Tyrosine Hydroxylase in the Olfactory System, Forebrain and Pituitary of the Indian Major Carp, Cirrhinus cirrhosus: Organisation and Interaction with Neuropeptide Y in the Preoptic Area

Abstract

Dopamine (DA) inhibits, whereas gonadotrophin-releasing hormone (GnRH) stimulates, luteinisiing (LH) cells in the pituitary of some but not all teleosts. A reduction in the hypophysiotropic dopaminergic tone is necessary for the stimulatory effect of GnRH on LH cells. Neuropeptide Y (NPY) has emerged as one of the potent, endogenous agent that modulates LH secretion directly or indirectly via GnRH. Involvement of NPY in the regulation of hypophysiotropic DA neurones, however, is not known, but there is good evidence suggesting an interaction in the mammalian hypothalamus. DA neurones, identified by tyrosine hydroxylase (TH)-immunoreactivity, were observed widely throughout the brain of the Indian major carp, Cirrhinus cirrhosus. The granule cells and ganglion cells of terminal nerve in the olfactory bulb, and cells in ventral telencephalon and preoptic area (POA) showed conspicuous TH immunoreactivity. In the POA, the nucleus preopticus periventricularis (NPP), divisible into anterior (NPPa) and posterior (NPPp) components, showed prominent TH-immunoreactivity. The majority of TH neurones in NPPa showed axonal extensions to the pituitary and were closely associated with LH cells. The NPPa also appeared to be the site for intense interaction between NPY and DA because it contains a rich network of NPY fibres and few immunoreactive cells. Approximately 89.7 ± 1.5% TH neurones in NPPa were contacted by NPY fibres. Superfused POA slices treated with a NPY Y2 -receptor agonist, NPY 13-36 resulted in a significant (P < 0.001) reduction in TH-immunoreactivity in NPPa. TH neurones in NPPa did not respond to NPY Y1 -receptor agonist, [Leu(31) , Pro(34) ] Neuropeptide Y treatment. We suggest that, by inhibiting DAergic neurones in NPPa via Y2 -receptors, NPY may contribute to the up-regulation of the GnRH-LH cells axis. The microcircuitry of DA and NPY and their interaction in NPPa might be a crucial component in the central regulation of LH secretion in the teleosts.

Thyrotropin‐releasing hormone (TRH) in the brain and pituitary of the teleost, Clarias batrachus and its role in regulation of hypophysiotropic dopamine neurons

“…The effect of TRH peptide treatment on DA neurons in the NPPa was determined using POA slice superfusion, followed by western blot analysis and immunofluorescence. The method of slice superfusion and treatment has already been described previously (Kumar et al, ; Singh et al, ; Singh, Kumar, Singh, Bhute, & Singru, ). Briefly, the fish were anesthetized in 2‐phenoxy ethanol (1:2,000 in water) and perfused transcardially with 50 mL sterile HEPES‐buffer Hank's balanced salt solution (pH 7.2).…”

“…2.2 | Total RNA isolation and transcriptome analysis of pro-TRH Adult, female, C. batrachus (n = 2) were anesthetized in 2-phenoxy ethanol (Sigma; 1:2,000 in water), and the brains were rapidly removed and frozen in dry ice. Using a cryostat, a hypothalamic block was isolated, then homogenized to obtain total RNA, as previously described (Kumar, Singh, Saha, & Singru, 2014). Total RNA was isolated using TRIZOL reagent as per manufacturer's instructions (Ambion, Carlsbad, CA).…”

Evidence for the Involvement of Dopamine in Stress‐Induced Suppression of Reproduction in the Cichlid Fish Oreochromis mossambicus

“…This NPOav hypophysial DA pathway has also been characterised in some other teleost species, such as the rainbow trout O. mykiss and the European eel A. anguilla . In the catfish C. batrachus and the carp Cirrhinus cirrhosus , the NPP is subdivided into anterior (NPPa) and posterior (NPPp) components. Although majority of TH neurones in NPPa showed axonal extensions to the pituitary and were closely associated with LH cells in carp C. cirrhosus , using retrograde neuronal tracing, Singh et al ., found that majority of the DA neurones in the NPPa, but none from the NPPp, project to the pituitary.…”

“…In the catfish C. batrachus and the carp Cirrhinus cirrhosus , the NPP is subdivided into anterior (NPPa) and posterior (NPPp) components. Although majority of TH neurones in NPPa showed axonal extensions to the pituitary and were closely associated with LH cells in carp C. cirrhosus , using retrograde neuronal tracing, Singh et al ., found that majority of the DA neurones in the NPPa, but none from the NPPp, project to the pituitary. In the present study, TH immunoreactive neurones from the POA showed fibre extensions to the HHT and PPD in the pituitary, suggesting that the TH cells present in POA are hypophysiotrophic in the tilapia O. mossambicus .…”

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

“…In the western blot analysis of the POA‐hypothalamic tissue of C. batrachus , application of the TH antiserum recognised a single band of approximately 64 kDa, corresponding to the molecular weight of TH . The antiserum has also been used for immunohistochemical localisation of the DAergic system in the brain of other teleosts, including the Indian major carp, Cirrhinus cirrhosis , African cichlid fish, Astatotilapia burtoni , and zebrafish, Danio rerio . The specificity of oxytocin antibody in the POA‐hypothalamus of C. batrachus has also been established .…”