Marco Antonio Campana Benedito

Effects of cannabidiol on behavioral seizures caused by convulsant drugs or current in mice

In mice, running, clonic and tonic convulsions and lethality were assessed following transcorneal (electroshock) current or convulsant drugs, each administered alone and after cannabidiol (CBD) pretreatment. CBD prevented tonic convulsions caused by a convulsant current (CC) 99.99, and by the convulsant dose (CD) 99.99 values of gamma-aminobutyric acid (GABA) inhibitors, 3-mercaptoproprionic acid (3MPA), picrotoxin (PIC), isonicotinic acid hydrazine (INH), pentylenetetrazol (PTZ) and bicuculline (BIC). Rankorder potencies, based on the antitonic ED50 of CBD, were: 3MPA greater than PIC = current = PTZ = BIC. Further, CBD prevented 3MPA-induced lethality, but failed to prevent the occurrence of the other behavioral endpoints of the above treatments. CBD also failed to prevent convulsions and lethality caused by the CD 99.99 of strychnine, a glycine antagonist. The differential effects of CBD suggest that the cannabinoid acts to inhibit seizure spread in the CNS by an action on GABA, but not glycine, mechanisms.

Daily changes in pentylenetrazol-induced convulsions and open-field behavior in rats

Susceptibility to pentylenetetrazol (PTZ)-induced clonic convulsions was measured in rats over the 24-hr light-dark cycle at four-hour intervals. The results showed a higher sensitivity to PTZ around 2200 hr. Other groups of rats were exposed to a four-min open-field session. In the first two min of the session the animals were submitted to open-field environmental stimuli. The next two-min observation occurred with sound and light presented to the animals. Differences through the 24-hr period of the day for both sessions were seen. A reduction in rearing at 2200 hr and increase in defecation at 2200 hr and 0200 hr was observed.

REM sleep deprivation induces a decrease in norepinephrine-stimulated 3H-cyclic AMP accumulation in slices from rat brain

Beta adrenergic sites in rat brain are reduced after repeated treatment with antidepressant drugs, with REM sleep deprivation (REMSd) having the same effect. This paper reports the effects of REMSd in the production of 3H-cyclic AMP in frontal cortical slices by NE challenge. Data presented in this paper report a marked decrease in 3H-cyclic AMP synthesis after REMSd, which is in accordance with previous results showing adrenergic receptor down-regulation following REMSd. Results are discussed in view of possible interaction with dopaminergic systems and depression management.

Rosewood oil induces sedation and inhibits compound action potential in rodents

AIM OF THE STUDY Aniba rosaeodora is an aromatic plant which has been used in Brazil folk medicine due to its sedative effect. Therefore, the purpose of the present study was to evaluate the sedative effect of linalool-rich rosewood oil in mice. In addition we sought to investigate the linalool-rich oil effects on the isolated nerve using the single sucrose-gap technique. MATERIALS AND METHODS Sedative effect was determined by measuring the potentiation of the pentobarbital-induced sleeping time. The compound action potential amplitude was evaluated as a way to detect changes in excitability of the isolated nerve. RESULTS The results showed that administration of rosewood oil at the doses of 200 and 300 mg/kg significantly decreased latency and increased the duration of sleeping time. On the other hand, the dose of 100 mg/kg potentiated significantly the pentobarbital action decreasing pentobarbital latency time and increasing pentobarbital sleeping time. In addition, the effect of linalool-rich rosewood oil on the isolated nerve of the rat was also investigated through the single sucrose-gap technique. The amplitude of the action potential decreased almost 100% when it was incubated for 30 min at 100 microg/ml. CONCLUSIONS From this study, it is suggested a sedative effect of linalool-rich rosewood oil that could, at least in part, be explained by the reduction in action potential amplitude that provokes a decrease in neuronal excitability.

Behavioral differences between subgroups of rats with high and low threshold to clonic convulsions induced by DMCM, a benzodiazepine inverse agonist

