Single Spike Responses Research Articles

Electrophysiological analysis of the circuitry and of the corticonuclear relationships in the agranular cerebellum of irradiated rats.

The cerebellar circuitry and the corticonuclear relationships were studied in the cerebellum of adult rats rendered agranular through 7 successive exposures to X-ray radiations during infancy. Data were obtained through examination of electrical responses induced in Purkinje cells (PC) and in neurons of the lateral vestibular nucleus (LVN) by cerebellar and spinal stimulations. In irradiated rats, PC exhibited antidromic activation with a high axonal threshold and 70% of them also presented typical climbing fiber responses (CFRs). By contrast, they exceptionnally exhibited responses via the mossy fiber (MF)-granule cell pathway, but two other classes of responses were identified: i) short latency single spike responses attributed to a direct excitatory impingement of MF onto PC; ii) atypical CFRs formed of high frequency bursts of simple spikes which were seen in 76% of PC tested. Furthermore, 53% of these cells also presented typical CFRs, strongly suggesting these PC were innervated by more than one CF, thus confirming previous data on the same type of agranular cerebellum. In the LVN neurons of control and irradiated rats, spinal and cerebellar stimulations evoked clear cut IPSPs. On the basis of their shape, latency, and occurrence in animals with or without cerebellum and with or without lesion of the CF pathway, they were interpreted as mediated through direct or synaptic activation of PC or through an extracerebellar pathway. In irradiated rats, the quantitative study of these IPSPs gave further arguments in favor of a multiinnervation of PC by CF and of an important reafferentation of MF onto PC. However, the functional efficiency of this reafferentation appeared very low, as tested by activation of MF originating in the spinal cord. Finally, the intracellular recording of LVN neurons showed that a large majority of PC axons retained normal synaptic connections with nuclear cells in treated animals, indicating that corticonuclear relationships do not markedly depend upon granule cells and normal CF input.

Unit activity in somatosensory area II (SII) and tooth pulp stimulation in a cat.

Within and near the rostral half of the anterior ectosylvian gyrus of an unanesthetized chronic cat, properties of units which responded to stimulation of the ipsilateral upper canine tooth pulp were studied. In total 75 responsive units were recorded by 192 microelectrode penetrations. Discharge patterns of these units to pulp stimulation were classified into 3 types: single spike response (4 units), short burst response (66 units) and prolonged response continuing up to several hundred msec (4 units). Spontaneous activities of one exceptional unit were depressed for 200-300 msec after pulp stimulation. These units were scattered in the explored cortical area, indicating that the SII somatotopically organized area may also receive nociceptive inputs. Most of these units responded to some modalities of mechanical stimuli applied to various parts of the body surface including face and head. This result suggests that they may correspond to the neurons unspecific with regard to modality and place observed in the anesthetized cat. Few units activated by pulp stimulation were encountered in the rostral portion of the anterior ectosylvian gyrus, where MELZACK and HAUGEN (1957) recorded the evoked potential by pulp stimulation. Five tooth pulp-sensitive units which were excited only by pin pricks and/or firm pressure were encountered on the dorsal bank of the anterior ectosylvian sulcus, the non-somatotopically organized area of SII.

The synaptic activation of neurones of the feline ventrolateral thalamic nucleus: possible cholinergic mechanisms.

The responses of individual neurones of nucleus ventrolateralis thalami (VL) have been recorded extracellularly following stimulation of the brachium conjunctivum (BC), nucleus entopeduncularis (EN) and precruciate cortex. In anaesthetized cats stimulation of these structures produced either short latency single spike responses or brief bursts of action potentials with somewhat longer latency: the latter responses could be converted to single spikes by the electrophoretic application of acetylcholine or an excitatory amino acid to the neurone. Atropine attenuated the effect of BC stimulation but did not alter excitations from the cortex or EN. Acetylcholine was found to depress the excitation of VL neurones from EN. Collateral fibres of the EN neurones were shown to innervate neurones in the lateral parts of the centrum medianum — parafascicular complex and in VL.

Responses of purkinje cells in the frog cerebellum to electrical and natural stimulation

The responses of single neurons in the cerebellum to natural stimulation of peripheral nerves were investigated in the unanesthetized frog. These responses, as well as those elicited by electrical stimulation of the cerebellar cortex and spinal pathways, were characterized using computer assisted statistical spike train analysis techniques. Purkinje cell responses to climbing fiber inputs were described and cells with these inputs from the hindlimb and forelimb were localized in the ipsilateral ventral portion of the corpus cerebelli. Climbing fiber responses could be elicited by sciatic nerve stimulation only at stimulus frequencies below 5/sec. The latency for these responses, evoked by stimulation of the whole sciatic nerve, the peroneal or tibial branches of the sciatic nerve or of forelimb innervation (radial nerve), was a minimum of 25 msec. It was concluded that the climbing fiber afferent system and its projections in the frog were strikingly similar to the climbing fiber inputs reaching the vermis of the cat cerebellum. Stimulation of the sciatic nerve with high frequency pulse trains evoked single spike responses in Purkinje cells with latencies of 25 msec or longer. The peak probability for these responses occurred with a latency of 50–70 msec. Only a few climbing fiber responses were recorded under these stimulus conditions. The isolated gastrocnemius muscle or tibialis anterior muscle was stretched by a computer-controlled solenoid device. Records from the muscle afferents showed brisk responses to this mechanical stimulus. However, Purkinje cell responses to this input were very small or non-existent. When the foot was moved about the ankle joint in a preparation in which the hindlimbs were left intact, Purkinje cell responses were larger and more frequent. It was concluded that the functional organization of the frog cerebellum and its spinal afferents is such that Purkinje cell responses to naturally coded stimuli are most effectively elicited when afferent information is coded in a form similar to that seen during a normal limb movement.

Influence of Noradrenaline on Spinal Interneuron Activity

AbstractSkoglund C. R. Influence of noradrenaline on spinal interneuron activity.The effects of intra‐arterial and intravenous injections of noradrenaline on spinal interneurons have been studied on decapitate, curarized cats by means of intracellular technique. The most common effect, observed at a threshold dose of 1 μg per kg bodyweight, was an increase in excitability. Interneuron responses to single afferent volleys were facilitated, a typical effect being transformation of single spike responses into repetitive discharges. In the absence of any induced afferent stimulation noradrenaline injections were observed to set up discharges in initially silent cells and to cause an increase in frequency of prevailing activity, sometimes followed by a decrease. An initial decrease in excitability was only occasionally seen.