Activation of hypothalamic neurons by intraovarian pressure signals in a teleost fish, Clarias batrachus: role of mechanosensitive channels.

Application of intraovarian pressure is known to trigger profound cytomorphological changes in the neurosecretory cells of nucleus preopticus in the teleost Clarias batrachus. These findings indicate the presence of stretch receptors in the ovaries, perhaps equipped with mechanosensitive channels that transduce the stretch signals to be transmitted to the brain. To test the occurrence of the mechanosensitive channels in the ovaries, we administered a range of pharmacological agents (lignocaine, quinidine, tetraethylammonium chloride, ethylene-diaminetetraacetic acid and gadolinium) known to block the mechanosensitive ion channels, in the ovarian lumen prior to the administration of the intraovarian pressure. Pretreatment with the above agents inhibited the response by the nucleus preopticus neurosecretory cells to intraovarian pressure. The results suggest the occurrence of the mechanosensitive channels in the ovaries of teleostean fishes. In terms of function we speculate that the stretch sensory system and the ensuing pathway connecting the ovaries with the hypothalamus might play a role in apprising the brain of the status of ovarian maturity and in the initiation of the spawning reflex.

The response of nucleus preopticus neurosecretory cells to ovarian pressure in the teleost, Clarias batrachus (Linn.).

The changes undergone by the neurosecretory cells of the nucleus preopticus (NPO) were investigated histologically and immunocytochemically following pressure stimulation of the ovaries in the teleost, Clarias batrachus. Application of intraovarian pressure of 10 mm Hg revealed marked hypertrophy of the cells, while pressures of 20 and 30 mm Hg resulted in hypertrophy and exhaustion of the cells. No changes were observed when the treatment was preceded by transection of the spinal cord. The results suggest the existence of a pressure-excitable neural pathway from the ovary capable of eliciting profound cytological changes in the NPO.