In epileptic patients, there is a high incidence of psychiatric comorbidities, such as anxiety. Gamma-aminobutyric acid (GABA) ionotropic receptor GABA(A)/benzodiazepine allosteric site is involved in both epilepsy and anxiety. This involvement is based on the fact that benzodiazepine allosteric site agonists are anticonvulsant and anxiolytic drugs; on the other hand, benzodiazepine inverse agonists are potent convulsant and anxiogenic drugs. The aim of this work was to determine if subgroups of rats selected according to their susceptibility to clonic convulsions induced by a convulsant dose 50% (CD50) of DMCM, a benzodiazepine inverse agonist, would differ in behavioral tests commonly used to measure anxiety (elevated plus-maze, open field) and depression (forced swimming test). In the first experiment, subgroups of adult male Wistar rats were selected after a single dose of DMCM and in the second experiment they were selected after two injections of DMCM given after an interval of 1 week. Those rats presenting full clonic convulsions were termed Low Threshold rats to DMCM-induced clonic convulsions (LTR) and those not having clonic convulsions High Threshold rats to DMCM-induced clonic convulsions (HTR). In both experiments, only those rats presenting full clonic convulsions induced by DMCM and those not showing any signs of motor disturbances were used in the behavioral tests. The results showed that the LTR subgroup selected after two injections of a CD50 of DMCM spent a significantly lower time in the open arms of the elevated plus-maze and in the off the walls area of the open field; moreover, this group also presented a higher number of rearings in the open field. There were no significant differences between HTR and LTR subgroups in the forced swimming test. LTR and HTR subgroups selected after only one injection of DMCM did not differ in the three behavioral tests. To verify if the behavioral differences between HTR and LTR subgroups of rats selected after two injections of DMCM were due to the clonic convulsion, another experiment was carried out in which subgroups of rats susceptible and nonsusceptible to clonic convulsions induced by a CD50 of picrotoxin, a GABA(A) receptor channel blocker, were selected and submitted to the elevated plus-maze and open field tests. The results obtained did not show any significant differences between these two subgroups in the elevated plus-maze and open field tests. In another approach to determine the relation between fear/anxiety and susceptibility to clonic convulsions, subgroups of rats were selected in the elevated plus-maze as more or less fearful/anxious. The CD50 for clonic convulsions induced by DMCM was determined for each of these two subgroups. The results showed a significantly lower CD50 for the more fearful/anxious subgroup, which means a higher susceptibility to clonic convulsions induced by DMCM. The present findings show a relation between susceptibility to clonic convulsions and fear/anxiety and vice versa which may be due to differences in the assembly of GABA(A)/allosteric benzodiazepine site receptors in regions of the brain.

High and low rearing subgroups of rats selected in the open field differ in the activity of K+-stimulated p-nitrophenylphosphatase in the hippocampus

Na(+)/K(+)-adenosinetriphosphatase (Na(+)/K(+)-ATPase) is of paramount importance for the proper functioning of the organism. The enzyme is involved in several aspects of brain function, such as the repolarization of the neuronal membranes and neurotransmitters uptake/release. Therefore, individual differences in the activity of brain Na(+)/K(+)-ATPase may result in differences in the functioning of the brain, which, in consequence, could lead to behavioral divergences. Individual differences in rearing, an exploratory behavior, have been shown to be genetically determined. In rats, the inhibition of the activity of Na(+)/K(+)-ATPase was reported to induce changes in the exploratory behavior. The aim of this work was to verify if subgroups of rats selected according to the number of rearings (high and low rearing subgroups) in the open field test differ in the activity of Na(+)/K(+)-ATPase in brain regions. Adult, male outbred Wistar rats were selected in the open field test according to the number of rearings in subgroups of high (HR) and low (LR) rearing responders. After a rest of about 20 days after the open field session, HR and LR rats were sacrificed. In the first experiment, frontal cortex, striatum, brainstem, hippocampus and the amygdala (including the overlying limbic cortex) were dissected. The reaction of dephosphorylation of Na(+)/K(+)-ATPase (K(+) stimulated p-nitrophenylphosphatase) was assayed in homogenates rich in synaptosomes. The results obtained showed a statistically significant higher activity of K(+)p-nitrophenylphosphatase only in the hippocampus of HR subgroup of rats. This result was replicated in two other subsequent experiments with different HR and LR subgroups of rats selected at different times of the year. Our data suggest that the difference in the activity of Na(+)/K(+)-ATPase in the hippocampus is innate and is involved in the expression of the rearing behavior.

Activities of Monoamine Oxidase (MAO) A and B in Discrete Regions of Rat Brain After Rapid Eye Movement (REM) Sleep Deprivation

