The level of GABA in the brain and locomotor behavior

Acute toxicity of broflanilide on neurosecretory system and locomotory behavior of zebrafish (Danio rerio)

Broflanilide, a novel meta-diamide insecticide, possesses moderate acute toxicity to zebrafish, with a 96-h median lethal concentration (96-LC₅₀) of 0.76 mg/L. However, its effect on fish behavior and the underlying mechanisms are still unclear. The present study evaluated the effects of broflanilide on the zebrafish brain over a 96-h exposure by comparing the histopathological changes and relative expression of targeted genes with the behavioral metrics. The results of the toxicity test showed that broflanilide could cause deformities, such as deformation of the operculum and spinal curvature, at 0.6, 0.82 and 1.15 mg/L. Results also showed tissue damage and apoptosis in the cerebellum under 0.27 and 0.6 mg/L exposure. Additionally, broflanilide affected the neurotransmitters, metabolites and transcripts of genes associated with dopamine, gamma-aminobutyric acid expression. and the signaling pathways in zebrafish brains at 0.60 mg/L after 1 h and 96 h of exposure, while the levels of glutamate, glutamate decarboxylase, GABA transaminase, nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP) were also inhibited at 0.27 mg/L after 96 h of exposure. The accumulated swimming distance was significantly longer and the average speed was significantly faster than the control at 0.27 and 0.6 mg/L after 1-h of exposure, while these metrics were lowered at 0.6 mg/L after 96 h of exposure. The study results demonstrates that broflanilide affects the zebrafish brain, neurotransmitters and associated fish behaviors. This study also provides deeper insight into the mechanistic understanding of the effects of broflanilide on the zebrafish brain.

Median raphe region GABAergic neurons contribute to social interest in mouse

Gamma-aminobutyric acid (GABA) is a well-known inhibitory neurotransmitter implicated in numerous physiological and pathological behaviors including social interest. Dysregulation of the median raphe region (MRR), a main serotoninergic nucleus, is also characterized by increased social problems. As the majority of MRR cells are GABAergic, we aimed to reveal the social role of these cells. Chemogenetic techniques were used in vesicular GABA transporter Cre mice and with the help of adeno-associated virus vectors artificial receptors (DREADDs, stimulatory, inhibitory or control, containing only a fluorophore) were expressed in MRR GABAergic cells confirmed by immunohistochemistry. Four weeks after viral injection a behavioral test battery (sociability; social interaction; resident-intruder) was conducted. The artificial ligand (clozapine-N-oxide, 1 mg/10 ml/kg) was administrated 30 min before the tests. As possible confounding factors, locomotion (open field/OF), anxiety-like behavior (elevated plus maze/EPM), and short-term memory (Y-maze) were also evaluated. Stimulation of the GABAergic cells in MRR had no effect on locomotion or working and social memory; however, it increased social interest during sociability and social interaction but not in resident-intruder tests. Accordingly, c-Fos elevation in MRR-GABAergic cells was detected after sociability, but not resident-intruder tests. In the EPM test, the inhibitory group entered into the open arms later, suggesting an anxiogenic-like tendency. We confirmed the role of MRR-GABAergic cells in promoting social interest. However, different subpopulations (e.g. long vs short projecting, various neuropeptide containing) might have divergent roles, which might remain hidden and requires further studies.

Role of hydrogen sulfide in ventilatory responses to hypercapnia in the medullary raphe of adult rats

NEW FINDINGS

What is the central question of this study? There is evidence that H₂ S plays a role in the control of breathing: what are its actions on the ventilatory and thermoregulatory responses to hypercapnia via effects in the medullary raphe, a brainstem region that participates in the ventilatory adjustments to hypercapnia? What is the main finding and its importance? Hypercapnia increased the endogenous production of H₂ S in the medullary raphe. Inhibition of endogenous H₂ S attenuated the ventilatory response to hypercapnia in unanaesthetized rats, suggesting its excitatory action via the cystathionine β-synthase-H₂ S pathway in the medullary raphe.

