Changes in signal transmission by neurons of the cat lateral geniculate nucleus by acute deafferentation and early degeneration.
1. The responses of single principal cells of the cat lateral geniculate nucleus (LGN) were recorded extracellulary from the optic radiation (OR) axons or intracellularly from the LGN. Electrical stimuli at different frequencies were applied to the optic tract (OT) to test the transneuronal and the synaptic signal transmission in the LGN. 2. The effect of acute deafferentation (by photocoagulation of the retinal receptive field) or of synaptic degeneration induced 2-4 days prior to the recording time on the LGN neuron signal transfer was studied. Immediately after deafferentation, the synaptic signal transfer by LGN neurons exhibits signs of hyperexcitability leading to multiple neuronal discharges. This acute deafferentation hyperexicitability is probably caused mainly by the disapperance of lateral inhibition mediated by LGN interneurons. The deafferentation hyperexcitability disappeared during electrical stimulation of the OT at frequencies greater than 10/sec. 3. With progressing degeneration of the synaptic terminals during the 2nd to 4th day after interruption of the optic nerve axoplasmic flow, the synaptic signal transfer by LGN neurons gradually deteriorates and ceases at the end of the fourth day. The signs of this deterioration (larger temporal scatter, increased exhaustability and reduced upper frequency limit of the transneuronal signal transmission and gradual reduction of the EPSP amplitude in D-neurons) were quantitatively investigated. 4. The neurophysiological data obtained at different levels of synaptic terminal degeneration are well correlated with morphological changes found within the degenerating synaptic terminals.
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D002415:Cats; D005829:Geniculate Bodies / Q000502:physiology*; D009410:Nerve Degeneration; D009474:Neurons / Q000502:physiology; D009900:Optic Nerve / Q000166:cytology / Q000502:physiology; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure; D009435:Synaptic Transmission; D013997:Time Factors; D014795:Visual Pathways / Q000166:cytology / Q000502:physiology