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Role of Isotocin in the Regulation of the Hypophysiotropic Dopamine Neurones in the Preoptic Area of the Catfish, Clarias batrachus
Author(s) -
Singh O.,
Kumar S.,
Singh U.,
Bhute Y.,
Singru P. S.
Publication year - 2016
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/jne.12441
Subject(s) - medicine , endocrinology , biology , dopamine , preoptic area , prolactin , hypothalamus , catfish , hormone , fish <actinopterygii> , fishery
Dopamine ( DA ) has emerged as a potent inhibitory neuromodulator of luteinsing hormone ( LH) secretion and reproduction in teleosts. The DA neurones located in the anterior subdivision of nucleus preopticus periventricularis ( NPP a) in the preoptic area ( POA ) innervate the pituitary gland and regulate LH cells. Although a reduction in the inhibitory DA ergic tone is crucial for stimulatory action of gonadotrophin‐releasing hormone (Gn RH) on LH cells, the role of other hypothalamic factors is suggested but not fully understood. Nonapeptide, isotocin ( IST ) has emerged as a likely candidate that may also influence the LH cell function. IST neurones reside in the nucleus preopticus and innervate LH cells. While IST treatment dramatically elevated LH secretion, the IST levels in brain peaked during spawning. In a pilot study on the catfish, Clarias batrachus , we observed a dense network of IST ‐immunoreactive (IST‐IR) fibres in the NPP a, the region known to harbour hypophysiotropic DA neurones. Application of the double immunofluorescence method showed a dense IST ‐IR fibre network around the tyrosine hydroxylase‐immunoreactive (TH‐IR) neurones in the NPP a region. A great majority of the TH ‐IR neurones in the NPP a were contacted by IST ‐IR fibres during the spawning phase. The NPP a therefore appears to be a site for the intense interaction of DA and IST . IST ‐IR fibre innervation in NPP a showed reproduction phase‐dependent changes. The percent fluorescent area of IST ‐IR fibres showed a gradual increase from the resting through prespawning phases (resting: 7.5 ± 1.04; preparatory: 8.6 ± 0.8; prespawning: 15.5 ± 1.4), reaching a peak in the spawning phase (28 ± 2.3; P < 0.001). Compared to the spawning phase, a drastic reduction in IST ‐IR fibres in the NPP a was observed during the postspawning phase (8.4 ± 0.9; P < 0.001). Superfused slices of the POA of C. batrachus treated with IST peptide resulted in a significant reduction in TH immunoreactivity in the NPP a (Control: 45.3 ± 4.2; IST peptide, 5 μ m : 29.4 ± 4.7; P < 0.05). We suggest that the intense interaction between IST and DA in the NPP a, most probably of an inhibitory nature, may be critical for the regulation of LH cells and reproduction in teleosts.