ABSTRACT

Hydrogen sulfide (H₂ S) has been recently recognized as a gasotransmitter alongside carbon monoxide (CO) and nitric oxide (NO). H₂ S seems to modulate the ventilatory and thermoregulatory responses to hypoxia and hypercapnia. However, the action of the H₂ S in the medullary raphe (MR) on the ventilatory responses to hypercapnia remains to be elucidated. The present study aimed to assess the role of H₂ S in the MR (a brainstem region that contains CO₂ -sensitive cells and participates in the ventilatory adjustments to hypercapnia) in the ventilatory responses to hypercapnia in adult unanaesthetized Wistar rats. To do so, aminooxyacetic acid (AOA; a cystathionine β-synthase (CBS) enzyme inhibitor), propargylglycine (PAG; a cystathionine γ-lyase enzyme inhibitor) and sodium sulfide (Na₂ S; an H₂ S donor) were microinjected into the MR. Respiratory frequency (f_R ), tidal volume (V_T ), ventilation ( V ̇ E ), oxygen consumption ( V ̇ O 2 ) and body temperature (T_b ) were measured under normocapnic (room air) and hypercapnic (7% CO₂ ) conditions. H₂ S concentration within the MR was determined. Microinjection of the drugs did not affect f_R , V_T and V ̇ E during normocapnia when compared to the control group. However, the microinjection of AOA, but not PAG, attenuated f_R and V ̇ E during hypercapnia in comparison to the vehicle group, but had no effects on T_b . In addition, we observed an increase in the endogenous production of H₂ S in the MR during hypercapnia. Our findings indicate that endogenously produced H₂ S in the MR plays an excitatory role in the ventilatory response to hypercapnia, acting through the CBS-H₂ S pathway.

Excitatory Modulation of the preBötzinger Complex Inspiratory Rhythm Generating Network by Endogenous Hydrogen Sulfide

Hydrogen Sulfide (H2S) is one of three gasotransmitters that modulate excitability in the CNS. Global application of H2S donors or inhibitors of H2S synthesis to the respiratory network has suggested that inspiratory rhythm is modulated by exogenous and endogenous H2S. However, effects have been variable, which may reflect that the RTN/pFRG (retrotrapezoid nucleus, parafacial respiratory group) and the preBötzinger Complex (preBötC, critical for inspiratory rhythm generation) are differentially modulated by exogenous H2S. Importantly, site-specific modulation of respiratory nuclei by H2S means that targeted, rather than global, manipulation of respiratory nuclei is required to understand the role of H2S signaling in respiratory control. Thus, our aim was to test whether endogenous H2S, which is produced by cystathionine-β-synthase (CBS) in the CNS, acts specifically within the preBötC to modulate inspiratory activity under basal (in vitro/in vivo) and hypoxic conditions (in vivo). Inhibition of endogenous H2S production by bath application of the CBS inhibitor, aminooxyacetic acid (AOAA, 0.1-1.0 mM) to rhythmic brainstem spinal cord (BSSC) and medullary slice preparations from newborn rats, or local application of AOAA into the preBötC (slices only) caused a dose-dependent decrease in burst frequency. Unilateral injection of AOAA into the preBötC of anesthetized, paralyzed adult rats decreased basal inspiratory burst frequency, amplitude and ventilatory output. AOAA in vivo did not affect the initial hypoxia-induced (10% O2, 5 min) increase in ventilatory output, but enhanced the secondary hypoxic respiratory depression. These data suggest that the preBötC inspiratory network receives tonic excitatory modulation from the CBS-H2S system, and that endogenous H2S attenuates the secondary hypoxic respiratory depression.

Adult-like biphasic neurobehavioral changes induced by a GABA-A agonist in infant and weanling mice

