D1-class dopamine receptor involvement in the behavioral recovery from prefrontal cortical injury

Post-stroke mortality, stroke severity, and preadmission antipsychotic medicine use--a population-based cohort study

Background and Purpose

It has been suggested that antipsychotic medication may be neuroprotective and may reduce post-stroke mortality, but studies are few and ambiguous. We aimed to investigate the post-stroke effects of preadmission antipsychotic use.

Methods

We conducted a nationwide, population-based cohort study of 81,143 persons admitted with stroke in Denmark from 2003–2010. Using Danish health care databases, we extracted data on preadmission use of antipsychotics and confounding factors. We examined the association between current, former, and never use of antipsychotics and stroke severity, length of hospital stay, and 30-day post-stroke mortality using logistic regression analysis, survival analysis, and propensity score matching.

Results

Current users of antipsychotics had a higher risk of severe or very severe stroke on The Scandinavian Stroke Scale than never users of antipsychotics (adjusted odds ratios, 1.43; 95% CI, 1.29–1.58). Current users were less likely to be discharged from hospital within 30 days of admission than never users (probability of non-discharge, 27.0% vs. 21.9%). Antipsychotics was associated with an increased 30-day post-stroke mortality among current users (adjusted mortality rate ratios, 1.42; 95% CI, 1.29–1.55), but not among former users (adjusted mortality rate ratios, 1.05; 95% CI, 0.98–1.14).

Conclusions

Preadmission use of antipsychotics was associated with a higher risk of severe stroke, a longer duration of hospital stay, and a higher post-stroke mortality, even after adjustment for known confounders. Antipsychotics play an important role in the treatment of many psychiatric conditions, but our findings do not support the hypothesis that they reduce stroke severity or post-stroke mortality.

Intrastriatal dopamine D1 antagonism dampens neural plasticity in response to motor cortex lesion

Motor cortex lesions in rats partially denervate the striatum, producing behavioral deficits and inducing reactive neuroplasticity. Plastic responses include changes in growth-associated protein marker expression and anatomical restructuring. Corticostriatal plasticity is dependent on dopamine at the striatal target, where D1 receptor signaling reinforces behaviorally relevant neural activity. To determine whether striatal dopamine D1 receptor signaling is important for the growth-associated protein responses and behavioral recovery that follow unilateral motor cortex aspiration, the dopamine D1 receptor antagonist SCH23390 was intrastriatally infused in cortically lesioned animals. After a cortical aspiration lesion in Long Evans rats, the growth-associated proteins SCG10 and GAP-43 were upregulated in the cortex contralateral to the lesion at 30 days post-lesion. However, continuous unilateral intrastriatal infusion of SCH23390 prevented this aspiration-induced upregulation. Furthermore, lesioned rats demonstrated spontaneous sensorimotor improvement, in terms of limb-use symmetry, about 1 month post-lesion. This improvement was prevented with chronic intrastriatal SCH23390 infusion. The D1 receptor influence may be important to normalize corticostriatal activity (and observable behavior), either in a long-term manner or temporarily until other more permanent means of synaptic regulation, such as sprouting or synaptogenesis, may be implemented.

Infusion of apomorphine into the dorsocentral striatum produces acute drug-induced recovery from neglect produced by unilateral medial agranular cortex lesions in rats

Previous studies have shown that systemic administration of apomorphine is effective in producing acute drug-induced recovery from neglect induced by unilateral medial agranular cortex (AGm) lesions. More recent studies have demonstrated that recovery from neglect may be due to plastic changes occurring in the dorsal central striatum (DCS). Further, lesions of the DCS produce neglect that does not respond to systemic administration of apomorphine, suggesting that this area may be crucial for the therapeutic effects of apomorphine. In the present study, the behavioral effects of apomorphine infused into the DCS of animals with AGm lesion-induced neglect were examined to determine whether the DCS is a site of drug action. An infusion of 0.375 micro g of apomorphine into the DCS, but not a lateral striatal control area, was effective in producing acute recovery from neglect. The results of this study support the crucial role of the DCS in recovery from neglect induced by unilateral AGm lesions and suggest that the DCS may be an important site of action for the therapeutic effects of apomorphine. Because dopamine agonist therapy has been shown to be effective in humans with neglect, the results of the current study may represent an important step in the development of future pharmacotherapies.

