Mukund M. Hanumante

Localization of substance P-like, leucine-enkephalin-like, methionine-enkephalin-like, and FMRFamide-like immunoreactivity in the eyestalk of the fiddler crab, Uca pugilator

SummaryThe occurrence and distribution of substance P (SP)-like, methionine-(Met)- and leucine-(Leu)-enkephalinlike, and FMRFamide-like immunoreactivities were determined in the neuroendocrine complex of the eyestalk of the fiddler crab, Uca pugilator, by immunocytochemistry. SP-like immunoreactivity was found in the optic peduncle, sinus gland, medulla externa, medulla interna, lamina ganglionaris, and retinular cells. Met-enkephalin-like and Leuenkephalin-like immunoreactivity was observed in most of the retinular cells, optic peduncle, sinus gland, medulla terminalis, and lamina ganglionaris. However, Met-enkephalin-like, but no Leu-enkephalin-like, immunoreactivity was seen in the medulla terminalis X-organ. FMRFamide-like immunoreactivity could be seen in all parts of the eyestalk except in the sinus gland, lamina ganglionaris, and retinular cells. FMRF-amide-like activity was especially strong in the three chiasmatic regions connecting the optic ganglia. The possibility that these four peptides may function as neuroregulators in the fiddler crab is discussed.

EFFECTS OF NOREPINEPHRINE AND NOREPINEPHRINE AGONISTS AND ANTAGONISTS ON THE MELANOPHORES OF THE FIDDLER CRAB UCA PUGILATOR

Norepinephrine produces dose-related pigment dispersion in the melanophores of intact and eyestalkless fiddler crabs, Uca pugilator, but has no effect on the melanophores in isolated legs. 2. The effects of agonists and antagonists of norepinephrine on the rates of melanin dis- persion and concentration were determined. 3. The results are consistent with the hypothesis that norepinephrine exerted its effect by acting on the central nervous system to trigger the release of melanin-dispersing hormone. Migration of the pigment in the chromatophores of the fiddler crab Uca pugi- lator is hormonally regulated (Carlson, 1935; Sandeen, 1950; Brown, 1950; Fin- german, 1956a). A series of experiments performed with this crab has revealed that release of red pigment-dispersing hormone is triggered by 5-hydroxytrypt- amine (=serotonin) (Rao and Fingerman, 1970b) whereas release of red pigment- concentrating hormone is triggered by dopamine (Fingerman and Fingerman, 1977). However, no one has as yet identified a neurotransmitter substance which appears to be involved in triggering release of melanin-dispersing hormone (MDH), melanin-concentrating hormone (MCH), white pigment-dispersing hor- mone, or white pigment-concentrating hormone in any species of fiddler crab. Abramowitz and Abramowitz (1938) tested both acetylcholine and epinephrine on melanophores of Uca pugilator, and reported that they had no effect in either producing dispersion or aggregation of the pigment in these cells. Although Bau- chau and Mengeot (1966) found that 5-hydroxytryptamine will produce dispersion of the pigment in the melanophores of the shore crab Carcinus maenas, Rao and Fingerman (1970a) observed that this compound has no such effect on the me- lanophores of Uca pugilator. Presented below are the results of a series of ex- periments which led to identification of norepinephrine as a neurotransmitter substance that appears to be involved in triggering release of MDH in Uca pu- gilator. Experiments were also performed to identify a neurotransmitter sub- stance that might be involved in release of white pigment-dispersing hormone, but these were unsuccessful.

The effects of biogenic amines on color changes of the fiddler crab, Uca pugilator: Further evidence for roles of 5-hydroxytryptamine and dopamine as neurotransmitters triggering release of erythrophorotropic hormones☆

Abstract 1. 1. The effects of 5-hydroxytrytryptaminergic potentiators (Fluvoxamine and Fluoxetine), a 5-hydroxytryptaminergic antagonist (LY53857), a dopaminergic agonist (ADTN) and dopaminergic antagonists (Spiroperidol and γ-hydroxybutyrate) on color changes involving the erythrophores of the fiddler crab, Uca pugilator, were determined. 2. 2. The results were consistent with the hypotheses that 5-hydroxytryptamine triggers release of a red pigment-dispersing hormone and that dopamine triggers release of a red pigment-concentrating hormone in Uca pugilator.

Further evidence for norepinephrine as a neurotransmitter stimulating release of melanin-dispersing hormone in the fiddler crab, Uca pugilator: The changes in the melanophores of the crabs following reserpine, 6-hydroxydopamine and bretylium administration

1. The effects on the melanophores of the fiddler crab, Uca pugilator, of the amine depletor reserpine, the catecholamine neurotoxin 6-hydroxydopamine and the noradrenergic neuron blocker bretylium were investigated. 2. The most striking effect of these drugs was that they strongly reduced the amount of melanin dispersion that normally results on transferring the crabs from a white to a black background. the drugs had no effect on pigment migration in melanophores of isolated legs. These results are in accord with the hypothesis that norepinephrine serves as a neurotransmitter stimulating release of a melanin-dispersing hormone in Uca pugilator. 3. Norepinephrine was found in the central nervous system of Uca pugilator.

5-Hydroxytryptaminergic control of red pigment-dispersing hormone release in the fiddler crab, Uca pugilator: Effects of a 5-hydroxytryptamine uptake inhibitor and a 5-hydroxytryptamine receptor blocker on 5-hydroxytryptamine-induced and iproniazid-induced red pigment dispersion

Abstract The effects of the 5-hydroxytryptamine (5-HT, serotonin) uptake inhibitor, fluoxetine, and the 5-HT receptor blocker, LY53857, on red pigment migration induced by 5-HT and iproniazid in the fiddler crab, Uca pugilator , were determined. Fluoxetine potentiated and LY53857 antagonized (a) 5-HT- and iproniazid-induced red pigment dispersion in crabs kept on a white background, (b) the accelerated rate of red pigment dispersion that occurs in iproniazid-injected intact crabs transferred from a white to a black background, and (c) the decreased rate of red pigment concentration that occurs in ipronizaid-injected intact crabs transferred from a black to a white background. These results are consistent with the hypothesis that 5-HT triggers the release of red pigment-dispersing hormone in Uca pugilator .