The neurobehavioral responsivity to peripherally injected muscimol, a gamma-aminobutyric acid-A (GABA-A) agonist, was assessed in infant (14-day-old), weanling (20-day-old) and young adult (53-day-old) outbred male mice. In the first experiment, relatively high doses of muscimol (ranging from 0.05 to 0.40 mg/kg in developing and from 0.50 to 3 mg/kg in adult animals) were found to dose-dependently induced solid catalepsy and ataxia, evaluated 5 times at 20-min intervals. In the second experiment, the GABA agonist was injected in dose ranges which include relatively small concentrations in order to assess its excitatory properties, observable in adults, on rearing and locomotion in developing mice. It appeared that levels of rearing and especially locomotion were enhanced at the low doses (0.025 and 0.050 mg/kg in developing, and 1.3 and 1.9 mg/kg in adult mice) and inhibited at the higher ones (0.150 mg/kg in developing and 1.9 and 2.5 mg/kg in adult mice). This adult-like biphasic action of muscimol in developing mice--excitation at low and depression/sedation at high doses--strongly suggests a full maturation of the GABA-A-related behavioral functions at a period of ontogeny where adult-like locomotion emerges. Given that previous studies have shown that muscimol can biphasically affect behavioral activity in newborn murines as well, it is suggested that GABA-related behavioral functions mature near-monotonically during ontogeny, unlike those related to other major neurotransmitter systems.

Effect of ethanol on gamma-vinyl GABA-induced GABA accumulation in the substantia nigra and on synaptosomal GABA content in six rat brain regions

Two recently developed methods for estimating changes in presynaptic gamma-aminobutyric acid (GABA) homeostasis were used for the first time to evaluate the effects of acute and chronic ethanol treatments on GABA utilization. GABA accumulation in the left substantia nigra zona reticulata (SNR) following unilateral microinjection of gamma-vinyl GABA (GVG; 5 micrograms) was linear for at least 180 min while GABA concentrations in the uninjected right SNR did not change over this period. Net GABA accumulation (left minus right SNR) also increased linearly over this interval. Intraperitoneal (i.p.) administration of ethanol (0.3, 1 or 3 g/kg) 15 min after GVG microinjection did not significantly change either the rate of GABA accumulation in left SNR, the net GABA accumulated or the concentration of GABA in the uninjected right SNR relative to saline injected controls over the 45-min test interval. Likewise, GABA accumulation in the left SNR or steady-state GABA concentrations in the right SNR of chronically intoxicated rats or physically dependent animals withdrawn from ethanol for 12 h did not change significantly from that dextrose-fed controls. In a separate study, the effects of acute and chronic ethanol treatments on the concentration of GABA in synaptosomes isolated from the frontal cortex, hippocampus, tectum, striatum, cerebellum or brainstem were determined. Thirty min after acute treatment with ethanol (0.5, 1, 2 or 4 g/kg, i.p.) the concentration of GABA in synaptosomes from any of these brain regions was not significantly altered. Furthermore, chronic ethanol treatment sufficient to induce physical dependence and a severe ethanol withdrawal syndrome also did not significantly modify synaptosomal GABA concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of ethyl (R,S)-nipecotate on the behaviors of highly and minimally aggressive female golden hamsters

The GABA uptake inhibitor ethyl (R,S)-nipecotate produces a dose-dependent suppression of aggression in highly aggressive hamsters but not in minimally aggressive ones. This suppression occurs at doses below those producing peripheral cholinergic effects; at the highest dose used it persists after these effects have dissipated. Doses sufficient to suppress aggression have no significant effect on grooming, locomotor activity and other behaviors but do affect sunflower seed acceptance. The differential effects of the drug on highly and minimally aggressive animals may indicate that their differences in aggression are due to differences in endogenous GABAergic activity. These results, together with previous evidence for parallel circadian variation in GABA uptake and aggressive behavior, suggest that GABA uptake may be an important endogenous regulator of aggression.

The locomotor-reducing effects of GABAergic drugs do not depend on the GABAA receptor

The locomotion-reducing effect of the GABAB agonist baclofen was compared with that of the GABAA agonists, aminopropanesulfonic acid (APSA) and THIP. It was found that baclofen was more potent than the other drugs. After intraventricular injection, baclofen induced almost complete immobility, whereas APSA did not affect locomotor activity. THIP had an intermediate effect. The GABA transaminase inhibitor gamma-acetylenic GABA (GAG) provoked a dose-dependent reduction of locomotion. Neither the effects of THIP nor those of GAG could be blocked by concurrent administration of bicuculline. The antagonist itself did not affect locomotor activity. It is concluded that the GABAA receptor is not important for the locomotion-reducing effects of GABAergic drugs.

