Possible involvement of GABA in the central actions of benzodiazepines.

The effects of several benzodiazepines on a variety of nervous activities known or presumed to depend on GABA are presented and compared with those of agents that deplete or increase the level of endogenous GABA: antagonism of various convulsant agents in mice, enhancement of presynaptic inhibition in the spinal cord and the cuneate nucleus of cats, decrease of the spontaneous firing rate of cerebellar Purkinje cells in cats and rats, antagonism of bicuculine-induced depression of the strio-nigral-evoked potential in the cat, potentiation of haloperidol-induced catalepsy in rats, GABA-mimetic actions on drug-induced PGO-waves in cats and on eserine-induced circling in guinea pigs. Diazepam slightly increased the GABA level in the cat spinal cord and in the total brain of mice and rats; this increase does not seem to be due to an increase of GABA synthesis. It is concluded that benzodiazepines probably enhance presynaptic inhibition at all levels of the neuraxis and that this effect requires not only the presence of GABA but is also dependent on an activity of GABA-ergic neurons. Benzodiazepines also appear to enhance postsynaptic inhibition where this is mediated by GABA. Many actions of benzodiazepines can be tentatively explained by a stimulus-bound enhancement of GABA effects.     

Effect of substance P on behavior in the rabbit and the activity of cortical neurons during training

Subcutaneous injection of substance P to rabbits in a dose of 250 mcg/kg elicited a transitory disappearance of motor reactions to painful reinforcing stimuli and a reduction of their probability to reinforced and inhibitory light flashes, as well as a protracted heart rate increase and decrease of respiration rate. One third of the neurones recorded decreased their background firing level and or excitatory components of the reactions to reinforcement and conditioned light flashes. The decrease was most distinctly seen in the sensorimotor cortex and less pronounced in the visual cortical area and hippocampus. The influence of the substance P on different types of cortical inhibition was not the same. Tonic inhibition of neuronal activity in response to reinforcement was enhanced. Bioelectrical parameters which reflect an enhancement of inhibitory hyperpolarization during elaboration of internal inhibition (i.e. inhibitory firing delays and corresponding background and evoked slow potentials oscillations) were not changed.     

Pharmacological analysis of the activation and receptor properties of the tonic GABA(C)R current in retinal bipolar cell terminals

GABAergic inhibition in the central nervous system (CNS) can occur via rapid, transient postsynaptic currents and via a tonic increase in membrane conductance, mediated by synaptic and extrasynaptic GABA(A) receptors (GABA(A)Rs) respectively. Retinal bipolar cells (BCs) exhibit a tonic current mediated by GABA(C)Rs in their axon terminal, in addition to synaptic GABA(A)R and GABA(C)R currents, which strongly regulate BC output. The tonic GABA(C)R current in BC terminals (BCTs) is not dependent on vesicular GABA release, but properties such as the alternative source of GABA and the identity of the GABA(C)Rs remain unknown. Following a recent report that tonic GABA release from cerebellar glial cells is mediated by Bestrophin 1 anion channels, we have investigated their role in non-vesicular GABA release in the retina. Using patch-clamp recordings from BCTs in goldfish retinal slices, we find that the tonic GABA(C)R current is not reduced by the anion channel inhibitors NPPB or flufenamic acid but is reduced by DIDS, which decreases the tonic current without directly affecting GABA(C)Rs. All three drugs also exhibit non-specific effects including inhibition of GABA transporters. GABA(C)R ρ subunits can form homomeric and heteromeric receptors that differ in their properties, but BC GABA(C)Rs are thought to be ρ1-ρ2 heteromers. To investigate whether GABA(C)Rs mediating tonic and synaptic currents may differ in their subunit composition, as is the case for GABA(A)Rs, we have examined the effects of two antagonists that show partial ρ subunit selectivity: picrotoxin and cyclothiazide. Tonic and synaptic GABA(C)R currents were differentially affected by both drugs, suggesting that a population of homomeric ρ1 receptors contributes to the tonic current. These results extend our understanding of the multiple forms of GABAergic inhibition that exist in the CNS and contribute to visual signal processing in the retina.     

