Thesis (M.S.)--Texas State University-San Marcos, 2007. / Vita. Includes bibliographical references (leaves 68-75).

Thesis (M.S.)--Texas State University-San Marcos, 2007. / Vita. Includes bibliographical references (leaves 68-75).

Thesis (M.S.)--Texas State University-San Marcos, 2006. / Vita. Appendix: leaves 31-35. Includes bibliographical references (leaves 36-39).

Thesis (M.S.)--Texas State University-San Marcos, 2006. / Vita. Appendix: leaves 31-35. Includes bibliographical references (leaves 36-39).

M2 muscarinic receptor extracted from Sf9 cells in cholate-NaCl differs from that extracted from porcine sarcolemmal membranes. Whereas the latter has been shown to exhibit non-competitive effects in the binding of N-methylscopolamine (NMS) and quinuclidinylbenzilate (QNB), which can be explained in terms of cooperativity within a receptor that is at least tetravalent, binding to the former is essentially competitive. Levels of cholesterol in Sf9 membranes were only 5% of those in sarcolemmal membranes and were increased to about 100% by means of cholesterol-methyl-β-cyclodextrin. M2 receptors extracted from CHL-treated Sf9 membranes resembled those from heart; that is, cholesterol induced a pronounced heterogeneity detected in the binding of both radioligands, including a shortfall in the apparent capacity for [3H]NMS, and there were marked discrepancies in the apparent affinity of NMS as estimated directly and via the inhibition of [3H]QNB. The data can be described quantitatively in terms of cooperative effects among six or more interacting sites, apparently within an oligomer. Cholesterol also was found to increase the affinity of the receptor for NMS and QNB, and the effect was examined for its possible relationship to the known interconversion of cardiac muscarinic receptors between an agonist-specific (R*) and an antagonist-specific (R) state. Cholesterol and N-ethylmaleimide (NEM) were compared for their effect on the affinity of NMS, QNB and four muscarinic agonists, and the data were assessed in terms of an explicit mechanistic model for a receptor that interconverts spontaneously between two states. The data can be described equally well by an effect of cholesterol on either the distribution of receptors between R and R* or the affinity of all ligands for both states, with an accompanying effect of NEM on either the affinity or the distribution between states, respectively. Since NEM is known from other data to favor R* over R, cholesterol appears to increase affinity per se. Cholesterol therefore is a determinant of affinity and cooperativity in the binding of orthosteric ligands to the M2 receptor. Both effects are observed in solution and therefore appear to arise from a direct interaction between the lipid and the receptor.

M2 muscarinic receptor extracted from Sf9 cells in cholate-NaCl differs from that extracted from porcine sarcolemmal membranes. Whereas the latter has been shown to exhibit non-competitive effects in the binding of N-methylscopolamine (NMS) and quinuclidinylbenzilate (QNB), which can be explained in terms of cooperativity within a receptor that is at least tetravalent, binding to the former is essentially competitive. Levels of cholesterol in Sf9 membranes were only 5% of those in sarcolemmal membranes and were increased to about 100% by means of cholesterol-methyl-β-cyclodextrin. M2 receptors extracted from CHL-treated Sf9 membranes resembled those from heart; that is, cholesterol induced a pronounced heterogeneity detected in the binding of both radioligands, including a shortfall in the apparent capacity for [3H]NMS, and there were marked discrepancies in the apparent affinity of NMS as estimated directly and via the inhibition of [3H]QNB. The data can be described quantitatively in terms of cooperative effects among six or more interacting sites, apparently within an oligomer. Cholesterol also was found to increase the affinity of the receptor for NMS and QNB, and the effect was examined for its possible relationship to the known interconversion of cardiac muscarinic receptors between an agonist-specific (R*) and an antagonist-specific (R) state. Cholesterol and N-ethylmaleimide (NEM) were compared for their effect on the affinity of NMS, QNB and four muscarinic agonists, and the data were assessed in terms of an explicit mechanistic model for a receptor that interconverts spontaneously between two states. The data can be described equally well by an effect of cholesterol on either the distribution of receptors between R and R* or the affinity of all ligands for both states, with an accompanying effect of NEM on either the affinity or the distribution between states, respectively. Since NEM is known from other data to favor R* over R, cholesterol appears to increase affinity per se. Cholesterol therefore is a determinant of affinity and cooperativity in the binding of orthosteric ligands to the M2 receptor. Both effects are observed in solution and therefore appear to arise from a direct interaction between the lipid and the receptor.

