Excitatory and inhibitory responses of neurones of the cerebellar fastigial nucleus.

This paper gives an account of the responses of cerebellar fastigial cells to various afferent inputs from ipsilateral forelimb or hindlimb. Most of the preparations (17 out of 25) have been decerebrate and unanesthetized. The remainder were under anesthesia - chloralose, pentothal or surital. The afferent inputs have been provided by stimulation of predominantly cutaneous limb nerves or by three types of mechanical stimulation: taps to foot pads; pressure on foot pads; air jets to hairy skin. Recording from single fastigial cells was extracellular by glass microelectrodes, and computer averaging techniques of spike responses were employed as described in previous papers. Identification of fastigial cells was simply from location in the large fastigial nucleus, this location being later confirmed by identification of microelectrode tracks in histological sections. Fastigial cells display a fairly steady background discharge, the mean being 37 Hz for the decerebrate and considerably lower for the anesthetized. Pad taps usually evoked a diphasic (excitatory-inhibitory) response, but in some cases the inhibitory was dominant, in others the excitatory. The threshold was below 0.2 mm, and several fastigial cells were excited or inhibited by taps of only 0.01 mm. Air jet stimulation of hairy skin of the foot evoked similar responses. Durations of excitation were usually about 10 msec but inhibition was longer, usually about 50 msec. Nerve stimulation evoked responses of comparable type, but the latency was at least 4 msec shorter, corresponding to the more direct and shorter pathways from the site of stimulation. With some fastigial cells steady pressure to central foot pads of 2 sec duration evoked only brief phasic responses (excitatory or inhibitory) at 'on' and 'off'. With other cells there were tonic responses - excitation or inhibition or admixtures thereof - for the whole duration of the pressure. Usually 500 g was almost maximally effective, and the threshold was always below 100 g. In an indeterminate type of response (the semitonic) the excitation or inhibition at 'on' persisted for up to 500 msec, an effect matching the response of the rapidly adapting receptors of the pads. With repetitive stimulation both the excitatory and inhibitory responses to pad taps were reduced with frequencies above 1 Hz and greatly depressed at 5 to 7 Hz. However a small inhibition was observed to persist during tap frequencies as high as 65 Hz. In a preliminary study both the background and the evoked responses of fastigial cells were found to be very sensitive to barbiturate anesthesia. [ABSTRACT FROM AUTHOR]