Post-translational modification of glutamic acid decarboxylase 67 by intermittent hypoxia: evidence for the involvement of dopamine D1 receptor signaling

Intermittent hypoxia (IH) associated with sleep apnea leads to cardio-respiratory morbidities. Previous studies have shown that IH alters the synthesis of neurotransmitters including catecholamines and neuropeptides in brainstem regions associated with regulation of cardio-respiratory functions. GABA, a major inhibitory neurotransmitter in the CNS, has been implicated in cardio-respiratory control. GABA synthesis is primarily catalyzed by glutamic acid decarboxylase (GAD). In this study, we tested the hypothesis that IH like its effect on other transmitters also alters GABA synthesis. The impact of IH on GABA synthesis was investigated in pheochromocytoma 12 cells, a neuronal cell line which is known to express active form of GAD67 in the cytosolic fraction and also assessed the underlying mechanisms contributing to IH-evoked response. Exposure of cell cultures to IH decreased GAD67 activity and GABA level. IH-evoked decrease in GAD67 activity was caused by increased cAMP - protein kinase A (PKA) - dependent phosphorylation of GAD67, but not as a result of changes in either GAD67 mRNA or protein expression. PKA inhibitor restored GAD67 activity and GABA levels in IH treated cells. Pheochromocytoma 12 cells express dopamine 1 receptor (D1R), a G-protein coupled receptor whose activation increased adenylyl cyclase activity. Treatment with either D1R antagonist or adenylyl cyclase inhibitor reversed IH-evoked GAD67 inhibition. Silencing D1R expression with siRNA reversed cAMP elevation and GAD67 inhibition by IH. These results provide evidence for the role of D1R-cAMP-PKA signaling in IH-mediated inhibition of GAD67 via protein phosphorylation resulting in down-regulation of GABA synthesis.     

Transient presence and functional interaction of endogenous GABA and GABAA receptors in developing rat optic nerve.

GABA (gamma-aminobutyric acid) is a major inhibitory synaptic neurotransmitter with widespread distribution in the central nervous system (CNS). GABA can also modulate axonal excitability by activation of GABAA receptors in CNS white matter regions where synapses and neuronal cell bodies are not present. Studies on cultured glia cells have revealed the synthesis of GABA in rat optic nerve O-2A progenitor cells that give rise to oligodendrocytes and type 2 astrocytes in vitro. We report here that: (i) GABA is detected by immuno-electron microscopy in intact rat optic nerve and is localized to glia and pre-myelinated axons during the first few weeks of postnatal development, but is markedly reduced or absent in the adult; and (ii) neonatal optic nerve is depolarized by GABAA receptor agonists or by the inhibition of GABA uptake. These results demonstrate the presence of functional GABAA receptors, and GABA uptake and release mechanisms in developing rat optic nerve, and suggest that excitability of developing axons can be modulated by endogenous neurotransmitter at non-synaptic sites.     

Receptor modifiers indicate that 4-aminobutyric acid (GABA) is a potential modulator of ion transport in plants

