Behavioral and neurochemical indices of barrel cortex-basal ganglia interaction

Vibrissal paralysis produces increased corticosterone levels and impairment of spatial memory retrieval

This research was aimed at establishing how the absence of active whisking in rats affects acquisition and recovery of spatial memory. The mystacial vibrissae were irreversibly paralyzed by cutting the facial nerve's mandibular and buccal branches bilaterally in the facial nerve lesion group (N=14); control animals were submitted to sham-surgery (N=15). Sham-operated (N=11) and facial nerve-lesioned (N=10) animals were trained (one session, eight acquisition trials) and tested 24h later in a circular Barnes maze. It was found that facial nerve lesioned-animals adequately acquired the spatial task, but had impaired recovery of it when tested 24h after training as compared to control ones. Plasma corticosterone levels were measured after memory testing in four randomly chosen animals of each trained group and after a single training trial in the maze in additional facial nerve-lesioned (N=4) and sham-operated animals (N=4). Significant differences respecting the elevation of corticosterone concentration after either a single training trial or memory testing indicated that stress response was enhanced in facial nerve-lesioned animals as compared to control ones. Increased corticosterone levels during training and testing might have elicited the observed whisker paralysis-induced spatial memory retrieval impairment.

Contralateral increase in thigmotactic scanning following unilateral barrel-cortex lesion in mice

Adult C57BL/6 mice received uni- or bilateral cryogenic or sham-lesions over the barrel field and their exploratory behaviour was assessed in an open field between 1 and 7 days post-lesion. Bilateral cortical lesions produced a short-lasting increase in thigmotactic scanning with both sides of the face on the first day of testing. Mice with a unilateral barrel-cortex lesion showed more contralateral wall scanning with a recovery to behavioural symmetry after 5-7 days. Furthermore, the increase in contralateral thigmotaxis was most pronounced in animals with damage to the left barrel field, indicative of a lateralization of the lesion-induced behavioural changes. The cortical lesions did not influence locomotor activity and the rate of habituation to the open field (habituation 'learning'). Referring to recent electrophysiological findings, we hypothesize that the lesion established a lateralized source of increased neuronal excitability within the affected barrel-cortex, leading to more behaviour with its corresponding vibrissae. Alternatively, if the lesion results in contralateral 'neglect' in terms of input, the increased scanning with the affected vibrissae may reflect an attempt of the system to compensate for this with an increase in usage.

Early behavioral changes after nigro-striatal system damage can serve as predictors of striatal dopamine depletion

1. Rats which had received a unilateral injection of 6-OHDA into the substantia nigra were assigned to four lesion groups according to the degree of DA depletion in the neostriatum. In these animals, behavioral changes in the open-field were investigated during the first postoperative week. Overall, this analysis showed that the animals could adequately be characterized by behavior on day 1 and day 7 after lesion. 2. On the first day after lesion, the groups with the severest DA depletions (> 80% and 55-80%) showed an ipsilateral asymmetry in turning. After one week, these groups showed a tendency to recover from this deficit; however, the group with the most strongest lesions (> 80%) was still asymmetric. 3. In scanning behavior, in contrast to turning, all the lesion groups displayed an initial ipsilateral asymmetry. On day 7 after lesion, only the group with DA depletions of > 80% still had an ipsilateral asymmetry. Locomotor activity and rearing were initially reduced after lesion, and showed a tendency to recover, especially in the group with the most severe DA depletions (> 80%). There were no differences between groups neither on day 1 nor on day 7 by grooming, but this behavior increased in all the lesion groups with time. 4. The correlational analyses yielded a positive relationship between the asymmetry in turning and neostriatal DA depletion. Locomotor activity and rearing on day 1 were both negatively correlated with DA depletion. The present results show that a number of behavioral parameters obtained in the open-field are affected by unilateral lesions of the nigro-striatal DA system. The degree of deficit, its time course and relation to lesion size differs among the various behavioral measures. Some of these early behavioral changes after unilateral nigrostriatal lesion are related to DA depletion and should therefore be useful to predict lesion size.Together, these data suggest that the study of such behavioral changes can provide an important tool, to investigate the compensatory mechanisms underlying striatal DA depletion and to understand preclinical states of the Parkinson's disease.

