Seasonal and daily variations in hypothalamic monoamine levels and monoamine oxidase activity in the teleost Channa punctatus (Bloch)

Possible roles of photoperiod and melatonin in reproductive activity via changes in dopaminergic activity in the brain of a tropical damselfish, Chrysiptera cyanea

The perception of periodical change in photoperiodic conditions by photosensory organs is the first step to initiating reproductive activity in fish. To date, it is not known how photoperiodic cues are endogenously transduced to the endocrine network of the brain-pituitary-gonad axis after the perception of photoperiodic stimuli. Because dopamine (DA) inhibits gonadotropin release from the pituitary in certain teleosts, it is likely that it is a key mediator of photoperiodic stimulation. We examined the relationship between photoperiodicity and dopaminergic activity in the brain of the sapphire devil Chrysiptera cyanea, which is a reef-associated damselfish and uses long-day conditions for triggering gonadal development. DA and 3,4-dihydroxyphenylacetic acid (DOPAC; DA metabolite) were measured electrochemically with a high-performance liquid chromatography (HPLC) system, and then DOPAC/DA (metabolic rate of DA activity) was determined. Daily fluctuations in DA, DOPAC, and DOPAC/DA were observed under LD 12:12. Light-dark cycles, but not constant conditions, influenced DA and DOPAC contents as well as DOPAC/DA in the brain; DOPAC content and DOPAC/DA increased under LD 14:10, while DA increased under LD 10:14. When fish were reared in melatonin-containing water, DOPAC and DOPAC/DA, but not DA, decreased within 6h after treatment. Culturing the isolated brain with melatonin stimulated DA release into the medium. Active vitellogenesis in females during the reproductive season was suppressed by melatonin treatment. These results suggest that day length alters DA metabolism in the brain of the sapphire devil through fluctuations in melatonin caused by external light stimuli, and that inhibitory effects on gonadal development are partially controlled by interactions within the melatonin-DA system.

Influence of temporal relationships between serotonergic and dopaminergic precursors on the regulation of gonadal development in birds

This article is focused on the effect of specific phase relation of serotonergic and dopaminergic oscillations on the gonadal responses of different avian species. These species include (i) summer breeding birds - Red headed bunting (exhibiting post-reproductive absolute photorefractoriness) and Indian Weaver bird (which lacks absolute photorefractoriness), (ii) autumn breeding - Spotted munia and Lal munia (photoperiodic responses of which are distinctly different from that of any long day birds described thus far) and (iii) domesticated Japanese quail (which under natural day length breeds in summer, exhibits relative photorefractoriness, but breeds continuously if maintained in long photoperiod). Previous experiments have shown that daily administration of serotonin precursor 5-hydroxytryptophan and dopamine precursor L-dihydroxyphenylalanine given 8h apart during progressive phase of gonadal cycle can lead to a significant decrease in gonadal activity. However, if given at an interval of 12h it leads to an increase in gonadal activity and the effect of other intervals (0-, 4-, 16- and 20-h) were not different from control. Similar effects were observed during regressive phase of the gonadal cycle of above species except in those which display absolute photorefractory phase in their breeding cycle. This shows that, gonad of such species not only develop post-reproductive photorefractoriness but also becomes insensitive to the stimulatory effects of 5-HTP and L-DOPA when given at the interval of 12h. It is suggested that, temporal phase relation of circadian serotonergic and dopaminergic oscillations is the basis of seasonality in birds and may alter the activity of neuroendocrine-gonadal axis not only under natural day length but also under experimental/different photoperiodic conditions. These results are in agreement with the internal coincidence model of photoperiodic time measurement and indicate that birds can detect specific phase relationship between the two neural oscillations for their reproductive regulations and circadian organization is intricately involved in the regulation of seasonality.

