Split-brain Rats Research Articles

Effect of Cerebral Laterality on the Healing of Cutaneous Wounds in Normal and Split-brain Rats

The immune system and the nervous system maintain extensive communication. Sensory innervation plays a vital role in normal wound healing. In the present study, we performed corpus callosotomy to evaluate the role of corpus callosum on brain laterality and the influence of brain laterality on wound healing in dominant and nondominant sides of the body in rats. After detecting the cerebral laterality by T-maze, 200 young male Wistar rats were divided into 3 groups. In the control group, rats underwent wounding, but no craniotomy and callosotomy. In the sham group, rats underwent wounding and craniotomy without callosotomy. In the operation group, wounding was performed with craniotomy and callosotomy. The length and the inflammatory cell count of the created wound in both sides of the body in same days were measured and analyzed statistically. Wound healing took significantly shorter in dominant side in comparison with nondominant side of body in control and sham groups (P=0.010, 0.031, 0.029, and 0.036). In the operation group, there was no significant difference of complete wound healing between dominant and nondominant sides of the body (P=0.875, 0.604). Inflammatory cell count showed no statistically significant difference between groups (P>0.05). Taken together, our results constitute an endorsement to the hypothesis that brain laterality has a meaningful influence on wound healing in different sides of the body.

Interocular transfer in the split-brain rat.

After the 1991 development of a method to transect the optic chiasm in the rat, the authors investigated interocular transfer in split-chiasm rats with corpus callosum section and callosum intact. Rats were monocularly trained on an orientation discrimination, reversed with the other eye, and retrained with the 1st eye on the 2nd-eye problem or reversal. In split-chiasm rats, the 2nd-eye S+ (correct stimulus) showed strong transfer (55% savings) to the 1st eye. S- (incorrect stimulus) did not; reversal and transfer groups differed significantly. Split-brain rats retrained with the 1st eye on the 2nd eye S+ required no more trials than original learning, as if they had not experienced this problem. Split-brain rats retested with the original S+ showed modest (19%) savings. The findings establish interhemispheric communication via the callosum and suggest, as in findings of cat and monkey studies, the disruption of transfer by callosal section.

Interocular transfer in the split-brain rat.

Interocular transfer in the split-brain rat.

Spontaneous firing of nigrostriatal dopaminergic neurons in split-brain rats

The regulatory action of the contralateral brain side on nigrostriatal dopaminergic (NSDA) neurons was examined in anesthetized rats using extracellular single-unit recording techniques. The spontaneous activity of NSDA cells was recorded from split-brain, sham-lesioned or intact-brain rats. The three groups of cells did not differ in antidromic latency and firing rate. However, cells from split-brain rats exhibited a more regular pattern of discharge than those recorded in the two control groups as shown by autocorrelograms and the standard deviation and variation coefficient of the interspike intervals. In addition, burst firing was found to be markedly reduced in the split-brain group. It is concluded that decussating pathways are involved in the regulation of the discharge pattern of NSDA neurons.

Effects of unilateral parietal lesions on spatial localization in the rat.

In the first of two experiments, rats with left or right parietal lesions and controls were tested in place and landmark navigation in the water maize. Right parietal lesions resulted in deficits in both tasks, but especially landmark navigation. Lateralized effects appeared mainly in latency to find the platform. Experiment 2 investigated the role of the corpus callosum. Split-brain rats with unilateral parietal lesions were tested on the same two tasks. Place and landmark deficits were particularly severe, but lateralization was weaker. Callosum section had its own effect, impairing the learning of both tasks. There appear to be additive effects of unilateral cortical lesions and bisection of the hemispheres. The impairment from left lesions equaled the right-lesion deficit because of the interruption of compensatory information from the intact right hemisphere and the effect of callosum section itself.

Completing the split in the split-brain rat: transection of the optic chiasm

We describe a stereotaxic technique to transect the optic chiasm in the rat and present illustrative data on the interocular transfer of visual discrimination in chiasm-sectioned and chiasm-plus-forebrain commissure-sectioned animals. Applications of the technique are discussed.

Visuospatial asymmetries and interocular transfer in the split-brain rat.

