Oxytocin induces penile erection and yawning when injected into the bed nucleus of the stria terminalis: A microdialysis and immunohistochemical study

Oxytocin (5, 20 and 100 ng) injected unilaterally into the bed nucleus of the stria terminalis (BNST) of male rats stereotaxically implanted with a microinjection cannula coupled to a microdialysis probe, induces penile erection and yawning that occur concomitantly with a dose-dependent increase in the extracellular concentration of glutamic acid, dopamine and its main metabolite 3,4-dihydroxyphenilacetic acid (DOPAC), and nitrites (NO₂^-) in the dialysate obtained from the BNST by intracerebral microdialysis. The responses induced by oxytocin (100 ng) were all abolished by the oxytocin receptor antagonist d(CH₂)₅Tyr(Me)²-Orn⁸-vasotocin (1 μg), and reduced by CNQX (1 μg), a competitive antagonist of the AMPA receptors, both given into the BNST 25 min before oxytocin. In contrast, (+) MK-801 (1 μg), a non-competitive antagonist of NMDA receptors, and SCH 23390 (1 μg), a selective dopamine D1 receptor antagonist, reduced penile erection and yawning, but not glutamic acid and dopamine increases in the BNST dialysate induced by oxytocin. Immunohistochemistry revealed oxytocin-labelled neuronal structures in close proximity to tyrosine hydroxylase-labelled neurons or nitric oxide synthase-labelled cell bodies surrounded by intense vesicular glutamate transporter1-stained synapses in BNST sections where oxytocin injections induce the above responses. Together, these findings show that oxytocin injected into the BNST induces penile erection and yawning by activating not only the glutamatergic (and nitrergic) but also the dopaminergic neurotransmission, leading in turn to the activation of neural pathways mediating penile erection and yawning.