THE HYPOTHALAMIC NEUROSECRETORY SYSTEM OF COTURNIX COTURNIX JAPONICA.

Abstract

1. The neurosecretory cells of Coturnix coturnix japonica occur in two areas, the supraoptic nucleus and the paraventricular nucleus. These nuclear areas consist of a series of extended groups of cells (divisions) that are interconnected through irregular chains of neurosecretory cells. The paraventricular nucleus is large and well-developed. 2. Morphologically the neurosecretory cells vary extensively even in normal or control birds. There may by indistinct, small cells with very little neurosecretory material or relatively large cells filled with homogeneous neurosecretory material. In the latter the initial sections of axons are frequently conspicuous because of the presence of neurosecretory granules. The large paraventricular nucleus is striking because of its very intense neurosecretory activity. The initial part of the neurosecretory tract is clearly evident because of stainable neurosecretory substance. 3. In addition to the accumulation of neurosecretory material in the neural lobe there is a second storage site in the zona externa of the median eminence. 4. When NaCl solution is used for drinking fluid the neurosecretory cells are activated. With NaCl concentrations of 0.1–0.15 M only a mild enlargement of these cells occurs and the amount neurosecretory material in the neural lobe is only gradually decreased. However, with 0.2–0.25 M there are significant changes. The neurosecretory cells attain a very marked enlargement with the neurosecretory material being in the form of fine granules. Simultaneously there is a marked depletion of neurosecretory material in the posterior lobe. 5. When the neurosecretory material of the posterior lobe is depleted because of the drinking of NaCl solutions of 0.2–0.25 M, the neurosecretory material in the zona externa of the median eminence appears to be unaffected. In contrast to the complete depletion of neurosecretory material in the neurosecretory pathway leading to the neural lobe, the fiber bundles leading to the zona externa contain a significant amount of neurosecretory material. 6. It is not possible, on the basis of this investigation, to indicate the relative participation of axons from the supraoptic nucleus and paraventricular nucleus with respect to the median eminence and neural lobe. 7. The functional significance of individual divisions of neurosecretory nuclei is still unknown. The higher concentrations of NaCl used in our experiments stimulated all parts of the neurosecretory nuclei. What significance can be attached to certain regional differences in activity in untreated quail or in experiments with low concentrations of NaCl, is still not clear.