Interocular transfer (IOT), hemispheric superiority, and cerebral dominance were examined in split-brain female albino rats. Callosum-sectioned and intact animals were monocularly trained in the Morris water maze and tested in IOT and reversal phases. In the IOT phase, split-brain rats entered more nontarget quadrants and headed less accurately toward the platform than did controls. For both split-brain animals and controls, right-eye training resulted in shorter latencies and fewer nontarget entries than did left-eye training. Analyses of cerebral dominance showed shorter latencies and smaller heading errors over all 3 phases in rats that were trained with the nondominant eye. Right-eye dominant controls were less affected by platform reversal. Split-brain rats were inferior to controls in latency to find the platform and in target quadrant entries. This finding establishes a spatial cognitive deficit from callosum section.

Visuospatial asymmetries and interocular transfer in the split-brain rat.

Visuospatial asymmetries and interocular transfer in the split-brain rat.

Status epilepticus following stimulation of a kindled hippocampal focus in intact and commissurotomized rats

Status epilepticus of either a nonconvulsive, partial, or generalized form was provoked in rats by 60 min of electrical stimulation of a kindled focus in the posteriorventral hippocampus. Following spontaneous offset of the nonconvulsive status epilepticus, minor pathology occurred which was largely restricted to the hippocampus, whereas partial or generalized status epilepticus produced considerable bilateral damage in the hippocampus, basolateral amygdala, and pyriform cortex. Bisection of the anterior half of the corpus callosum lateralized the forelimb motor seizures and bisection of the hippocampal commissure lateralized the hippocampal afterdischarge and the associated brain pathology. Paradoxically, commissurotomy also increased the probability of developing status epilepticus while reducing its severity. Further, it was shown that the right hippocampus precipitated status epilepticus with a higher probability than the left hippocampus in both intact and split-brain rats.

Lateralized state-dependent learning produced by hippocampal kindled convulsions: Effect of split-brain

In previous experiments, it was demonstrated that convulsions kindled from a ventral hippocampal focus in rats supported state-dependent learning which tended to lateralized to, and asymmetrical in, the right hemisphere [26]. The question of the differential contribution of the left and right hippocampus to the production of state-dependency can best be addressed through confining the seizure to one or the other hemisphere via commissurotomy. In the present investigation, then, commissurally-intact and split-brain rats were implanted with bilateral hippocampal electrodes, then a left or a right focus was kindled. Later behavioral testing in an aversive inhibitory avoidance (IA) paradigm, revealed that intact animals, both left and right kindled groups, displayed good state-dependency. Split-brain animals, however, exhibited differential state-dependent responses to convulsive stimulation. Those kindled in the left hippocampus showed good retention when the conditions of seizure during training and testing were the same (same-state conditions), while showing deficient recall in changed-state conditions (a good state-dependent profile). On the other hand, those kindled in the right hippocampus displayed good retention of the IA experience in both same- and changed-state conditions. Differential recall after a left versus a right hippocampal convulsion in split-brain animals could not be accounted for in terms of differential seizure parameters, laterality of afterdischarge, extent of extracommissural damage or the extent of the actual transection. Possible mechanisms underlying this effect were discussed.

State-dependent learning following electrical stimulation of the hippocampus: Intact and split-brain rats

In experiment 1, electrical stimulation of the posterior hippocampus was shown to produce state-dependent learning (SDL) for a step-out inhibitory avoidance task in rats. Stimulation sites in either the right or left hippocampus were equally effective in producing this effect. Similarly, the presence or absence of afterdischarge (AD) following the stimulation did not differentially affect performance on the task. In experiment 2, forebrain bisection ameliorated the behavioral deficits in the animals receiving stimulation before testing but not before training (N/S group), while those stimulated before training but not before testing (S/N group) remained impaired; thus, providing a demonstration of asymmetrical SDL. Variations in extent of the commissurotomy differentially affected the laterality of the afterdischarge but not the performance in the SDL task. Speculation as to the mechanisms of this SDL effect was presented.

Response determinants of interocular transfer in normal and split-brain rats

Response determinants of interocular transfer in normal and split-brain rats

Lateralized effects of monocular training on dendritic branching in adult split-brain rats

A number of experimental approaches have indicated differential interneuronal connectivity following differential experience during both development and adulthood. In Golgi preparations, prolonged maze training was reported to alter dendritic branching of distal apical dendrites of Layer IV and V pyramidal neurons in adult rat occipital cortex. To determine the specificity of this effect to direct involvement in the visual aspects of training, the effects of monocular maze training, using a split-brain procedure and opaque contact occluders, was examined in the present study. Rats were maze trained with unilateral or alternating monocular occlusion, while non-trained rats with unilateral or alternating monocular occlusion were handled briefly and given water reward. There was no within-animal effect of fixed occluder position in non-trained controls. In unilaterally-occluded trained rats, Layer V pyramidal neurons in occipital cortex opposite the open eye had greater oblique dendritic length in the distal region of the apical dendrite than did those opposite the occluded eye. Similarly, rats trained with alternating occlusion had greater distal apical oblique dendritic length in Layer V occipital pyramidal neurons than did non-trained controls. This indicates that morphological sequelae of training are concentrated in areas processing information associated with visual aspects of the training and renders unlikely general metabolic or hormonal causation of such effects.