Temporal and periovulatory changes in ovarian catecholamines in the catfish Heteropneustes fossilis

A high performance liquid chromatography-fluorescence detection method was employed to demonstrate temporal and periovulatory changes in ovarian catecholamines in the catfish Heteropneustes fossilis. Tyrosine, L-DOPA, dopamine (DA), norepinephrine (NE) and epinephrine showed significant seasonal and diurnal changes during the reproductive cycle. A high concentration of tyrosine was detected, the values increased in day and decreased in night during recrudescence from preparatory to spawning phases. Similarly, L-DOPA increased during the breeding phase giving the day value concentration peak in the spawning phase and the night value peak in the postspawning phase. DA activity or turnover index (calculated as a ratio of DA to 3,4-dihydroxyphenylacetic acid, DOPAC) showed a bimodal pattern with the major activity peak in the postspawning phase and the minor one in the prespawning phase, the spawning phase registered the lowest activity. NE activity or turnover index (ratio of NE to normetanephrine, NME) increased during the recrudescent phase to give the peak in the spawning phase and decreased in the quiescent phase. Epinephrine elicited an inverse relationship in the day-night pattern, the day values increased to the peak in the spawning phase. All the study correlates showed significant periovulatory changes after hCG treatment. DA activity dropped to the nadir at 8h but recovered at 16 and 24h. NE activity showed only a marginal decrease up to 16h but decreased drastically at 24h. Epinephrine levels remained unchanged but only to increase at 24h. The seasonal patterns and periovulatory changes strongly point to important functions for catecholamines in the ovary. The occurrence of tyramine (an invertebrate neurotransmitter) suggests the presence of alternate catecholamine pathway in fish ovary.

Temperature variation in the 24 hours before the initial symptoms of stroke

A few studies have performed to evaluate the temperature variation influences over on the stroke rates in Brazil.

METHOD

176 medical records of inpatients were analyzed after having had a stroke between 2004 and 2006 at Hospital Israelita Albert Einstein. The temperature preceding the occurrence of the symptoms was recorded, as well as the temperature 6, 12 and 24 hours before the symptoms in 6 different weather substations, closest to their houses in São Paulo.

RESULTS

Strokes occurred more frequently after a variation of 3 C between 6 and 24 hours before the symptoms. There were most hospitalizations between 23-24 C.

CONCLUSION

Incidence of stroke on these patients was increased after a variation of 3 masculine Celsius within 24 hours before the ictus. The temperature variations could be an important factor in the occurrence of strokes in this population.

Dopaminergic activity in the brain of a tropical wrasse in response to changes in light and hydrostatic pressure

Many tropical wrasses show a daily pattern of spawning with gamete release typically near daytime high tide. The environmental cues the fish obtains from day-night and tidal cycles to ensure spawning synchrony and how those cues are transduced, however, are not fully understood. To gain insight into these issues, the involvement of monoamines in mediating endogenous day-night and tidal rhythms in the threespot wrasse, Halichoeres trimaculatus, were examined. Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC, a metabolite of DA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA, a metabolite of 5-HT) in the brain of the fish were measured with high-performance liquid chromatography and electrochemical detection. DOPAC and the metabolic rate of DA activity (DOPAC/DA) were found to increase during the day and decrease during the night for fish held under a natural photoperiod. Fish acclimated to a 12:12 light-dark cycle and to constant dark conditions exhibited similar changes, whereas fish acclimated to constant light conditions exhibited little or no change. Intraperitoneal injection of melatonin resulted in a significant reduction in DOPAC/DA. Furthermore, DOPAC/DA was significantly lower in fish held at 3m compared to 0m depth, suggesting that hydrostatic pressure influences DA metabolic rate. These results indicate that light and hydrostatic pressure control dopaminergic turnover in the brain of threespot wrasse. Day-night and tidal changes in these two factors therefore may be the main environmental cues the fish uses to synchronize its spawning activity.

Evidence for an endogenous clock in the retina of rainbow trout: II. Circadian rhythmicity of serotonin metabolism

The purpose of the present study was to investigate patterns of circadian rhythmicity in the retina of a salmonid fish, the rainbow trout (Oncorhynchus mykiss). Our data present the first demonstration of intraretinal variations of serotonergic substances under light/dark-conditions (LD) and during continuous darkness (DD). All substances examined (serotonin, N-acetyl serotonin, 5-hydroxytryptophol, 5-hydroxyindole acetic acid) were rhythmic in LD. Serotonin, N-acetyl-serotonin, and 5-hydroxyindole acetic acid showed a preservation of specific features of rhythmicity in DD indicating the involvement of an endogenous pacemaker in the regulation of serotonin metabolism in the rainbow trout eye.

