The Histology And Electrophysiological Characteristics Of Thermotaxic Center Of Onychodactylus Fischeri

ObjectiveThis article discussed the morphological and histological characteristics of the genesis and development of corpus pineale and hypothalamic preoptic area in diencephalon of salamanders associated with thermoregulation, revealing the electrophysiological properties of the area associated with thermoregulation at different temperatures (6℃,10℃,15℃,20℃,25℃), determining the area of temperature regulation, to enrich the data of temperature regulation of poikilothermal animals.MethodsWe observed the morphological changes of various development stages of corpus pineale and hypothalamic preoptic area in diencephalon of salamanders associated with thermoregulation under entity dissecting microscope after the treatments of conventional paraffin section, HE staining, Nissl staining and staining of nerve fibers. Simultaneously, we also observed the histological changes of various development stages of this area, and based on the results observed, we used microelectrode electrophysiological technique to record the spontaneous discharges of corpus pineale and hypothalamic preoptic area in diencephalon at different temperatures (6℃,10℃,15℃,20℃and 25℃).ResultsThe Salamander diencephalon is divided into three parts:epithalamus, thalamus and hypothalamus. The pineal gland is an integral part of the hypothalamus, located in the back of the telencephalon, it was a bulge appeared in the middle of the two lateral ventricles of each cerebral hemisphere after their connection, the bulge seemed like an inverted triangle covering the end of the telencephalon, protruding downward as a shank to the lateral ventricles forming choroid plexus. The development of the pineal gland in the larval period had completed basically, and the pineal gland had the maximum volume in the adult period. The hypothalamus experienced regional differentiation and localization of nuclei during its development. From front to back, the hypothalamus was divided into the preoptic area and the funnel area. The optic chiasm appearing at the bottom of hypothalamus divided the preoptic area into the anterior preoptic area (PPa) and the posterior preoptic area (PPd). The anterior preoptic area differentiated into preoptic nucleus (POa); the posterior preoptic area differentiated into the supraoptic nucleus (SC) and the large nucleus preoptic (Mg).Electrophysiologically, the number of discharges of pineal gland increased as the temperature increased, and the amplitude and frequency of discharges changed too. The anterior preoptic area and the posterior preoptic area presented regular discharge changes as the temperature changed:the amplitude, duration and frequency of the discharges of the anterior preoptic area increased as the temperature increased, showed excitatory changes, but declined at 25℃; the amplitude, duration and frequency of the discharges of the posterior preoptic area decreased as the temperature increased, showed inhibitory changes. The electrical activity of hypothalamic preoptic area changed significantly higher than that of the pineal gland at different temperatures.ConclusionThe regional differentiation and localization of nuclei in diencephalon of salamander had been completed in the larval period, but the nucleus boundaries were not obvious. The diencephalons of adult and sub-adult salamander were similar, their nuclei boundaries of diencephalons were more clearly. The electrical activities of the pineal gland, anterior preoptic area and posterior preoptic area changed as the temperature changed at different temperatures, but the anterior preoptic area had more significant electrical changes compared with the pineal gland. We presume that the hypothalamic preoptic area and the pineal gland in diencephalon were all involved in the thermoregulation of salamander.