Pakistan Journal of Biological Sciences1028-88801812-5735Asian Network for Scientific Information10.3923/pjbs.2009.1.10Siganus canaliculatus)]]>AmiriM.H. 12009121The present investigation was undertaken to study the
nature of neuro-melanophore junction in the white-spotted rabbit fish
Siganus cancliculatus. In vitro experiments using split
fin preparation indicated that melanophores of S. cancliculatus
are highly responsive to potassium ions and adrenergic agonists. Potassium
ions and the adrenergic agonists induced prompt melanosome aggregation
that could be competitively blocked by yohimbine (alpha-2 specific adrenergic
antagonist) and phentolamine (non-specific alpha adrenergic antagonist).
The melanophore responses to repeated potassium stimulation (up to 20
stimuli) did not show any sign of fatigue. However, statistically significant
enhancement was observed in responses to potassium that followed the first
five stimulations. Adrenergic agonists acted in a time and concentration-dependent
manner and their relative potency had the following rank order: clonidine
(alpha-2 specific agonist) > norepinephrine (non-specific adrenergic
agonist) > phenylephrine (alpha-1 specific agonist) > methoxamine
(alpha-1-specific agonist). Yohimbine exerted a more potent inhibiting
effect on norepinephrine induced melanosome aggregation compared to phentolamine.
Prazosine (alpha-1 specific antagonist) had no effect on such aggregation.
Chemically denervated melanophores displayed hypersensitivity to alpha-adrenergic
agonists but were refractive to potassium ion stimulation. The refractivity
of denervated melanophores to potassium indicates the effect of potassium
ion is not direct on melanophores but it is rather through depolarization
effect of potassium on the neuro-melanophore peripheral sympathetic fibers
and hence release of norepinephrine. In denervated melanophores, similar
to intact melanophores, only phentolamine and yohimbine but not prazosine,
significantly inhibited melanosome aggregation effect of norepinephrine,
indicating that norepinephrine effect is through postsynaptic alpha-2
adrenoceptors. The present data demonstrate that the nature of melanophore
innervation in this teleost is adrenergic and neuro-melanophore signals
mediating melanosome aggregation are transmitted through alpha-2 postsynaptic
adrenoceptors.]]>Andersson, R.G.G., J.O. Karlsson and N. Grundstrom,1984121173179Burton, D. and B. A. Everard,1990in vitro Na and K+ induction of teleost melanosome movements.]]>946631633Burton, D. and B.A. Everard,1991in vitro K+ and Na>sup>+ stimulus repetition in pseudopleuronectes americanus.]]>98A413416Burton, D. and M.P. O’Driscall,1992168289299Burton, D. and J.E. Vokey,20001- and α2-adrenoceptor mediation in melanosome aggregation in cryptic patterning of pleuronectes americanus.]]>125A359365Custrucci, A.M.,1975Tilapia melanopleura-I. Ultrastructure and effect of sodium and potassium on melanosome migration.]]>50A453456Fujii, R.,1959324759Fujii, R.,19931993pp: 535-556pp: 535-556Fujii, R.,200013300319Fujii, R. and R.R. Novales,19721972pp: 315-326pp: 315-326Fujii, R. and Y. Miyashita,19761976pp: 336-344pp: 336-344Fujii, R. and N. Oshima,198631347Fujii, R. and N. Oshima,199420154Hogben, L.T. and D. Slome,19311081053Karlsson, J.O.G., N. Grundstrom, J.E.S. Wikberg, R. Friedman and R.G.G. Andersson,19853710431049Karlsson, J.O.G., R.G.G. Andersson, H. Elwing and N. Grundstrom,198788C287291 Kasukawa, H, M. Sugimoto, N. Oshima and R. Fujii,1985C 81253257Katayama, H, Y. Isogai, F. Morishita and K. Yamada,1990342939Kumazawa, T. and R. Fujii,198478C263266Martensson, L.G.E. and R.G.G. Andersson,19976015751582Miyata, S. and K. Yamada,19872413139Morishita, F.,198788C6974Musaiger, A. O. and R. D’Souza,2008115561Novales, R.R. and R. Fujii,197075133136Smith, D.C.,1941132245248Starke, K., T. Endo and H.D. Taube,19752915578Strake, K.,198188199263Visconti, M. A. and A.M.L. Castrucci,19903132140