Ching-Lin Tsai

Effect of exogenous tryptophan on cannibalism, survival and growth in juvenile grouper, Epinephelus coioides

Abstract Tryptophan (TRP) is a precursor of serotonin (5-HT), which is known to affect food intake and aggression in vertebrates, including fishes. The effects of TRP-supplemented diets (0.25%, 0.5% and 1% of dry diet) on growth and cannibalism were evaluated in 38-day-old juvenile groupers (200-l tank, 750 fish per tank, 0.13 g in body weight and 2.16 cm in total length) over 10 days. HPLC analysis showed that TRP-supplemented diets were effective in increasing the levels of 5-HT in the brain of groupers. TRP supplementation resulted in slightly lower cannibalism than in controls. However, body weight and total length of TRP groups were significantly smaller than those of the control. The results indicated that cannibalism among juvenile groupers could be mitigated by the oral administration of TRP, in addition or in place of environmental factors, and the recommendation on supplementary TRP level to be used is 0.5% of dry diet.

Effects of temperature on the deformity and sex differentiation of tilapia, Oreochromis mossambicus

The effects of temperature on the deformity and sex differentiation of tilapia, Oreochromis mossambicus, were investigated. Zero- (the hatching day), 5-, and 10-day-old tilapia were respectively divided into 4 groups that were reared at 20, 24, 28, and 32 degrees C for 5 days. Percentages of deformity were significantly increased when tilapia were kept in the elevated temperatures (28 and 32 degrees C) before 5 days old during this experiment, whereas the lower temperature (20 degrees C) had no effect on the development of morphology. On the other hand, exposure to the lower temperature before 10 days old induced a high proportion of females whereas a high proportion of males was induced by the elevated temperature after 10 days old during this experiment. These results indicate that morphological development is influenced by temperature, particularly by the elevated temperature during a restricted developmental period. Both lower and elevated temperatures induce the gonadal feminization and masculinization, respectively, during its restricted developmental period. J. Exp. Zool. 286:534-537, 2000.

Effects of Gonadal Steroids on Brain Serotonergic and Aromatase Activity During the Critical Period of Sexual Differentiation in Tilapia, Oreochromis mossambicus

The effects of gonadal steroids on brain serotonin (5‐HT) and aromatase activity during the critical period of sexual differentiation were investigated in tilapia, Oreochromis mossambicus. Treatment of tilapia with 17β‐oestradiol (E2) between days 7 and 10 posthatching resulted in a significant increase in the female : male ratio as determined at day 90, and a significant reduction in brain 5‐HT content. Treatment between days 10 and 20, or between days 20 and 30, had no significant effect. Since the 5‐HT system may influence sexual differentiation, we examined the effects of para‐chlorophenylalanine (p‐CPA), a 5‐HT synthesis inhibitor. As with E2, treatment of tilapia with p‐CPA between days 7 and 10 posthatching resulted in a significant increase in the female : male ratio. Again, treatment between days 10 and 20, or between days 20 and 30, had no significant effect. Both p‐CPA and E2 significantly depressed brain aromatase activity when administrated between days 7 and 10, but not subsequently. In tilapia treated between days 7 and 10, the brain 5‐HT content was lowered by E2 to an extent similar to that seen with p‐CPA, which is consistent with the suggestion that the effect of E2 on sexual differentiation may be mediated by the 5‐HT system. Treatment of tilapia with 17α‐methyltestosterone (MT), by contrast, resulted in a reduction in the female : male ratio, and treatment was most effective when given between days 10 and 20. The period of maximal effect of MT upon sex ratio appears to coincide with the ability of MT to induce an increase in brain aromatase activity.

