Effects of exercise on plasma catecholamine levels in the toad, Bufo paracnemis: role of the adrenals and neural control.

Resting plasma epinephrine (E) and norepinephrine (N) concentrations for intact toads (Bufo paracnemis) were 5.57+/-1.0 and 0.88+/-0.38 ng/ml, respectively. Exercise induced a significant increase in heart rate, blood pressure and plasma epinephrine (about 4.3 times), whereas norepinephrine remained unchanged. The resting [E]/[N] ratio was 6.3 and increased to 32.9 during exercise. Adrenal denervation did not alter the basal plasma catecholamine or norepinephrine levels after exercise, but prevented the increase in epinephrine during exercise, suggesting that in the intact toad this increase is due to adrenal secretion whereas resting norepinephrine may be liberated by extra-adrenal chromaffin tissues. This also suggests that the adrenal glands can release selectively the two catecholamines. The increases in heart rate and blood pressure in denervated toads were not significantly different from those of intact animals, suggesting that during exercise the sympathetic nerves play the main role in inducing cardiovascular responses. Spinal transection induced a significant increase in basal norepinephrine levels, which remained elevated after exercise. Since spinal toads are unable to perform spontaneous movements it is possible that this increase may be caused by this stressful condition. The increases in heart rate and blood pressure observed in spinal toads during exercise may be due to direct mechanical effects of venous return on the heart.

Fisiologia sensorial: uma abordagem comparativa / Sensory physiology: a comparative approach

A recepção de informações é a primeira e fundamental etapa que leva a ajustes homeostáticos e/ou comportamentais. Nos seres unicelulares a capacidade de reagir a estímulos é uma propriedade essencial da membrana celular. Com o advento da multicelularidade, desenvolve-se um sistema nervoso com tendência a divisão de trabalho, que conduz à separação dos sistemas receptor e efetor e ao desenvolvimento de um centro integrador. Existe, ao longo de toda filogenia, uma extensa lista de estímulos aos quais os diferentes animais respondem, por meio de receptores especializados. Destes, os mais amplamente difundidos são os quimiorreceptores, fotorreceptores e mecanorreceptores. O presente artigo tem por objetivo analisar comparativamente estes três tipos de receptores, bem como seu funcionamento, na escala evolutiva (AU)