant supplementation on brain function. Doctor of Philolosophy (Biomedical Sciences), October, 2007, 229 pp., 5 tables, 18 figures, bibliography, 284 titles. Purpose: Aging is associated with mild to moderate loss in brain function over time. These functional losses are thought to involve reversible changes disrupting important cellular signaling processes. One of the theories that proposes to explain the reversible losses of function is the ‘oxidative stress’ hypothesis of aging. According to the oxidative stress hypothesis, there is an inherent cellular imbalance between production of oxidants and antioxidative defenses that increases with age and that leads to an increase in oxidative damage to macromolecules that are involved in crucial cell functions. Previous studies have established a link between these cellular changes associated with aging and the impairments in cognitive and psychomotor function. Further it has also been suggested that dietary interventions can modulate the level of oxidative stress, reducing oxidative damage and perhaps even ameliorate age-related dysfunction. Most interventions have been implemented relatively early in life and maintained until old age. However, the current studies were based on the rationale that interventions initiated in late-life could potentially lower oxidative damage and thereby alter cellular components responsible for functional impairments. Methods: In study I, separate groups of young (4 months) and old mice male C57BL/6 (18 months) were fed a control diet or a diet supplemented with low (105 mg/kg/day) or high (368 mg/kg/day) concentrations of CoQ10 for a period of 15 weeks. After 6 weeks on the diets, the mice were subjected to a battery of age-sensitive behavioral tests. In study II, separate groups of male C57BL/6 young mice aged 3-4 months and old mice 17-18 months (total of n=124) were fed ad libitum either a control diet (cyclodextrin in base diet), or the same diet supplemented with D- α-tocopheryl acetate (Toc) (200 mg/kg body wt/day), or with CoQ10 (148 mg/kg body wt/day) or a diet containing a combination of CoQ and Toc (200 mg/kg body wt/day + 148 mg/kg body wt/day) for a period of 13-14 weeks. In both studies mice were subjected to a battery of behavioral tests that required utilization of various component of memory and learning and sensorimotor reflexes. Results: In study I, low CoQ10 failed to improve cognitive and psychomotor function in old mice. However, the high CoQ10 marginally helped the old mice to navigate in the swim maze task with greater efficiency than control mice but did not affect their performance in probe trials. Conversely, the high CoQ10 diet selectively impaired the spatial performance in young mice in probe trials. The results from study I indicated that intake of CoQ10 initiated in late-life had minimal beneficial effects on behavior function. In study II, an age-associated decline of behavioral functioning was observed; however CoQ10 treatment failed to improve the performance of mice in any of the age-sensitive tests. Moreover, young mice supplemented with a high CoQ diet performed poorly in the probe trial in a swim maze task, suggesting a possible deleterious effect. The results from study II indicated that there was a significant improvement in performance of old mice in the coordinated running and the learning ability in discriminated avoidance task when supplemented with Toc or with a combination of CoQ10 and Toc. Conclusions: In conclusion, these studies suggest that benefits of single antioxidant supplementation when initiated late in life are limited; however dietary supplementation with a combination of antioxidants has a greater impact in reversing age-related decline in behavioral function.Item The Effects of Short-Term Intermittent Hypoxic Apneas on Sympathetic Nerve Activity and the Chemoreflex Control of Sympathetic Nerve Activity in Humans(2004-05-01) Cutler, Michael J.; Smith, Michael L.; Raven, Peter B.; Downey, H. FredCutler, Michael J., The Effects of Short-Term Intermittent Hypoxic Apneas on Sympathetic Nerve Activity and the Chemorelex Control of Sympathetic Nerve Activity in Humans. Doctor of Philosophy (Integrative Physiology), May 2004. Obstructive sleep apnea is associated with sustained elevation of muscle sympathetic nerve activity (MSNA) and altered chemoreflex control of MSNA both of which likely play an important role in the development of hypertension in these patients. Hypoxia is postulated to be primary stimulus for elevated daytime MSNA and altered chemoreflex control of MSNA both of which likely play an important role in the development of hypertension in these patients. Hypoxia is postulated to be the primary stimulus for elevated daytime MSNA and altered chemoreflex control of MSNA in OSA patients. Recently, short-term exposure to hypoxia was shown to produce sustained elevation of MSNA. Therefore, we studied the effects of 20 min of intermittent voluntary hypoxic apneas (to mimic OSA) on MSNA and the chemoreflex control of MSNA during 180 min post exposure. Also, we compared MSNA and chemoreflex control of MSNA for 180 min following either 20 min of intermittent voluntary hypoxic apneas, hypercapnic hypoxia, or isocapnic hypoxia. Consistent with our hypotheses, both total MSNA and MSNA burst frequency were elevated following 20 min of intermittent hypoxic apnea compared to baseline (p [less than] 0.05). Both total MSNA and MSNA burst