Neuropeptides
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Arginine-vasopressin (AVP) is synthesized and released centrally in several brain structures. AVP is thought to mediate anxiety-related behavior through two central receptor subtypes, Avpr1a and Avpr1b. Although these AVP receptor subtypes are expressed in several brain regions, including the hippocampus, little is known about their explicit role in unconditioned fear or anxiety. ⋯ Neither antagonist reduced anxiety-like behavior in the shock-probe burying test. Overall, the results show that both receptor subtypes of AVP are involved in anxiety-related responses, but their specific contributions depend on three variables: (1) the anxiety-related response (shock-probe avoidance versus open-arm avoidance), (2) the receptor subtype antagonized (Avpr1a versus Avpr1b), and (3) the area of hippocampus (dorsal versus ventral) into which these antagonists are infused. These dissociations suggest that different fear responses are under the control of specific AVP receptor systems within discrete parts of the hippocampus.