GABA (4-aminobutyric acid) is a ubiquitousnon-protein amino acid that accumulates rapidly inplants in response to stress. GABA was firstidentified in plants (potato tubers) and animals(brain tissue) 50 years ago. Although GABA is nowrecognized as the most important inhibitoryneurotransmitter in the mammalian central nervoussystem (CNS), the role of GABA in plants remainsunclear. Studies were performed using Lemna toinvestigate the possibility that GABA elicits aresponse in plants that may be related to that of asignaling molecule as described for GABA effects onthe CNS. Lemna growth was increased 2 to 3-foldby 5 mM GABA, but growth was strongly inhibited by 0.5mM of the isomers 3-aminobutyric acid and2-aminobutyric acid. Growth promotion by GABA wasrapidly terminated by addition of 2-aminobutyric acidto the culture medium, but inhibitory effects of2-aminobutyric acid were not reversed by GABAregardless of amounts added. Promotion of Lemnagrowth by GABA was associated with an increase inmineral content of treated plants in a dose dependentmanner. Results support the hypothesis that GABAactivity in plants involves an effect on ion transportand an interaction with a receptor. Evidence for GABAreceptors in Lemna was obtained from experimentswith pharmacological agents that have been used toidentify GABA receptors in animals. GABA mediatedpromotion of Lemna growth was inhibited bybicuculline and picrotoxin, which are respectivelycompetitive and non-competitive antagonists of GABAreceptors in the CNS. Growth inhibition bybicuculline was not relieved by increasing the amountsof GABA in the medium, indicating that the alkaloid isnot acting, as in the CNS, by competitive antagonismof GABA at GABA receptor sites. Baclofen, a GABAagonist that promotes GABA activity in animalssignificantly increased GABA mediated promotion ofLemna growth. These findings and the knownaction of GABA in regulating ion channels in animalssuggests a way that GABA could amplify the stressresponse in plants.     

Convulsions induced by kynurenine and quinolinic acid as a sensitive test for assessing the anticonvulsant activity of GABA-ergic preparations

Phenibut, sodium hydroxybutyrate and baclofen are selectively effective against seizures induced in mice by the endogenous metabolites of tryptophan, L-kynurenine and quinolinic acid. The seizures were not affected by the drugs in doses under study. Depakine and aminooxyacetic acid as well as diazepam and phenobarbital appeared the most effective against pentylenetetrazole seizures. GABA and muscimol administered intracerebroventricularly merely prolonged the latency of seizures. Dissimilarities in the GABA-ergic mechanisms of the anticonvulsant effects of the drugs under consideration are discussed.     

γ-Aminobutyric Acid Turnover in Rat Striatum: Effects of Glutamate and Kainic Acid

The turnover rate of gamma-aminobutyric acid (GABA) in the rat striatum was estimated by measuring its accumulation after inhibition of GABA-transaminase (GABA-T) with gabaculine. Intrastriatal injections of 100 micrograms gabaculine induced a rapid and complete inhibition of GABA-T. GABA accumulation was linear with time for at least 60 min (estimated turnover rate = 25 nmol/mg protein/h). The accumulation of GABA after gabaculine administration in animals that had been treated with kainic acid (5 nmol intrastriatally, 7 days) was only 40% of the control value, indicating that a major fraction of the net increase in GABA content induced by gabaculine originates in kainic acid-sensitive neurons. Intrastriatal injection of a mixture of kainic acid (5 nmol) and gabaculine caused a net increase in striatal GABA content significantly greater than that observed in controls, suggesting that neuronal death induced by kainic acid is preceded by a period of increased neuronal activity. Glutamic acid, the putative neurotransmitter for the excitatory corticostriatal pathway, also produced a significant increase in striatal GABA accumulation when injected together with gabaculine. This effect was blocked by the administration of the glutamate receptor antagonist glutamic acid diethyl ester. The interactions between GABAergic neurons and other neurotransmitters present in the striatum were also analyzed.     

THE METABOLISM OF GABA AND OTHER AMINO ACIDS IN RAT SUBSTANTIA NIGRA SLICES FOLLOWING LESIONS OF THE STRIATO-NIGRAL PATHWAY

The metabolism of GABA and other amino acids from various radioactive precursors has been studied in the rat substantia nigra using a sensitive double isotope dansyl derivative assay. Labelled acetate gave greater labelling of glutamate than of glutamine in substantia nigra slices whereas the reverse was the case for cerebral cortex slices. Unilateral transection of the striato-nigral pathway caused a parallel decrease in the GABA and GAD content of the substantia nigra. It also reduced the total synthesis of GABA from all labelled precursors used, namely acetate, glutamate and glucose. After incubation with [1-¹⁴C]acetate the specific activity of glutamate and aspartate, but not that of GABA, increased on the lesioned side compared with the normal side. The specific activity of glutamate, but not that of GABA or aspartate, decreased after incubation with [U-¹⁴C]glucose on the lesioned side compared with the normal side. The results could be explained by the previously proposed hypothesis concerning differential labelling of metabolic pools by the two precursors. [U-¹⁴C]Glutamate lead to increased labelling of GABA on the lesioned side relative to the normal side. Incubation of slices from substantia nigra with β-mercaptopropionic acid caused a decrease of labelling of GABA from glucose and acetate, probably as the result of GAD inhibition. The labelling pattern of the other amino acids, apart from that of glutamate which showed a decrease when synthesised from acetate, did not change appreciably.     

