Combined use of immunocytochemistry and lectin histochemistry for the study of the hypothalamic neurosecretory system of the snake Natrix maura (L.)

Plasticity of nonapeptidergic neurosecretory cells in fish hypothalamus and neurohypophysis

The structure and function of nonapeptidergic neurosecretory cells (NP-NSC) are considered in terms of comparative morphology. Among NSC of different ergicity for NP-NSC the most characteristic involve massive accumulation and storage of neurohormonal products. Only in NP-NSC are the secretory cycles of functioning clearly expressed. Their highest reactivity is established during experimental and physiological stresses. In contrast, liberinergic, statinergic, and monoaminergic NSC, unlike NP-NSC, are characterized even in the "norm" by a constantly high level of extrusion processes. As signs of maximum NP-NSC plasticity, we consider the largest size of elementary neurosecretory granules, the diversity of secretion forms, and the maximum development of Herring bodies-clear manifestations of secretory cycles of functioning. In particular, phases of massive storage of neurosecretory granules in the extrusion cycle of NP-NSC neurosecretory terminals express accumulation of neurosecretory products. It is concluded that a particularly high degree of plasticity of NP-NSC is provided by their capability for functional reversion. This reversion is manifested first in the form of the restoration of the initial moderate level of functioning and especially in the accumulation of neurosecretory products. The reversion is considered an important mechanism providing a high degree of NSC plasticity. This degree turns out to be sufficient for participation of NP-NSC in the integration of fish reproduction. It is shown that NP-NSC are organized by the principle of a triad of the balanced system. This system consists of two alternative states: accumulation and release of neurosecretory products and the center of control of dynamics of their interrelations, the self-regulating center. In the latter, the key role is probably played by the Golgi complex.

Renal responses to mesotocin in Western painted turtles compared with the antidiuretic response to arginine vasotocin

We have examined the renal responses to the two neurohypophysial peptides mesotocin (MT) and arginine vasotocin (AVT) in Western painted turtles (Chrysemis picta). Ureteral urine was collected, after removal of the urinary bladder, to exclude modification by trans-bladder fluxes of ions and or water. Test doses of MT ranged from 5 to 500 ng kg(-1) i.v. but only the uppermost pharmacological doses of 300 and 500 ng kg(-1) were followed by even a small reduction in GFR, a renal tubular antidiuresis, and a decrease in percent relative free-water one word clearance. A much lower, physiological, dose of 5 ng kg(-1) of AVT attenuated significantly the GFR for 30 min and decreased the percent relative free-water clearance until the end of a 150 min observation period. This is the first report of the renal response to MT in a reptile. It was concluded that MT is not a diuretic hormone, as it is in amphibians and that AVT may be the naturally occurring antidiuretic hormone in the Chelonians.