SUMMARY1. Stable extracellular unitary recordings were made from 138 cerebellar interpositus nuclear neurones (IPNs) in awake cats. Mean background discharge, in animals in a state of relaxed wakefulness and in the absence of overt movement, was 41P0 + 2-6 impulses/sec (mean + S.E.M).2. Animals were trained to accept a variety of sensory testing procedures without producing detectable motor reactions. Mechanical taps (1 mm amplitude; 20 msec overall duration) applied to the main pads or dorsal surfaces of the forepaws and/or hind paws modified discharge in forty-eight of 110 IPNs tested. Response patterns to taps generally comprised one or more of three basic components, namely:short-latency excitation, el, at onset latencies of 13-0+0-9msec (mean+s.E.M.) for ipsilateral forepaw (iF) and 17-0+007 msec for ipsilateral hind paw (iH); a period of reduced discharge, at latencies 25-6 + 2-6 msec for iF and 32-3 + 2-1 msec for iH; a delayed acceleration of discharge, e2, at latencies 47*4 + 4-6 msec for iF and 46-4 + 41 msec for iH. The component el was the most common (present in 80 % of responses) and e2 the least common (present in 18 % of responses). 5. Approximately one third ofIPNs so tested were sensitive to passive manipulation of limb joints in the quiet, awake cat. Sixteen of the forty-three IPNs so tested responded to displacement of the ipsilateral wrist and/or elbow joints and three of ten IPNs so tested responded to movement of contralateral forepaw joints. Corresponding proportions of IPNs responding to passive ankle and/or knee joint displacements were sixteen of thirty-six units tested and three of three units tested for ipsilateral and contralateral hind paws respectively. Convergence of input generated by manipulation of iF and iH joints on to individual IPNs was apparent in only three of twenty-four units tested at each site.

We have labelled clones of neurons in the cerebral cortex of rats by introducing a retroviral vector, called BAG, into the cerebral vesicles of embryos in utero. BAG encodes the enzyme beta-galactosidase, which acts as a histochemical marker for the subsequent identification of clones derived from infected precursor cells. We have studied the distribution of neuronal clones in the rat somatosensory cortex, and have asked whether clonally-related neurons were dispersed randomly. We have discovered that they are not. Rather, clones disperse predominantly such that the earliest progeny of ventricular zone cell are found posterolateral to later generated cells. This distribution fits with what would be expected were neurons dispersed passively in accordance with the lateral to medial cortical neurogenic gradient.

No abstract

No abstract