Interaction between Dopamine‐ and Isotocin‐Containing Neurones in the Preoptic Area of the Catfish, Clarias batrachus: Role in the Regulation of Luteinising Hormone Cells

Abstract

Apart from gonadotrophin-releasing hormone (GnRH) and dopamine (DA), oxytocin has emerged as an important endogenous agent that regulates reproduction. Although the interaction between these factors has been extensively studied in mammals, parallel information in teleosts is much limited. We studied the organisation of tyrosine hydroxylase (TH; a marker for dopamine) and isotocin neurones in the preoptic area (POA) and hypothalamus of the catfish, Clarias batrachus and its implication in the regulation of luteinising hormone (LH) cells in the pituitary. Nucleus preopticus periventricularis (NPP), a major dopaminergic centre in the brain, consists of anterior (NPPa) and posterior (NPPp) subdivisions. Using retrograde neuronal tracing, we found that majority of the DA neurones in NPPa, but none from NPPp, project to the pituitary. The nucleus preopticus (NPO) of C. batrachus contains a conspicuous assemblage of large isotocin-positive neurones. It consists of a paraventricular subdivision (NPOpv) located on either side of the third ventricle and lies roughly sandwiched between the dopaminergic neurones of NPPa and NPPp. An additional subset of isotocin neurones was located above the optic chiasm in the supraoptic subdivision of the NPO (NPOso). Isotocin-containing neurones in both the subdivisions of NPO were densely innervated by DA fibres. Superfusion of the POA-containing brain slices with DA D(1) -like receptor agonist (SKF-38393) resulted in significant increase in isotocin immunoreactivity in the NPOpv neurones; NPOso neurones did not respond. However, treatment with DA D(2) -like receptor agonist (quinpirole) reduced isotocin immunoreactivity in the NPOso, but not in the NPOpv. Thus, DA appears to differentially regulate the components of isotocinergic system. Isotocin fibres extend to the pituitary and terminate on LH cells and the superfused pituitary slices treated with isotocin caused significant reduction in LHβ-immunoreactivity. An elaborate interplay between the DA and isotocin systems appears to be an important component of the LH regulatory system.

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

“…TH antiserum used in the present study has been shown to recognise two different forms of TH, TH1 and TH2, in the teleost . We suggest that, as in other teleosts , two types of TH may be present in the POA‐hypothalamus of C. cirrhosus . TH immunoreactive neurones in the POA of C. cirrhosus appear to be DAergic because application of TH, DA and dopamine‐β‐hydroxylase antisera resulted in similar labelling in other teleosts .…”

“…TH antiserum (AB152; Millipore) has been used previously for localisation of dopaminergic neurones in the POA and pituitary of the catfish . To further validate the specificity of TH antiserum in the brain of C. cirrhosus , immunoblot analysis of the OB and POA‐hypothalamus was performed as described below.…”

“…Evidence that GnRH neurones are innervated by NPY fibres , and that NPY stimulates GnRH release and the GnRH–LH axis , also support an indirect effect of NPY on LH. The anterior preoptic area (POA) of the teleost contains neurones synthesising GnRH , NPY and DA . In the POA, NPY‐ and GnRH‐containing systems appear to interact , although the interplay between NPY and DA has not been elucidated.…”

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

“…They noticed many striking similarities in these gene expression profiles between dopaminergic cell populations in teleosts and their putative mammalian homologues and suggested that the DA cell groups are evolutionarily ancient and conserved across vertebrates. Indeed, several studies have employed TH antiserum as a marker for identifying dopaminergic neurones; for example, in the rainbow trout O. mykiss , the Senegalese sole S. senegalensis the zebrafish Danio rerio , the sturgeons Acipenser baeri and Huso huso , the platyfish Xiphophorus maculatus , the goldfish Carassius auratus , the brown ghost knifefish Apteronotus leptorhynchus , the sea bass Dicentrarchus labrax , and the catfish Clarias gariepinus and C. batrachus . Some of these studies have also employed DA or dopamine β hydroxylase immunohistochemistry to show that most of the catecholaminergic neurones in POA and/or NPO are dopaminergic.…”

“…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 .…”