Effects of light deprivation on recovery from neglect and extinction induced by unilateral lesions of the medial agranular cortex and dorsocentral striatum

A number of previous studies have indicated that an environmental manipulation, 48 h of light deprivation (LD), produces virtually complete and permanent behavioral recovery of function from neglect induced by medial agranular cortex (AGm) lesions. LD-induced behavioral recovery from neglect is correlated with physiological changes in the dorsolateral striatum, an area that contains the projection zone of AGm efferents in the dorsocentral striatum (DCS). In this study, the behavioral effects of 48 h of LD on subjects with either unilateral DCS, AGm, or combined AGm/DCS lesions were investigated to examine whether the integrity of the DCS is crucial for behavioral recovery from neglect and whether LD will have a therapeutic effect on extinction deficits. Subjects were tested for extinction to bilateral simultaneous stimulation of the forepaws, and visual, auditory and tactile neglect. Forty-eight hours of LD failed to produce behavioral recovery from neglect in rats with DCS lesions, or a therapeutic affect on extinction deficits in any of the groups. The results of this study further support the crucial role of the DCS in recovery from neglect induced by AGm lesions and suggests that the DCS may be the crucial site for the mechanisms leading to LD-induced recovery. Further, the ineffectiveness of LD on extinction suggests that components of the neglect syndrome are dissociable and may require different therapeutic interventions.

Sulpiride alleviates the attentional impairments of rats with medial prefrontal cortex lesions

Recent studies have shown that medial prefrontal cortex (mPFC) lesions impair performance on a number of rodent tests of attention. Although this evidence clearly suggests a role for the rat mPFC in attentional functions, it is unclear whether subcortical changes associated with mPFC lesions might also be relevant to the neuropsychological deficits observed. Given the ample evidence suggesting increased dopaminergic mechanisms in the basal ganglia following mPFC lesions, we investigated the effects of dopamine receptor agonists and antagonists on the attentional deficits associated with mPFC lesions. Rats trained on a five-choice reaction time task received either complete mPFC lesions or lesions restricted to its ventral subregions, the prelimbic and infralimbic cortices (PRL-IL). Compared with sham-operated rats, animals in both the lesioned groups were impaired at responding correctly to the visual targets, although this deficit was more marked in mPFC-lesioned rats. In addition, both lesions were associated with increased perseverative responding. The accuracy deficits of rats with mPFC lesions were alleviated by systemic administration of the dopamine D2 receptor antagonist sulpiride. In contrast, rats with PRL-IL damage were not affected and control rats were impaired by sulpiride. Administration of either the dopamine D1 receptor antagonist SCH 23390 or of pre-synaptic doses of apomorphine had similar, albeit non-significant effects. Higher doses of any of these drugs non-specifically impaired performance. These results extend previous findings of attentional impairments in rats with mPFC lesions and are compatible with recent hypotheses concerning the role of dopaminergic dysregulation in the pathogenesis of schizophrenia.

Unilateral destruction of the dorsocentral striatum in rats produces neglect but not extinction to bilateral simultaneous stimulation

A number of previous studies have indicated that lesions of the medial agranular cortex (AGm) in rats induce multimodal neglect and extinction to bilateral simultaneous stimulation (extinction), the two major symptoms of the neglect syndrome in humans. A recent study demonstrated that lesions of dorsocentral striatum (DCS), the site of AGm projections to the striatum, produce multimodal neglect qualitatively similar to that found with AGm lesions. In the present study, the behavioral effects of unilateral DCS lesions were examined in more detail for the major manifestations of neglect: hemineglect, extinction, and allesthesia/allokinesia. Subjects were tested for extinction to bilateral simultaneous stimulation of the forepaws three times a week for 3 weeks. Neglect testing occurred twice weekly and the subjects were tested for the presence of neglect by rating the magnitude of orientation to visual, tactile, and auditory stimulation. The results indicated that DCS operates, while demonstrating severe neglect, failed to demonstrate extinction or allesthesia/allokinesia. These findings suggest that the neural mechanisms that underlie neglect and extinction are dissociable in this system. A better understanding of the neural mechanisms that underlie extinction is particularly important because humans that have recovered from neglect often continue to demonstrate the debilitating symptoms of extinction.

