Akira Horita - US grants

This research proposal is concerned with studies on the behavioral, analeptic and gastrointestinal (GI) effects of centrally administered TRH. In barbiturate narcotized rats and rabbits TRH produces an analeptic effect, antagonism of hypothermia and a shaking behavior. The analeptic effect is blocked by atropine, indicating a central cholinergic mechanism. Our recent microinjection studies indicate that the medial septum is the most sensitive brain area to TRH in producing the analeptic effect. Because the medial septum is closely associated with the hippocampus via the septo-hippocampal cholinergic pathway, and from various other supporting evidence, we are postulating that these brain structures are involved in the TRH analeptic response. Much lesioning techniques will be employed to determine whether the septum and the septohippocampal pathway are required for the response. We shall also carry out several neurochemical procedures (ACh turnover and TRH receptor binding assays) to attempt to complete the picture of TRH acting via septal receptors and activating, via the septohippocampal cholinergic pathway, the hippocampal arousal system. The GI tract exhibits marked increases in motility (as measured by strain gauge) and propulsive activity (as measured by 51Cr or charcoal movement) after icv, but not iv, administration of TRH. Bilateral vagotomy abolishes these effects, but atropine blocked only the motility effect. Very recently we found that two antiserotonin compounds blocked only the propulsive effect of TRH. From these preliminary data we are postulating that vagally released serotonin is responsible for the atropine-resistant propulsive effect. Part of the proposal is aimed at confirming this hypothesis. We shall measure portal blood serotonin levels before and after TRH and in control and vagotomized animals. If these experiments are positive, we shall attempt to clarify how vagally stimulated release of serotonin takes place. Other studies will attempt to localize brain site at which TRH exerts its GI effects. These studies will be done with stereotaxic microinjections of TRH into different regions of the rabbit brain.

This research proposal is concerned with our earlier findings that either morphine or codeine administered intraventricularly to pentobarbital-anesthetized rabbits and/or rats exerted an analeptic effect which was potentiated by naloxone or naltrexone pretreatment. Codeine, but not morphine, also exerted its analeptic effect when given intravenously, even without prior treatment with an opiate antagonist. The analeptic effect was abolished by atropine pretreatment, suggesting involvement of a cholinergic mechanism. We propose to fully characterize the dose-response, time-effect and phramacological profile of this opiate arousal effect in the rat, and then proceed to determine by stereotaxic microinjection techniques their sites(s) of action in the brain. Upon establishing these properties we plan to determine whether other opiates of different analgesic potencies and chemical structures possess analeptic activity. They will be ranked according to their analeptic potencies, and possible correlations made between this property and any of their other known actions. Similar studies will be carried out with the various endogenous opioids and opiate antagonists. We shall then attempt to establish whether specific opiate receptor subtypes are involved in this action. Because the data thus far suggest possible relationships between opiate-induced arousal and cholinergic mechanisms, we plan to focus much of our neuroanatomical and neurochemical studies on central cholinergic pathways. Central cholinergic activity will be assessed by measuring high affinity choline uptake into synaptosomes from various regions of the brain, and levels of ACh and choline will be monitored. The main objective of this proposal is to understand the nature of this previously unknown property of the opiates and to determine whether it contributes to the overall pharmacology of those agents. Recent reports suggest that the arousal property of codeine may be useful in the treatment of narcolepsy, while that same property of morphine in chronic pain management may lead to sleep disorders. These studies may help establish the pharmacological bases of such clinical observations.

The objectives of this proposal are to understand the role of the central cholinergic system in (1) the analeptic action and (2) the sensitization phenomenon associated with cocaine and amphetamine. Both of these stimulants, when administered to pentobarbital-anesthetized rabbits, shorten the duration of narcosis. This arousal (analeptic) response, and the appearance of hippocampal theta in the EEG, are blocked by atropine or scopolamine. In this proposal we plan to characterize further the cocaine and amphetamine-induced analeptic effect, then to localize by microinjection techniques the brain site(s) at which these drugs initiate the analeptic response. Upon finding the site(s) we will conduct lesioning experiments to determine the brain pathways that are involved in the response. Drug interaction studies with specific neurotransmitter antagonists and depletors that are known to affect aspects of cocaine and amphetamine effects, will also be carried out to determine if other neurotransmitters might be involved in the cholinergically mediated analeptic effect. These studies should clarify the role of central cholinergic mechanisms in the analeptic effect of cocaine and amphetamine. In recent preliminary experiments we discovered that atropine attenuated the development of locomotor sensitization when it was administered daily with cocaine to rats. Also, high affinity choline uptake (HACU) was increased in cortex and hippocampus of rats given repeated intermittent doses of cocaine. These two sets of data, while preliminary, suggest that central cholinergic mechanisms might be associated with the sensitization process. The present proposal will attempt to clarify that association. Rats will be administered cocaine chronically with and without anticholinergies or their quaternary analogs. In other studies medial septal lesions to block hippocampal cholinergic activity will be examined for their influence on development of supersensitivity. Changes in HACU activity and 3H-QNB binding in several brain regions will be monitored during chronic cocaine treatment of rats. These studies will provide new information of the role of central cholinergic mechanisms in cocaine and amphetamine sensitization.