Evidence for an Inhibitory Dopaminergic and Stimulatory Noradrenergic Hypothalamic Influence of PMS-Induced Ovulation in the Immature Rat. I. Catecholamine Turnover Changes in Relation to the Critical Period

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Abstract
Using quantitative microfluorimetry in combination with tyrosine hydroxylase (TH) inhibition (α-methyltyrosine-p-methylester; H 44/68), the effect of pregnant mare’s serum gonadotropin (PMS, 10 IU day 30) on the levels and turnover of catecholamine (CA) in the subependymal layer (SEL), the medial (MPZ) and lateral palisade zone (LPZ) of the median eminence (ME) was studied on days 30, 31, 32 and 33 of life in the female rat. Serum LH concentrations were studied by radioimmunoassay. LH concentrations reached maximal levels between 18.00–20.00 on day 32. During 15.00–17.00 in the critical period of day 32 the reticulo-hypothalamic noradrenaline (NA) turnover was dramatically increased in SEL compared to other times during day 32 and the same time on day 33 and day 30, whereas the dopamine (DA) levels in the LPZ were increased and the DA turnover decreased in this region when compared with PMS-treated rats studied on day 31 during 15.00–17.00. A partial increase of NA turnover in SEL was already seen in the afternoon of day 31 compared with PMS-treated rats studied one day earlier. Also NA turnover in the medial preoptic area (MPOA) and DA turnover in the olfactory tubercle (TO) were increased and decreased respectively during the critical period in the afternoon of day 32 compared with PMS-treated rats studied in the morning of the same day, whereas such comparisons did not reveal any difference in DA turnover in the parts of the nuc. caudatus (CAUD) and nuc. accumbens (ACQ studied and in NA turnover in nuc. interstitialis striae terminalis, ventral part (NISTV). The present findings give support for the view that an inhibitory DA and a facilitory NA mechanism exist in the control of PMS-induced ovulation. It is suggested that this control may partly be exerted via NA terminals in MPOA (and possibly in SEL) and via DA terminals in LPZ.