Time course of degeneration of short and long postganglionic sympathetic nerve fibres and effect of pentobarbitone and colchicine on degeneration.

Abstract

1 The time-course of degeneration of sympathetic nerves was investigated by measurement of the endogenous noradrenaline content of the rat vas deferens, submandibular gland and spleen following sympathectomy.2 Extirpation of the hypogastric plexus, superior cervical ganglion and coeliac plexus under pentobarbitone anaesthesia caused 50% depletion of the noradrenaline content of the vas deferens, submandibular gland and spleen in approximately 16, 19 and 21 h, respectively.3 Under pentobarbitone anaesthesia, proximal sympathectomy (i.e., close to the end organ) produced depletion of the noradrenaline content of the submandibular gland 8 h earlier than that caused by distal sympathectomy. Under ether anaesthesia, the time difference in obtaining the same degree of depletion after the two procedures of sympathectomy was only 2 hours.4 Removal of the superior cervical ganglion under ether anaesthesia resulted in almost complete depletion of noradrenaline content of the submandibular gland in 17 h, whereas when a similar operation was performed under pentobarbitone anaesthesia, nearly 24 h were required for the same degree of depletion. Similarly, the noradrenaline content of the spleen was depleted 4 h earlier if the coeliac plexus was ablated under ether as compared to pentobarbitone anaesthesia.5 Local application of colchicine (10 mg/ml, 30 min) to postganglionic sympathetic nerve axons had no effect on the noradrenaline content of the submandibular gland up to 24 hours. However, removal of the superior ganglion following colchicine application considerably slowed the depletion of the noradrenaline content of the submandibular gland (at 17 and 20 h after ganglionectomy, 10 and 20% depletion, respectively, in the experimental gland, as compared to 70 and 80%, respectively, in the control gland).6 To explain the results, it is proposed that injury to the sympathetic nerves at the site of sectioning triggers a signal (messenger substance) which travels down to the nerve endings to produce degeneration. Thus, the length of the extrinsic nerve fibre influences the time course of degeneration by changing the rate of transport of the messenger substance, whereas pentobarbitone and colchicine alter the synthesis and/or transport of the messenger substance to modify the time-course of degeneration.