Activation of Hypothalamic Neurons by Intraovarian Pressure Signals in a Teleost Fish, <i>Clams batrachus:</i> Role of Mechanosensitive Channels

Abstract

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, ethylenediaminetetraacetic 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.

Sexual dimorphism in the hypophysiotropic tyrosine hydroxylase-positive neurons in the preoptic area of the teleost, Clarias batrachus

“…The GSI of females in the prespawning and spawning phases is greater than that in the males, and there is relatively more pressure created by the growing mass of the ovaries compared to the testes on the gonad wall. Increasing GSI from the prespawning through spawning phases [ 52 ] and build up of intra-ovarian pressure following maturation of oocytes are believed to activate stretch pathways in the ovarian wall, which may impinge on neurons of NPO in the POA of C. batrachus [ 62 , 63 ]. While neurons of NPO in teleosts synthesize isotocin (a homolog of mammalian oxytocin), administration of the fish neurophysial hormones/synthetic oxytocin initiates spawning reflex in the killifish, Fundulus heteroclitus [ 64 ].…”

Role of Isotocin in the Regulation of the Hypophysiotropic Dopamine Neurones in the Preoptic Area of the Catfish, Clarias batrachus

“…In addition, IST stimulates the spawning reflex in the killifish, Fundulus heteroclitus . Mechanosensitive pathways from the ovarian wall control activity of the NPO neurones in C. batrachus . An increase in intra‐ovarian pressure may activate these pathways and NPO neurones.…”

Involvement of corticotropin-releasing factor and adrenocorticotropic hormone in the ovarian maturation, seawater acclimation, and induced spawning of Liza ramada

“…The authors also showed that the application of intraovarian pressure of 10 mm Hg (low pressure) revealed a marked hypertrophy of the cells, while pressures of 20 and 30 mm Hg (high pressure) resulted in hypotrophy and exhaustion of the cells suggesting the existence of a pressure-excitable neural pathway from the ovary capable of eliciting profound cytological changes in the NPO in the teleost C. batrachus. Moreover, Subhedar et al (1996) reported the presence of stretch receptors in the ovaries, equipped with mechanosensitive channels that transduce the stretch signals to be transmitted to the brain and the authors suggested that the stretch sensory system and ensuing pathway connecting the ovaries with the hypothalamus might play a role in apprising the brain of the status of ovarian maturity and the initiation of the spawning reflex.…”