Sites In Cerebral Cortex Research Articles

The lack of CB1 receptors prevents neuroadapatations of both NMDA and GABAA receptors after chronic ethanol exposure

As the contribution of cannabinoid (CB1) receptors in the neuroadaptations following chronic alcohol exposure is unknown, we investigated the neuroadaptations induced by chronic alcohol exposure on both NMDA and GABA(A) receptors in CB1-/- mice. Our results show that basal levels of hippocampal [(3)H]MK-801 ((1)-5-methyl-10,11-dihydro-5Hdibenzo[a,d]cyclohepten-5,10-imine) binding sites were decreased in CB1-/- mice and that these mice were also less sensitive to the locomotor effects of MK-801. Basal level of both hippocampal and cerebellar [(3)H]muscimol binding was lower and sensitivity to the hypothermic effects of diazepam and pentobarbital was increased in CB1-/- mice. GABA(A)alpha1, beta2, and gamma2 and NMDA receptor (NR) 1 and 2B subunit mRNA levels were altered in striatum of CB1-/- mice. Our results also showed that [(3)H]MK-801 binding sites were increased in cerebral cortex and hippocampus after chronic ethanol ingestion only in wild-type mice. Chronic ethanol ingestion did not modify the sensitivity to the locomotor effects of MK-801 in both genotypes. Similarly, chronic ethanol ingestion reduced the number of [(3)H]muscimol binding sites in cerebral cortex, but not in cerebellum, only in CB1+/+ mice. We conclude that lifelong deletion of CB1 receptors impairs neuroadaptations of both NMDA and GABA(A) receptors after chronic ethanol exposure and that the endocannabinoid/CB1 receptor system is involved in alcohol dependence.

Prolonged exposure to hypobaric hypoxia transiently reduces GABA A receptor number in mice cerebral cortex

The central nervous system is severely affected by hypoxic conditions, which produce alterations in neural cytoarchitecture and neurotransmission, resulting in a variety of neuropathological conditions such as convulsive states, neurobehavioral impairment and motor CNS alterations. Some of the neuropathologies observed in hypobaric hypoxia, corresponding to high altitude conditions, have been correlated with a loss of balance between excitatory and inhibitory neurotransmission, produced by alterations in glutamatergic and GABAergic receptors. In the present work, we have studied the effect of chronic hypobaric hypoxia (506 hPa, 18 h/day×21 days) applied to adult male mice on GABA A receptors from cerebral cortex, to determine whether hypoxic exposure may irreversibly affect central inhibitory neurotransmission. Saturation curves for [ 3H]GABA specifically bound to GABA A receptors in isolated synaptic membranes showed a 30% decrease in maximal binding capacity after hypoxic exposure ( B max control, 4.70±0.19, hypoxic, 3.33±0.10 pmol/mg protein), with no effect on GABA binding sites affinity ( K d control: 159.3±13.3 nM, hypoxic: 164.2±15.1 nM). Decreased B max values were observed up to the 10th post-hypoxic day, returning to control values by the 15th post-hypoxic day. Pharmacological properties of GABA A receptor were also affected by hypoxic exposure, with a 45 to 51% increase in the maximal effect by positive allosteric modulators (pentobarbital and 5α-pregnan-3α-ol-20-one). We conclude that long-term hypoxia produces a significant but reversible reduction on GABA binding to GABA A receptor sites in cerebral cortex, which may reflect an adaptive response to this sustained pathophysiological state.

Effects of Perinatal Nicotine Exposure on Development of [3H]Hemicholinium-3 Binding Sites in Rat Neonate Brain

In this study, [3H]hemicholinium-3 ([3H]HC-3) binding, which labels the presynaptic high affinity-choline transport sites, was examined in two brain regions, cerebral cortex and midbrain, of nicotine-treated and -untreated rat neonates. In nicotine-untreated neonates, [3H]HC-3 binding sites of cerebral cortex increased from 64 fmol/mg protein at postnatal day 7 to 142 fmol/mg protein at postnatal day 35. In nicotine-treated neonates, the development of [3H]HC-3 binding sites in cerebral cortex was significantly retarded, compared with control neonates on the 7th, 14th and 21st postnatal days. In parallel with this, the development of muscarinic receptor in cerebral cortex, which was detected by [3H]quinuclidinyl benzylate ([3H]QNB) binding, was also retarded by nicotine treatment. However, in midbrain, neither [3H]HC-3 nor [3H]QNB binding sites at postnatal day 14 was affected by nicotine treatment. These results strongly suggest that perinatal treatment with nicotine inhibits presynaptic and postsynaptic development of the cholinergic pathway in cerebral cortex but not in midbrain of rat neonate.