Responses of the melanophores of the fiddler crab, Uca pugilator, to drugs affecting noradrenergic neurotransmission: Further evidence for norepinephrine as a neurotransmitter triggering release of melanin-dispersing hormone

Abstract 1. The effects on the melanophores of the fiddler crab, U ca pugilator , prazosin which blocks α 1 -adrenoceptors, yohimbine which is an α 2 -adrenoceptor blocker, phentolamine which blocks both types of α-adrenoceptors and nisoxetine which inhibits norepinephrine uptake were determined. 2. The results are consistent with the hypothesis that norepinephrine is the neurotransmitter which triggers release of melanin-dispersing hormone in U. pugilator .

Roles of 5-hydroxytryptamine and dopamine as neurotransmitters eliciting release of erythrophorotropic hormones in the fiddler crab, Uca pugilator

This article reviews the endocrinological, pharmacological and biochemical evidence ascribing neurotransmitter roles for 5-hydroxytryptamine (5-HT, serotonin) in eliciting the release of red pigment-dispersing hormone (RPDH) and for dopamine (DA) in stimulating the release of red pigment-concentrating hormone (RPCH) in the fiddler crab, Uca pugilator. 5-HT produces red pigment dispersion in intact crabs, but only indirectly. Likewise, DA evokes red pigment concentration in vivo but it has no effect on red chromatophores (erythrophores) in isolated legs. The data obtained with 5-HT and DA agonists and antagonists on red pigment translocation in vivo and in vitro, are consistent with their neurotransmitter candidacies in evoking the release of these erythrophorotropic hormones.

Pharmacological Evidence for Involvement of Presynaptic Alpha2 Adrenoceptors in Norepinephrinergic Neurotransmission Triggering the Release of Melanin-dispersing Hormone in the Fiddler Crab Uca Pugilator

ABSTRACT 1. The specific alpha2 adrenoceptor agonist B-HT 933 significantly reduced the rate of melanin dispersion in crabs transferred from a white to a black background. 2. The specific alpha2 adrenoceptor blockers rauwolscine and yohimbine significantly increased the rate of melanin dispersion in crabs transferred from a white to a black background. 3. Rauwolscine and yohimbine, but not the alpha, adrenoceptor blocker indoramin, antagonized B-HT 933. 4. In crabs pretreated with the catecholaminergic neurotoxin 6-hydroxydopamine, which inhibits melanin dispersion, B-HT 933 did not produce further significant inhibition in the rate of melanin dispersion. 5. None of the drugs has been found to affect melanin migration in melanophores of isolated legs. 6. The results are consistent with the hypothesis that presynaptic adrenoceptors very similar to alpha2 adrenoceptors of mammals regulate impulse-mediated norepinephrinergic neurotransmission in the fiddler crab Uca pugilator, norepinephrine triggering release of a melanin-dispersing hormone.

INHIBITORY EFFECT OF HISTAMINE ON THE RELEASE OF MELANIN-DISPERSING HORMONE IN THE FIDDLER CRAB, UCA PUGILATOR

Histamine (HA), a stimulator of H1 and H2 receptors, produced dose-dependent inhibition of the melanin dispersion which normally occurs when fiddler crabs, Uca pugilator, are transferred from a white to a black background. The HA precursor L-histidine, and 4-methyl histamine (4-MeHA), an H2 receptor agonist, also inhibited melanin dispersion. 2-Methyl histamine (2-MeHA), an H1 receptor agonist, enhanced melanin dispersion. The inhibitory effects of HA and 4-MeHA were abolished by the H2 receptor blocker metiamide but not by blockers of either H1 receptors or alpha1 adrenoceptors. Melanin-dispersing hormone (MDH) release is accomplished mainly by stimulation of alpha1 adrenoceptors with norepinephrine appearing to be the neurotransmitter involved. The H1 receptor blockers pyrilamine and SA-97 antagonized 2-MeHA. HA-induced inhibition of melanin dispersion was potentiated by the noradrenergic neuron blocker bretylium and the alpha2 adrenoceptor agonist B-HT 933. HA did not significantly affect melanin dispe...

Effects of monoamines and monoaminergic agents on migration of the red pigment in chromatophores of the shrimp, Macrobrachium ohione

Abstract 1. The effects of 5-hydroxytryptamine (5-HT) and the 5-hydroxytryptaminergic agents fenfluramine, fluoxetine and 5-MeODMT, and of dopamine (DA) and the dopaminergic agents ADTN, apor-morphine and piribedil on the disposition and translocation of the red pigment in chromatophores of the shrimp, Macrobrachium ohione, were determined. 2. 5-HT evoked dose-dependent red pigment dispersion whereas DA produced dose-related concentration of the red pigment, but only in intact shrimp. Neither of these monoamines affected red pigment migration in vitro. 3. The data obtained using drugs known to act selectively in mammals via 5-hydroxytryptaminergic and dopaminergic mechanisms on the translocation of the red pigment from the chromatophores both in vitro and in vitro lead to the hypothesis that 5-HT and DA serve as neurotransmitters triggering release of red pigment-dispersing hormone and red pigment-concentrating hormone, respectively, in the shrimp, Macrobrachium ohione.