Psychopathological conditions in which decision making is impaired are common and include schizophrenia, attention deficit hyperactivity disorder, and addiction, among others. This dissertation aimed to investigate the role of cholinergic signaling in risky and impulsive decision making. Rats were trained in either a “probability discounting” task in which they chose between small guaranteed and large probabilistically delivered food rewards (a measure of risky decision making), or a “delay discounting” task in which they chose between small immediate and large delayed food rewards (a measure of impulsive decision making). Rats were also divided into high and low “risk-taking” or “impulsive” groups on the basis of their performance in the tasks. Experiments 1 and 2 examined the effects of cholinergic drugs on performance in the probability and delay discounting task, respectively. In Experiment 1, acute administration of the acetylcholinesterase inhibitor donepezil decreased choice of the large risky reward in “risk-taking” rats. Acute administration of nicotine increased choice of the large risky reward in both groups, whereas administration of the nicotinic receptor antagonist mecamylamine decreased choice of the large risky reward in “risktaking” rats. In Experiment 2, nicotine increased choice of the large delayed reward and mecamylamine shifted impulsive choice in a non-specific manner in “impulsive” rats. The muscarinic receptor agonist oxotremorine decreased choice of the large delayed reward in “non-impulsive” rats and increased choice in “impulsive” rats, while treatment with the muscarinic receptor antagonist atropine increased impulsive choice in all rats. In Experiment 3, another group of rats was used to examine correlations between baseline performance in both discounting tasks and nicotinic receptor density levels in several brain regions. Impulsive choice was positively correlated with α4β2 receptor levels in ventral hippocampus and nucleus accumbens shell, and α7 receptor levels in the basolateral amygdala, such that greater impulsivity was associated with higher receptor levels. Additionally, risky choice was negatively correlated with α4β2 receptor levels in nucleus accumbens shell, such that greater risk was associated with lower receptor levels. These experiments suggest that cholinergic receptors are involved in cost-benefit decision making and that they may prove a useful target for treatment of psychopathological conditions in which decision-making deficits are present.

The monosynaptic connection between the locust forewing stretch receptor (fSR) and the first basalar motoneuron (BAl) is part of a sensory pathway involved in flight. The fSR is a single sensory afferent, triggered during wing elevation, that makes central connections with the wing depressor motoneuron, BAl. The fSR/BAl synapse in Locusta migratoria was used as a model to study the modulation of cholinergic synaptic transmission. Electrophysiological experiments indicate that presynaptic muscarinic cholinergic receptors are involved in the down-regulation of acetylcholine release from the fSR terminals and at least some of these are located on and activate GABAergic intemeurons that inhibit the fSR. These experiments are supported by electron microscopical (EM) immunocytochemical (ICC) studies, which show that the fSR receives synaptic inputs from neurons immunoreactive (IR) for GABA.Additional EM ICC studies reveal that the fSR also receives synaptic inputs from glutamate-IR neurons. The EM ICC studies also showed that neurons that are not immunoreactive for GABA or glutamate are presynaptic to the fSR and its postsynaptic member, suggesting that the fSR/BAl synapse is modulated by other neuromodulators. Further electrophysiological studies revealed that the biogenic amines, octopamine and dopamine are potentially capable of modulating the fSR/BAl synapse, by suppressing the postsynaptic response of BAl to ACh (at least in part). The biogenic amine, 5- hydroxytryptamine (5HT) is also potentially capable of modulating the fSR/Bal synapse but may act through octopamine receptors. This is supported by confocal microscopical ICC studies, which show that the neuropil region containing the fSR/BAl synapses is octopamine-IR but not 5HT-LR. These results indicate that a range of neuromodulators acting via different mechanisms interact to modulate cholinergic synaptic transmission between the fSR and BAl.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [110]-127).

Thesis (Ph.D.)--Biology, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Nael A. McCarty; Committee Co-Chair: Dr. Darrell Jackson; Committee Member: Dr. Alfred H. Merrill; Committee Member: Dr. Barbara D. Boyan; Committee Member: Dr. Harish Radhakrishna; Committee Member: Dr. Marion B. Sewer