Effects of estradiol on the serotonin secretion and turnover in the hypothalamus of male tilapia, Oreochromis mossambicus, in vitro

The effects of estradiol on the secretion and turnover of serotonin in the hypothalamic fragments of male tilapia, Oreochromis mossambicus, were studied using a static incubation system. The quantitative analysis of serotonin and its related metabolite, 5-hydroxyindoleacetic acid, were performed by high-performance liquid chromatography with electrochemical detection. The hypothalamic fragments were incubated with 17 beta-estradiol at a concentration of 2 x 10(-8), 8 x 10(-8), 2 x 10(-7), 4 x 10(-7), or 4 x 10(-6) g/ml. The low dose of estradiol, 2 x 10(-8) g/ml, had no effect on the concentration of serotonin and 5-hydroxyindoleacetic acid or serotonin turnover in the hypothalamic incubation media. The moderate doses of estradiol 8 x 10(-8) and 2 x 10(-7) g/ml, increased the concentrations of serotonin and 5-hydroxyindoleacetic acid in the hypothalamic incubation media, but had no effect on the serotonin turnover. The high doses of estradiol, 4 x 10(-7) and 4 x 10(-6) g/ml, did not alter the serotonin concentration in the hypothalamic incubation media, but increased the 5-hydroxyindoleacetic acid concentration and serotonin turnover. These results demonstrate that the moderate dose of estradiol increases the serotonin activity by increasing the serotonin concentration, whereas the high dose of estradiol increases the serotonin activity by increasing the ratio of 5-hydroxyindoleacetic acid and serotonin. However, the serotonin concentration is homeostatically maintained in the extracellular fluid of hypothalamus under the high dose of E2 treatment.

Effects of photoperiod alterations on day-night variations in hypothalamic serotonin content and turnover, and monoamine oxidase activity in the female catfish, Heteropneustes fossilis (Bloch)

The effects of different photoperiod regimes, and total darkness on day-night variations in hypothalamic serotonin (5-HT) content and turnover index (TI), and monoamine oxidase (MAO) activity that occur exclusively during the gonadal preparatory phase (February-March) were investigated in female Heteropneustes fossilis. Exposure of the fish to long photoperiods (16L:8D; light between 06.00-22.00h, for 40 days elevated both the midphotophase and midscotophase values of 5-HT content and MAO, and abolished their day-night differences. The daily variations of 5-HT-TI was further intensified by the treatment. Under short photoperiods (4L:20D; light between 18.00-22.00h for 40 days), there was a significant decrease in both 5-HT content and TI, a reversal of the day-night variations of 5-HT content and MAO activity, and loss of the 5-HT-TI pattern. In fish maintained in total darkness the day-night variations were not found and there was a significant inhibition of 5-HT. Exposure of the fish to continuous light abolished the day-night variations of these correlates and elevated their values at both intervals. When the LD cycle was reversed, there was a corresponding shift in the day-night patterns. The gonadosomatic index (GSI) was significantly elevated in the long photoperiod and continuous illumination groups, significantly decreased in the short photoperiod and total darkness groups, and unchanged in the reversed LD cycle regime. The results indicate that the day-night variations of 5-HT and MAO are photoperiod-dependent and are controlled by the prevailing LD cycle during the gonadal preparatory phase of the annual reproductive cycle. The photoperiod effects on the gonadal activity may be mediated through the hypothalamic serotonergic system.