Effects of mercury on serotonin concentration in the brain of tilapia, Oreochromis mossambicus

In order to know the effect of mercury pollution on the serotonergic system of fish, serotonin concentrations in a discrete brain region of tilapia, Oreochromis mossambicus, were examined. Serotonin concentration was measured using a high performance liquid chromatography system with electrochemical detector. In male fish, the concentrations of serotonin were 1.468 +/- 0.350, 0.811 +/- 0.190 and 0.330 +/- 0.061 micrograms/g wet tissue in hypothalamus, telencephalon and optic lobe, respectively. The serotonin content was significantly different between each region; the hypothalamus had a higher content than that of the telencephalon and optic lobe. The serotonin concentration in female hypothalamus was 1.102 +/- 0.112 micrograms/g wet tissue which was significantly lower than that in males. However, serotonin concentration in the telencephalon and optic lobe showed no difference between male and female. After exposure to 0.015 and 0.03 ppm HgCl2 for 6 months beginning 7 days posthatching, male sample fish showed a significantly dose-dependent decrease in serotonin concentration in the hypothalamus. But a similar phenomenon was not found in other regions of the brain. These results suggest that exposure to HgCl2 results in an attenuated development of the serotonergic system in the hypothalamus of fish.

Temperature Influences the Ontogenetic Expression of Aromatase and Oestrogen Receptor mRNA in the Developing Tilapia (Oreochromis mossambicus) Brain

Water temperature has a differential influence on the development of central neurotransmitter systems according to the developmental period in tilapia (Oreochromis mossambicus). Aromatase and oestrogen receptors (ERs) represent important components of the mechanism of brain differentiation. Gene expression of aromatase and ERs is modulated by neurotransmitters in the developing brain. In the present study, the quantitative reverse transcription‐polymerase chain reaction method was used to investigate the effects of temperature on the ontogenetic expression of aromatase and ERs in the developing tilapia brain. Before day 10 posthatching, exposure to a higher temperature (32 °C) resulted in a significant increase in the expression of brain aromatase; conversely, a lower temperature (20 °C) resulted in a decrease. ERα expression was depressed in accordance with the decrease of temperature, but ERβ was unaffected by temperature. Between days 10 and 20, neither brain aromatase nor ERα expression was altered by temperature, whereas ERβ expression was significantly enhanced by exposure to 32 °C. Between days 20 and 30, brain aromatase significantly increased at the higher temperature and decreased at 20 °C, but neither ERα nor ERβ was affected by temperature. The expression of both brain aromatase and ERs, differentially regulated according to the temperature and to the developmental period, could be related to brain–sex differentiation.

Spinal somatosensory evoked potential to evaluate neurophysiologic changes associated with postlaminotomy fibrosis: an experimental study.

Study Design. We evaluated electrophysiologic changes of the cauda equina after lumbar laminotomy in rats. Objective. To clarify immediate and long-term electrophysiologic and neurologic responses in an experimental postlaminotomy animal fibrosis model. Summary of Background Data. Postspinal surgery-induced epidural fibrosis is assessed using either Gadolinium- enhanced magnetic resonance imaging (MRI) or intraoperative observations. In experimental animal models mimicking this complication, many approaches are used: advanced imaging (computed tomography, CT; and MRI), functional observations, biomechanical techniques, and histologic examinations. However, no study has reported the substantial neurophysiologic changes of the cauda equina in such a model. Methods. Rats were given a sham operation (laminar exposure only), a left L5 hemilaminotomy alone, or a left L5 hemilaminotomy with extradural topical collagen. Mixed-nerve-elicited somatosensory-evoked potentials (M-SSEPs) and dermatomal (D)-SSEPs were recorded at the thoracolumbar junction after percutaneous stimulation of the posterior tibial nerve at the bilateral medial ankles and the L5 dermatomal field, respectively. Potentials recorded on the operated and nonoperated sides before surgery and then 30 minutes, 2 weeks, and 1, 2, and 3 months after surgery were compared. Walking track and thermal hyperalgesia test results and a final histologic analysis of perineural fibrosis were correlated. Results. Electrical stimulation yielded reproducible responses in all rats on all tests. Preoperative and postoperative measurements showed no statistically significant differences in M-SSEP or D-SSEP. Postoperative D-SSEPs in both experimental groups showed significant reductions in relative amplitude, but the M-SSEPs of all groups and D-SSEPs of the control groups remained constant. Conclusion. SSEP is valuable for detecting electrophysiologic changes after laminotomy fibrosis, but acceptable accuracy requires proper stimulation and recording settings. D-SSEP monitoring provided reliable, useful information about the functional integrity of the cauda equina in this animal model. We recommend D-SSEP monitoring as a supplemental tool for quantifying the effect of postlaminotomy fibrosis on neuropathy.