Psychostimulant treatment of stroke and brain injury

Psychopharmacology is rapidly becoming an adjuvant treatment to traditional rehabilitation strategies for patients with stroke or brain injury because it helps to facilitate recovery in a time-efficient manner. Norepinephrine, dopamine, acetylcholine, and serotonin appear to play important roles in recovery from stroke or brain injury. Animal models have shown that blockade of these neurotransmitters inhibits recovery, whereas recovery is promoted by drugs that promote norepinephrine, dopamine, acetylcholine, and serotonin activity. Preliminary evidence from human trials supports these findings. Further study is needed, but expanded use of pharmacologic agents for stroke and brain-injured patients appears imminent.

Light deprivation soon after frontal brain trauma accelerates recovery from attentional deficits and promotes functional normalization of basal ganglia

BACKGROUND

Light deprivation significantly accelerates recovery from attention deficits (neglect) after cortical ablation in rats. We hypothesized that light deprivation would improve recovery after traumatic contusive brain injury (TBI) and do so by enhancing dopaminergic function in the ipsilateral basal ganglia.

METHODS

Adult rats received left frontal contusion injury and were placed into darkness or standard light/dark cycling for 48 hours. Neurologic evaluation included attentional and sensorimotor tasks. Amphetamine-induced production of the immediate early gene protein product Fos was quantified to determine neuronal dopaminergic response in caudate-putamen (striatum).

RESULTS

Unilateral frontal TBI produced severe contralateral deficits in all tasks. Postoperative light deprivation resulted in improved recovery from attentional but not sensorimotor deficits. Five days after injury, ipsilateral striatal Fos expression was reduced by 51% in TBI rats experiencing normal light cycling (p < 0.006). In contrast, postoperative light deprivation normalized striatal Fos expression. By 6 weeks, all TBI rats demonstrated nearly full recovery and striatal Fos expression was symmetrical between the two striata.

CONCLUSION

Postoperative light deprivation may improve recovery from TBI-induced attention deficits by normalizing basal ganglia function.

Light deprivation produces a therapeutic effect on neglect induced by unilateral destruction of the posterior parietal cortex in rats

Light deprivation has been found to produce accelerated recovery from severe multimodal neglect induced by unilateral destruction of medial agranular cortex, the rat analog of area 8 in humans. However, neglect in humans is most often produced by destruction of the parietal association cortex. Therefore, the present study examined whether light deprivation would produce accelerated recovery from severe multimodal neglect induced by unilateral destruction of the rodent analog of the parietal association cortex. Subjects received unilateral parietal association cortex lesions, and 4 h after surgery were tested for neglect of visual, tactile, and auditory stimuli. If severe neglect was obtained, subjects experienced either light deprivation, constant light, or a 12:12 light/dark cycle for 48 h. The results indicated that, relative to the other groups, the light deprivation group demonstrated significant accelerated recovery from neglect. Recovery was evident on the first post-light deprivation behavioral test, and was maintained for the 3 weeks of behavioral testing. The results provide further support for the therapeutic effects of light deprivation on neglect induced by cortical lesions when light deprivation is administered in the immediate postoperative period.

Disconnection of medial agranular and posterior parietal cortex produces multimodal neglect in rats

Two cortical areas in rats have been found to be important in directed attention and spatial processing: the medial agranular cortex (AGm), the rodent analog of the frontal eye fields; and the posterior parietal cortex (PPC), the rodent analog of area 7 in primates. As in primates, unilateral destruction of either of these cortical association areas produces severe contralesional neglect of visual, auditory, and tactile stimulation. AGm and PPC are reciprocally interconnected by longitudinally oriented axons traveling in layer VI of the cortex. Their trajectory provides a unique opportunity to examine the effects of disconnection of these two areas. The key question is whether these two regions function independently or as components of a cortical network for directed attention. Unilateral disconnection of the PPC and AGm was achieved via transverse knife-cuts extending through layer VI of cortex, and the disconnection verified by tract-tracing methods. The knife-cuts produced severe multimodal neglect and allesthesia/allokinesia. The deficits produced by the knife-cuts were virtually identical to those produced by unilateral destruction of these regions. The control operates, which received knife-cuts that spared the interconnections between the AGm and PPC, were unimpaired. The results indicate that AGm and PPC in rats function as parts of a cortical system for directed attention.

