POSTNATAL-DEVELOPMENT OF SYNCHRONIZED NETWORK OSCILLATIONS IN THE FERRET DORSAL LATERAL GENICULATE AND PERIGENICULATE NUCLEI

Extracellular and intracellular recordings from slices of ferret dorsa l lateral geniculate nucleus (LGNd) at postnatal ages P10-53 were perf ormed to examine the postnatal development of spindle waves and the ab ility of block of GABA(A) receptors to alter these spindle waves into a slower, synchronous oscillation. As in prior studies in the adult, i ntracellular and extracellular recordings at ages P33-53 revealed robu st spindle waves to be present in both the LGNd and perigeniculate nuc leus (PGN). Intracellular recordings from thalamocortical relay cells in the A-laminae of the LGNd revealed that these cells received repeti tive inhibitory postsynaptic potentials (IPSPs) at 6-9 Hz during the g eneration of spindle waves, and generated rebound low threshold Ca2+ s pikes and bursts of 2-6 action potentials following each second or thi rd IPSP. Intracellular recordings from the GABAergic neurons of the PG N at P3353 revealed barrages of EPSPs that activated low threshold Ca2 + spikes and high frequency burst discharges of 2-10 action potentials during spindle wave generation. In contrast, full spindle waves were absent at ages prior to approximately P22 and spindle waves between th e ages of P26 and approximately P30 were relatively weak and associate d with only one or two action potentials per burst in both PGN neurons and LGNd relay cells. Bath application of the GABA(A) antagonist bicu culline methiodide at P41-53 resulted in a conversion of normal spindl e waves into a marked 2-4 Hz oscillation in which the action potential firing of both thalamocortical relay and PGN neurons was greatly incr eased. In contrast, block of GABA(A) receptors prior to age P39 did no t result in the generation of the slowed, 2-4 Hz network oscillation. Investigation of the electrophysiological properties of PGN neurons re vealed that the postnatal development of spindle waves and bicuculline -induced slow oscillations were associated with an increase in the abi lity of PGN neurons to generate high frequency bursts of action potent ials, suggesting that these changes in electrophysiological properties may contribute to the late development of synchronized oscillations i n the ferret LGNd.