HORMONAL AND PHYSICAL INTERACTIONS WITH ACETYLCHOLINESTERASE AND CATIONS IN THE PORCINE BRAIN AND HYPOPHYSES IN A HOT HUMID CLIMATE

Abstract

Prenatal and Postnatal changes in the physiological development of the porcine brain were determined. The results indicated a decline in amniotic fluid volume with increased gestation length. Marked fetal brain and body development was observed between four and six weeks of gestation where mean embryo weight increased by 48,878% from four weeks to six weeks with a concomitant increase of 1,300% in mean fetal brain weight. Acetylcholinesterase (AChE) activity in the amniotic fluid declined progressively with age (r=-0.56) while AChE activity in the fetal brain increased with gestation length (r=0.88). Total protein in both the amniotic fluid and in fetal brain did not correlate significantly with gestation length (P>0.05). Specific acetylcholinesterase (SAChE) activities in the amniotic fluid declined significantly between four and six weeks of gestation while activity in the fetal brain increased significantly from 5.12 ± 0.39 at 6 weeks to 21.54 + 2.6 at 12 weeks. Postnatally, AChE activity declined significantly with age in the pons, hypothalamus, midbrain, medulla and hypophyses while no significant changes were observed in the cerebellum, cerebral cortex and hippocampus. A significant rise was observed in the amygdala. Total protein increased significantly with age in all brain regions and hypophyses while SAChE activities declined steadily with age. Significant and Positive correlations were observed in the calcium and sodium content of the embryonic brain while negative correlations were observed in the copper and zinc content. Postnatally, Positive correlations were observed in the calcium, magnesium, potassium, sodium, copper and zinc contents of the pons, cerebellum, medulla and midbrain. The effects of castration at different ages and hormonal therapy on brain and hypophyseal physiology of pigs were also evaluated. Castration significantly depressed AChE activity in the cerebellum, amygdala, hippocampus, hypothalamus, midbrain and medulla in all age groups except at 7-8 months of age while testosterone maintained AChE activity at levels similar to controls. The cortex was not significantly affected except in the Pre-weaners where a depression was recorded. AChE activity in the adenohypophyses of testosterone-treated castrates and controls were similar and inferior to the untreated castrates. Protein levels of all the brain regions and hypophyses of boars were depressed by castration. In addition treated castrates were still inferior to the controls. A decline was also observed in the concentrations of calcium, sodium, potassium, copper and zinc in castrated boars. Exogenous Progesterone or estradiol administration also significantly depressed AChE activity in the cerebellum, amygdala, hippocampus, midbrain and the medulla with the Progesterone - induced depression being significantly lower than that caused by estradiol. Total protein in the brain regions of ovariectomized gilts was depressed by estrogen and progesterone but to varying extents. Progesterone tended to elevate magnesium and zinc in the amygdale, hippocampus and cerebellum while estradiol facilitated retention of copper and potassium in several brain regions and the neurohypophyses. Testosterone injection also significantly depressed AChE activity in all brain regions. However no significant differences were observed in the hypophyses. Testosterone further depressed total protein levels in the cerebellum, hypothalamus, cortex, medulla and elevated it in the pons. Testosterone injection in gilts also depressed calcium levels in all brain regions and hypophyses while causing a rise in the magnesium, zinc, and potassium levels in several regions. Lastly, heat stress caused significant increases in respiratory rates and rectal temperatures of heat-stressed boars. Heat stress also elevated AChE and SAChE activities in the Pons, cerebellum, amygdala, hippocampus and medulla. No significant effect was found in the cortex. Total protein levels in the heat-stressed pigs were generally inferior to the controls but the amygdala and cortex were unaffected. Heat stress significantly increased calcium, potassium levels and depressed magnesium, zinc and copper levels in several regions. Water deprivation also depressed AChE activity in the amygdala, medulla and hippocampus but no effect was observed in the cortex. Total protein levels were also depressed by water deprivation in several regions whereas SAChE activities were elevated in water deprived animals above the controls. Water deprivation resulted in a decline in Calcium and Sodium levels of several regions while increases were recorded in magnesium, potassium and zinc concentrations in some brain regions and the hypophyses.