Effects of dopaminergic drugs on locomotor activity in teleost fish of the genus Oreochromis (Cichlidae): involvement of the telencephalon.

Single Oreochromis niloticus and O. mossambicus were placed in an unfamiliar white basin for 21 min, and their activity in this open-field situation was recorded from overhead on video. Apomorphine added to the water (2-8 mg/liter) caused a significant increase in locomotor activity, as assessed by the frequency that a fish swam over a rectilinear array of lines drawn on the base. This effect was attenuated by chlorpromazine (2 mg/liter) and abolished by the D1 antagonist SCH-23390 (1 mg/liter); the D2 antagonist metoclopramide (8 mg/liter) had no effect. Removal of both hemispheres of the telencephalon abolished the response to apomorphine, whereas removal of only one hemisphere or cauterization of the nostrils had no effect. It is concluded that the role of the dopaminergic system in the regulation of locomotor activity is reminiscent of the mammalian mesolimbic, rather than the nigrostriatal, system but that further studies are required to determine the source of the dopaminergic innervation and its likely telencephalic targets.

Hypothalamic regulation of the pituitary-thyroid axis in the tilapia Oreochromis mossambicus.

Electrolytic lesioning of the preoptic area resulted in an increase in plasma thyroxine (T4) and reverse triiodothyronine (rT3) 10 days later; plasma triiodothyronine (T3) levels were not affected, so that there was also a significant decrease in the T3:T4, but not rT3:T4, ratios. No significant changes in T4, T3, or rT3 levels were observed in fish with lesions in either the anterior or posterior portions of the lateral tuberal nucleus. The pituitary contents of growth hormone and the two prolactins were not affected by any lesion. This indicates that the preoptic area may play a role in the inhibitory regulation of the pituitary-thyroid axis in Oreochromis mossambicus, presumably by way of effects on thyrotropin secretion.

Biosynthesis in vivo and excretion of cortisol by fish larvae.

There is a posthatching rise in levels of endogenous cortisol during the ontogeny of those teleosts studied to date. This is thought to be the result of de novo synthesis of cortisol by the larvae, although there is no direct evidence for this. The present study aimed to demonstrate this process in Asian seabass (Lates calcarifer). Larvae (4 days posthatching) were maintained for up to 12 hours in seawater containing [3H]17 alpha-hydroxyprogesterone. High performance liquid chromatography analysis of extracts of the medium, before and after treatment with glucuronidase, indicates conversion of the precursor to several metabolites. One of these was identified as cortisol on the basis of its isopolarity with authentic standard in thin-layer chromatography, and confirmed by recrystallisation to constant specific activity. Immunohistochemistry on siblings shows that the interrenals are immunoreactive for adrenodoxin (adrenal ferredoxin) and cytochrome P-450(21) (steroid 21-monooxygenase [steroid, hydrogen-donor:oxygen oxidoreductase, 21-hydroxylating]; EC 1.14.99.10), and the pituitary for adrenocorticotrophic hormone. These findings suggest that the pituitary-interrenal axis is functional even at this early stage, and are consistent with the hypothesis that the posthatching rise in endogenous cortisol levels is the result of de novo steroidogenesis.

Ontogeny of immunoreactive steroidogenic proteins (adrenodoxin and cytochrome p-450(21)) in the interrenals of the teleost Lates calcarifer.

Antisera against bovine adrenodoxin and cytochrome P-450(21) (steroid 21-hydroxylase) cross-reacted with the interrenal cells of the adult Asian seabass (Lates calcarifer); the cells were arranged as cords, two cells thick, in the headkidney. During larval development, cells immunoreactive for adrenodoxin were first observed 1 day posthatching (dph); immunoreactivity for cytochrome P-450(21) was first detected at 1.5 dph. Initially, the interrenal cells occurred as a mass in each headkidney, which only became identifiable histologically at 5 dph. The number of interrenal cells increased with age, becoming associated with the cardinal veins at 14 dph. The present study thus indicates that the posthatching rise in cortisol may originate from the nascent interrenal tissue.

Osmoregulation in the mudskipper,Boleophthalmus boddaerti II. transepithelial potential and hormonal control.

Boleophthalmus boddaerti submerged in 10%, 50% and 80% seawater (sw) for 7 days, had whole body transepithelial potentials (TEP) of 3.3, 18.3 and 22.9 mV, respectively. Hypophysectomy significantly decreased the TEP ofB. boddaerti and reversed the polarity of the TEP of the fish exposed to 10% sw.Hypophysectomy also significantly decreased the branchial Na(+)-K(+) activated adenosine triphosphatase (Na(+),K(+)-ATPase) activity but increased the activity of branchial HCO3 (-)-Cl(-) stimulated adenosine triphosphatase (HCO3 (-),Cl(-)-ATPase) inB. boddaerti exposed to 10% sw. However, survival in 10% sw was not significantly impaired by hypophysectomy and no significant change in plasma osmolality and plasma Na(+) and Cl(-) concentrations was observed.Various doses of ovine-prolactin or salmon-prolactin were unable to restore the TEP of hypophysectomizedB. boddaerti in 10% sw to that of the sham-operated fish. However, cortisol increased TEP to a positive value in hypophysectomizedB. boddaerti, though it was still lower than the sham-operated control. Cortisol treatment also affected the plasma osmolality, plasma Na(+) and Cl(-) contents and branchial Na(+),K(+)-ATPase and HCO3 (-),Cl(-)-ATPase activities. Overall, the hormonal control of osmoregulation inB. boddaerti appeared to differ from that of other teleosts.

Retinopetal projections from a subpopulation of ganglion cells of the nervus terminalis in the dwarf gourami (Colisa lalia).

