Ontogeny of the diurnal rhythm of tuberoinfundibular dopaminergic neuronalactivity in peripubertal female rats: Possible involvement of cholinergic and opioidergic systems

The ontogeny of the diurnal change of tuberoinfundibular dopaminergic (TIDA ) neuronal activity in female rats and its control mechanism were the foci of this study. Intact pre (28. and 35-day-old)-, peri (39- and 42-day-old)- and post (49- and 56-day-old)-pubertal female, as well as pre (28-day-old) - and post (56-day-old)-pubertal male Sprague-Dawley rats were used. Basal TIDA neuronal activity, determined by measuring 3,4-dihydroxyphenylalanine or 3,4-dihydroxyphenylacetic acid in the median eminence, increased 3- to 4 -fold in the female and less than 2-fold in the male rats from day 28 to 49 ; so did serum prolactin levels. The diurnal rhythm of TIDA neuronal activi ty was not evident until day 42 in the female, but not male, rats. Neither nigrostriatal, nor mesolimbic DA neurons exhibited any significant change b etween pre- and postpubertal stages. In postpubertal (56-day-old) female ra ts, injection of nicotine (10 mu g/kg) in the morning, but not in the after noon, inhibited TIDA neuronal activity while similar injections of mecamyla mine (1 mg/kg) or naloxone (2.5 mg/kg) stimulated these neurons in the afte rnoon, but not in the morning. Serum prolactin levels changed accordingly. In contrast, none of the injections had any effect in prepubertal (28-day-o ld) female rats. These results indicate that the genesis of the diurnal rhy thm of TIDA neuronal activity in female rats occurs during the peripubertal stage, and endogenous cholinergic and opioidergic neurons may play a signi ficant role.