Plasticity in dendrites shown by continuous GABA administration in superior cervical ganglion of adult rat

Abstract

FINE structural investigations of the normal development of neurones have drawn attention to the transitory appearance of specialised postsynaptic membrane thickenings preceding the establishment of Gray type I synaptic contacts with axon terminals^1–4. Non-innervated free postsynaptic membrane thickenings (f-post) occur more frequently in certain developmental stages and in certain laminae of the occipital cortex than in others⁵. Temporo–spatial aspects of the cortical development^6–8 suggested to us that the maturation of inhibitory neurones might have an important impact on the formation of f-post. We describe here our investigations on the validity of this working hypothesis by searching for structural changes at the receptive surfaces of neurones in response to extracellularly applied γ-aminobutyric acid (GABA), a substance known to act in an inhibitory way on neurones⁹. The superior cervical ganglion (SCG) was selected as a comparatively simple neuronal system which has a uniform preganglionic input and probably no neuronal feedback to the spinal cord. We found that the dendrites of the ganglion cells responded to a prolonged infusion of GABA by the formation of non-innervated postsynaptic membrane thickenings, changes in shape and the accumulation of microvesicles.