Forebrain expression of c-fos due to active maternal behaviour in lactating rats

To reveal brain sites simultaneously active during the expression of maternal behaviour in lactating rats, we used immunocytochemical visualization of the nuclear protein product Fos of the immediate-early gene c-fos as a marker of neuronal activity. After a 48 h separation from their litter, day 7 postpartum dams received a 1 h period of physical interaction with pups either capable or incapable of suckling, inaccessible pups in a wire-mesh box, an empty box, or no stimulation. Physical interaction with pups elicited high levels of pronurturant maternal behaviour (retrieval, licking, mouthing), and suckling elicited nursing behaviour as well. Exposure to the box, with or without pups, elicited high levels of investigatory sniffing, self-grooming, and general activity. Distal stimulation from pups did not differentially activate Fos in any of 20 sites, including olfactory-processing structures such as the piriform cortex and medial amygdala. Physical interaction with pups, with or without suckling, elicited higher levels of Fos-immunoreactive nuclei than that of other conditions in numerous sites, including many previously implicated in maternal behaviour (medial preoptic nucleus, nucleus accumbens, lateral septum, lateral habenula, and the bed nucleus of the stria terminalis). Similar group patterns of Fos expression also occurred in sites not previously implicated in maternal behaviour (somatosensory cortex and paraventricular thalamic nucleus). Interaction with nonsuckling pups elicited the highest levels of Fos in the cortical amygdala, whereas suckling did not activate higher Fos than nonsuckling interaction in any site included in this report, including hypothalamic nuclei involved in lactation (paraventricular, supraoptic, and arcuate). There was little or no Fos in cingulate cortex, olfactory tubercle, medial septum, medial habenula, or ventromedial hypothalamus. These data suggest that trigeminal stimuli received by lactating rats during the performance of pronurturant maternal behaviour promote cellular activity resulting in neuronal expression of c-fos in many forebrain sites including the medial preoptic nucleus, several sites connected with it that are part of the mesotelencephalic dopamine system, and in the somatosensory cortex. In contrast, in these forebrain sites suckling does not elicit greater levels of Fos than that seen in nonsuckled rats and distal stimuli from pups are ineffective in increasing Fos levels compared with non-stimulated controls.

Changes in extracellular levels of dopamine metabolites in somatosensory cortex after peripheral denervation

This study examined the effects of a nerve transection on monoamine release from primary somatosensory cortex. The technique of microdialysis was employed to sample extracellular levels of norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in the barrel field of freely moving rats following the surgical transection of the contralateral infraorbital nerve. Microdialysates obtained 3, 4, and 5 days after deafferentation were analyzed using high-performance liquid chromatography with electrochemical detection. We found a significant increase in the release of the dopamine metabolites, DOPAC and HVA from the deafferented cortex. Three days after deafferentation the release of DOPAC was three-fold higher in the deafferented than in the control animals, and remained about 100% higher in the next two days in this group of animals. The release of HVA showed a gradual increase following the deafferentation procedure, since a 92% larger value on day 3 increased to a 338% difference on day 5. On the other hand, the release rate of NE and the levels of the serotonin metabolite 5-HIAA were not significantly affected by the deafferentation procedure. These results are discussed in the context of the possible participation of dopamine in the reorganization of the deafferented somatosensory cortex.

Lateralized effect of unilateral somatosensory cortex contusion on behavior and cortical reorganization

Previous studies have shown that rats recover function after unilateral somatosensory cortex lesions, possibly by transfer of information processing to other brain areas not normally involved in those functions. In the present study, adult rats underwent unilateral contusions of the somatosensory cortex with ablation of the barrel receptor field. Behavioral testing with modified beam-walking and sensory neglect tasks demonstrated persistent somatosensory deficits in rats with left contusions but no apparent deficits in right injured animals. After 2 months, the [14C]2-deoxyglucose (2-DG) method was used to show the metabolic activity produced by unilateral stimulation of the facial vibrissae. In left injured animals, cortical metabolic activity rostral and caudal to the injury site was depressed both under basal conditions and during right vibrissal stimulation. On the other hand, comparison of the pattern of [14C]2-DG uptake in the intact, right cortex revealed changes in the pattern of glucose utilization associated with left injury combined with right vibrissal stimulation. Pattern changes were quantified by measuring the area in which glucose utilization was within the highest 25% of this range (high activity area; HAA). Right vibrissal stimulation in left injured rats caused an expansion of this HAA in the intact occipital/temporal cortex. Also, in the intact somatosensory cortex of left injured rats, there was an enlarged HAA whether or not vibrissal stimulation was performed. Thus, a combination of depressed peri-injury metabolic activity and aberrant activity in remote brain areas occurs following unilateral somatosensory cortex injury. It remains to be shown whether these factors ameliorate or contribute to persistent behavioral deficits.

