Cannabinoid Receptors and Modulation of Cyclic AMP Accumulation in the Rat Brain

The mechanism by which cannabinoid compounds produce their effects in the rat brain was evaluated in this investigation. Cannabinoid receptors, quantitated by [3H]CP-55,940 binding, were found in greatest abundance in the rat cortex, cerebellum, hippocampus, and striatum, with smaller but significant binding also found in the hypothalamus, brainstem, and spinal cord. Using rat brain slice preparations, we evaluated the effect of desacetyllevonantradol on basal and forskolin-stimulated cyclic AMP accumulation in the regions exhibiting the greatest cannabinoid receptor density. Desacetyllevonantradol (10 microM) reduced cyclic AMP levels in the hippocampus, frontal cortex, and striatum. In the cerebellum, however, the response to desacetyllevonantradol was biphasic with cyclic AMP accumulation being decreased at lower and increased at higher concentrations. Desacetyllevonantradol reduced cyclic AMP accumulation in isoproterenol-stimulated slices in the cortex and cerebellum, but not in the hippocampus. Cells that responded to vasoactive intestinal peptide with an increase in cyclic AMP accumulation in the hippocampus and cortex also responded to desacetyllevonantradol. The modulation of cyclic AMP accumulation by desacetyllevonantradol could be attenuated following stereotaxic implantation of pertussis toxin, supporting the involvement of a G protein in the cannabinoid response in the brain. However, other actions of cannabinoid compounds may also affect the cyclic AMP levels in brain slice preparations.     

Cyclic Nucleotide Response of the Hippocampal Formation to Septal Stimulation in Naive and Kindled Rats

Rats were kindled through nonmagnetic electrodes stereotaxically implanted into the medial septum. Concentrations of cyclic AMP and cyclic GMP were measured by radioimmunoassay in seven brain regions after microwave fixation during the development and expression of kindled seizures. Hippocampal concentrations were similar to untreated controls (cyclic GMP level in the left and right hippocampus, 0.66 +/- 0.04 and 0.68 +/- 0.07 pmol/mg of protein, respectively; cyclic AMP, 9.4 +/- 0.9 and 9.6 +/- 0.8 pmol/mg of protein, respectively), in kindled animals that were not stimulated, and in naive animals in response to septal stimulation, in spite of the presence in the latter group of bilateral hippocampal afterdischarges. Animals that failed to develop kindling and kindled animals that failed to have a seizure in response to stimulation also showed no change in cyclic nucleotide concentrations in any brain region. Kindled animals that developed a seizure following stimulation showed significant elevations in levels of both cyclic GMP and cyclic AMP in hippocampus and in several other brain regions. A single naive animal that had a seizure in response to its first stimulation also appeared to have elevated concentrations of both cyclic nucleotides in hippocampus. These data suggest that the elevation in levels of both cyclic GMP and cyclic AMP during kindled seizures is associated with seizure development rather than with the generation of afterdischarges or with the kindling engram.     

Mechanisms of Cyclic AMP Regulation in Cerebral Anoxia and Their Relationship to Glycogenolysis

Abstract: Anoxia elevates levels of cyclic AMP and depresses levels of cyclic GMP in cerebral cortex of mice. Similar effects are also observed in other regions of the brain. Aminophylline inhibits accumulation of cyclic AMP about 50% in hippocampus and cerebellum, but not in cerebral cortex and striaturn; however, this effect requires high doses (²⁵⁰ mgikg). Pretreatment of animals with reserpine, which depletes brain stores of norepinephrine, dopamine, and serotonin, and also produces sedation and mild hypothermia, markedly inhibits accumulation of cyclic AMP in all regions of anoxic brain. Destruction of norepinephrine terminals by treatment of neonatal animals with ⁶-OH- dopamine, which does not sedate or produce hypothermia, has an effect on cyclic AMP levels similar to that of reserpine. None of the above treatments modifies the effect of anoxia on cyclic GMP levels. These data indicate that norepinephrine is a major regulator of cyclic AMP levels in anoxic brain and that adenosine and, perhaps, other unidentified substances have lesser roles in this process. In contrast, biogenic amines and adenosine appear to have no effect on cyclic GMP regulation in anoxic brain. Reserpine slows the activation of phosphorylase and the utilization of ATP, and slightly attenuates the breakdown of glycogen caused by anoxia, but has no effect on the changes in glucose, lactate, or phosphocreatine. In contrast, ⁶-OH-dopamine has no effect on any of these anoxiainduced changes. It is concluded that the effect of reserpine on phosphorylase, glycogen, and ATP is most likely related to the hypothermic and sedative effect of the drug, and that either cyclic AMP is not responsible for initiating glycogenolysis in anoxic brain or only a small rise in cyclic AMP levels is necessary for this process.     

