Lesions of the locus coeruleus abolish baroreceptor-induced depression of supraoptic neurones in the rat.

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Abstract
Urethane-anesthetized rats were used to investigate the influence of lesions within the locus coeruleus on the inhibition of phasically discharging supraoptic neurons that normally follows the activation of arterial baroreceptors. The locus coeruleus of 1 side only was destroyed either by thermal (radio-frequency) lesions, or by the injection of 6-hydroxydopamine (1 .mu.l, 0.5 mg/ml). The extent of each lesion was assessed histologically in stained tissue and with fluorescence histochemistry. 6-Hydroxydopamine lesions (1 .mu.l, 2 mg/ml) in the rostral part of the ventrolateral A1 catecholamine neurons were less consistent in their abolition of baroreceptor input to the supraoptic nucleus. When the input from ipsilateral carotid sinus baroreceptors was abolished, there was an equivalent effect on the influence of the carotid body chemoreceptors. Input from other arterial baroreceptors, activated by phenylephrine injection, was not affected. It is proposed that the baroreceptor-induced depression of phasically discharging supraoptic neurons is mediated via a direct noradrenergic input from the locus coeruleus.