Induced multiple nucleoli, nucleolar margination, and cell size changes in supraoptic neurons during dehydration and rehydration in the rat

Abstract

Rats were deprived of water for 0, 2, 4, 8, 12, 24, 48, 72, 96, 120 or 168 h. Other rats were deprived for 24 h, then allowed to rehydrate for 12, 24, 36, 48, 96, 120 or 240 h before being sacrified. The cells of the supraoptic nuclear complex (SON) were studied in animals sacrified at each of these times. For each of these rats, two random samples of 200 cells each were taken from pars anterior (Soa) and pars tuberalis (Sot) of SON. Determinations were made of (a) percentage of cells containing multiple (two or more) nucleoli, (b) percentage of cells containing nucleoli which were in contact with the nuclear membrane (marginated), and (c) mean cell size (area). These measurements were made on cells from brains sectioned in both the parasagittal and horizontal planes. The percentage of SON cells with multiple nucleoli in non-deprived rats was less than 5%. There was a measurable increase in multiple nucleoli after 2 h of deprivation and a continued rise up to 24 h without water. No further increases in multiple nucleoli were apparent with prolonged deprivation. Soa and Sot showed nucleolar responses which were similar in all respects, except that during prolonged dehydration Soa was found to have a higher percentage of multiple nucleolar cells than did Sot. Control hypothalamic cells showed no changes in multiple nucleoli with dehydration. The effects on nucleolar proliferation of 24 h dehydration were only partially reversed by 10 days of free access to water. Throughout the dehydration conditions, the percentage of cells showing margination of one or more nucleoli remained relatively constant. During the second or third day of rehydration, however, a sudden increase in margination appeared which lasted for about 3 days. Cell size increases in SON were measurable early in dehydration and continued as long as the deprivation conditions persisted. Size increases appeared to occur at different times in the two planes studied. As with multiple nucleoli, rehydration of 10 days did not completely return SON cells to the size of those in non-deprived controls. We interpret these results to indicate that: (a) the mechanisms of RNA and protein synthesis in these neurosecretory cells are sensitive to slight fluctuations in the physiological state of the animal; (b) specific experimental manipulations can induce a nucleolar response in nerve cells; (c) nucleolar fusion probably accompanies prolongation of the conditions which initially induce multiple nucleoli; (d) SON cells are more refractory than expected in their return of the predeprived state after 24 h of water deprivation; (e) cell size changes with increased hormone production proceed as if the cell is going through peristalsis-like movements; and (f) our data partially support the contention that Soa and Sot are functionally similar.