Induction of spinal seizures by natural stimulation in cats.

Transection of the spinal cord of the cat at a thoracic or lumbar level results, after as short a period as 12 days, in a preparation with such altered excitability that repeated natural stimulation of the dermatome just caudal to the transection site will induce, in as short a time as 3 days, seizure discharges. The trigger zone for the seizure spreads to caudal dermatomes when these caudal regions are repeatedly stimulated. The 'typical' T4-T7 seizure is a scratch reflex followed by the tonic-clonic seizure lasting for 20-30 s and ending with a scratch afterdischarge lasting for several minutes. Lower thoracic and upper lumbar seizures consist of tonic-clonic co-contractions of the muscles of the hindlegs, followed by rhythmical stepping movements lasting less than 1 min. Partial dorsal rhizotomy or local Cobalt application to the spinal cord may reduce the threshold for induction of seizure by natural stimulation and local Penicillin application to spinal cord induces seizure discharges similar to those induced by natural stimulation. Retransection of the spinal cord caudally, with elimination of the primary trigger zone, does not abolish the secondarily acquired triggers. The findings suggest that spinal circuits possess the ability to acquire new neuronal patterns of discharge and to transfer them to other more caudal segments.

The effects of subcortical sensory and motor lesions on conditioned tactile placing in cats with pyramid section.

Cats after unilateral bulbar pyramid section showed permanent loss of tactile placing in the contralateral limbs. However, the cats could be trained to place the forelimb following light touch in a conditioning situation with food as a reward. This conditioned response survived subsequent unilateral red nucleus and cerebellar interposed nucleus lesions. Dorsal quadrant spinal cord lesion at the cervical level produced initial loss of the conditioned tactile placing but is recovered without retraining. Since those lesions interrupted subcortical afferent and efferent pathways essential to reflex tactile placing, these results indicate that reflex and conditioned responses involve different pathways and mechanisms. Training recruits or activates additional pathways for conditioned responses rather than strengthening those subserving the reflex responses.

The effects of cerebral sensory cortical ablation on instrumental conditioned reflex in cats with cerebellar lesions.

Cats were trained to reach with their fore limbs for food placed in horizontally mounted cylinders of various diameters. The chain instrumental reflex (entering cylinder, reaching for, grasping and bringing food toward the mouth) survived cerebellar paravermal cortical ablation or interposite-dentate nuclear lesion, with some exaggerated flexor or extensor responses respectively. Movements improved with time. Cats were then subjected to ablation of cerebral sensory cortex, SI and SII. SI or compined SI and SII lesion resulted in an initial period of decompensation of cerebellar symptoms. Sensory loss was also noted for 30-40 days after SI lesion and throughout the observation period up to 53 days after combined SI and SII lesion. The conditioned responses were soon accomplished at preoperative level. Furthermore, visual occlusion did not change the performance in conditioning situation. The result indicates that the compensation of cerebellar symptoms does not depend on an intact cerebral sensory cortex. It also suggests that functional accomplishment can be obtained through training despite neurological deficits following certain brain damage.

Cerebral influence on postural effects of cerebellar vermal zonal lesions or eighth nerve section in monkeys.

In monkeys, cerebellar vermal cortical or fastigial nuclear lesion resulted in no significant postural asymmetry. Combined decerebration (but not bulbar pyramid section) and unilateral vermal cortical or fastigial nuclear lesion gave marked ipsilateral hyperextension and contralateral hyperflexion of limbs. Unilateral eighth nerve section resulted in only ipsilateral head tilt but combined unilateral eighth nerve section and decerebration or bilateral or contralateral cerebral cortical areas 4 and 6 lesion gave also ipsilateral flexion and contralateral extension of limbs. Cervical deafferentation or postbrachial spinal cord transection did not alter these results. This study indicates a powerful cerebral influence on postural effects of cerebellar vermal zonal lesion or eighth nerve section in monkeys. Possible mechanisms mediating these effects in monkeys as compared to cats were discussed.

Instrumental conditioned responses in cats with bulbar pyramid and red nucleus lesions.

