Effects of vasopressin and involvement of receptor subtypes in the rat central amygdaloid nucleus in vitro

Effects of arginine-vasopressin (AVP) on neurons in the central amygdaloid nucleus (ACe) were investigated with rat brain slice preparations using extracellular recording methods. Of 160 ACe neurons tested, 70 cells (44%) were excited and 9 cells (6%) were inhibited by bath application of AVP at 3×10⁻⁷ M. The excitatory effects of AVP were dose-dependent and the threshold concentration was approximately 10⁻¹⁰ to 10⁻⁹ M. The excitatory effects of AVP persisted under blockade of synaptic transmission by perfusing with Ca²⁺-free and high-Mg²⁺ medium, whereas the inhibitory effects were abolished by synaptic blockade. AVP-induced effects were mimicked by a V₁-receptor agonist and completely blocked by a selective V₁-antagonist. V₂-agonist produced no effects on ACe neurons and V₂-antagonist had no effect on AVP-induced excitation. These results showed that the excitatory effect of AVP on ACe neurons was produced by a direct action through the V₁-receptors, whereas the inhibitory response of ACe neurons to AVP seemed to be produced by an indirect action. The results of this study suggest that AVP is involved in the amygdala-relevant functions as a neurotransmitter or a neuromodulator.