Apomorphine-induced penile erection and yawning: site of action in brain

Abstract

Microinjection of the dopamine (DA) agonist apomorphine into the paraventricular nucleus of the hypothalamus (PVN) induced penile erection and yawning in rats. A significant effect was elicited by a dose of apomorphine as low as 5 ng. The symptomatology usually began within 5 min after the microinjection, lasted for 30–50 min, and was identical to that induced by the systemic administration of the drug. Stereotypy and hypermotility were nerve observed after apomorphine microinjection into the PVN, even at the highest dose tested (1 μg). Microinjections of the same doses of apomorphine into the hypothalamic ventromedial and dorsomedial nucleus, preoptic area, caudate nucleus, nucleus accumbens and substantia and substantia nigra, were ineffective. LY 171555, a specific D 2 DA receptor agonist, and (+)-3-PPP, but not (−)-3-PPP nor the specific D 1 DA receptor agonist SKF 38393, were as effective as apomorphine when injected into the PVN. Apomorphine-induced penile erection and yawning were antagonized by pretreatment with neuroleptic drugs, such as haloperidol, (−)-sulpiride, a specific D 2 DA antagonist, and SCH 23390, a specific D 1 DA antagonist. The present results suggest that the PVN is the brain area where D 2 DA agonists act to induce penile erection and yawning. Moreover, since the PVN contains the cell bodies of a group of incertohypothalamic DA neurons, the above results suggest for the first time a possible involvement of the incerto-hypothalamic DA system in the expression of penile erection and yawning.