Cortical Regions Of Rat Brain Research Articles

Cyclooxygenase 2 and intermittent hypoxia-induced spatial deficits in the rat.

Intermittent hypoxia (IH) during sleep, a critical feature of sleep apnea, induces significant neurobehavioral deficits in the rat. Cyclooxygenase (COX)-2 is induced during stressful conditions such as cerebral ischemia and could play an important role in IH-induced learning deficits. We therefore examined COX-1 and COX-2 genes and COX-2 protein expression and activity (prostaglandin E2 [PGE2] tissue concentration) in cortical regions of rat brain after exposure to either IH (10% O2 alternating with 21% O2 every 90 seconds) or sustained hypoxia (10% O2). In addition, the effect of selective COX-2 inhibition with NS-398 on IH-induced neurobehavioral deficits was assessed. IH was associated with increased COX-2 protein and gene expression from Day 1 to Day 14 of exposure. No changes were found in COX-1 gene expression after exposure to hypoxia. IH-induced COX-2 upregulation was associated with increased PGE2 tissue levels, neuronal apoptosis, and neurobehavioral deficits. Administration of NS-398 abolished IH-induced apoptosis and PGE2 increases without modifying COX-2 mRNA expression. Furthermore, NS-398 treatment attenuated IH-induced deficits in the acquisition and retention of a spatial task in the water maze. We conclude that IH induces upregulation and activation of COX-2 in rat cortex and that COX-2 may play a role in IH-mediated neurobehavioral deficits.

Glucose metabolism in cholinoceptive cortical ratbrain regions after basal forebrain cholinergic lesion

To address the question whether the changes in cortical glucose metabolism observedin patients with Alzheimers disease are interrelated with, or consequences of, basal forebraincholinergic cell loss, an experimental approach was employed to produce cortical cholinergicdysfunction in rat brain by administration of the cholinergic immunotoxin 192IgG-saporin. [14C]d-glucose utilization in brain homogenates, d-glucose-displaceable [3H]cytochalasin B binding to glucose transporters (GLUT),Northern and Western analyses, as well as in vivo [14]2-deoxyglucoseautoradiography were used to quantify the regional glucose metabolism.Basal forebrain cholinergic lesion resulted in transient increases in glucose transporterbinding in cortical regions displaying reduced acetylcholinesterase activity, already detectableseven days after lesion with peak values around 30 days post lesion. Western analysis revealedthat the changes in total glucose transporter binding are mainly due to changes in the GLUT3subtype only, while the levels of GLUT1 and GLUT3 mRNA (Northern analysis) were notaffected by cholinergic lesion. Both immunocytochemistry and in situ hybridizationdemonstrated preferential localizations of GLUT1 on brain capillaries and GLUT3 on neurons,respectively. A lesion-induced transient decrease in [14C]d-glucoseutilization seven days post lesion was detected in the lesion site, whereas cholinoceptive corticalregions were not affected. In vivo [14C]deoxyglucose uptake was transientlyincreased in cholinoceptive cortical regions and in the lesion site being highest between three toseven days after lesion.The cholinergic lesion-induced transient up-regulation of cortical glucose transporters anddeoxyglucose uptake reflects an increased glucose demand in regions depleted by acetylcholinesuggesting functional links between cortical cholinergic activity and glucose metabolism incholinoceptive target regions.

