CIRCANNUAL MORPHOMETRIC INVESTIGATIONS OF THE RAT SUPRACHIASMATIC NUCLEUS AFTER PINEALECTOMY, GANGLIONECTOMY AND THYROIDECTOMY

We karyometrically investigated the nucleus suprachiasmaticus (SCN) wh ich had been manipulated in several ways in order to analyze the funct ional importance of the pineal gland on the primary pacemaker of mamma ls in the course of the year. The manipulation modes were (i) pinealec tomy (PX), and (ii) sympathetic denervation of the pineal by bilateral extirpation of the upper cervical ganglia (ganglionectomy, GX). Addit ionally, the influence of the inactivated pineal, obtained through hyp othyroidism which was realized by (nl) subtotal thyroidectomy (TX), wa s also investigated. With respect to annual oscillations the results o f our investigations were able to illustrate the following. (1) The SC N consists of at least two parts (ventrolateral and dorsomedial) each with different functions and relationships. The nuclei of the ventrola teral cells are bigger and there are many indications both in our own research and from literature that the neurons of this part are involve d in the generation of rhythms. (2) The size of the cell nuclei of the ventrolateral part shows annual patterns. In the course of the year t he maxima of the nuclear volume were registered in March and September (bimodal pattern, equinox, L:D = 12:12). PX, GX or TX only negligibly changed the bimodal annual pattern. However, in comparison the smalle st cell nuclei were registered in the winter (short day). The much sma ller cell nuclei of the dorsomedial part likewise show bimodal pattern s but only in the experimental groups. The control group of this part shows an unimodal annual curve with a minimum at long-day conditions ( June, L:D = 16:8). (3) All manipulations which inactivated the pineal or reduced the content of melatonin (PX, GX, and TX) were followed by an increase (activation) of cell nuclei of the SCN. In contrast to the se effects, an increase of thyroxine (by exposure to cold), has an opp osite effect (not documented here). In conclusion these results indica te, without a doubt, that a negative correlation exists, functionally, between the SCN and the pineal (in the same annual experiment the nuc lear size of the pinealocytes was increased, under short-day condition s in December, and decreased under long-day circumstances in June). Ad ditionally, it could be shown that the degree of negative correlation between the pineal and the SCN was seasonally dependent. The lowest ef fects of PX, GX and TX were registered at short-day conditions (Decemb er, L:D = 8:16).