Morphological Study On The Mechanism Of Food Intake Regulation Of Serotonin In Duck

The regulation of food intake and energy metabolism involves the interaction of several neurotransmitters and neuromodulators at multiple hypothalamic areas. Serotonin (5-hydroxytryptamine, 5-HT), a classical neurotransmitter, has multiple physiological functions. 5-HT has been suggested to play a modulatory role in the regulation of both central sympathetic and feeding pathways. Although there are some studies on the food intake regulation of serotonin in mammals, few studies have been reported in birds.So in the present study, healthy Cherry Valley Ducks were used to morphologically investigate the mechanism of food intake regulation of serotonin by SABC method. The present study includes four parts:1 The effect of energy on serotonergic and neuropeptide Y neurons in duck hypothalamusIn order to study whether 5-HT participates in food intake regulation in birds and whether there is interaction between 5-HT and NPY in food intake regulation. Sixty healthy Cherry Valley Ducks from the same parents (1 day old) were obtained in the present study. They were divided into two groups at random and fed with high energy feed and low energy feed respectively. After 5 weeks of feeding, they were anaesthetized deeply and men were perfused. The hypothalamus was removed to make serial traverse paraffin sections (6μm thick). The immunohistochemical method streptavidin-biotin-peroxidase complex (SABC) was used to examine the distribution of serotonergic and neuropeptide Y neurons in hypothalamus. All films were analysed by using a computer-assisted image analysis system. The results are as follows: in high energy group, serotonin positive cells are widely distributed in paraventricular nucleus(PVN, 17.73 ± 1.41 neurons/19.46 × 103 μm2) and nucleus ventromedial hypothalamus (VMH, 15.80 ± 1.71 neurons/19.46 × 103 μm2), labeled cells are widely distributed in lateral hypothalamus(LH, 11.25 ± 1.53 neurons/ 19.46 × 103 μ m2) in low energy group;neuropeptide Y neurons are distributed in PVN, supraoptic nucleus(SON) and LH, there is a significant difference when the optical density averages of NPY neurons in SON and LH in low energy group were compared with the high energy group(p<0.01). There is no significant difference in PVN. These results indicate that serotonergic neurons in duck hypothalamus are involved in the regulation of food intake and energy metabolism; the action sites of food intake regulation of hypothalamic NPY are possibly localized in SON and LH, which is different from the food intake regulation pathway of mammals; serotonin inhibits food intake maybe through inhibiting NPY in lateral hypothalamus.2 The effect of tryptophan on duck food intakeTryptophan, an essential amino acid, is the precursor of serotonin. In order to investigate whether excessive tryptophan has inhibition effect on duck food intake, the healthy Cherry Valley Ducks were used in the present study. They were given 12h/12h linght/dark cycle (8:00pm-8:00am light cycle), free standard feeds and water, and housed individually. On the experiment day, they were fasted 4h later (8:00am-12:00am), and different doses of tryptophan were injected intraperitoneally to them. One hour later, preweighed food was introduced into the cages. The amounts of food consumed after 1h, 2h and 4h were determined. The amounts of the food intake were 67.20±0.91 g/kg, 80.74±2.92 g/kg and 87.15±2.53 g/kg 1h, 2h and 4h later respectively in control group. The food intake dose-dependently decreased in experimental groups, and there is a statistically significant diferrence (p<0.01) when compared with the control group. The results indicate that tryptophan peripherally injected dose-dependently inhibited the food intak of ducks.3 The effect of tryptophan on serotonergic and neuropeptide Y neurons in duck brainstemIn order to study the mechanism of food intake inhibition of excessive tryptophan and provide morphological evidence for mechanism of food intake regulation of serotonin,the healthy Cherry Valley Ducks were used in the present study. Different doses of tryptophan were injected intraperitoneally to them, and the SABC method was used to study the distribution of serotonin and NPY in the brainstem. All films were analysed by using a computer-assisted image analysis system. The results are as follows: The serotonin neurons are localized in PVN, mesencephalic lineal nucleus (ML), interpeduncular nucleus(IP), nucleus nervi trochlearis(NIV), tegmental ventral nucleus (TV), nucleus locus ceruleus(LoC), pontine medial nucleus (PM), pontine lateral nucleus (PL) , pontine raphe nuclei(R), nucleus motorius nervi vagi (NX), nucleus nervi hypoglossi(NXn), ambiguus nucleus and reticular nucleus in different groups. The optical density averages of 5-HT in ML, IP, R, PM, PL and LoC in 200 mg / kg and 100 mg / kg group are significantly higher than that of 0 mg / kg group(p<0.01). NPY neurons are distributed in PVN, SON, LH, LoC, R, PM, PL, reticular nucleus and NX. The optical density averages of NPY in PVN and R in 100 mg / kg group and 200 mg/kg group are significantly higher than that of 0 mg / kg group(p<0.01), and the optical density averages of NPY in LoC and LH in 0 mg / kg group are significantly higher than that of 100mg / kg and 200mg/kg group(p<0.01). The results suggest that tryptophan may be absorbed by LoC, R, IP, PM and PL to accelerate the biosynthesis of 5-HT, which has effect on NPY and other factors through the extensive connections with other regions to modulate food intake.4 The effect of tryptophan on serotonergic and neuropeptide Y neurons in duck cerebellumIt has been reported that rat cerebellum participates not only in the regulation of motor but also in the modulation of food intake. In order to investigate whether duck cerebellum is concerned with food intake behaviour, healthy Cherry Valley Ducks were used in the present study. Different doses of tryptophan were injected intraperitoneally to them, and the SABC method was used to study the distribution of serotonin and NPY in the cerebellum. All films were analysed by using a computer-assisted image analysis system. Serotonergic neurons are localized in Purkinje cell layer, and the optical densityaverages of 5-HT in 200 mg / kg group are significantly higher than that of 100 mg / kg and 0 mg / kg group(p<0.01). NPY neurons are distributed in Purkinje cell layer, and the optical density averages of NPY in 0 mg / kg group are significantly higher than that of 100 mg / kg and 200 mg / kg group(p<0.01). These results show that excessive tryptophan can affect the content of 5-HT and NPY in cerebellum; 5-HT in cerebellum is possible to inhibit the expression of NPY; duck cerebellum maybe participates in the regulation of food intake and energy metabolism.