By means of semiquantitative immunocytochemistry and quantitative receptor autoradiography a correlation analysis has been performed on the pre- and post-synaptic features of enkephalin and beta-endorphin immunoreactive neuron systems of the 3- and 24-month-old male rat. A parallel disappearance of enkephalin- and beta-endorphin-like immunoreactivity and of the density of mu and delta opiate receptors is shown during ageing. Furthermore, the lack of an overall correlation between the amount of pre- and post-synaptic components of the enkephalin and beta-endorphin synapses give evidence for the existence of a volume type of transmission in such systems in the telencephalic, diencephalic and mesencephalic areas analysed.

Using the Falck-Hillarp fluorescence technique, the effect of various hypophyseal hormones on the rate of depletion of catecholamines (CA) from certain central neuron systems was investigated in the rat, after inhibition of CA synthesis. Prolactin, but not LH, FSH, ACTH, or vasopressin, caused a dose-dependent increase in the turnover of dopamine (DA) in nerve terminals of the external layer of the median eminence. The effects were marked in hypophysectomized males and females, with or without castration, and less marked in castrated males and females and in normal males. In normally cycling females, prolactin caused a blockade of the cyclic changes in activity in the tubero-infundibular DA neurons, resulting in constant high turnover as is found in diestrus. Prolactin had no effects on the ascending noradrenaline (NA) neurons terminating in the hypothalamus or on the nigro-neostriatal DA neurons. During lactation, an endocrinological state with high prolactin secretion, the DA turnover in the external layer of the median eminence is very high. Both this increase in DA turnover and the increase found during pregnancy were reduced by hypophysectomy or by administration of ergocornine methanesulfonate (ECO-580) and 2-Br-α-ergokryptine methanesulfonate (CB-154), two drugs that probably decrease prolactin secretion from the anterior pituitary. The present results suggest that the tubero-infundibular DA neurons are part of a feedback system involved in the regulation of prolactin secretion from the anterior pituitary. The hypothesis is forwarded that one of the functions of the tubero-infundibular DA neurons is to stimulate the secretion of PIF at the level of the median eminence, and thus to exert an inhibitory effect on prolactin release. Previous studies have indicated a role of the tubero-infundibular DA neurons in the regulation of FSHRF-LHRF release. This complex role of the DA neurons is discussed.

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The effects of centrally administered neuropeptide Y (NPY) on the sleep-wakefulness cycle have been studied by analyzing its action in different strains of rats with or without spontaneous hypertension and during two different phases of the circadian cycle. Normal adult Sprague-Dawley (SD), Wistar-Kyoto (WKy) and spontaneous hypertensive (SH) rats were used. By means of EEG electrodes the recording of the fronto-parietal electrocorticogram and the electromyogram could be made. Stainless steel cannula were also implanted into the lateral ventricle. The effects of an intraventricular injection of NPY (1.25 nmol/rat) was compared with the effects of the vehicle (saline) alone. The EEG patterns were classified as desynchronized, mixed or synchronized. In the SD rats NPY produced behavioural signs of sedation and a significant reduction of synchronized EEG activity as well as significant increase of synchronized and mixed EEG activities in comparison with the saline treated rats. In the WKy rats NPY administration produced an increase of synchronized EEG activity during evening sessions. In SH rats NPY produced a significant increase of desynchronized EEG activity and a decrease in mixed EEG activity indicating an awakening effect of the peptide. In view of the NPY innervation of the locus ceruleus, it therefore seems possible that the neuronal and hormonal regulation of the locus ceruleus noradrenaline nerve cells is different in the two strains of rats. It also seems possible that the ability of NPY to increase wakefulness in hypertensive animals is related to abnormal changes in the alpha 2-adrenoreceptors taking place in SH rats.