Severing the corpus callosum in rats using ultrasound: Theoretical and experimental correlations

A single, focused, ultrasound beam of 3.5 W total acoustic output for 2 s at 3.3 MHz was used to create a series of overlapping lesions to sever the corpus callosum of the rat on the midline. A theoretical and experimental determination of the ultrasound field is described and histological evidence of the lesions is provided. Good correlation occurred between the theoretical and experimental results only for the intensity contour lines examined. The experimentally derived focal intensity of 162 W cm−2 (at 25 °C) was 24% of the intensity predicted from theoretical calculations. A difference of 2 mm was found for the axial position of maximal intensity, thermocouple plotting showing the focal region to be nearer the transducer than expected from the theory. Histological results indicated that, under certain conditions, from a single dose of ultrasound two lesions could be obtained corresponding to both the theoretically and experimentally derived locations. At lower intensities it was possible to ulitize the upper location to sever the corpus callosum, the lower intensity site then being subthreshold for the rat brain. The trackless localized damage caused by ultrasound makes this method of obtaining split-brain rats suitable for behavioral and biochemical studies, where any nonspecific damage may have undesirable effects.

Long term induction of kindled seizures in rats: interhemispheric factors.

Previous research indicated that sequential alternation of stimulation of certain homologous brain areas via chronically implanted electrodes resulted in oscillation of high and low latencies for convulsions. This phenomenon suggested the establishement of interhemispheric facilitatory-inhibitory effects as a result of repeated stimulation of the two brain sites. In the present study, the latency oscillation pattern was observed in split-brain rats as well as in bilaterally stimulated controls, but not in rats stimulated on one side only. Significant differences were observed between split-brain and control rats in terms of initial kindling rates, duration of convulsions and type of oscillation. Results are discussed in the context of possible interhemispheric mechanisms involved in long term kindling.

Split-brain rat: transfer and interference of kindled amygdala convulsions.

Rats were subjected to varying degrees of commissurotomy, followed by implantation of a bipolar electrode into each amygdala. After the kindling of six convulsions at one electrode (primary site), the procedure was applied to the contralateral amygdala (secondary site). Convulsions were observed to develop more rapidly, independent of the degree or kind of transection. After 6 secondary site convulsions, the primary site was re-tested and convulsion-triggering was blocked, except in animals with transection of the rostral portion of the corpus callosum (CC). Collectively, the data indicate: (i) amygdala kindling develops a lasting trace which operates through the midbrain or brainstem; (ii) kindling from a second site utilizes this trace; (iii) a series of 6 convulsions produces negative after-effect which manifests itself at the convulsion level via the anterior CC; (iv) the anterior CC is important in determining the laterality of the forelimb clonus; and (v) the inter-amygdala propagation of after-discharge is blocked by the combined sectioning of the anterior CC and the anterior commissure.

Split brain rat: A new surgical approach

The corpus callosum was sectioned in the midline by insertion of a 24 gauge needle and retractable knife horizontally through the dorsal cerebellum of five rats. The callosum was sectioned through most of its extent and incidental damage to the midline cerebral cortex was either minimal or absent. Gross postoperative motor deficits or other behavioural changes were absent in all animals.

Lateralization of olfactory memory in the split-brain rat.

Lateralization of olfactory memory in the split-brain rat.

Task difficulty and lateralization of learning in the functional split-brain rat

The present experiment was concerned to evaluate whether or not task difficulty determines lateralization of learning in the functional split-brain animal. Complete lateralization was obtained at all difficulty levels not only for integrated escape responses but also for all instrumental components of the behaviour. Classically conditioned CERs failed to lateralize, but they did not facilitate the acquisition of escape behaviour with the new hemisphere. Analysis of the learning pathways taken by each hemisphere indicated that in the split-brain the two hemispheres learn in different ways. The presence of a hemidecorticate learning deficit for escape learning was confirmed and evidence for a retention deficit found. The relationships between classical conditioning and instrumental learning were discussed.