GABA-ergic drugs: effects on conditioning, memory and learning

In order to study the role of GABA in behaviour, various GABA-mimetic and GABA-blocking drugs were tested for their effects on a conditioned avoidance response (CAR). Sodium valproate slowed the acquisition of CAR and failed to affect the latency of a well-learned CAR, but interestingly, showed a marked anti-conflict effect similar to that of benzodiazepine-derivatives. The similarity of effects of drugs such as benzodiazepines and sodium valproate, which are postulated to potentiate GABA-ergic transmission, suggests that GABA plays a role in conditioning, memory and learning.

GABAergic influences on defensive fighting in rats

The involvement of GABAergic mechanisms in shock-induced defensive fighting in rats was investigated in a series of three experiments. In Experiment 1, sodium n-dipropylacetate (100-200 mg/kg) failed to produce significant behavioural change whilst gamma-vinyl-GABA (100-200 mg/kg) induced a selective and dose-dependent reduction in fighting. In Experiment 2, although inconsistent behavioural effects were obtained with (+)-bicuculline (0.25-4 mg/kg), a biphasic influence on defensive fighting was observed with picrotoxin (0.125-2 mg/kg). The inhibitory effect on fighting, induced by the highest dose of picrotoxin, was related to motor impairment. In Experiment 3, muscimol reduced fighting at doses above 0.25 mg/kg with motor disruption evident only at the highest dose used (1 mg/kg). A dose-dependent inhibition of defensive fighting was observed with 1-baclofen (0.15-1.2 mg/kg) which, at the highest dose tested, also impaired motor coordination. None of the compounds tested significantly altered shock thresholds. Results are discussed in relation to the hypothesized inhibitory role of GABA in the mediation of aggressive behaviours.

The effect of prenatal exposure to diazepam on aspects of postnatal development and behavior in rats

In the present study the effects of chronic treatment of pregnant rats with diazepam on the physical and behavioral development of their offspring were investigated. Rats that were diazepam-exposed prenatally were compared to age-matched controls in terms of the following: number of littermates; birth weight and weight gain until weaning: motor development and coordination; simple motor learning; open field activity; performance on learning tasks of varying complexity; retention of these tasks. Nulliparous Wistar rats were injected s.c. for 16 days of their pregnancy was either 2.5, 5, of 10 mg/kg diazepam or an equal volume of vehicle. Prenatal diazepam treatment did not alter litter size, birth weight, or the righting reflex, but seemed to retard early motor development transiently. Diazepam pups showed longer latencies and less rearing in the open field. There were no differences between animals exposed to drug and vehicle in simple motor learning or in acquiring a simple successive discrimination task. However, there were significant dose-dependent differences on a complex six-choice simultaneous discrimination learning task, the diazepam-exposed rats making more errors and taking more time to reach the goal. A significant difference was seen again between diazepam- and vehicle-exposed rats on the retention test 10 days later. The results indicate that diazepam administered to pregnant rats has long-range effects on the behavior of the offspring, some becoming manifest even in maturity.

A dual role for GABA in quasi-morphine abstinence behavior induced by di-n-propylacetate involving both initiation and termination

Di-n-propylacetate (DPA) induces a behavioral syndrome in rats resembling morphine abstinence behavior. The inhibitory action of DPA on GABA degradation, resulting in an enhanced release of GABA, is probably responsible for this behavioral effect, since GABA antagonists, like bicuculline and picrotoxin, have been shown to suppress this behavior. However, the time-course of the DPA-induced behavior is much shorter than that of the DPA-induced increase of GABA concentrations. Therefore, we have studied the influence of enhanced GABA levels caused by a first injection of DPA and the behavior evoked by a second injection of DPA at different time intervals after the first injection. The results indicate that GABA fulfills a role in both the initiation and termination of DPA-induced behavior. The mechanism responsible for this dual action of GABA is ascribed to a differential sensitivity to DPA of the nerve terminal and glial metabolic compartments of GABA in the brain. The increase of GABA in the nerve terminal caused by DPA is probably responsible for the initiation of the quasi-abstinence behavior, whereas the overflow of GABA into the synaptic cleft may be responsible for the suppression of this behavior via stimulation of presynaptic autoreceptors. Another mechanism responsible for the rapid termination of the DPA-evoked behavior could be the formation of DPA metabolites which antagonize this behavior. From the results of experiments using some primary metabolites of DPA, a role for these metabolites in the termination of the DPA-induced behavior seems unlikely.