Effects of chronic treatment with (+)-nicotine on the stress-induced hypertension and downregulation of central nicotinic receptors in rats Comparative study with (−)-nicotine

The effects of chronic treatment with (+)-nicotine on the immobilization stress-induced changes in blood pressure, body weight, and [ 3H]cytisine binding to brain nicotinic receptors were examined in rats and were compared with those of (−)-nicotine. Immobilization stress (2 hr/day −1, for 2 weeks) induced a moderate elevation of blood pressure, loss of body weight gain, and downregulation of [ 3H]cytisine binding sites in cerebral cortex and midbrain. Chronic treatment with (+)- or (−)-nicotine inhibited the stress-induced hypertension but did not suppress the inhibition of body weight gain by stress. Body weight before stress load was also reduced by (−)-nicotine but not (+)-nicotine treatment. Treatment with each isomer increased the maximum number of [ 3H]cytisine binding sites (B max) of brain stem, cerebral cortex, and hippocampus. The B max in midbrain was also increased by (+)-nicotine but not by (−)-nicotine. Stress-induced downregulation in cerebral cortex was inhibited by both isomers. These results suggest that (+)- and (−)-nicotine cause various effects, including anti-stress effect, on the central nervous system in rats, which are slightly different between the isomers.

Differential spatiotemporal alterations in adrenoceptor mRNAs and binding sites in cerebral cortex following spreading depression: selective and prolonged up-regulation of alpha1B-adrenoceptors.

Noradrenaline, an important transmitter in the CNS, is involved in cerebral plasticity and functional recovery after injury. Experimental brain injury, including KCl application onto the brain surface, induces a slow-moving cortical depolarization/depression wave called cortical spreading depression (CSD). Interestingly, CSD does not produce neuronal damage but can protect cortical neurons against subsequent neurotoxic insults, although the mechanisms involved are unknown. This study examined the status of alpha- and beta-adrenoceptors (ARs) in cerebral cortex following CSD. Anesthetized rats had unilateral CSD induced by a 10-min topical application of KCl to the frontoparietal cortex and were killed at various times thereafter. Levels of alpha1-, alpha2-, beta1-, and beta2-AR mRNA and binding were examined using in situ hybridization histochemistry and radioligand autoradiography. Levels of alpha1b-AR mRNA in the affected neocortex were significantly increased by 20-40% at 1, 2, and 7 days (P </= 0.01) compared with contralateral levels, but were not significantly above control values at 2 and 4 weeks after CSD induction. Cortical alpha1B-AR binding sites were also increased by 45-65% 1 and 2 weeks (P </= 0.01) after CSD in a similar, but delayed, profile to alpha1b-AR mRNA. CSD rapidly increased beta1-AR mRNA by 45% at 1 h (P </= 0.01) and produced a delayed decrease of 25% in alpha2a-AR mRNA at 2 days and 1 week (P </= 0.05), but had no effect on corresponding levels of binding sites. In contrast, CSD had no effect on the remaining AR-subtype mRNAs or binding levels in neocortex under identical conditions. These results reveal a long-term up-regulation of alpha1B-ARs induced by an acute cortical stimulation/depression. Subtype-selective responses of ARs to CSD reflect an important differential regulation of expression of each receptor in vivo and suggest that alpha1B-ARs are particularly likely to be involved in cortical adaptive responses to physical injury at both local and distant locations.

