Mice with genetically altered GABA transporter subtype I (GAT1) expression show altered behavioral responses to ethanol.

It is widely accepted that the GABAergic system plays an important role in the action of ethanol in vivo. GABA transporter subtype 1 (GAT1) constructs high affinity reuptake sites in the CNS and regulates GABAergic transmissions. In this study, mice lacking the GAT1 were developed by homologous recombination. Both hetero- and homozygous GAT1 mutant mice were tested for ethanol, saccharin or quinine consumption, ethanol-conditioned place preference, ethanol-conditioned taste aversion, ethanol-simulated motor activity, and ethanol-induced sedation/hypnosis. The GAT1(-/-) mice showed decreased ethanol aversion and ethanol reward, and insensitivity to both the sedative/hypnotic and the motor stimulant effects of ethanol, along with increased avoidance of quinine preference and consumption. GAT1(+/-) mice showed significantly increased consumption of ethanol and saccharin, however, enhanced the rewarding and preference effect of ethanol, increased avoidance of quinine, and higher sensitivity to the motor stimulant effect of ethanol. These results demonstrate that GAT1, perhaps in a bi-directional way, modulates some behavioral effects of ethanol. The GAT1 mutant mice provided us a very useful model to investigate the mechanisms of ethanol action in vivo.

Cognitive impairment in mice over-expressing gamma-aminobutyric acid transporter 1 (GAT1).

There is increasing evidence that GABAergic system plays an important role in the neural control of learning and memory processes. GAT1 over-expressing mice (NA) were generated, in which GAT1 is under the control of a neuron-specific enolase (NSE) promoter, to investigate effects of GABA transporter on cognitive function. Our results revealed that NA mice displayed cognitive deterioration in associative learning ability and new object recognition retention, compared with the wild-type littermates (WT2). However, the impaired cognitive function of transgenic mice could be rescued after chronic administration of GAT1 selective inhibitor for 6 days. In addition, there was no change of the expression of NMDA receptors in NA mice. Taken together, we show a potentially important role for GAT1 in the neural control of cognitive processes, and indicate great potential for GAT1 as a clinical target of cognitive disorders.

Decrease of morphine-induced reward effects and withdrawal symptoms in mice overexpressing gamma-aminobutyric acid transporter I.

Morphine addiction has been shown to result from neural adaptations produced by repeated drug exposure, but the mechanism is still unclear. In the present study, we found that gamma-aminobutyric acid (GABA) uptake was increased in mouse brain 120 min after, but not 20 min after, morphine (10 mg/kg, s.c.) injection. We generated GABA transporter I (GAT1)-overexpressing mice to investigate whether the GABAergic system and GABA transporter are involved in morphine-induced reward effects and withdrawal symptoms. Our results revealed that the rewarding effects induced by morphine were significantly decreased in GAT1-overexpressing mice as measured by the conditioned place preference (CPP) paradigm. Moreover, both somatic and vegetative signs of naloxone-induced morphine withdrawal symptoms were substantially reduced in GAT1-overexpressing mice. In addition, the decreased morphine rewarding in transgenic mice could be recovered when mice were coinjected with NO-711 (a GAT1 selective inhibitor) in the CPP paradigm. These findings suggest that the GABAergic system plays an important role in morphine addiction and point to the possibility of developing drugs that target GAT1 and extend the clinical application of opiates.

Increase in drug-induced seizure susceptibility of transgenic mice overexpressing GABA transporter-1.

AIM: The changes of seizure susceptibility of transgenic mice overexpressing GABA transporter-1 (GAT-1) were studied to clarify the possible role of GABAergic transmission in epileptogenesis. METHODS: Seizures were induced by intraperitoneal administration of pentylenetetrazol (PTZ), picrotoxin (PIC), or kainic acid (KA) respectively. The anticonvulsant effect of ethyl nipecotate was tested by its intraperitoneal injection 15 min before the administration of the epileptogenic agents. RESULTS: The percentages of occurrence of clonic seizures induced by PTZ 45 mg/kg, PIC 2.5 mg/kg, or KA 20 mg/kg in GAT-1 transgenic mice were 88.9 %, 100 %, and 83.3 % respectively, whereas those in control C57BL/6J mice were 42.9 %, 57.1 %, and 33.3 %. The percentages of occurrence of tonic seizures induced by PTZ 45 mg/kg, PIC 2.5 mg/kg, or KA 20 mg/kg in transgenic mice were 88.9 %, 100 %, and 83.3 % respectively, and whereas those in control mice were 28.6 %, 42.9 %, and 16.7 %. The latencies of both clonic and tonic seizures onset in transgenic mice were markedly shortened compared with those in control animals. The results indicated that GAT-1 transgenic mice showed increased susceptibility to seizures induced by the anti-GABAergic convulsive drugs (PTZ, PIC), as well as glutamic receptor agonist (KA). Ethyl nipecotate, inhibitor of GAT-1, inhibited PTZ-induced seizures in both GAT-1 transgenic and C57BL/6J mice. The incidence of seizures was decreased after the application of ethyl nipecotate, and the latencies to the onset of clonic or tonic seizures were also prolonged. CONCLUSION: The increase in seizure susceptibility of transgenic mice over-expressing GAT-1 is an evidence for involvement of GABAergic transmission in epileptogenesis, and this transgenic mouse might be a useful animal model for study on the role of GABAergic transmission in epileptogenesis.

Hyperalgesic effects of gamma-aminobutyric acid transporter I in mice.

The present study focused on the involvement of gamma-aminobutyric acid transporter I (GAT1) in pain. We found that GABA uptake was increased in mouse spinal cord at 20 min and 120 min after formalin injection and in mouse brain at 120 min, but not 20 min, after formalin injection. In addition, the antinociceptive effects of GAT1-selective inhibitors were examined using assays of thermal (tail-flick) and chemical (formalin and acetic acid) nociception in C57BL/6J mice. The GAT1-selective inhibitors, ethyl nipecotate and NO-711, exhibited significant antinociceptive effects in these nociceptive assays. To study further the effects of GAT1 on pain, we used two kinds of GAT1-overexpressing transgenic mice (under the control of a CMV promoter or a NSE promoter) to examine the nociceptive responses in these mice. In the thermal, formalin, and acetic acid assays, both kinds of transgenic mice displayed significant hyperalgesia after nociceptive stimuli. In addition, the micro opioid receptor antagonist naloxone had no influence on nociceptive responses in wild-type and transgenic mice. The results indicate that GAT1 is involved in the regulation of pain processes, and point to the possibility of developing analgesic drugs that target GAT1 other than opioid receptors.