Dopamine D 3 receptors are not involved in the induction of c- fos mRNA by neuroleptic drugs: comparison of the dopamine D 3 receptor antagonist GR103691 with typical and atypical neuroleptics

The effect of acute and chronic administration of dopamine receptor antagonists on the expression of mRNA encoding the cellular immediate-early gene c- fos was investigated in rat brain by in situ hybridization using 35S-labelled oligonucleotide probes. The selective dopamine D 3 receptor antagonist GR103691 had no effect on the level of c- fos mRNA after acute or chronic treatment. Acute treatment with haloperidol increased the level of c- fos mRNA in the caudate-putamen, nucleus accumbens shell and core, olfactory tubercle and parietal cortex. After chronic treatment with haloperidol increases in the level of c- fos mRNA in the caudate-putamen and nucleus accumbens core were no longer observed. The increase in the level of c- fos mRNA in the nucleus accumbens shell was attenuated but still significantly elevated above the level measured in vehicle-treated animals. In the olfactory tubercle, parietal cortex, frontal cortex and cingulate cortex the level of c- fos mRNA was decreased after chronic haloperidol treatment. Acute sulpiride treatment reduced the level of c- fos mRNA in the olfactory tubercle, parietal cortex and cingulate cortex. After chronic treatment with sulpiride the level of c- fos mRNA was reduced in the dorsal caudate-putamen only. Acute clozapine treatment increased the level of c- fos mRNA in the nucleus accumbens shell and islands of Calleja. After chronic treatment with clozapine the level of c- fos mRNA remained elevated in the islands of Calleja but not in the nucleus accumbens shell. These results indicate that acute and chronic blockade of dopamine D 3 receptors does not cause induction of c- fos transcription in limbic, striatal or cortical regions of rat brain. This study also demonstrated that acute blockade of dopamine receptors with haloperidol, sulpiride and clozapine induced different regionally specific patterns of c- fos expression which were altered after chronic blockade.

192IgG-saporin-induced immunotoxic lesions of cholinergic basal forebrain system differentially affect glutamatergic and GABAergic markers in cortical rat brain regions

To study the effect of reduced cortical cholinergic activity on GABAergic and glutamatergic mechanisms in cholinoceptive cortical target regions a novel cholinergic immunotoxin (conjugate of the monoclonal antibody 192IgG against the low-affinity nerve growth factor receptor with the cytotoxic protein saporin) was applied, which specifically and selectively destroys cholinergic cells in rat basal forebrain nuclei. To correlate the responses to cholinergic immunolesion in cholinoceptive cortical target regions with cholinergic hypoactivity, quantitative receptor autoradiography to measure NMDA, AMPA and kainate glutamate receptor subtypes, GABA A and benzodiazepine receptors as well as choline uptake sites, and histochemistry to estimate acetylcholinesterase activity were performed in adjacent brain sections. One week after a single intraventricular injection of 4 μg of 192IgG-saporin, NMDA receptor binding was markedly reduced in cortical regions displaying a reduced activity of acetylcholinesterase and high-affinity choline uptake sites as a consequence of cholinergic lesion, whereas AMPA and kainate binding sites were significantly increased in these regions. Muscimol binding to GABA A receptors was increased in the caudal portions and frontal and parietal cortices as well as occipital and temporal cortex as compared to the corresponding brain regions from vehicle-injected control rats. Binding levels of benzodiazepine receptors were not affected by the lesion in any of the cortical regions studied. The differential changes in glutamate and GABA receptor subtypes following cholinergic immunolesion might be regarded as the consequence of a cortical reorganization compensating for the reduced cholinergic presynaptic input. The data further suggest that presynaptic cortical cholinergic deficits might affect both glutamatergic and GABAergic functions with different intensity and different directions.

Persistent Translocation of Ca2+/Calmodulin‐Dependent Protein Kinase II to Synaptic Junctions in the Vulnerable Hippocampal CA1 Region Following Transient Ischemia