Nicotine administration decreases the number of binding sites and mRNA of M 1 and M 2 muscarinic receptors in specific brain regions of rat neonates

Nicotine has been shown to delay the developmental increase of muscarinic receptors in brain of rat neonates. In this study, we have examined the muscarinic receptor binding sites and corresponding messenger RNA in rat neonates, whose mothers received nicotine in the drinking water, using competition binding study and northern blot analysis. On postnatal 14th day, nicotine treatment led to a 61% reduction in the proportion of high-affinity sites for pirenzepine (M1-subtype) to total [ 3H]quinuclidinyl benzilate binding sites in cerebral cortex in rat neonate. Nicotine treatment also decreased that for 11-2[[2-[(diethylamino)methyl]-1-piperidinyl]-5,11-dihydro-6H-pyrido [2,3-b] [1,4] benzodiazepin-6-one (AF-DX 116) (M2-subtype) by 77% in cerebellum on postnatal 14th day. The levels of m1 and m2 muscarinic receptor messenger RNAs in the same brain regions were also decreased in the same day after nicotine treatment. On postnatal 35th day, no difference was observed in binding sites or in messenger RNA levels of the brain regions tested (cerebral cortex, midbrain, hippocampus, cerebellum and brainstem). Our results show that nicotine reduces muscarinic receptor subtypes in developing rat brain, in part, through suppression of the messenger RNA expression, but that the effects are different among brain regions and subtypes.

Imipramine-induced changes in 5-HT2 receptor sites and inositoltrisphosphate levels in rat brain.

The effect of chronic administration of Imipramine on [3H]Spiperone binding to 5-HT2 sites and inositoltrisphosphate (IP3) levels in rat cerebral cortex was studied. Our data shows that treatment with imipramine (5 mg/kg body weight, intraperitoneally) for 30 days significantly down regulates 5-HT2 receptors sites (262 +/- 29 fmol/mg protein) in cerebral cortex (38%), compared to control rats (425 +/- 60 fmol/mg protein., P < 0.001). However there was no significant change in the affinity of [3H]-Spiperone binding (kd) to 5-HT2 sites in cerebral cortex after exposure to imipramine (Kd = 0.84 +/- 0.11 nM). It is also observed that imipramine treatment significantly reduces 5-HT stimulated [3H]IP3 formation in cerebral cortex (6,411 +/- 708 dpm/mg protein), compared to the saline treated rats (12,238 +/- 1,544 dpm/mg protein; P < 0.001), with concomitant decrease in Pdtlns-4-5-P2. This study suggests that the therapeutic action of imipramine in brain might be by reducing hypersensitivity of 5-HT2 receptors by down regulation, which leads to reduced levels of inositolphospholipids. This inturn reduces the levels of IP3. In conclusion, imipramine acts at presynaptic site by blocking the reuptake of serotonin and at post synaptic site it downregulates 5-HT2 sites with decreased IP3 levels after chronic exposure.

Loss of [3H]kainate and of NMDA-displaceable [3H]glutamate binding sites in brain in thiamine deficiency: results of a quantitative autoradiographic study.

Previous studies suggest that alterations of brain glutamate synthesis and release occur in experimental thiamine deficiency. In order to assess the integrity of post-synaptic glutamatergic receptors in thiamine deficiency, binding sites for [3H]glutamate (displaced by NMDA), [3H]-kainate, and [3H]quisqualate (AMPA sites) were evaluated using Quantitative Receptor Autoradiography in rat brain following 14 days of treatment with the central thiamine antagonist pyrithiamine. Compared to pair-fed controls, brains of symptomatic thiamine-deficient animals contained significantly fewer NMDA-displaceable binding sites in cerebral cortex, medial septum and hippocampus. It has been suggested that NMDA-receptor mediated glutamate excitotoxicity plays a role in the pathogenesis of neuronal loss in thiamine deficiency. If such is the case, the selective loss of NMDA binding sites in cerebral cortex and hippocampus offers a possible explanation for the relative nonvulnerability of these brain regions to pyrithiamine-induced thiamine deficiency. [3H]quisqualate (AMPA) binding sites were unchanged in all brain regions of pyrithiamine-treated rats whereas [3H]kainate sites were significantly reduced in density in medial and lateral thalamus. The decline in these binding sites may be due to neuronal loss in pyrithiamine-induced thiamine deficiency. Alterations of glutamatergic synaptic function involving both NMDA and kainate receptor subclasses could contribute to the pathogenesis of neurological dysfunction in Wernicke's Encephalopathy in humans.