GABA-mediated synaptic inhibition of projection neurons in the antennal lobes of the sphinx moth,Manduca sexta

Responses of neurons in the antennal lobe (AL) of the moth Manduca sexta to stimulation of the ipsilateral antenna by odors consist of excitatory and inhibitory synaptic potentials. Stimulation of primary afferent fibers by electrical shock of the antennal nerve causes a characteristic IPSP-EPSP synaptic response in AL projection neurons. The IPSP in projection neurons reverses below the resting potential, is sensitive to changes in external and internal chloride concentration, and thus is apparently mediated by an increase in chloride conductance. The IPSP is reversibly blocked by 100 microM picrotoxin or bicuculline. Many AL neurons respond to application of GABA with a strong hyperpolarization and an inhibition of spontaneous spiking activity. GABA responses are associated with an increase in neuronal input conductance and a reversal potential below the resting potential. Application of GABA blocks inhibitory synaptic inputs and reduces or blocks excitatory inputs. EPSPs can be protected from depression by application of GABA. Muscimol, a GABA analog that mimics GABA responses at GABAA receptors but not at GABAB receptors in the vertebrate CNS, inhibits many AL neurons in the moth.     

PEG Minocycline-Liposomes Ameliorate CNS Autoimmune Disease

Background

Minocycline is an oral tetracycline derivative with good bioavailability in the central nervous system (CNS). Minocycline, a potent inhibitor of matrix metalloproteinase (MMP)-9, attenuates disease activity in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Potential adverse effects associated with long-term daily minocycline therapy in human patients are concerning. Here, we investigated whether less frequent treatment with long-circulating polyethylene glycol (PEG) minocycline liposomes are effective in treating EAE.

Findings

Performing in vitro time kinetic studies of PEG minocycline-liposomes in human peripheral blood mononuclear cells (PBMCs), we determined that PEG minocycline-liposome preparations stabilized with CaCl₂ are effective in diminishing MMP-9 activity. Intravenous injections of PEG minocycline-liposomes every five days were as effective in ameliorating clinical EAE as daily intraperitoneal injections of minocycline. Treatment of animals with PEG minocycline-liposomes significantly reduced the number of CNS-infiltrating leukocytes, and the overall expression of MMP-9 in the CNS. There was also a significant suppression of MMP-9 expression and proteolytic activity in splenocytes of treated animals, but not in CNS-infiltrating leukocytes. Thus, leukocytes gaining access to the brain and spinal cord require the same absolute amount of MMP-9 in all treatment groups, but minocycline decreases the absolute cell number.

Conclusions

Our data indicate that less frequent injections of PEG minocycline-liposomes are an effective alternative pharmacotherapy to daily minocycline injections for the treatment of CNS autoimmune diseases. Also, inhibition of MMP-9 remains a promising treatment target in EAE and patients with MS.     