Effects of gonadal steroids on the serotonin synthesis and metabolism in the early developing tilapia brain.

The effects of gonadal steroids on serotonin (5-HT) synthesis and metabolism in the early developing brain were investigated. Seven-day-old (7 days post-hatch) tilapia, Oreochromis mossambicus were continuously treated with 17beta-estradiol (E2), methyltestosterone (MT) and para-chlorophenylalanine (p-PCA) up to the age of 30 days. The brain 5-HT content, before 30 days, increased with age. The result indicates that this is a developing period of the central 5-HTergic system. During this developing period, the activity of tryptophan hydroxylase (TPH) and monoamine oxidase (MAO) was not altered by age. Both E2 and MT influence the central 5-HT content during its restricted developmental period. E2 has an initial inhibitory effect and then a facilitative effect while MT only has a facilitative effect. The initial inhibitory effect of E2 is mediated by decreasing TPH activity and increasing MAO activity to decrease the 5-HT content. The facilitative effect of both E2 and MT is suppressed by p-CPA.

Effects of thermal acclimation on the neurotransmitters, serotonin and norepinephrine in the discrete brain of male and female tilapia, Oreochromis mossambicus.

Effects of thermal acclimation on the serotonin (5-HT) and norepinephrine (NE) contents in the discrete brain of male and female tilapia, Oreochromis mossambicus were investigated. Sexually mature males and females were exposed to 26 degrees C, 29 degrees C, or 32 degrees C of water temperature for 3 weeks. The hypothalamic 5-HT content in the 29 degrees C and 32 degrees C acclimated male was lower than that in the 26 degrees C group. In females, the hypothalamic 5-HT content in the 32 degrees C acclimated group was less than those in the 26 degrees C and 29 degrees C groups. Similar results were found in the hypothalamic NE contents of males and females. In the optic lobe, the elevated temperature acclimation (29 degrees C and 32 degrees C) resulted in a higher 5-HT content in both males and females; whereas, the NE content was increased by the elevated temperature acclimation in females but not altered in that of males. In the telencephalon, the elevated temperature acclimation had no influence on the 5-HT content of males and females, but resulted in a lower NE content in both males and females. These results demonstrate that the neurotransmitter activity of teleost is influenced by the thermal acclimation in a sex- and regional-dependent pattern. The alterations of 5-HT and NE in the central nervous system might be involved in the physiological and biochemical responses that occur during thermal acclimation in fish.

Thermal responses of ventromedial hypothalamic neurons in vivo and in vitro

The ventromedial hypothalamic neurons were recorded in anesthetized rats and in slice preparations. Whereas almost all thermosensitive neurons (27 out of 28) in the slice preparations showed warm sensitivity, cold-responsive neurons were recorded more frequently than warm-responsive ones during preoptic thermal stimulation in anesthetized rats. These results suggest that most cold-responsive neurons excited by preoptic cooling in the anesthetized rats were influenced by synaptic inputs.

Photoperiod affects the development of central neurotransmitter systems of tilapia, Oreochromis mossambicus

The effects of photoperiod on the development of central neurotransmitters were investigated with tilapia, Oreochromis mossambicus. Zero-day-old (the hatching day) tilapia were raised in three different photoperiods (light/dark cycle): 12/1, 24/0, and 0/24 h, respectively. On the 5th day, brain serotonin (5-HT), norepinephrine (NE), gamma-aminobutyric acid (GABA), and glutamate (Glu) contents were quantified by a high-performance liquid chromatograph with electrochemical detection. Similar experiments were performed on the 5-, 10-, 15-, 20-, and 25-day-olds. These results showed that the photoperiod influenced both brain NE and GABA contents during its respective restricted period, before days 10 posthatching. Brain 5-HT content was influenced, either facilitated or suppressed according to the developing stage, whereas, brain Glu content was not altered by the different photoperiod exposure throughout the present studies.