Formation of synapses between parasympathetic neurones deprived of preganglionic innervation

Abstract

MUSCLE fibres will accept innervation from a foreign nerve only if synaptic transmission from the appropriate nerve has been interrupted¹. The native nerve supply thus exerts an influence which renders muscle resistant to abnormal innervation. Do such influences act to prevent neurones from receiving inappropriate synapses ? In the central nervous system (CNS) surviving inputs to partially denervated neurones will sprout to form additional synapses on those same neurones^2–4. Furthermore, in partially denervated autonomic ganglia, surviving inputs will sprout to form synapses on postganglionic neurones they did not innervate originally^5–7. But there has been no electro-physiological demonstration that denervated neurones will spontaneously receive synapses from a class of nerve cells with which there is normally no contact. We report here that the parasympathetic ganglion cells of the frog heart form functional synaptic connections with each other when their preganglionic synaptic input is removed; these intraganglionic connections do not occur normally.