Effects of Lead In Vivo and In Vitro on GABAergic Neurochemistry

Abstract: Alterations in aspects of neurotransmission utilizing -γ-aminobutyric acid (GABA) are associated with in vivo exposure of rats to lead at doses that do not produce convulsions, but sensitize animals to convulsant agents. These effects are observed regionally and include: decreased GABA levels in cerebellum; increased activity of glutamate decarboxylase (GAD) in caudate; and decreased GABA release (both resting and K⁺-stimulated) in cortex, caudate, cerebellum and substantia nigra. Sodium-dependent uptake of GABA by synaptosomes of cerebellum, substantia nigra and caudate was also affected: in these regions, affinity (K_m) was increased and maximal velocity (V_max) was reduced. Sodium-independent binding of GABA to synaptic membranes was increased in cerebellum, but was observed only when tissue was Tritonized and prepared without freezing and washing. No effects on GAD or on GABA uptake, release, or binding were observed when lead was added to brain tissue in vitro in concentrations as high as 100 μM. The results suggest that lead may produce chronic inhibition of presynaptic GABAergic function, notably in the cerebellum, which is associated with supersensitivity of postsynaptic GABA receptors. Failure of lead to affect GABAergic function in vitro may indicate that these effects are secondary to another neurotoxic action of lead in the CNS or are consequent to a nonneuronal metabolic action of lead.     

GABA(A) receptor trafficking and its role in the dynamic modulation of neuronal inhibition

GABA (gamma-aminobutyric acid) type A receptors (GABA(A)Rs) mediate most fast synaptic inhibition in the mammalian brain, controlling activity at both the network and the cellular levels. The diverse functions of GABA in the CNS are matched not just by the heterogeneity of GABA(A)Rs, but also by the complex trafficking mechanisms and protein-protein interactions that generate and maintain an appropriate receptor cell-surface localization. In this Review, we discuss recent progress in our understanding of the dynamic regulation of GABA(A)R composition, trafficking to and from the neuronal surface, and lateral movement of receptors between synaptic and extrasynaptic locations. Finally, we highlight a number of neurological disorders, including epilepsy and schizophrenia, in which alterations in GABA(A)R trafficking occur.     

Biochemical and Immunochemical Studies on the GABAergic System in the Rat Fallopian Tube and Ovary

gamma-Aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD) activities were measured in the ovary and the Fallopian tube of rats and compared with brain values. GABA levels in the Fallopian tube were about twice as high as in the brain, while in the ovary they represented only about 5% of the amino acid content of the CNS. In vitro decarboxylation of glutamate, measured via CO2 formation, occurred both in the Fallopian tube and in the ovary. These two organs contained, respectively, 10% and 1% of brain GAD activity. However, the actual formation of GABA from glutamate in a high-speed supernatant was detectable only in the Fallopian tube, where it represented about 5% of brain GAD activity. In contrast with the enzyme present in ovary, liver, anterior pituitary, and kidney, that in the Fallopian tube was quantitatively precipitated by a specific antiserum directed against rat neuronal GAD. Moreover, subcutaneous transplantation resulted in a quantitative decrease of both GABA levels and GAD activity in the Fallopian tube while no change occurred in the ovary, and vagus nerve section induced a 50% decrease of GAD activity in the Fallopian tube, although GABA levels were not significantly altered. The findings suggest an extrinsic GABAergic innervation in the rat Fallopian tube but not in the ovary.     

Selective Inhibition of Synaptosomal γ-Aminobutyric Acid Uptake by Triethyllead: Role of Energy Transduction and Chloride Ion

Triethyllead (TEL) is a CNS neurotoxin producing bizarre neurobehavioral changes. The principal objective of this study was to determine if TEL-induced defects in energy metabolism were responsible for the inhibition of synaptosomal Na+-dependent high-affinity uptake of gamma-aminobutyric acid (GABA). A dose-dependent inhibition of GABA uptake (ID50 = 10 microM TEL) was found during 30-s incubations. Uptake of glutamate was more resistant to the inhibitory effects of TEL. A TEL-induced Cl(-)-dependent synaptosomal deficit of ATP was observed. Such deficit in high-energy phosphate was time-dependent and did not occur in the absence of Cl- or as early as 30 s. Inhibition of GABA uptake, on the other hand, was a Cl(-)-independent phenomenon and was observed at as early as 30 s. TEL was not competitive with Na+ or GABA itself, as the effects of TEL were not overcome with high [Na+] or [GABA]. These results indicate that the locus of TEL inhibition of GABA uptake is not a Cl(-)-dependent event and does not involve a perturbed transmembrane electrochemical gradient, due to either an observed mitochondrial defect or an inhibition of Na+, K+-ATPase directly.     