frequency remained elevated throughout the 180 min recovery period and were statistically different from time control subjects throughout this period (p [less than] 0.05). Additionally, a significant main effect for chemoreflex control of SNA was observed following 20 min of intermittent hypoxic apneas (p [less than] 0.001). Specifically, the MSNA response to a single hypoxic apnea was attenuated 1 min post exposure compared to baseline (p [less than] 0.001), became augmented within 30 min of recovery, and remained augmented through 165 min of recovery (p [less than] 0.05). Finally, comparison of treatment groups (hypoxic apnea, hypercapnic hypoxia, and isocapnic hypoxia) revealed no differences in resting MSNA (p=0.50) and the chemoreflex control of MSNA (p=0.69) during recovery. Therefore, these data support the hypothesis that short-term exposure to intermittent hypoxic apneas resulted in sustained elevation of MSNA and altered chemoreflex control of MSNA. Furthermore, these responses appear to be mediated by hypoxia.Item The Influence of CNS stimulants, opioid antagonists and an NMDA antagonist on the reinforcing effect of cocaine using a progressive-ratio schedule(1996-07-01) Li, Donghang; Forster, Michael J.; Martin, Michael; Luedtke, Robert R.It has been hypothesized that there is a common dopaminergic pathway mediating the reward properties of abused drugs, and that dopamine is involved in tolerance to the reinforcing effect of cocaine. The progressive-ratio (PR) schedule can be used to test both potentiation and reduction of the reinforcing effects of cocaine by other factors. Under the PR schedule, an increasing number of responses is required to obtain each subsequent cocaine injection, and failure to complete the required number of responses within 1 h of the previous cocaine injection terminates the session. The number of total reinforcers obtained during a session is defined as “the breaking point” and was used as the primary dependent measure. Fisher F344 male rats acquired the self-administration task under the PR schedule within forty sessions and showed a stable daily acquisition baseline. The breaking point and inter-reinforcer time (ISRT) were positively correlated within each ratio. A motor-incapacitating side effect of a pretreatment can be determined by a change in the relationship between the ISRT and the breaking point. d-Amphetamine pretreatment (0.32-3.2 mg/kg, i.p., 30 min) potentiates the reinforcing effect of cocaine as demonstrated by a higher breaking point of self-administration without changing the ISRT. Morphine pretreatment (0.32-3.2 mg/kg, i.p., 30 min failed to change the breaking point of cocaine self-administration but it did increase the ISRT. These results support an additive reinforcing effect for amphetamines and cocaine, but do not support an additive reinforcing effect of morphine and cocaine. The reinforcing effect of cocaine was reduced by pretreatment with ketamine (0.032-0.32 mg/kg, i.p., 20 min) as indicated by a reduction in the breaking point. In a concurrent experiment, animals were trained to self-administer cocaine under a fixed ratio 2 schedule (FR2). Ketamine pretreatment did not modify the ISRT in FR2 trained animals except at the highest dose (0.32 mg/kg, i.p., 20 min), where significant motor incoordination was observed. Both chronic treatment with cocaine (20 mg/kg/ 8hr x 7 days, iv) or amphetamine (3.2 mg/kg /12 hr x 7 days, i.p.) resulted in a reduction in breaking point at any given dose, providing direct evidence of tolerance and cross-tolerance to the reinforcing effects of cocaine. Chronic treatment with ketamine (0.32 mg/kg/8hr x 7 days, i.v.) failed to modify either the breaking point under a PR schedule of reinforcement or the ISRT under a FR2 schedule of reinforcement. Co-administration of ketamine (0.32 mg/kg/8hr x 7 days, i.v.) with chronic cocaine (20 mg/kg/8hr x 7days, i.v.) failed to prevent tolerance to the reinforcing effect of cocaine as indicated by either the breaking point under a PR schedule of reinforcement of the ISRT under an FR2 schedule of reinforcement. These data indicate that the breaking point in the PR schedule is more sensitive to changes in the dopamine reward system, whereas changes in rate of response are not consistently related to the changes in the dopamine reward system. These data support the use of PR schedule as a better method than FR schedule for determining reward properties of drugs of abuse with fewer complications due to the central nervous system inhibitory effects of some drugs of abuse.Item The Role of Advanced Glycation End Products in Brain Aging(2007-10-01) Thangthaeng, Nopporn; Michael J. Forster; Tina MachuThangthaeng, Nopporn, The Role of Advanced Glycation End Products in Brain Aging. Doctor of Philosophy (Biomedical Sciences), October, 2007, 178 pp., 9 tables, 6 figures, bibliography, 213 titles. Glycoxidation is a process of post-translational modification of proteins, involving both glycation and oxidation that ultimately generated advanced glycation end products (AGEs). Glycoxidation, which pay promote oxidative stress and disrupt protein structure and function, is hypothesized to be responsible for pathological conditions related to aging, diabetes, neurodegenerative diseases, and degenerative ophthalmic diseases. Previous studies have demonstrated that AGEs accumulate in the brains of aged animals and humans, yet few studies have directly addressed