Tissue-specific alterations of binding sites for peripheral-type benzodiazepine receptor ligand [3H]PK11195 in rats following portacaval anastomosis

Kinetics of binding of [3H]PK11195, an antagonist ligand with high selectivity for the peripheral-type (mitochondrial) benzodiazepine receptor (PTBR), was studied in homogenates of cerebral cortex, kidney, heart, and testis of portacaval shunted rats and sham-operated controls. Portacaval anastomosis resulted in a significant two- to threefold increase in the number of [3H]PK11195 binding sites in cerebral cortex and kidney. A reduction in the number of [3H]PK11195 binding sites was observed in testis preparations, while the number of binding sites in the heart remained unaltered. These differences in the response of PTBRs to portacaval anastomosis, in different organs suggest that the physiological function of these receptors and the factors regulating them are modulated by distinct mechanisms. The finding of increased densities of [3H]PK11195 binding sites in brain and kidney following portacaval anastomosis parallels the cellular hypertrophy in these tissues and, together with previous observations of similar increases of these binding sites in brain and kidney in congenital hyperammonemia, suggest a pathophysiologic role for ammonia in these changes. In contrast, the significant loss of [3H]PK11195 binding sites in testicular preparations following portacaval anastomosis together with the known effects of steroid hormones on these sites suggests a role for PTBRs in the pathogenesis of testicular atrophy in chronic liver disease.

Increases in strychnine-insensiive glycine binding sites in cerebral cortex of chronic schizophrenics: Evidence for glutamate hypothesis

Strychnine-insensitive glycine binding sites, an absolute requirement of the responses mediated by N- methyl- d-aspartate (NMDA) receptors, were measured in the postmortem brains of 13 chronic schizophrenics and 10 controls, using a radiolabeled receptor assay. Specific [ 3H]glycine binding was significantly increased in six of the 16 areas of the cerebral cortex that were investigated. Scatchard analysis performed in these areas showed a significant increase in the maximum number of binding sites, with no change in the affinity of binding. Multiple regression analysis confirmed that the increase was not due to age at death or interval from death to freezing. The increase was also observed in the off-drug cases of schizophrenics who had not taken antipsychotics for more than 40 days before death. These results suggest that the increases in NMDA-associated glycine binding sites, possibly ascribed to the postsynaptic compensation for impaired glutamatergic neurotransmission, might be implicated in the pathophysiology of schizophrenia.

Lack of influence of aromatase and 5 alpha-reductase inhibition on [3H]imipramine binding in the male rat brain.

In intact adult male rats an inhibitor of aromatase and an inhibitor of 5 alpha-reductase did not change the characteristics of [3H]imipramine binding sites in cerebral cortex, hypothalamus, and hippocampus. Testosterone, estradiol and dihydrotestosterone prevented the effect of castration on the number of [3H]imipramine binding sites, but had no effect in non-castrated animals. These data suggest that testosterone and its major metabolites, estradiol and dihydrotestosterone, are equally effective with regard to imipramine binding sites.

Regulation of beta 1-adrenergic receptor mRNA and ligand binding by antidepressant treatments and norepinephrine depletion in rat frontal cortex.

The number of beta 1-adrenergic receptor (beta 1AR) binding sites is decreased by chronic antidepressant treatments, including electroconvulsive seizure (ECS) and imipramine, whereas administration of agents that deplete norepinephrine (NE) increases the number of beta 1AR binding sites in cerebral cortex. The present study was carried out to examine the influence of these treatments on levels of beta 1AR mRNA in frontal cortex to study the molecular mechanisms that underlie the regulation of beta 1ARs in brain. Levels of beta 1AR mRNA were measured by RNase protection analysis using a riboprobe derived from rat beta 1AR cDNA, and the levels of beta AR binding were measured using the nonselective ligand [3H]CGP-12177. Studies to verify the specificity of the RNase protection assay revealed that the distribution of beta 1AR mRNA was in agreement with the reported distribution of beta 1AR ligand binding: Levels of beta 1AR mRNA were highest in cerebral cortex or frontal cortex, intermediate in neostriatum, hippocampus, lung, and heart, and lowest in cerebellum, kidney, and liver. Chronic ECS treatment (once daily for 10 days) significantly decreased levels of beta AR ligand binding and resulted in a corresponding, time-dependent down-regulation of beta 1AR mRNA levels in frontal cortex. However, imipramine administration regulated levels of beta 1AR mRNA in a biphasic manner, with treatments for 7-14 days increasing and treatments for 18-21 days decreasing levels of beta 1AR mRNA in frontal cortex. In contrast, levels of [3H]CGP-12177 ligand binding were decreased at all time points examined (3-21 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of foetal treatment with methylazoxymethanol on noradrenergic synapses in rat cerebral cortex.

