Central alpha-adrenoceptor influence over the cardiovascular reflexes activated by veratrine.

Intravenous veratrine induced alterations in cardiovascular parameters in cats were used as a tool for assessing the influence of central alpha-adrenoceptors over reflex adjustments in the heart rate and blood pressure. Blockade of central alpha 2-adrenoceptors with idazoxan or yohimbine, inhibited, while their activation by clonidine, as also blockade of alpha 1-adrenoceptors, with prazosin, potentiated the veratrine induced bradycardia. The hypotensive effect was relatively unaltered by these treatments. Low doses of clonidine potentiated the veratrine-induced bradycardia. It appears that alpha 2-adrenoceptor mechanisms exert greater control over the reflex regulation of heart rate than over reflex control of blood pressure.

Lack of in vitro spontaneous activity following axotomy of hamster sensory neurones.

Although peripheral axotomy of dorsal root ganglion cells in mice, rats and cats has been reported to generate spontaneous activity in sensory nerves, we did not find evidence for such activity in the hamster. In vitro, intracellular recording from L6-S1 dorsal root ganglion cells up to 6 weeks after axotomy did not reveal any evidence for either increased membrane excitability or spontaneous activity. Also, in the sciatic nerve-sectioned hamsters, there was a total absence of the self-mutilatory behaviour which has been reported in other rodents. These results support the hypothesis that species specific factors are important for the development of ongoing activity in sensory nerves following injury.