GABA representation in hypoxia sensing: a ventilatory study in the rat

Phenibut, a nonspecific GABA derivative, is clinically used as an anxiolytic and tranquilizer in psychosomatic conditions. A GABA-ergic inhibitory pathway is engaged in respiratory control at both central and peripheral levels. However, the potential of phenibut to affect the O2-related chemoreflexes has not yet been studied. In this study we seek to determine the ventilatory responses to changes in inspired O2 content in anesthetized, spontaneously-breathing rats. Steady-state 5-min responses to 10% O2 in N2 and 100% O2 were taken in each animal before and 1 h after phenibut administration in a dose 450 mg/kg, i.p. Minute ventilation and its frequency and tidal components were obtained from the respiratory flow signal. We found that after a period of irregular extension of the respiratory cycle, phenibut stabilized resting ventilation at a lower level [20.0±3.3 (SD) vs 31.1±5.2 ml/min before phenibut; P<0.01]. The ventilatory depressant effect of phenibut was not reflected in the hypoxic response. In relative terms, this response was actually accentuated after phenibut; the peak hypoxic ventilation increased by 164% from baseline vs the 100% increase before phenibut. Regarding hyperoxia, its inhibitory effect on breathing was more expressed after phenibut. In conclusion, the GABA-mimetic phenibut did not curtail hypoxic ventilatory responsiveness, despite the presence of GABA-ergic pathways in both central and peripheral, carotid body mechanisms mediating the hypoxic chemoreflex. Thus, GABA-mediated synaptic inhibition may be elaborated in a way to sustain the primarily defensive ventilatory chemoreflex.     

Effect of activation and blockade of the GABA-ergic system of the substantia nigra in the midbrain on the realization of conditioned food reflexes in dogs

Bilateral injection of 45 mcg of GABA into substantia nigra pars compacta produced in dogs a manifested improvement of parameters of the conditioned differentiation inhibition but failed to influence the positive Pavlovian alimentary conditioned reflex. Injection of GABA synaptic antagonist--picrotoxin impaired conditioned alimentary behaviour. Numerous injections of the GABAergic pharmacological agents resulted in motor disturbance--rotatory movements--and skin trophic deviations. The data obtained and literature references give ground for discussion of the role of striato-nigral and internal GABAergic substantia nigra systems in the positive modulation of adaptive alimentary behaviour and conditioned stimuli differentiation.     

杀虫药剂的神经毒理学研究进展

大多数杀虫药剂都具有较强的神经毒性,它们对神经系统的作用靶标不同。有机磷类杀虫剂不仅抑制乙酰胆碱酯酶活性和乙酰胆碱受体功能,影响乙酰胆碱的释放,而且还具有非胆碱能毒性,有些有机磷杀虫剂还能引发迟发性神经毒性。新烟碱类杀虫剂作为烟碱型乙酰胆碱受体（nAChR）的激动剂,作用于该类受体的α亚基;它对昆虫的毒性比对哺乳动物的毒性大得多,乃是因为它对昆虫和哺乳动物nAChR的作用位点不同。拟除虫菊酯类杀虫剂主要作用于神经细胞钠通道,引起持续开放,导致传导阻滞;该类杀虫剂也可抑制钙通道。另外,这类杀虫剂还干扰谷氨酸递质和多巴胺神经元递质的释放。拟除虫菊酯类杀虫剂对昆虫的选择毒性很可能是因为昆虫神经元的钠通道结构与哺乳动物的不同。阿维菌素类杀虫剂主要作用于γ-氨基丁酸（GABA）受体,它能促进GABA的释放,增强GABA与GABA受体的结合,使氯离子内流增加,导致突触后膜超级化。由于这类杀虫剂难以穿透脊椎动物的血脑屏障而与中枢神经系统的GABA受体结合,故该类杀虫剂对脊椎动物的毒性远低于对昆虫的毒性。多杀菌素类杀虫剂可与中枢神经系统的nAChR作用,引起Ach长时间释放,此外,这类杀虫剂还可作用于昆虫的GABA受体,改变GABA门控氯通道的功能。     

