Implication of central neurohypophyseal hormone receptor-mediated action in timing of reproductive events: evidence from novel observations on the effect of a vasotocin analogue on singing behaviour of the canary.

A highly discrete distribution of neurohypophyseal hormone receptors was discovered in the mammalian and avian brain. These receptors are heterogeneous. In rat brain oxytocin (OT) and V1a receptors can be distinguished which bind OT with an order of magnitude difference in affinity and which are located in discrete sites of the limbic-midbrain circuitry. In the brain of the canary low and high affinity vasotocin (VT) sites were identified; the latter putative VT receptors were found exclusively localized in the area encapsulating the nucleus robustus archistriatalis (RA). We show with recordings of singing behaviour that a VT analogue promotes the chain of seasonal events in this behaviour.