Regional distributions of gamma-aminobutyric acid (GABA), glutamate decarboxylase (GAD), and gamma-aminobutyrate transaminase (GABA-T) in the central nervous brains of C57/BR, C3H/He, and F1 hybrid mice

The distributions of gamma-aminobutyric acid (GABA), glutamate decarboxylase (GAD), and gamma-aminobutyrate transaminase (GABA-T) have been studied in various brain areas of mice. These neurochemical markers, which are related to inhibitory neurotransmission, were investigated in different inbred strains of mice (C3H/He, C57/BR, and their F1 hybrids). The regional distributions of GABA, GAD activity, and GABA-T activity in adult mice of these three strains were quite similar. No significant differences were found in any brain area for GAD or GABA-T activity. However, significant differences in GABA level were found in several brain areas among these strains of mice, especially in hypothalamus, hippocampus, olfactory bulb, and occipital cortex. These results provide further information to the possible influence of the GABAergic system in these brain areas.

Motor depression and head twitches induced by IP injection of GABA

Influence of GABA onlocomotor activity and gross behavior of mice, rats, and rabbits was studied. In mice and rats, IP GABA injection produced decreased locomotor activity, but in rats and rabbits head twitches and disturbances in body balance were seen. GABA-induced head twitches were inhibited by picrotoxin, clonidine, morphine, or cyproheptadine. Our results suggest a serotonergic component in GABA-induced head twitches, but it is not the only mechanism involved in this behavior.

GABA involvement in memory consolidation: evidence from posttrial amino-oxyacetic acid

In order to assess the possible effects of central GABA activation on the consolidation of shock avoidance, the GABA-T inhibitor amino-oxyacetic acid (AOAA) was administered posttrial to adult male rats. Learning was assessed over nine widely spaced sessions of 20 trials each. AOAA-treated animals showed learning within sessions and a lack of consolidation across sessions. Controls, on the other hand, showed learning both within and across sessions. This evidence agrees with previous reports suggesting GABA involvement in memory processes.

Effect of di-n-propylacetate on the 'binding of GABA to synaptosome-enriched fraction of rat cerebral cortex

The effect of di-n-propylacetate (DPA) on the 'binding' of gamma-aminobutyric acid (GABA) to a synaptosome-enriched fraction of rat cerebral cortex has been examined using differential centrifugation and double-isotope liquid scintillation spectrometry. DPA at 10(-4) M caused a slight decrease in GABA binding. This effect could explain in part the in vivo anticonvulsant and behavioral effects of this drug when administered to animals in high systemic doses.

Acute functional tolerance to the motor impairment effects of di-n-propylacetate

Rats were trained to run treadmill fashion along a moving belt to avoid electric shock. After stabilization of performance, the effects of the anticonvulsant di-n-propylacetate (DPA; 100, 200 and 400 mg/kg) on treadmill locomotion were measured. Disturbances in gait and balance were reflected by an increased time off belt in a dose-related manner. In addition, animals showed a progressive improvement over the 3 two-min trials. A second experiment which measured the effects of 300 mg/kg DPA either 5 or 20 min postinjection revealed that the progressive improvement noted in the first experiment was not due to a diminished drug concentration or to an increased exposure to the drug. Thus, acute functional tolerance to the performance decrement produced by DPA appears to depend upon behavioural processes which enable an animal to overcome the drug-induced functional deficit by practicing the task while in the drug state.

Effects of intracisternal GABA or glutamic acid upon behavioral activity in the rat

It has been postulated that GABA acts as an inhibitor of command neurons, the activity of which initiates behavior. A prediction of this hypothesis is that elevations in functional GABA levels in the brain will cause decreases in behavioral output. Accordingly, in this study rats were injected intracisternally with either saline or one micromole of GABA or its excitatory precursor, glutamic acid, and behavioral activity in a novel environment was recorded as it habituated over the course of the subsequent 4 hours. The activity of the animals that were injected with GABA was greatly decreased, while the activity of the animals that were injected with glutamic acid was apparently unaffected, as compared to animals given saline. These data provide support for the hypothesis that GABA functions as an inhibitory neurotransmitter for behavior-activating command neurons.