Plasma Cortisol of Conscious Cats during Cerebroventricular Perfusion with Adrenergic, Cholinergic and Gabanergic Antagonists

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Abstract
Adrenergic (.alpha. and .beta.), cholinergic (m and n) and gabanergic (.gamma.) influences on the regulation of basal hypothalamo-hypophyseal-adrenocortical (HHA) activity, as assessed by plasma cortisol levels, were investigated in non-stressed conscious cats. Alterations in neurotransmitter activities were induced by perfusing the cerebroventricles for 60 min with mock CSF containing .alpha., .beta., m, n and .gamma. antagonists given alone or in various combinations. Neither .gamma., m nor n blockers altered basal HHA activity, whereas both .alpha. and .beta. blockers given alone or together, or combined with m, n and .gamma. blockers markedly elevated plasma cortisol. These responses were inhibited by the addition of dexamethasone to the perfusion fluid. Basal HHA activity in the cat is apparently maintained by a central inhibitory action of the adrenergic system on spontaneously discharging corticotropin-releasing factor neurons, and not via an adrenergic-cholinergic-gabanergic neural chain.