Vasopressin and V1-receptor antagonists modulate the activity of NTS neurons receiving baroreceptor input

Arginine vasopressin (AVP) may act as a neurotransmitter or neuromodulator in the solitary tract nucleus (NTS). To determine whether AVP influences the activity of NTS neurons receiving cardiovascular afferent input, we used single-unit extracellular recording combined with local microinjection to test the effects of AVP and V1-receptor antagonists (antAVP) on spontaneously active NTS neurons in anesthetized rats. Phenylephrine-induced increases in arterial pressure were used to identify neurons receiving baroreceptor input. Phenylbiguanide was used to stimulate chemosensitive cardiopulmonary receptors. AVP excited 31 of 81 NTS neurons tested and inhibited 15 of 81 neurons. AntAVP had independent effects on NTS neurons: in addition to blocking the effects of AVP, antAVP inhibited 26 of 72 neurons but excited only 13. Eighty-two percent of NTS neurons receiving excitatory or inhibitory baroreceptor inputs responded to AVP; 61% of these were excited by AVP. Fifty-eight percent of neurons receiving cardiopulmonary receptor input responded to AVP. These results suggest that AVP in rat NTS has a tonic, predominantly excitatory influence on a significant proportion of baroreceptor-related neurons.