Tactile sensory input regulates basal and apomorphine-induced immediate-early gene expression in rat barrel cortex

Clipping of mystacial vibrissae on one side of the rat's snout results in sensorimotor asymmetries in normal behavior and in behavior induced by the dopamine receptor agonist, apomorphine. Immediate-early gene expression, a marker for short-term changes in neuron function, was used to examine whether this sensory deprivation leads to functional changes in the somatosensory barrel cortex under experimental conditions which reveal behavioral asymmetries. The expression of c-fos and zif268 immediate-early genes was assessed with in situ hybridization histochemistry. Four hours after unilateral clipping of the mystacial vibrissae, the level of zif268 mRNA was reduced in the corresponding part of the contralateral barrel field. Injection of apomorphine (5 mg/kg) resulted in increased expression of both c-fos and zif268 immediate-early genes in cortex and striatum. This apomorphine-induced increase was blocked in the sensory-deprived somatosensory cortex. Laminar analysis of gene regulation showed that vibrissae removal affected immediate-early gene expression in all layers of the barrel cortex. These results demonstrate that: (1) basal zif268 gene expression in neurons of the somatosensory cortex is dependent on sensory input, (2) cortical immediate-early gene expression is increased after dopamine receptor activation, and (3) in the barrel cortex, this increase is also dependent on sensory input. We suggest that the observed reduction in gene expression after vibrissae removal reflects decreased activation of neurons in the barrel column by removal of sensory input.

Behavioral and neurochemical asymmetries following unilateral trephination of the rat skull: is this control operation always appropriate?

The present results are from rats that were intended as sham-operated controls in a study of unilateral lesion of the cortical barrel fields. These animals received a trephine hole through the skull, centered over the barrel fields of one hemisphere. Unexpectedly, they showed time-dependent behavioral and neurochemical asymmetries: 1 + 4 days after unilateral skull trephination they scanned an open field mainly with the contralateral vibrissae. Thereafter (days 7 + 14), scanning recovered to symmetry; however, an ipsilateral asymmetry was induced now by challenge with the dopamine receptor agonist apomorphine. At the same time period after skull trephination, an asymmetry of thigmotactic swimming had developed, with more thigmotactic swimming ipsilateral to the side of skull trephination. Neurochemically, there were indications for changes in neostriatal dopamine metabolism because the tissue levels of dopamine and dihydroxyphenylacetic acid were lower on the ipsilateral side in animals killed 6-16 days after trephination. The time courses of behavioral and neurochemical asymmetries after unilateral skull trephination paralleled those seen following unilateral barrel cortex lesion or unilateral removal of the corresponding contralateral vibrissae; however, without exception, the asymmetries after trephination were in the opposite direction than after cortex lesion or vibrissae removal. The possible mechanisms by which skull trephination might have affected behavior and neurochemistry are discussed, especially with respect to the vibrissae-barrel cortex system and the basal ganglia. Because trephination of the skull is routinely employed, both as a control procedure and for CNS manipulation, these results may have important implications for the design of future experiments.

A video image analyzing system for open-field behavior in the rat focusing on behavioral asymmetries

A video image analyzing system is presented which measures turning behavior, thigmotactic scanning and locomotion in rats. The system works by analyzing digitized video images obtained by a black/white video camera. Turning behavior is expressed in different diameter classes and as partial or full turns. Thigmotactic scanning is expressed as distance or time locomoted with the left or right side of the body along one of the walls of the testing environment. Locomotion is measured as distance travelled and is expressed in meters. Examples for the application of these behavioral measures are given which include: the measurement of spontaneous or drug-dependent behavioral asymmetries after brain lesion (the unilateral 6-hydroxydopamine model), a unilateral peripheral manipulation (hemivibrissotomy), and the measurement of open-field behavior (spontaneous or drug-induced) in intact animals. Among others, these examples show that the analysis of thigmotactic scanning may provide an alternative behavioral measure, which may be especially useful in the study of functional asymmetries.