Effect of Electroconvulsive Shock on Mitochondrial Respiratory Chain in Rat Brain

It is well described that impairment of energy production has been implicated in the pathogenesis of a number of diseases. Although several advances have occurred over the past 20 years concerning the use and administration of electroconvulsive therapy (ECT) to minimize its side effects, little progress has been made in understanding its mechanism of action. In this work, our aim was to measure the activities of mitochondrial respiratory chain complexes II and IV and succinate dehydrogenase from rat brain after acute and chronic electroconvulsive shock (ECS). Our results showed that mitochondrial respiratory chain enzymes activities were increased after acute ECS in hippocampus, striatum and cortex of rats. Besides, we also demonstrated that complex II activity was increased after chronic ECS in cortex, while hippocampus and striatum were not affected. Succinate dehydrogenase, however, was inhibited after chronic ECS in striatum, activated in cortex and not affected in hippocampus. Finally, complex IV was not affected by chronic ECS in hippocampus, striatum and cortex. Our findings demonstrated that brain metabolism is altered by ECS.     

Amygdala Kindling Potentiates Seizure-Stimulated Immediate-Early Gene Expression in Rat Cerebral Cortex

Kindling induces long-term adaptations in neuronal function that lead to a decreased threshold for induction of seizures. In the present study, the influence of amygdala kindling on levels of mRNA for the immediate-early genes (IEGs) c-fos, c-jun, and NGF1-A were examined both before and after an acute electroconvulsive seizure (ECS). Although amygdala kindling did not significantly influence resting levels of c-fos mRNA in cerebral cortex, ECS-stimulated levels of c-fos mRNA (examined 45 min after ECS) were approximately twofold greater in the cerebral cortex of kindled rats relative to sham-treated controls. The influence of kindling on IEG expression was dependent on the time course of kindling, as ECS-stimulated levels of c-fos mRNA were not significantly increased in stage 2 kindled animals. ECS-stimulated levels of c-jun and NGF1-A mRNA were also significantly increased in cerebral cortex of kindled rats relative to sham-treated controls. The influence of kindling on IEG expression was long-lasting because an acute ECS stimulus significantly elevated levels of c-fos and c-jun mRNA in the cerebral cortex of animals that were kindled 5 months previously. In contrast to these effects in cerebral cortex, kindling did not influence ECS-stimulated levels of c-fos mRNA in hippocampus. Finally, immunohistochemical studies revealed lamina-specific changes in the cerebral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of regulators of G protein signaling mRNA expression in rat brain by acute and chronic electroconvulsive seizures

G protein-coupled receptor (GPCR) signaling cascades may be key substrates for the antidepressant effects of chronic electroconvulsive seizures (ECS). To better understand changes in these signaling pathways, alterations in levels of mRNA's encoding regulators of G protein signaling (RGS) protein subtypes-2, -4, -7, -8 and -10 were evaluated in rat brain using northern blotting and in situ hybridization. In prefrontal cortex, RGS2 mRNA levels were increased several-fold 2 h following an acute ECS. Increases in RGS8 mRNA were of lesser magnitude (30%), and no changes were evident for the other RGS subtypes. At 24 h following a chronic ECS regimen, RGS4, -7, and -10 mRNA levels were reduced by 20-30%; only RGS10 was significantly reduced 24 h after acute ECS. Levels of RGS2 mRNA were unchanged 24 h following either acute or chronic ECS. In hippocampus, RGS2 mRNA levels were markedly increased 2 h following acute ECS. More modest increases were seen for RGS4 mRNA expression, whereas levels of the other RGS subtypes were unaltered. At 24 h following chronic ECS, RGS7, -8 and -10 mRNA levels were decreased in the granule cell layer, and RGS7 and -8 mRNA levels were decreased in the pyramidal cell layers. Only RGS8 and -10 mRNA levels were significantly reduced in hippocampus 24 h following an acute ECS. Paralleling neocortex, RGS2 mRNA content was unchanged in hippocampus 24 h following either acute or chronic ECS. In ventromedial hypothalamus, RGS4 mRNA content was increased 24 h following chronic ECS, whereas RGS7 mRNA levels were only increased 24 h following an acute ECS. The increased RGS4 mRNA levels in hypothalamus were significant by 2 h following an acute ECS. These studies demonstrate subtype-, time-, and region-specific regulation of RGS proteins by ECS, adaptations that may contribute to the antidepressant effects of this treatment.     

Evidence for increased expression of the vesicular glutamate transporter, VGLUT1, by a course of antidepressant treatment

The therapeutic effect of a course of antidepressant treatment is believed to involve a cascade of neuroadaptive changes in gene expression leading to increased neural plasticity. Because glutamate is linked to mechanisms of neural plasticity, this transmitter may play a role in these changes. This study investigated the effect of antidepressant treatment on expression of the vesicular glutamate transporters, VGLUT1-3 in brain regions of the rat. Repeated treatment with fluoxetine, paroxetine or desipramine increased VGLUT1 mRNA abundance in frontal, orbital, cingulate and parietal cortices, and regions of the hippocampus. Immunoautoradiography analysis showed that repeated antidepressant drug treatment increased VGLUT1 protein expression. Repeated electroconvulsive shock (ECS) also increased VGLUT1 mRNA abundance in regions of the cortex and hippocampus compared to sham controls. The antidepressant drugs and ECS did not alter VGLUT1 mRNA abundance after acute administration, and no change was detected after repeated treatment with the antipsychotic agents, haloperidol and chlorpromazine. In contrast to VGLUT1, the different antidepressant treatments did not commonly increase the expression of VGLUT2 or VGLUT3 mRNA. These data suggest that a course of antidepressant drug or ECS treatment increases expression of VGLUT1, a key gene involved in the regulation of glutamate secretion.