Participation of the hippocampus in the facilitatory effect of an exteroceptive stimulus on milk ejection.

The auditory exteroceptive stimulus emanating from a lactating rat and the litter while suckling was used to facilitate milk ejection in another "induced" mother suckled by her own litter. Sectioning of the tractus corticohypothalamicus medialis (TCM) or the columns of the fornix, prevented the facilitatory effect of the exteroceptive stimulus on milk ejection. Sham operated induced mothers gave significantly more milk than noninduced rats. Electrolytic lesioning of the stria terminalis did not affect normal milk ejection nor the response to the exteroceptive stimulus. It is proposed that the hippocampus through the TCM may facilitate the suckling-induced milk ejection when an appropiate exteroceptive stimulus is applied. Neither the lesion of the stria terminalis nor the section of the fornix or the TCM seems to alter the normal suckling-induced milk ejection. A general modulatory role of the limbic system is described.