Rapid eye movement (REM) sleep deprivation increases monoaminergic (noradrenergic and serotonergic) turnover and their metabolites in whole brain of rats. This increase in metabolites may indicate increased activity of the enzymes responsible for the inactivation of monoamines. To test this hypothesis, we assayed the activity of monoamineoxidases (MAOs) A and B in hippocampus, hypothalamus, brainstem and its divisions pons and medulla oblongata in rats deprived of REM sleep for 96 h. REM sleep deprivation was carried out by the flower-pot technique. A control group remained in their home cages. MAO A was assayed by using [14C]-5-hydroxytryptamine as the substrate (50 microM final concentration) and MAO B by using [14C]-beta-phenylethylamine (2 microM final concentration). The enzymes were assayed in the mitochondrial fraction.The results obtained showed that a significant decrease in the activity of MAO A was obtained in the brainstem and an increase in medulla oblongata and no statistical differences in the activity of MAO B in brainstem, pons and medulla oblongata and MAO A in pons; there were also no differences in the activities of both MAO A and B in hippocampus and hypothalamus. Although our results confirmed previous data regarding changes in MAO A activity in brainstem and medulla oblongata, they did not confirm our hypothesis that the increase in monamine turnover and metabolites in the brain would be the result of increased MAO activity.

Rapid eye movement sleep deprivation-induced down-regulation of beta-adrenergic receptors in the rat brainstem and hippocampus

Rapid eye movement (REM) sleep deprivation induces a cortical down-regulation of beta-adrenergic receptors. Down-regulation of cortical beta-adrenergic receptors is consistently observed after a number of different chronic antidepressant treatments (drugs and electroconvulsive shock). REM sleep deprivation has an antidepressant effect in humans, and in rats, it decreases immobility in the behavioral despair test, an effect also produced by antidepressant treatments. To verify whether REM sleep deprivation also affects hippocampal beta-adrenergic receptors, we carried out the binding of [3H]-dihydroalprenolol ([3H]-DHA) to hippocampal membranes from rats deprived of REM sleep for 96 h. We also determined the binding of [3H]-DHA to brainstem membranes, a brain region where noradrenergic nuclei are located. Rats were deprived of REM sleep using a water tank with multiple small platforms. [3H-DHA] saturation conditions (concentrations ranging from 0.15 to 6 nM) were obtained in a crude hippocampus and brainstem membrane preparation. Nonspecific binding was determined using DL-propranolol in hippocampus homogenates. In the brainstem homogenates, nonspecific binding was determined in the presence of DL-propranolol or L-isoproterenol. The results obtained showed statistically significant down-regulation of beta-adrenergic receptors in both the hippocampus and the brainstem after REM sleep deprivation. In the hippocampus, there was also a significant decrease in the dissociation constant (KD). In the brainstem, a significant decrease in KD was observed when DL-propranolol was used to determine nonspecific binding. The down-regulation of beta-adrenergic receptors in the hippocampus and brainstem suggests the involvement of these brain areas in the antidepressant effect of REM sleep deprivation.

Fluorimetric Determination of Tissue Distribution and Differences Between the Activity of Aspirin Esterases I and II in Mice and Rats

A modification of available fluorimetric methods, based on the native fluorescence of salicylic acid, has been used to assay the activity of aspirin esterases I and II in small amounts of several tissues from rats and mice.

Rapid eye movement sleep deprivation induces changes in the high-affinity binding of [3H]-ouabain to the rat cortical membranes.

Rapid eye movement sleep (REMS) suppresses seizures. On the other hand, REMS deprivation (REMSD) increases brain susceptibility to seizures. Sodium-potassium/ATPase is involved in the control of brain excitability. Ouabain, a cardiotonic glycoside, binds to a regulatory extracellular allosteric site in the sodium-potassium/ATPase inhibiting/stimulating its activity depending on its concentration. Endogenous ouabain-like substances exist in the brain; therefore, changes in the ouabain binding site may be involved in the increased brain excitability induced by REMSD. Adult, Wistar male rats were deprived of REMS for 96 hours by the flower-pot method (REMSD). A stress control group was kept in the same environment on a larger platform (LP). A third group of rats was kept in the same room in their home-cages (CONTROL). After REMSD all rats were sacrificed by decapitation and their cerebral cortex dissected. High-affinity [3H]-ouabain binding was carried out in cortical crude membrane preparation using 8 concentrations of [3H]-ouabain (1-24 nM). The results show a statistically significant increase of KD in the REMSD rats compared to both CONTROL and LP groups. There were no statistically significant differences in the Bmax among the experimental groups. There was also no change either in cortical activity of K+ stimulated p-nitrophenylphosphatase, the dephosphorylation reaction of phosphorylated sodium-potassium/ATPase or in Mg2+-stimulated p-nitrophenylphosphatase. An increase in the KD of [3H]-ouabain binding to the sodium-potassium/ATPase in REMSD rats indicates a lower affinity to the endogenous inhibitors/stimulators of the enzyme. Therefore, this decreased affinity of the endogenous ouabain-like substances may be involved in the increased excitability induced by REMSD.