Hypothalamic-evoked effects in cat nucleus tractus solitarius facilitating chemoreceptor reflexes.

In anaesthetized cats intracellular recordings in the nucleus tractus solitarius (NTS) have been used to identify neurones receiving inputs from the carotid sinus nerve (SN), the aortic nerve and hypothalamic defence area (HDA). In forty-four neurones activated by SN stimulation HDA activation evoked an IPSP in fourteen (32%) and an EPSP in eight (11%). Those neurones receiving an HDA-evoked IPSP, and tested for reflex inputs, responded only to baroreceptor activation. Neurones receiving HDA-evoked EPSPs responded only to chemoreceptor activation. In three neurones unaffected by SN stimulation, short latency inputs from HDA were observed, suggesting direct monosynaptic inputs.