Seasonal and daily variations in the plasma gonadotropin II response to a LHRH analog and serotonin in Atlantic croaker (Micropogonias undulatus): evidence for mediation by 5-HT2 receptors

The effects of serotonin (5-hydroxytryptamine; 5-HT) alone, and in combination with luteinizing hormone-releasing hormone analog (LHRHa), on plasma levels of maturational gonadotropin (GtH II) in the post-vitellogenic female and spermiating male Atlantic croaker were investigated during mid-light, late-light, mid-dark, and late-dark phases of the day-night (12 hr light: 12 hr dark) cycle. Although LHRHa stimulated GtH II secretion throughout the day-night cycle, maximal stimulation was observed during the mid-dark phase. Serotonin significantly potentiated LHRHa-induced GtH II secretion at all time points tested except during the late-dark phase. The plasma GtH II response to LHRHa was markedly reduced, and the response to 5-HT was abolished in regressed Atlantic croaker. Pretreatment of the fish with a 5-HT2 antagonist, LY 53,857 maleate, almost completely abolished the stimulatory effect of 5-HT on LHRHa-induced GtH II secretion, whereas a 5-HT1 antagonist, methiothepin mesylate, failed to influence the stimulatory effect of 5-HT on GtH II secretion. In addition, a 5-HT2 agonist, (+/-) DOI hydrochloride, potentiated the effect of 5-HT on basal and LHRHa-induced GtH II secretion, while a 5-HT1 agonist, m-chlorophenylpiperazine dihydrochloride, did not. The results clearly demonstrate time- and season-dependent stimulatory effects of LHRHa and 5-HT on plasma GtH II levels in Atlantic croaker. Moreover, the stimulatory effect of 5-HT appears to be mediated by 5-HT2 receptors in this species.

Developmental changes in the brain-stem serotonergic nuclei of teleost fish and neural plasticity

1. During early ontogeny, the serotonergic neurons in the brain stem of the three-spined stickleback shows a temporal and spatial developmental pattern that closely resembles that of amniotes. 2. However, in the adult fish, only the midline nuclei of the rostral group (dorsal and median raphe nuclei) and the dorsal lateral tegmental nucleus are consistently serotonin-immunoreactive (5-HTir), whereas the groups of the upper and lower rhombencephalon (raphe pontis, raphe magnus, and raphe pallidus/obscurus nuclei) are variable and, when present, contain relatively small numbers of 5-HTir neurons. 3. Using specific antisera against tryptophan 5-hydroxylase and aromatic L-amino acid decarboxylase, we have shown that the lateral B9 group and the groups of the upper and lower rhombencephalon are consistently present in adult sticklebacks. The results are discussed in relation to other known instances of neurotransmitter plasticity or transient neurotransmitter expression in teleost fish. 4. While there are several instances of transient expression of neurotransmitter markers by discrete neuronal populations, there is so far no evidence of changes from one neurotransmitter phenotype to another in the brain of teleost fish. However, there are indications of plasticity of expression of catecholamines and indoleamines, and their respective synthesizing enzymes, as reflected in age-dependent changes and variation between individuals of different physiological status. 5. As the brain grows continuously in teleost fish, and new neurons are added from proliferative regions, synaptic connections may be expected to undergo remodeling in all brain regions throughout life. Thus, the teleostean brain may be considered a suitable model for experimental studies of different aspects of neural plasticity.

Stimulatory effects of serotonin on maturational gonadotropin release in the Atlantic croaker, Micropogonias undulatus

The effects of serotonin (5-HT) injection alone, and in combination with des Gly10 [D-Trp6]-luteinizing hormone-releasing hormone ethylamide (LHRHa), on plasma maturational gonadotropin (GtH) levels in the Atlantic croaker, Micropogonias undulatus, were examined. An injection of 5-HT (20 micrograms/g body wt) alone did not significantly elevate GtH levels, whereas simulatneous administration of LHRHa (20 ng/g body wt) and 5-HT elicited a greater elevation of plasma GtH levels than that induced by LHRHa alone. Pretreatment of 1-year-old fish with fluoxetine (10 micrograms/g), a 5-HT reuptake inhibitor, only slightly augmented the effect of 5-HT on GtH levels, whereas pretreatment with ketanserin (10 micrograms/g), a 5-HT receptor antagonist, completely inhibited the potentiating effect of 5-HT on the GtH response to LHRHa. Administration of LHRHa (20 ng/g) or 5-HT (20 micrograms/g) significantly elevated GtH levels in the 2- and 3-year-old croaker, but the combined treatment failed to increase GtH levels above those induced by LHRHa alone. However, with a lower dose of LHRHa (5 ng/g), the combination produced an additive effect. Serotonin (20 micrograms/ml media) alone, and in combination with LHRHa (10 ng/ml media), significantly stimulated GtH release from the pituitaries of gonadally mature 2- and 3-year-old female croaker during an 18-hr incubation in vitro, but not from pituitaries of gonadally regressed fish. The combined treatment of LHRHa with 5-HT also significantly stimulated in vitro GtH release during 6- and 12-hr pituitary incubations, whereas these treatments alone were ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of estradiol on brain aminergic turnover of the female rainbow trout (Oncorhynchus mykiss) at the beginning of vitellogenesis

