INACTIVATION OF BAROAFFERENTS LEADS TO LOSS OF BAROSENSITIVITY WITHOUT CHANGES IN NERVE MORPHOLOGY

Baroreceptors are stretch-sensitive mechanoreceptors, which are silenc ed by preventing distension of the receptor zone. Does chronic inactiv ation of these peripheral afferents alter their function or morphology ? Compound action potentials and morphometry of carotid sinus nerves o f 10 rabbits were investigated. The baroafferents were inactivated by embedding the pressure-released carotid sinus into silicon gel. The su ccess of this procedure was validated by the absence of spike activity of the sinus nerve during normal and elevated systemic blood pressure . The contralateral vessels of the same animals were sham-operated and also embedded into silicon, but without prevention of wall movements. After 5, 7, 14 or 28 days the nerves were functionally reinvestigated before and after release of the sinus wall. Afterwards, the morpholog y of the nerve cross-sections was analysed by morphometry of electron micrographs. Baroafferents did not regain spike activity during immobi lisation of the sinus wall. After release of the carotid sinus wall on ly nerves inactivated for five days regained their pulse synchronous b aroreceptor discharge. Following seven days of inactivation, barorecep tor discharge could be elicited by maximal pressure elevation in only one of three nerves. At any time later, the baroreceptor response to a rterial pressure changes was lost completely The activity of the contr ol nerves was preserved after 28 days. No obvious differences in fibre size and myelin thickness were observed between inactivated and contr ol nerves. Inactivation of baroafferents for more than one week leads to a loss of pressure-dependent spike activity. Since morphology did n ot differ between inactivated and control nerves, it is suggested that changes of baroreceptor endings are responsible for this loss of func tion. (C) 1998 Elsevier Science B.V.