the possibility that AGEs are a cause of age-related brain dysfunction. Therefore, the overall purpose of the present studies was to examine the role AGEs in normal brain again and the associated decline in cognitive and psychomotor function. In order to achieve the goals, two different approaches were taken. The first approach involved (i) determining whether or not AGEs accumulated in different regions of the brain as a function of age and (ii) determining whether these changes were correlated with individual differences in the ability of old mice to perform in tests of cognitive and psychomotor function. Age-associated accumulation of CML, a predominant form of AGEs in vivo, and expression of receptor for AGEs (RAGE) protein, inferred from densitometry quantification of immunoblots in different regions of the brain, were assessed by comparing groups of 8-or 25-month old mice. The 25-month-old mice were administered a series of behavioral tests to assess cognitive and psychomotor function prior to assessment of glycation status. In the second approach, groups of mature (6 mos) and older mice (18 mos) were fed with a control diet or a diet enriched with galactose (49% of caloric content), an intervention that was expected to promote formation of AGEs. The mice were subsequently tested for impairment of their cognitive and psychomotor functions after 8 weeks on the assigned diet. Upon completion of the behavioral tests (after 14 weeks on diet), amounts of CML and RAGE protein were assessed through densitometric analyses of the immunoblots. The main findings from the first approach were that (i) there was a robust increase in CML content and expression of RAGE protein in the aged mouse brain that occurred in a region-specific manner; (ii) the relative amounts of CML and RAGE were not closely associated with the degree of age-related impairment of mice tested for brain function. The main findings from the second approach were that high dietary galactose: (i) failed to induce aged-like behavioral impairments in young/mature mice; (ii) exacerbated age-related impairment of some psychomotor functions and (iii) had no significant effects on glycation status or oxidative damage. Comparison of the experimental outcomes from the first and second approaches was complicated by a difference in the fat content of the diets fed to the mice in the two studies, which had an apparent effect on the amounts of AGEs and protein oxidation present in young mice. However, considering the results of the two studies independently warrants the following conclusions: (i) Amounts of AGEs do not predict individualized brain aging as assessed by neurobehavioral impairment and may instead by largely reflective of chronological age. (ii) Diets enriched with galactose may produce deleterious effects in older mice that do not involve a change in oxidative damage or glycation status. Overall, these studies provide little support for a specific role of glycoxidation in normal brain aging. It is impossible that the extent of accrual of AGEs in the normally aging brain is insufficient to affect cellular function, whereas larger accumulations of AGEs may be associated with various pathological conditions discussed in the literature.Item Translational Control by Estrogen-Induced Signaling in Primary Rat Hippocampal Neurons(2008-07-01) Smith, Lonell T.; Simpkins, James; Das, Hriday K.; Machu, Tina K.Smith, Lonell T., Estrogen-Induced Signaling in Primary Rat Hippocampal Neurons. Masters (Biomedical Sciences). July 2008. 53 pages, 1 illustration, 7 figures. 37 titles. Abstract. The enhancing effects of 17-beta estradiol (E2) on performing cognitive tasks has been well demonstrated in laboratory mice, rats, and primates. Also there is ample clinical evidence indicating E2 enhances memory and reduces risk for Alzheimer’s disease. Furthermore, by increasing the capacity for long-term potentiation (LTP) in the hippocampus, E2 effectively increases the synaptic plasticity of this brain region in a manner that correlates with memory formation. The molecular mechanisms underlying LTP and synaptic plasticity have largely focused on the role of E2-induced signal transduction in the nucleus, and regulation of plasticity related gene expression at the transcriptional level. Conversely, the idea that E2-incuded signaling regulates at the level of translation and may play a role in these processes has yet to be explored. Recently, extracellular signal-regulated kinase (ERK) and mammalian target of rapamycin (mTOR) signaling pathways have been shown to couple synaptic activation to protein synthesis machinery. Here we investigate translational control by E2-induced ERK and mTOR signaling in primary neuronal culture. E2-induced signaling resulted in enhanced phosphorylation of ribosomal protein (S6) and eIF4E binding protein 1 (4EBP1) in an ERK and mTOR-dependent manner. Neuronal activity-dependent ERK and mTOR signaling have been shown to induce translation of a diverse array of dendritic resident mRNAs, including α-CaMKII and GluR1 subunits. Using a green fluorescent protein (GFP) translational reporter, we demonstrated that E2 stimulates GFP protein synthesis. We have also demonstrated that E2 treatment of hippocampal neurons increases surface expression of GluR1. Taken together, our results provide a mechanism by which E2 modulates the components necessary for persistent forms of LTP and long-term depression (LTD).