<i>In vitro</i> brain tyrosine hydroxylase activation in catfish <i>Heteropneustes</i> <i>fossilis </i>(Bloch): Seasonal changes in involvement of cAMP–dependent protein kinase A and Ca²⁺-dependent protein kinase C

Abstract

<smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="metricconverter"> In the present <i>in vitro</i> study, the involvement of cAMP dependent-protein kinase A (PKA) and calcium–dependent protein kinase C (PKC) in the regulation of forebrain (telencephalon and hypothalamus) tyrosine hydroxylase (TH) activity was demonstrated during the reproductive seasons of the female catfish <i>H. fossilis</i>. In the concentration studies conducted in prespawning phase, cAMP (0.05 n<i>M</i>, 0.5 n<i>M</i>, 1 m<i>M</i> and 2.0 m<i>M</i>) or the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX-0.5-2.0mM) stimulated enzyme activity. Likewise, the incubation of the enzyme preparations with the cAMP dependent-protein kinase A inhibitor H-89 (1 and 10 m<i>M</i>) and PKC inhibitor calphostin C (cal C; 1 and 10 m<i>M</i>) inhibited enzyme activity in a concentration-dependent manner. In seasonal studies, the incubation of the enzyme preparations with cAMP (1 m<i>M</i>), IBMX (1 m<i>M</i>), H-89 (10 m<i>M</i>) and cal-C (10 m<i>M</i>) produced season–dependent effects on enzyme activity. The stimulatory effect of cAMP and IBMX and the inhibitory effect of H-89 and cal C were greater in the resting and spawning phases. The results suggest the involvement of both signal transduction pathways in TH activation vis-à-vis catecholaminergic activity with a more dominant role by the cAMP-PKA pathway. </smarttagtype>