Intracellular records were obtained from 31 neurones isolated from the first somatosensory cortical projection area of chloralose-anaesthetized cats. These neurones, which are part of a wider sample of 197 cells recorded extracellularly during the same experiments, were all tested with the electrical stimulation of peripheral receptive fields (PRF) and hence classified as somatotopic (contralateral, specific PRF) or non-somatotopic (wide and bilateral PRF). Upon PRF shocks, sequences of EPSP-IPSP (excitatory reactions) or of primary IPSPs (inhibitory reactions) were recorded from the impaled neurones. Excitatory reactions recorded on PRF stimulation from somatotopic neurones were different in several aspects from those recorded from non-somatotopic cells. In respect of the EPSPs composing the excitatory reactions of the former neurones, those of the latter appeared after longer latencies, were longer in duration, slower in rising-time, and they triggered a higher number of spikes. In some non-somatotopic neurones, furthermore, the development of subsequent EPSPs and the appearence of slow depolarizing potentials and/or spikes at the end of the IPSPs made the excitatory responses more complex. In these cells, excitatory post-synaptic reactions were also observed, different in strength when different portions of their PRFs were stimulated. Purely inhibitory PRFs, from which primary IPSPs could be precipitated, were identified both for somatotopic and non-somatotopic units. Such IPSPs were recorded after latencies always longer than those of the earliest EPSPs of somatotopic cells. At an intermediate time between these slow inhibitory and excitatory potentials, extracellular discharges were sometimes recorded, which because of their patterns very likely came from inhibitory internuncial elements. Considering the spatial distribution of excitatory and inhibitory PRFs as well as the time relationships between the earliest EPSPs, the primary IPSPs and the discharges of the presumed inhibitory interneurones, it is inferred that somatotopic cells might inhibit non-somatotopic neurones by means of a recurrent collateral mechanism. The differences between the excitatory reactions recorded from somatotopic and non-somatotopic neurones are adso discussed.
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Con il contributo del Ministero per i Beni e le Attività Culturali