The ganglion cells of the nervus terminalis (NT cells) of the dwarf gourami could be classified into type I (giant) and type II (medium to large) cells. After unilateral application of cobaltic-lysine to the optic nerve, only the type II NT cells on the contralateral side were retrogradely labelled. The dendrites ramified near the cell bodies and invaded the olfactory bulb. The axons ran caudally, while taking dorsal and ventral courses, through the ventral telencephalon and the lateral preoptic area, and entered the optic tract.

The effects of apomorphine, d-amphetamine and chlorpromazine on the aggressiveness of isolated Aequidens pulcher (Teleostei, Cichlidae).

Apomorphine, d-amphetamine, chlorpromazine and dopamine, added to the aquarium water, were tested for their effects on the aggressive responses of isolated fish to mirrors and to models, compared with the responses of the same fish as non-treated controls tested at the start of, in the middle, and at the end of the experiment (Experiment 1). The effects of d-amphetamine administered by intracranial injection were also evaluated for responses to mirror presentations (Experiment 2). The three sets of controls in Experiment 1 indicate that the responses of the fish apparently changed over the 32-day experiment: they became more aggressive to mirrors whilst reacting less to models. Dopamine had no behavioural effect. Immersion in either apomorphine or d-amphetamine resulted in increased swimming activity, accompanied by apparent behavioural stereotypy. Immersion in apomorphine (Experiment 1) and intracranial injections of d-amphetamine (Experiment 2) also resulted in reduced aggression. Likewise, chlorpromazine also reduced some measures of overt aggression, whilst the appearance of other behaviours suggested that there is also an increased tendency to withdraw from the stimulus. It is concluded that the dopaminergic system plays an important role in the regulation of aggressive behaviour in this cichlid fish.

Effects of melatonin, serotonin, and naloxone on aggression in isolated cichlid fish (Aequidens pulcher).

Intracranial injections of 10 micrograms melatonin, with or without 4 micrograms naloxone, result in reduced aggressive responsiveness by the cichlid fish Aequidens pulcher to a mirror presented 20 min later. Naloxone, when administered on its own, had no behavioral effect. Intracranial injections of 25 micrograms serotonin-creatinine sulphate complex (5HT-CS) also reduced aggression. 5HT-CS's action was abolished if the injection included 10 micrograms S-adenosyl homocysteine (SAH), which inhibits the conversion of serotonin to melatonin. This suggests that the behavioral action of 5HT-CS may be mediated by its conversion to melatonin. There is inconclusive evidence to suggest that 37.5 micrograms 5HT-CS, administered in conjunction with 10 micrograms SAH, may reduce aggressiveness; injection of 50 micrograms 5HT-CS, with or without 10 micrograms SAH, induced a pronounced escape behavior which precluded any measurement of aggressiveness in the fish.

Steroid hormones and agonistic behavior in a cichlid teleost, Aequidens pulcher.

The effects of three steroid hormones on the agonistic behavior of female Aequidens pulcher have been evaluated. Testosterone, estradiol, and cortisol were tested using an immersion technique to minimize trauma, and we also examined metyrapone, a blocker of cortisol biosynthesis. Two different experimental protocols were employed, the first investigating agonistic interactions within groups of fish, and the second examining the responses of isolated fish to models and mirrors. Differences between replicates were small, and both protocols supported similar conclusions. Each of the three hormones produced a characteristically different spectrum of behaviors when compared to the controls. Testosterone increased agonistic behavior in all experimental situations, while estradiol had a generally opposite effect; this may reflect the natural modulation of behavior by hormones during the reproductive cycle of A. pulcher. Cortisol also had distinct behavioral effects; available evidence suggests that this steroid increases submissive components of agonistic behavior, and that observed increases in some aggressive components are an indirect consequence, dependent upon the feedback of social information received by each fish. Metyrapone treatment greatly reduced all agonistic behaviors, groups of fish forming shoals typical of juveniles. This was not reversed by replacement therapy with cortisol, which suggests that metyrapone affects behavior by an alternative, possibly toxic, mechanism.

The structure of the adenohypophysis of Aequidens pulcher (Teleostei, Cichlidae). I. Histological and immunohistochemical studies.

With standard staining techniques, five cell types can be identified in the pars distalis of the adenohypophysis of Aequidens pulcher; a sixth cell type prevails in the pars intermedia. Each of these cell types has been characterized immunohistochemically. Various treatments--metyrapone, thiourea, and thyroxine--have been used to confirm the identity of the corticotrophs and the thyrotrophs. It is concluded that the cells producing prolactin and growth hormone are tinctorially, immunologically, and topographically similar to descriptions for other teleosts. This also applies for the corticotrophs of the rostral pars distalis and the melanotrophs in the pars intermedia. The corticotrophs are stimulated by metyrapone treatment, on the basis of cell size and tinctorial properties, but immunohistochemical staining is not affected; thiourea, on the other hand, affects immunohistochemical, but not tinctorial, staining of the corticotrophs. The thyrotrophs are small, irregularly shaped cells in the rostrodorsal proximal pars distalis, adjacent to the neurohypophysis. They cross-react with an antiserum against bovine beta-TSH but (unlike the gonadotrophs) not with one against ovine LH. Thiourea treatment induces their hypertrophy, with a decrease in tinctorial and immunohistochemical stainability. Metyrapone, like thiourea, induces enlarged nuclei with pronounced nucleoli but, like thyroxine, also increases tinctorial and immunohistochemical staining. The gonadotrophs are basophilic, like the thyrotrophs, but cross-react with antisera against both bovine beta-TSH and ovine LH. These cells are not affected by any of the treatments used here. In some specimens, a second type of gonadotroph has been identified, which stains mainly with periodic acid-Schiff. The two types of gonadotrophs are immunohistochemically comparable.