Methylazoxymethanol (MAM)-induced cerebral hypoplasia resulted in a significant increase in densities of norepinephrine uptake sites in cerebral cortex, suggesting that norepinephrinergic axon terminals were compressed in the smaller brain volumes. The density of beta-adrenergic receptors in MAM-lesioned cerebral cortex was decreased probably due to down-regulation, while there were no changes in the proportions and affinities of agonist high-affinity sites and agonist low-affinity sites in the desensitized beta-receptors.

Characteristics of endothelin receptors in the cerebral cortex and spinal cord of aged rats

Characteristics of endothelin receptors were studied in male Fischer 344 rats at 4-, 15- and 24-months of age and [ 125I]ET-1 binding showed a single high affinity binding site in their cerebral cortex and spinal cord membranes. The density and affinity of ET binding sites were found to be similar in rats of various age groups. To determine the affinity of ET isotypes to ET-1 binding sites in cerebral cortex and spinal cord, competition studies were performed and K i values of ET-1, ET-2 and ET-3 for [ 125I]ET-1 binding sites were determined. It was found that ET-1 had 100 and ET-2 had 25–100 times lower K i values as compared to ET-3, indicating that ET receptors in cerebral cortex and spinal cord are of ET A type. In spinal cord, the K i values of ET-1 and ET-2 for ET receptor were found to be similar. However, in cerebral cortex the K i values of ET-1 were found to be at least 6 times lower than ET-2. It is inferred that there are two subtypes of ET A receptors, ET A1, which have higher affinity for ET-1 in comparison to ET-2, as found in cerebral cortex and ET A2 which have higher affinity for ET-2, as found in spinal cord. The K i and IC 50 values of ET-1, ET-2, and ET-3 for [ 125I]ET-1 binding sites in cerebral cortex and spinal cord were found to be similar in 4-, 15- and 24-month-old rats. [ 125I]SRT 6b, another ligand which binds to ET receptors, showed that the K i and IC 50 values of ET-1 and ET-2 for [ 125I]SRT 6b binding sites in cerebral cortex and spinal cord were similar in rats of different age groups. K i and IC 50 values of ET-3 for [ 125I]SRT 6b binding sites in cerebral cortex were found to be similar in rats of various age groups. However, the K i and IC 50 values of ET-3 for [ 125I] SRT 6b binding sites in spinal cord of 24-month-old rats were found to be significantly lower as compared to 4- and 15-month-old rats. It is concluded that in cerebral cortex and spinal cord of Fischer 344 rats, ET receptors are of ET A type and there are two subtypes of ET A receptors: ET A1 which have higher affinity for ET-1 as compared to ET-2, as found in cerebral cortex, and ET A2 which have higher affinity for ET-2, as found in spinal cord. The affinity and density of ET receptors in cerebral cortex and spinal cord is similar in rats 4-, 15- and 24-months of age. However, in the spinal cord of 24-month-old rats, the affinity of ET-3 to ET receptors increases significantly as compared to younger rats. The increased sensitivity of spinal cord ET receptors to ET-3 has been attributed to hypertension and the present data indicates a possible mechanism involved in the increase in blood pressure during aging.

Insulin-like growth factor I receptor binding in brains of Alzheimer's and alcoholic patients.

Patients with chronic alcoholism and/or Alzheimer's disease show degenerative changes in the cerebral cortex and hippocampus. To investigate possible changes in insulin-like growth factor I receptor binding sites in brain tissue of patients with these pathological conditions, the number of 125I-insulin-like growth factor I binding sites was determined in tissues obtained from control patients and those with Alzheimer's and/or with a history of alcoholism. The four experimental groups examined consisted of patients from similar age groups. Postmortem histology and a clinical history were used for the diagnosis of Alzheimer's disease and alcoholism, respectively. Careful clinical records were kept concerning other variables such as immediate cause of death and medications administered before death. Specific binding of 125I-insulin-like growth factor I to homogenates prepared from cerebral cortex of Alzheimer's, alcoholic, alcoholic Alzheimer's, and age-matched control patients was similar, although Alzheimer's patients tended to have slightly higher binding values. No significant differences in insulin-like growth factor I binding in cerebral cortex were found with regard to age of patients, the interval between death and autopsy, and CNS-active medications. No statistical differences in 125I-insulin-like growth factor I binding were noted in hippocampal tissue from the four patient groups. Thus, human insulin-like growth factor I binding sites in cerebral cortex and hippocampus appear unaffected by several variables.