Brain serotonin and dopamine (DA) turnovers in the female rainbow trout were studied at the beginning of the vitellogenesis and related to blood estradiol (E2) levels; pituitary and plasma gonadotropin (GtH) were also assayed. Ovariectomy did not modify brain aminergic turnover. E2 replacement on ovariectomized fish increased hypothalamic DA turnover (increased DA and increased DA metabolites). E2 stimulated GtH synthesis (positive feedback) but did not enhance GtH release; hypothalamic E2-mediated aminergic inhibition upon release was suspected. Individual relations between blood E2 levels and catecholaminergic neurotransmitters were determined. A linear positive correlation (r = 0.82) was found for the hypothalamus, but not for the pituitary, the preoptic area, or the telencephalon. These data suggest that an activation of hypothalamic tyrosine hydroxylase (the limiting step of catecholamines synthesis) by E2 could develop as vitellogenesis proceeds.

Serotonin and dopamine turnover in the female rainbow trout (Oncorhynchus mykiss) brain and pituitary: changes during the annual reproductive cycle

Brain serotonin (5HT) and dopamine (DA) turnover were studied at various stages of the reproductive cycle of the female rainbow trout by simultaneous determination by HPLC of neurotransmitters and major related metabolites. An increase of 5HT turnover in telencephalon and hypothalamus and a decrease of DA turnover in pituitary and hypothalamus were observed during the periovulatory period. Some changes also occurred during vitellogenesis: decreased 5HT metabolite in telencephalon and preoptic area and increased DA content in preoptic area. These data suggest that physiological fluctuations of biogenic amines could be involved in both ovarian recrudescence and ovulation, with major effects on the hypothalamo-hypophysial complex during the periovulatory period.

Pineal-gonadal relationship in the teleost Channa punctatus (Bloch): evidence for possible involvement of hypothalamic serotonergic system

In Channa punctatus, pinealectomy results in an accelerated growth (stimulatory effect) of the ovary in preparatory phase (March), but had no significant effect in prespawning (May-June) or postspawning (September) phases. Administration of melatonin (25 micrograms/fish or 0.4 mg/kg BW at 2-day intervals for 30 days) inhibits the stimulatory effect of a long photoperiod and high temperature (16L:8D; 22 +/- 1 degree C) on the ovary in the early preparatory phase (February). In the late preparatory phase (April), the administration of both melatonin (0.5 mg/kg BW at 2-day intervals) and parachlorophenylalanine (pCPA, a serotonin synthesis blocker; 100 mg/kg BW at 3-day intervals) for 30 days inhibits ovarian activity in comparison to that of the saline-treated control group. In the dose-response study, greater than or equal to 0.5 mg/kg BW of melatonin induced a significant increase in hypothalamic 5-HT content and greater than or equal to 10 mg/kg BW of pCPA decreased it significantly. In the time-course study, melatonin (2.0 mg/kg BW) elevates the 5-HT content significantly after an hr of the injection and maintained it up to 48 hrs. The administration of pCPA (200 mg/kg BW) had significantly inhibited the 5-HT content which was sustained for 72 hr. In another study, a single injection of melatonin (0.5 mg/kg BW) increased the 5-HT content significantly. A single injection of pCPA (100 mg/kg BW) decreased significantly both the content and activity of 5-HT. It is inferred that hypothalamic 5-HT may play a central role in photosexual mechanisms and mediate long photoperiodic effects on neuroendocrine-reproductive axis.