Adult cats were trained to insert a forelimb into horizontally mounted transparent cylinders and then either depress a barrier or pull a sliding tray against resistance in order to receive food reward. Unilateral lesions of both bulbar pyramid and red nucleus resulted in severe neurological deficits. However, the instrumental tasks were soon accomplished at preoperative levels of rapidity and strength, although movements of the digits and wrist were reduced and adjustive movements occurred chiefly at more proximal joints. These results support our hypothesis that conditioned and unconditioned behaviors are mediated through different mechanisms.

The role of the medial lemniscal and spinocervicothalamic pathways on tactile reactions in cats.

The role of dorsal column (DC)-medial lemniscus and spinocervicothalamic systems on tactile reactions, placing and tactile localization (turning to localize a point touched on the body) was studied in cats with spinal and bulbar lesions. The cats with vision occluded were trained preoperately on horizontal bars for tactile localization. The bulbar lesions of cervicothalamic tract (CTT), which anatomically overlaps with gracile nuclear efferent projection, resulted in permanent loss of tactile placing and localization in contralateral hindlimb. Section of dorsal half of lateral funiculus at C3, which interrupts afferents to lateral cervical nucleus but also involves descending motor pathways, gave loss of tactile placing without impairment of tactile localization. However, combined lesions of both systems abolished tactile placing and localization permanently. Results suggest that tactile placing and localization persists after CTT lesion alone; temporarily loss after DC section but permanently abolished after destruction of both systems. It. is also noted that cats after lesions of both systems without involving motor pathways could walk on bars without vision. The deficits following combined lesions are suggested to be primarily sensory in nature.

Effects of exercise on reflexes in paraplegic monkeys.

Eight monkeys, after complete spinal cord transection at the midthoracic level, were placed in a supine position and an exercise program was given to one hindlimb but not the other. Within 3 days, the exercised limb showed more muscle tone and more active cutaneous and proprioceptive reflexes. The difference increased progressively throughout the observation period of 11 to 36 days. These results suggest an important role of afferent influence on the recovery of spinal shock. The exercise program probably protects the neuromuscular apparatus from deterioration and thus maximize the recovery.

The effects of cerebellar lesions upon skilled movements and instrumental conditioned reflexes.

Eight cats were trained in reaching for food with their forelegs in cylinders 19-21.6 cm long of various diameters (3.9-10.1 cm). When the pre-operative training was completed, in six cats the interposite and dentate intracerebellar nuclei were destroyed, whereas in two cats the paravermal cortex was ablated. Interposite animals displayed big oscillatory movements around the entrance to the cylinder and overshooting in reaching for food with occasional forced grasping. Paravermal cats displayed overflexion leading to missing the entrance of the cylinder and wild batting movements observed in the large cylinder. The physiological mechanism of these disorders is discussed.

Visual discrimination learning and interhemispheric transfer in the cat, as affected by 6-hydroxydopamine.

Learning and interhemispheric transfer of visual flux, pattern and form discriminations were studied in the cat after selected exposure of one suprasylvian cortex to 6-hydroxydopamine (6-OHDA). Biochemical assay using High Performance Liquid Chromatography (HPLC) two weeks after 6-OHDA revealed no discernible norepinephrine or dopamine in the treated cortex, but elevated concentrations of these transmitters in the cortex of the opposite hemisphere. Visual discriminations learned before treatment with 6-OHDA were retained at a high level using either the eye on the side of chemical lesion or the eye on the untreated side. An asymmetric deficit in learning new form discriminations was present, however, when the eye on the untreated side was used, in contrast to normal learning using the eye on the side of the hemisphere with depleted adrenergic nerve supply. Once learning was achieved using the lesioned hemisphere transfer of the engram was found to the untreated hemisphere. Thus, the unlesioned hemisphere was unable to learn normally using direct retinal input from the ipsilateral eye, but showed good capacity for learning using indirect visual input from the contralateral eye. This suggests a powerful influence of the callosum on the learning abilities of the two hemispheres, an influence proved by sectioning the callosum. Callosotomy resulted in a reversal of the discriminative capacities seen after 6-OHDA, i.e. the lesioned hemisphere was defective relative to the unlesioned hemisphere.

Recovery of the hopping response after complete spinal cord transection in the cat.

The hopping response reappears in the hind limb of the cat after complete spinal cord transection at postoperative day means = 11.6. This response is hypermetric and slow compared with that in the normal cat and only forward, medial, and lateral hopping can be elicited. Anatomical and physiological changes in the spinal cord which may account for the reappearance of the hopping response are discussed.