Modification of ?-Aminobutyric AcidAReceptor Binding and Function by N-Ethoxycarbonyl-2-Ethoxy-1,2-Dihydroquinoline In Vitro and In Vivo: Effects of Aging

The irreversible protein-modifying reagent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) was used to investigate binding site characteristics on the gamma-aminobutyric acidA (GABAA) receptor complex. In vitro, preincubation with EEDQ led to a concentration-dependent decrease in receptor number for benzodiazepine, t-butylbicyclophosphorothionate (TBPS), and GABA binding sites in cerebral cortex. The effect was maximal at the highest concentration of EEDQ used (10(-4) M) and was greatest for the benzodiazepine site. Pretreatment of membranes with the benzodiazepine antagonist Ro 15-1788, 1 or 10 microM, or the agonist lorazepam, 10 microM, largely prevented the effects of EEDQ. Scatchard analysis indicated no effect of EEDQ, 10(-4) M, on apparent affinity, but a decrease in receptor density for each site. Administration of EEDQ to mice, 12.5 mg/kg i.p., led to a substantial (55-65%) decrease in number of benzodiazepine binding sites in cortex after 4 h. Slightly smaller changes were observed for TBPS and GABA binding. No changes were observed in apparent affinity at any site. Prior administration of Ro 15-1788, 5 mg/kg, prevented the effect of EEDQ on benzodiazepine binding. Density of benzodiazepine binding sites gradually recovered over time, and receptor density returned to control values by 96 h after EEDQ injection. Number of binding sites in cortex for TBPS and GABA also increased over time after EEDQ. Benzodiazepine sites in cerebellum were decreased proportionally to cortex after EEDQ, and increased over a similar time course. Function of the GABAA receptor in chloride uptake in cortex was markedly reduced (65%) by EEDQ.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of high‐dose fenfluramine treatment on monoamine uptake sites in rat brain: Assessment using quantitative autoradiography

Fenfluramine is an amphetamine derivative that in humans is used primarily as an anorectic agent in the treatment of obesity. In rats, subchronic high-dose d,l-fenfluramine treatment (24 mg/kg subcutaneously, twice daily for 4 days) causes long-lasting decreases in brain serotonin (5HT), its metabolite 5-hydroxyindoleacetic acid, and high-affinity 5HT uptake sites. Moreover, this high-dose treatment regimen causes both selective long-lasting decreases in fine-caliber 5HT-immunoreactive axons and appearance of other 5HT-immunoreactive axons with morphology characteristic of degenerating axons. Determination of the potential neurotoxic effects of fenfluramine treatment using immunohistochemistry is limited from the perspectives that staining is difficult to quantify and that it relies on presence of the antigen (in this case 5HT), and the 5HT-depleting effects of fenfluramine are well known. In the present study, we used quantitative in vitro autoradiography to assess, in detail, the density and regional distribution of [3H]paroxetine-labeled 5HT and [3H]mazindol-labeled catecholamine uptake sites in response to the high-dose fenfluramine treatment described above. Because monoamine uptake sites are concentrated on monoamine-containing nerve terminals, decreases in uptake site density would provide a quantitative assessment of potential neurotoxicity resulting from this fenfluramine treatment regimen. Marked decreases in densities of [3H]paroxetine-labeled 5HT uptake sites occurred in brain regions in which fenfluramine treatment decreased the density of 5HT-like immunostaining when compared to saline-treated control rats. These included cerebral cortex, caudate putamen, hippocampus, thalamus, and medial hypothalamus. Smaller, but nonetheless significant, decreases in density of [3H]paroxetine-labeled 5HT uptake sites were noted in brain regions in which partial sparing of 5HT-like immunoreactive fibers had been reported following fenfluramine treatment, specifically septum, lateral hypothalamus, and amygdala. In contrast, [3H]mazindol autoradiography revealed that total catecholamine (i.e., dopamine and norepinephrine) uptake sites in cerebral cortex, caudate putamen, and locus coeruleus, areas in which [3H]paroxetine-labeled 5HT uptake sites were significantly decreased, were unaffected by this fenfluramine treatment. These data support the hypothesis that subchronic, high-dose fenfluramine treatment causes selective degeneration of 5HT axons in rat brain. Since pharmacokinetic studies show that the dosing regimen used in this study exposes rat brain to concentrations of fenfluramine that are approximately 600 times greater than those resulting from the therapeutic oral dose, caution must be exercised in extrapolating these data to humans.

