Effects of intracerebroventricular infusions of naltrexone and phentolamine on central and peripheral oxytocin release and on maternal behaviour induced by vaginocervical stimulation in the ewe.

The effects of intracerebroventricular infusions of naltrexone and phentolamine on the ability of vaginocervical stimulation to induce maternal behaviour, and plasma and cerebrospinal fluid (CSF) levels of oxytocin, were measured in oestrogen-primed ewes. Results showed that naltrexone, but not phentolamine, significantly inhibited maternal behaviour following vaginocervical stimulation. Naltrexone also prevented the CSF increase in oxytocin following vaginocervical stimulation but was without effect on plasma levels. Phentolamine did not prevent either CSF or plasma increases in oxytocin, following vaginocervical stimulation, but reduced basal plasma levels. Results are discussed in terms of an opioid influence on maternal behaviour which may be mediated through a modulation of central oxytocin release.