Changes in hypothalamic monoamine oxidase activity in relation to 17 beta-estradiol and clomiphene citrate treatments in the teleost Channa punctatus during three seasons

Hypothalamic monoamine oxidase (MAO) activity displayed biphasic responses to administration of estradiol-17 beta (E2) depending on season. Lower doses of 0.05 and 0.10 microgram/g BW of E2 had enhanced enzyme activity and higher doses (0.5 and 1.0 microgram/g BW) depressed it significantly in preparatory season. In prespawning phase, the lowest dose of 0.05 microgram/g BW of E2 was stimulatory and the higher doses were inhibitory to MAO activity. In postspawning season, lower doses (0.05 and 0.10 microgram/g BW) of E2 failed to elicit any significant change in enzyme activity whereas the higher doses (0.5 and 1.0 microgram/g BW) elevated it significantly. Administration of clomid (5, 10, and 20 micrograms/g BW) inhibited MAO activity in a dose-dependent manner during all the three seasons. The results show that E2 may participate in feedback control of gonadotropin secretion by modifying monoaminergic activity at the level of oxidative deamination by MAO.

Rhythms in neurotransmitter turnover: focus on the serotonergic system

Circadian rhythms in the turnover of many neurotransmitters (e.g. serotonin, noradrenaline, melatonin, substance P, neuropeptide Y) are well known, but the mechanisms responsible for the rhythms in these transmitter systems are less well understood. One of the most extensively studied neurotransmitter systems, in terms of circadian rhythms, is the serotonergic system. This article has therefore focused on this system in order to highlight the approaches that have been taken and the possible mechanisms that may be involved in controlling the rhythmic nature of serotonergic neuronal function, and in particular, neurotransmitter release and metabolism.

Changes in hypothalamic catecholamine levels in relation to season, ovariectomy, and 17 beta-estradiol replacement in the catfish, Clarias batrachus (L.)

In female Clarias batrachus, hypothalamic levels of noradrenaline (NA) and dopamine (DA) exhibited seasonal changes during different phases of the annual reproductive cycle. The NA level was high during gonadal recrudescence (prespawning and spawning phases) and low during gonadal quiescence (postspawning and resting phases). A reverse trend was noticed in the DA level. After 3 weeks of ovariectomy (Ovx), the catecholamine (CA) levels were elevated significantly in the preparatory, prespawning, and spawning phases and were unaltered in the postspawning season. Administration of 17 beta-estradiol (E2, 1.0 microgram/g BW) to 3-week Ovx fish resulted in both seasonal and differential effects on the CA levels. The NA level was significantly elevated in the preparatory phase, decreased in the prespawning and spawning phases, and remained unaltered in the postspawning season. The DA level was restored by the steroid treatment in the preparatory phase, but registered a significant elevation in the prespawning and spawning phases. In the prespawning phase, Ovx induced a significant elevation of the hypothalamic NA level after 2, 3, and 4 weeks, but was significantly low after 5 weeks. The DA level registered a significant increase after 2, 3, and 5 weeks of Ovx. Administration of E2 to 3-week Ovx fish elicited dose-dependent responses on CA levels. The administration of a low dose of E2 (0.05 microgram) caused a significant elevation of the NA level, while the 0.1 microgram dose did not alter the amine level in comparison to that of the Ovx vehicle group. The higher doses (0.5 and 1.0 microgram) of E2, however, decreased the NA level significantly below that of the sham vehicle and Ovx vehicle groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of photoperiod and temperature on hypothalamic monoaminergic activity in the teleost Channa punctatus (Bloch)

In Channa punctatus maintained under ambient photothermal conditions (10.5L:13.5D; 13 ± 2°C) in the postspawning season, hypothalamic dopamine (DA) and norepinephrine (NE) content varied diurnally, but serotonin (5-HT) and monoamine oxidase (MAO) did not. Exposure of the fish to high temperature (25 ± 2°C), with or without altering the photopheriod, increased the NE and DA content, and NE turnover but decreased DA turnover. Increasing the photoperiod (16L:8D) alone had no significant effect on catecholaminergic (CA) content or activity. When the fish were exposed to long photoperiod, with or without altering the temperature, a day-night variation in 5-HT content and activity was induced in the postspawning season. An increase in temperature alone had no significant effect on 5-HT content or activity. Hypothalamic MAO activity was elevated in fish exposed to high temperature alone, or in combination with long photoperiod, but was not affected significantly by long photoperiod treatment. These results indicate that CA activity is influenced largely by ambient high temperature, whereas serotonergic activity is controlled primarily by photoperiod, with high temperature having an additive effect. MAO activity seems to be influenced by both temperature and photoperiod in this species.

