Functional Interactions Among Thyrotropin-Releasing Hormone (Trh), Prolactin (Prl) and Dopamine (Da) in the Brain

193 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.The goals of my thesis research centered in the study of the mechanisms that regulate the in vitro release of thyrotropin-releasing hormone (TRH) from the mediobasal hypothalamus (MBH) and in the actions of prolactin (PRL) on the activity of dopaminergic neurons in the striatum and the MBH. In the present work the spontaneous and induced release of TRH and dopamine (DA) from fragments of male rat MBH and the DA release from male and female rat striatal tissue superfused in vitro for several hours were examined.For the measurement of TRH, a specific and sensitive radioimmunoassay (RIA) for TRH was developed. The assay was capable of detecting below 10 pg of TRH in biological materials.During the superfusion of MBH, the spontaneous release rate of TRH over the initial 60 min of superfusion was 0.31 pg/mg/min. The MBH TRH content was 2128 pg/MBH after 4 hours of superfusion. Pulses or continuous infusion of high concentration of K('+) (60mM) enhanced the release of TRH from MBH during superfusion. The stimulatory of K('+) depolarization on TRH release from superfused MBH was inhibited in Ca('2+)-free EDTA medium. Pulses of serotonin (2 x 10('-8) M) stimulated TRH release to 466% of basal levels. This stimulatory effect of serotonin was blocked by pretreatment with a antagonist, methysergide. A constant infusion of serotonin (2 x 10('-8) M) for 1 hour resulted in episodic release of TRH. The stimulatory effects of K('+) and serotonin on TRH release from MBH were also confirmed in incubation experiments.Spontaneous and PRL-induced release of DA from superfused rat striatum and MBH was determined by a radioenzymatic assay with a sensitivity of 31 pg. The basal release rate of DA from male rat MBH over an initial 16 min period was 1.6 pg/mg/min, and from striatal tissue from intact male, castrated male, diestrous I female and ovariectomized female rats ranged from 23.2 to 27.2 pg/mg/min. However, the basal DN release rate from striatal tissue from proestrous afternoon female rats was 63.3 pg/mg/min. The results showed that PRL (0.01 or 0.1 (mu)g/ml) could feedback to MBH to stimulate DA release to regulate its own secretion from the pituitary. The results also indicated that PRL (0.1 (mu)g/ml) could stimulate DA release from male but not from female striatal tissues. This sexual difference was not modified by short-term castration.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD