Endocrine Abstracts

We examined the functional significance of the glutamatergic innervation of the dorsal raphe nucleus (DR) in the mediation of the suckling stimulus inducing prolactin release. A non-NMDA (6-cyano-7-nitroquinoxaline-2,3-dione disodium, CNQX) or an NMDA glutamate receptor antagonist (dizocilpine hydrogen malate, MK-801) was injected into the DR of freely moving lactating rats at the end of 4 h separation. The litters were then returned and blood samples for prolactin were taken at different time points. In addition, we studied the effect of the non-NMDA receptor antagonist on the diurnal fluctuations of plasma prolactin and corticosterone. Adult male rats received by means of ALZET minipump CNQX (0.5 or 10 pM/μl/h) into the lateral cerebral ventricle for 72 hrs before and during blood sampling. CNQX, when injected into the DR in higher dose, inhibited the suckling-induced prolactin release. After MK-801 administration the prolactin response was significantly diminished. There were no diurnal fluctuations in plasma prolactin concentrations and only attenuated changes in corticosterone levels of rats treated with CNQX compared to controls getting physiological saline into the lateral ventricle. The findings suggest that (1) the glutamatergic innervation of the dorsal raphe nucleus is involved in the mediation of the neural signal of the suckling stimulus inducing prolactin release and (2) glutamatergic innervation of brain structures participating in the control of diurnal fluctuations of plasma prolactin and corticosterone concentration contributes to the maintenance of the circadian rhythm of these hormones.

This work was supported by the National Scientific Research Fund (OTKA T-042516 to B.H.), the Ministry of Health (ETT 020/2006 to B.H.) and the Hungarian Academy of Sciences.