Effects of season, pinealectomy, and blinding, alone and in combination, on hypothalamic monoaminergic activity in the teleost Channa punctatus (Bloch)

In Channa punctatus, day-night variations in hypothalamic 5-HT (serotonin) and monoamine oxidase (MAO) activity were noticed in preparatory but not other phases (prespawning and postspawning) of the annual reproductive cycle. Hypothalamic MAO, 5-HT, and norepinephrine (NE) activity was found to be high in the prespawning phase and low in the postspawning phase. Dopamine (DA) activity, on the other hand, was high in the postspawning season and low in the prespawning phase. Pinealectomy caused season-dependent effects on hypothalamic monoaminergic activity, with a significant increase in serotonergic activity and a significant reduction in MAO activity at midscotophase during the preparatory phase (March) but not in the prespawning (May-June) or postspawning (September) phases. Hypothalamic catecholaminergic (CA) activity was not influenced by pinealectomy during any of the seasons. To determine whether or not the photoperiodic influences on daily variations of 5-HT and MAO in the preparatory phase are mediated via pineal and/or lateral eyes, fish were pinealectomized and/or blinded in January, when there is no rhythm, and sacrificed in February, when a day-night variation normally sets in. The day-night difference in 5-HT content and activity and MAO activity was not abolished by pinealectomy or blinding alone; but the combination (pinealectomy + blinding) obliterated the daily variation only in 5-HT content and in MAO activity. However, pinealectomy and blinding, alone or in combination, caused a significant elevation of 5-HT activity (not its level) and a significant decrease in MAO activity at midscotophase, with the combination having an additive effect. Hypothalamic CA content or activity was not affected by these regimes. The results show that photoperiodic influence on the daily pattern of 5-HT and MAO activity is mediated through and by the interaction of the pineal and lateral eyes.

Changes in hypothalamic monoamine oxidase activity in relation to season, ovariectomy, and 17 beta-estradiol administration in intact and ovariectomized catfish, Clarias batrachus (L.)

Cyclic changes in hypothalamic monoamine oxidase (MAO) activity were noted during the annual ovarian cycle of Clarias batrachus, with a high level in the preparatory phase and a low level in the spawning phase. Administration of 17 beta-estradiol (E2) daily for 3 days induced both season- and dose-dependent responses in enzyme activity. In the preparatory phase, 0.05, 0.1, and 0.5 microgram/g doses of E2 enhanced enzyme activity in a dose-dependent manner, with significant changes being observed in the latter two dose groups. Administration of 1.0 and 10.0 micrograms/g doses decreased enzyme activity, with a significant difference elicited by the latter dose. In the spawning phase, enzyme activity was significantly elevated by 0.05 and 0.1 microgram/g doses. MAO activity decreased insignificantly in the 0.5 and 1.0 microgram/g groups and significantly in the 10.0 micrograms/g E2 group. Enzyme activity decreased significantly 2, 3, and 4 weeks after ovariectomy (prespawning phase), in a time-dependent manner, and increased after 5 weeks (not significantly different from the sham control value) and 6 weeks. Administration of E2 to 3-week ovariectomized fish elicited dose-dependent effects on MAO activity. E2 injections at 0.05 and 0.1 microgram/g doses not only restored the ovariectomy-induced decrease, but also elevated enzyme activity significantly compared with the sham + vehicle control. The higher doses (0.5 and 1.0 microgram/g) were ineffective in restoring enzyme activity, which decreased significantly in the 1.0 microgram/g group compared with ovariectomy and sham control values.(ABSTRACT TRUNCATED AT 250 WORDS)