Reduced eticlopride-induced Fos expression in caudate-putamen and globus pallidus after unilateral frontal cortex injury: relation to neglect

Unilateral ablation of medial agranular cortex in rats results in neglect of contralateral stimuli and reductions in amphetamine-induced expression of the immediate early gene, c-fos, in both caudate-putamen and globus pallidus. Both unilateral neglect and the reductions in dopamine agonist induction of subcortical Fos immunoreactivity dissipate over a matter of weeks. Dopamine agonism induces Fos predominantly in striatonigral cells and in globus pallidus via striatopallidal disinhibition, whereas Fos is induced in striatopallidal cells by administration of antagonists of the D2 dopamine receptor subfamily. To examine more directly effects of cortical injury on striatopallidal function, induction of striatal Fos by the D2 antagonist eticlopride (0.1 mg/kg, s.c.) was examined in rats with medial agranular cortex ablation. In the same animals, eticlopride-induced Fos in globus pallidus was also examined. Five days after unilateral cortex injury, in rats showing neglect, the numbers of Fos immunoreactive nuclei induced by eticlopride were reduced by 50% in caudate-putamen and 25% in globus pallidus of the ipsilateral hemisphere. These lesion effects were restricted to dorsolateral caudate-putamen and dorsal pallidum. Three or more weeks after cortical injury, in rats recovered from neglect, eticlopride-induced Fos was normalized in caudate-putamen, but still decreased by 20% in globus pallidus. Along with previous findings, these results suggest that behavioral recovery from neglect produced by cortical injury may be at least partially mediated by normalizations of function of both striatopallidal and striatonigral neurons. In addition, the present findings suggest that normalization of function of pallidal cells activated by eticlopride is not necessary for behavioral recovery from frontal cortex ablation. Lingering reductions in excitatory cortico-subthalamo-pallidal input may be responsible for the longer-lasting dysfunctions of these pallidal cells.

Apomorphine produces an acute dose-dependent therapeutic effect on neglect produced by unilateral destruction of the posterior parietal cortex in rats

The neglect syndrome is a complex and devastating neurological disorder typically induced by unilateral destruction of one of three regions of the neocortex: the inferior parietal lobule, the dorsolateral prefrontal cortex or the cingulate cortex. Previous studies of neglect using a rodent model have indicated that disruption of dopaminergic mechanisms may underlie neglect. However, the pharmacological results were obtained using a rodent prefrontal model of the syndrome (medial agranular cortex), whereas the majority of cases of neglect in humans are produced by unilateral destruction of the posterior parietal cortex (inferior parietal lobule). The present study examined the effects of administration of the dopamine receptor agonist apomorphine on neglect induced by unilateral destruction of the posterior parietal cortex (PPC) in rats. The results indicated that administration of apomorphine produced a significant dose-dependent decrease in the severity of neglect. The results support the contention that neglect induced by cortical damage may be produced by a disruption of dopaminergic mechanisms, and that the PPC may be one component of a cortical system for directed attention.

Amphetamine-induced Fos expression in globus pallidus is altered by frontal cortex injury

Functional recovery from cortical injury may result from subcortical compensatory processes. This study examined basal gangliar expression of the immediate early gene c-fos after unilateral medial agranular cortex (AGm) ablation. In the ipsilateral dorsal globus pallidus of rats demonstrating neglect of contralateral stimuli (sacrificed 5 days postinjury), the numbers of amphetamine-induced Fos-positive nuclei were reduced 37% compared to intact hemisphere values. These reductions were no longer apparent in recovered AGm-ablated rats (sacrificed 21 + days postinjury). These findings mirror in timing and direction the changes in Fos seen in dorsolateral striatum after AGm ablation.