Transient increase in ligand binding to quisqualate and kainate sites in cerebral cortex of immature rats

The postnatal changes in the specific binding of [ 3H]kainate and [ 3H]AMPA (RS-α-amino-3-hydroxy-5-methyl-4-isoxasolopropionic acid, an agonist of quisqualate receptors) were studied in cerebral cortex of rats, aged 2–360 days. The binding of the two ligands was assayed in whole-tissue homogenates. Similar developmental time courses were found for kainate and AMPA binding, characterized by high perinatal levels, a further increase during the first few days after birth, an early maximum value around the age of one week, and a gradual decrease to adult values which were attained at an age of 3–4 weeks. As revealed by Scatchard analysis, the transient elevation of ligand binding was derived from an increased density of binding sites, which, in the case of AMPA, was accompanied also by an increase in binding affinity. The results indicate that, in the immature cerebral cortex, kainate and quisqualate receptors may play a role other than in synaptic transmission.

Electroconvulsive Shock (ECS) and the Adenosine Neuromodulatory System: Effect of Single and Repeated ECS on the Adenosine A1 and A2 Receptors, Adenylate Cyclase, and the Adenosine Uptake Site

The effect of a single electroconvulsive shock (ECS) (30 min and 24 h after treatment) and repeated ECS (10 once-daily) on the adenosine neuromodulatory system was investigated in rat cerebral cortex, cerebellum, hippocampus, and striatum. The present study examined the adenosine A1 receptor using N6-[3H]cyclohexyladenosine ([3H]CHA), the A2 receptor using 5'-N-[3H]ethylcarboxyamidoadenosine ([ 3H]NECA), adenylate cyclase using [3H]forskolin, and the adenosine uptake site using [3H]nitrobenzylthioinosine ([3H]NBI). At 30 min after a single ECS, the Bmax of the [3H]NBI binding in striatum was increased by 20%, which is in good agreement with the well-known postictal adenosine release. The Bmax of [3H]forskolin binding in striatum and cerebellum was increased by 60 and 20%, respectively. In contrast to earlier reported changes following chemically induced seizures, [3H]CHA binding was not altered postictally. At 24 h after a single ECS, there were no changes for any ligand in any brain region. Following repeated ECS, there was a 20% increase of [3H]CHA binding sites in cerebral cortex, which lasted for at least 14 days after the last ECS. [3H]Forskolin binding in hippocampus and striatum was 20% lowered 24 h after 10 once-daily ECS but had already returned to control levels 48 h after the last treatment. Evidence is provided that the upregulated adenosine A1 receptors are coupled to guanine nucleotide binding proteins and, furthermore, that this upregulation is not paralleled by an increase in adenylate cyclase activity as labeled by [3H]forskolin.

Dexamethasone and adrenalectomy alter (rain (Na +,K +)-ATPase responsses to noradrenergic stimulation or depletion

We investigated the effects of adrenalectomy or dexamethasone treatment on the regulation of brain (Na +,K +)- ATPase by noradrenaline. Noradrenergic stimulation was produced by repeated injections of yohimbine, and noradrenaline depletion by an injection of the selective toxin DSP4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine). Adrenalectomy had no effect on the number of quabain binding sites in cerebral cortex, but increased the number of sites synergistically with noradrenergic stimulation. Dexamethasone prevented the decrease in ouabain binding in rats treated with DSP4, but did not itself alter ouabain binding. Neither dexamethasone nor adrenalectomy altered the changes in β-receptor binding associated with the noradrenergic manipulations. Changes in exposure to corticosteroids may alter the coupling between adrenoceptor binding and second messenger activation in a way that affects (Na +,K +)-ATPase regulation.