Neurotransmitter levels in the hypothalamus during postnatal development of rats

The content of norepinephrine (NE), epinephrine (E), dopamine (DA) and serotonin (5-HT) in the rat hypothalamus was determined at four hours time interval during 24 hours period at the age of 12, 23, 27 and 75 days. It was found that the content of NE in the hypothalamus is low in 12 day-old rats, and during the postnatal period a gradual increase of NE was noted. The content of E in the hypothalamus is low in 12- to 27-day-old rats and an important increase was found in adult animals. The high values of DA and 5-HT concentration were found in the hypothalamus of 12-day-old rats and a transient decrease of 5-HT and DA at the age of 23 days was noted, further an important increase of the content of both neurotransmitters in the hypothalamus was demonstrated later in life. The presence of circadian rhythm of hypothalamic NE, E, DA and 5-HT content was found in 12-, 23-, 27-day-old and in adult rats overfed or underfed during the suckling period. However, no significant correlation was observed between the NE and E levels in the hypothalamus and the diurnal fluctuations of plasma corticosterone concentrations. In adult animals an inverse correlation between the plasma corticosterone level and hypothalamic 5-HT content was noted. In young 12- and 23-day-old rats the correlation between 5-HT in the hypothalamus and corticosterone in the plasma was positive. These results indicate that the shift of peak in plasma corticosterone levels during postnatal ontogenesis of rats observed in previous experiments is not dependent on the changes in diurnal fluctuation of hypothalamic neurotransmitter concentrations.