The general context of this study is the exploration of the central pathways responsible for the autonomic responses to nociception. The proposed work specifically focuses on how the trigeminal nucleus might control adrenal catecholamine secretion in the anesthetized cat. The work is divided into three parts.
The first aim i s to identify the putative trigeminal transmitters involved in controlling the secretion of ACTH and adrenal catecholamines. This will be achieved in part by measuring the rate of secretion of adrenal catecholamines, blood ACTH levels, and the hemodynamic effects produced by the microinjection into the trigeminal nucleus of agonists and antagonists to selected neurotransmitter receptors. A selection of receptor antagonists will then be injected into the trigeminal nucleus to determine if one type of chemical can successfully block the release of adrenal catecholamine evoked by orofacial nociceptive stimulation. Finally the hypothesis that nociceptive stimulation releases excitatory amino acids in the trigeminal nucleus will be directly tested by attempting to collect an overflow of one of these substances by the push-pull cannula method. The second part of the project is designed to identify potential relay nuclei interposed between the trigeminal nucleus and spinal preganglionic neurons which control the adrenal medulla. Each putative relay will be incapacitated in a reversible manner by microinjection of a local anesthetic until a significant attenuation of the adrenal response to nociceptive stimulation of the orofacial sphere is achieved.
The third aim explores the potentiative interactions between orofacial nociceptive stimulation and peripheral chemoreceptor activation on the release of ACTH and adrenal catecholamines. Finally, a series of neurophysiological unit recording experiments will test whether some integration between orofacial somatic nociceptive inputs and certain visceral inputs such as peripheral chemoreceptors occurs within the trigeminal complex perhaps on neurons which project directly to lower brainstem autonomic relays such as the parabrachial complex.
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