The influence of brain ischemia on the subcellular distribution and activity of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) was studied in various cortical rat brain regions during and after cerebral ischemia. Total CaM kinase II immunoreactivity (IR) and calmodulin binding in the crude synaptosomal fraction of all regions studied increase but decrease in the microsomal and cytosolic fractions, indicative of a translocation of CaM kinase II to synaptosomes. The translocation of CaM kinase II to synaptic junctions occurs but not to synaptic vesicles. The translocation in neocortex and CA3/DG (dentate gyrus) is transient, whereas in the hippocampal CA1 region, it persists for at least 1 day of reperfusion. The Ca2+/calmodulin-dependent activity of CaM kinase II in the subsynaptosomal fractions of neocortex is persistently decreased by up to 85%, despite the increase in CaM kinase II IR. The decrease in activity is more pronounced than the decline in IR, suggesting that CaM kinase II is covalently modified in the postischemic phase. The persistent translocation of CaM kinase II in the vulnerable ischemic CA1 region indicates that a pathological process is sustained in the area after the reperfusion phase and this may be of significance for ischemic brain injury.

Ibotenic acid lesion of nucleus basalis magnocellularis differentially affects cholinergic, glutamatergic and GABAergic markers in cortical rat brain regions

The present study was undertaken to study the effect of reduced cortical cholinergic activity on γ-aminobutyric acid (GABA)ergic and glutamatergic mechanisms in cholinoceptive cortical target regions which are assumed to play an important role for realizing cognitive functions. The densities of cortical muscarinic cholinergic receptor subtypes and corresponding receptor genes m 1 through m 4, N-methyl- d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) and kainate glutamate receptor subtypes as well as GABA A and benzodiazepine receptors were measured in rats 1 week after unilateral ibotenic acid lesion of the nucleus basalis magnocellularis (Nbm) applying quantitative receptor autoradiography and in situ hybridization. Ibotenic acid lesion resulted in a striking loss of acetylcholinesterase (AChE) staining in the lesioned Nbm which is associated with a 60% decrease in AChE staining and a 30% reduction in [ 3H]hemicholinium-3 binding in frontal and parietal cortical regions as well fore- and hindlimb areas ipsilateral to the lesion, being more prominent in the more rostral cortical regions. M 1-muscarinic cholinergic receptor binding was not changed in any of the cortical regions studied 1 week after lesion. M 2-muscarinic receptor binding levels are slightly increased in the parietal cortex only. The lesion-induced increase in parietal cortical M 2-muscarinic receptor binding is complemented by an increase in the hybridization signal for the corresponding m 4-mRNA transcript. In cortical regions displaying a reduced activity of AChE and decreased levels of high-affinity choline uptake sites due to forebrain cholinergic lesion, NMDA receptor binding was markedly reduced in comparison to the unlesioned brain side whereas AMPA and kainate binding has been significantly increased in these regions. Muscimol binding to GABA A receptors was increased in the rostral portions of frontal and parietal cortices as compared with the unlesioned brain side. Binding levels of benzodiazepine receptors were not affected by the lesion in any of the cortical regions studied. The differential changes in glutamate and GABA receptor subtypes following lesion might be regarded as the consequence of a cortical reorganization compensating for the reduced cholinergic presynaptic input. The data further suggest that presynaptic cortical cholinergic deficits might affect both glutamatergic and GABAergic functions with different intensity and different directions.

Stimulation of mono- and diacylglycerol lipase activities in ibotenate-induced lesions of nucleus basalis magnocellularis

Ibotenic acid was injected into the nucleus basalis magnocellularis region of rat brain in order to study whether an elevation of lipase activities was associated with the degeneration of cholinergic neurons in this potential animal model of Alzheimer's disease. Two plasma membrane fractions were prepared from different regions of ibotenate injected (right hemisphere) and non-injected (left hemisphere) rat brain. One plasma membrane fraction was from synaptosomes (SPM) and the other from glial and neuronal cell bodies (PM). Activities of mono- and diacylglycerol lipases in these plasma membrane fractions were markedly increased (3- to 5-fold) in hippocampus, midbrain and frontal cortical regions of rat brain at 10 days after the injection of ibotenate. The activity of choline acetyltransferase was decreased in frontal cortex but unchanged in hippocampus and midbrain. Our results suggest that the increase in lipase activity is much more widespread and non-specific than is the decrease in cholinergic function.