Pre-steady-state and reverse transport currents in the GABA transporter GAT1

The role of internal substrates in the biophysical properties of the GABA transporter GAT1 has been investigated electrophysiologically in Xenopus oocytes heterologously expressing the cotransporter. Increments in Cl(-) and/or Na(+) concentrations caused by intracellular injections did not produce significant effects on the pre-steady-state currents, while a positive shift of the charge-voltage (Q-V) and decay time constant (τ)-voltage (τ-V) curves, together with a slowing of τ at positive potentials, was observed following treatments producing cytosolic Cl(-) depletion. Activation of the reverse transport mode by injections of GABA caused a reduction in the displaced charge. In the absence of external Cl(-), a stronger reduction in the displaced charge, together with a significant increase in reverse transport current, was observed. Therefore, complementarity between pre-steady-state and transport currents, observed in the forward mode, is preserved in the reverse mode. All these findings can be qualitatively reproduced by a kinetic scheme in which, in the forward mode, the Cl(-) ion is released first, after the inward charge movement, while the two Na(+) ions can be released only after binding of external GABA. In the reverse mode, internal GABA must bind first to the empty transporter, followed by internal Na(+) and Cl(-).     

Neurochemical effects of the endocannabinoid uptake inhibitor UCM707 in various rat brain regions

To date, UCM707, (5Z,8Z,11Z,14Z)-N-(3-furylmethyl)eicosa-5,8,11,14-tetraenamide, has the highest potency and selectivity in vitro and in vivo as inhibitor of the endocannabinoid uptake. Its biochemical, pharmacological and therapeutic properties have been intensely studied recently, but the information on its capability to modify neurotransmitter activity, which obviously underlies the above properties, is still limited. In the present study, we conducted a time-course experiment in rats aimed at examining the neurochemical effects of UCM707 in several brain regions following a subchronic administration (5 injections during 2.5 days) of this inhibitor in a dose of 5 mg/kg weight. In the hypothalamus, the administration of UCM707 did not modify GABA contents but reduced norepinephrine levels at 5 h after administration, followed by an increase at 12 h. Similar trends were observed for dopamine, whereas serotonin content remained elevated at 1 and, in particular, 5 and 12 h after administration. In the case of the basal ganglia, UCM707 reduced GABA content in the substantia nigra but only at longer (5 or 12 h) times after administration. There were no changes in serotonin content, but a marked reduction in its metabolite 5HIAA was recorded in the substantia nigra. The same pattern was found for dopamine, contents of which were not altered by UCM707 in the caudate-putamen, but its major metabolite DOPAC exhibited a marked decrease at 5 h. In the cerebellum, UCM707 reduced GABA, serotonin and norepinephrine content, but only the reduction found for norepinephrine at 5 h reached statistical significance. The administration of UCM707 did not modify the contents of these neurotransmitters in the hippocampus and the frontal cortex. Lastly, in the case of limbic structures, the administration of UCM707 markedly reduced dopamine content in the nucleus accumbens at 5 h, whereas GABA content remained unchanged in this structure and also in the ventral-tegmental area and the amygdala. By contrast, norepinephrine and serotonin content increased at 5 h in the nucleus accumbens, but not in the other two limbic structures. In summary, UCM707 administered subchronically modified the contents of serotonin, GABA, dopamine and/or norepinephrine with a pattern strongly different in each brain region. So, changes in GABA transmission (decrease) were restricted to the substantia nigra, but did not appear in other regions, whereas dopamine transmission was also altered in the caudate-putamen and the nucleus accumbens. By contrast, norepinephrine and serotonin were altered by UCM707 in the hypothalamus, cerebellum (only norepinephrine), and nucleus accumbens, exhibiting biphasic effects in some cases.