The effect of photoperiodic stimulation on phosphatase activity in the hypothalamo-hypophysial system of the white-crowned sparrow, Zonotrichia leucophrys gambelii.

Abstract

1. The metabolic activity of the hypothalamo-hypophysial neurosecretory system of the White-crowned Sparrow, Zonotrichia leucophrys gambelii, has been investigated by means of quantitative estimates of acid- and alkaline-phosphatase activity. The activities of samples from the median eminence, samples from the supraoptic region, the adenohypophyses, and the neurohypophyses of photosensitive and refractory birds, both subjected to short and long daily photoperiods, have been compared. Histochemical demonstrations of the distribution of acid- and alkaline-phosphatase activity have been effected to provide a better basis for interpretation of the quantitative data. 2. The photosensitive birds which were subjected to 20-hour daily photoperiods showed the typical photoperiodically induced testicular growth and fat deposition. There was an increase in acid-phosphatase activity in the supraoptic region. This increase in acid-phosphatase activity may be correlated with increased activity of the neurosecretory cells as indicated by cytologic criteria, including an increased rate of formation of aldehyde-fuchsin stainable material. No such increase in acid phosphatase occurred in refractory birds on 20-hour photoperiods. In photosensitive birds, there was also an increase in acid-phosphatase activity in the median eminence, an increase which appears to be attributable primarily to changes in activity of the axons in the glandular layer although a contribution by the nucleus tuberis cannot be excluded. The change in acid-phosphatase activity in the median eminence coincides well with the observed increase in rate of disappearance of aldehyde-fuchsin-positive granules from the axons. Neither an increase in acid phosphatase nor a decrease in granules occurred in the median eminences of refractory birds subjected to 20-hour daily photoperiods. The acid-phosphatase activity of the adenohypophyses of photosensitive birds was greater than in refractory birds although neither was affected by long daily photoperiods. These results are consistent with the hypothesis that the photoperiodic response in Zonotrichia leucophrys gambelii involves, in the supraoptic region, an increase in acid-phosphatase activity associated with increased synthesis of aldehyde-fuchsin-positive material in the neurosecretory cells, and, in the axons of the glandular layer of the median eminence, an essentially simultaneous increase in acid-phosphatase activity associated with a humoral transfer to the capillaries of the hypophysial portal system. Our data suggest that the higher rate of production of gonadotropins in the adenohypophysis by photosensitive birds involves a higher acid-phosphatase activity but that the photoperiodically induced increase in release of these gonadotropins, mediated by a humoral agent in the hypophysial blood, does not involve a detectable further increase in acid-phosphatase activity. 3. The data on alkaline phosphatase in supraoptic-region, median-eminence region, and adenohypophysis give no indication that this enzyme is involved in the photoperiodically induced activity of the hypothalamo-hypophysial system. 4. In agreement with previous investigations in this laboratory (Okscheet al., 1959), the data obtained in this investigation on phosphatase activity indicate no participation by the neurohypophysis in the photoperiodic response. 5. The histochemical observations indicate that the neurosecretory cells of the paraventricular and supraoptic nuclei have acid- and alkaline-phosphatase activities similar to those of ordinary neurones. The axons of neurosecretory cells, except in the median eminence, are not identifiable by histochemical demonstration of phosphatase activity. In the fibers of the glandular layer of the median eminence there is a pronounced acid-phosphatase, but no alkaline-phosphatase reaction, in these fibers. Also the nuclei and nucleoli of cells of the mammillary and tuberal nuclei have a fairly strong acid-phosphatase activity. In the adenohypophysis there is a conspicuous acid-phosphatase and a strong alkalinephosphatase reaction in the nuclei and nucleoli, but only slight activities in the cytoplasm.