Tiagabine, a specific gamma-aminobutyric acid transporter-1 inhibitor, in the treatment of psychosis

Anticonvulsant and anxiolytic activity of FrPbAII, a novel GABA uptake inhibitor isolated from the venom of the social spider Parawixia bistriata (Araneidae: Araneae)

This study was aimed at determining the effects of FrPbAII (174 Da), a novel isolated component from Parawixia bistriata spider venom, in the CNS of Wistar rats. Considering that FrPbAII inhibits the high affinity GABAergic uptake in a dose-dependent manner, its anxiolytic and anticonvulsant effects were analyzed in well-established animal models. Injection of FrPbAII in the rat hippocampus induced a marked anxiolytic effect, increasing the occupancy in the open arms of the elevated plus maze (EC(50)=0.09 microg/microl) and increasing the time spent in the lit area of the light-dark apparatus (EC(50)=0.03 microg/microl). Anxiolytic effects were also observed considering the number of entries in the open arms of the EPM and in the lit compartment of the light-dark box. Interestingly, when microinjected bilaterally in the SNPr of freely moving rats, FrPbAII (0.6 microg/microl) effectively prevented seizures induced by the unilateral GABAergic blockade of Area tempestas (bicuculline, 0.75 microg/microl). This anticonvulsant effect was similar to that evoked by muscimol (0.1 microg/microl) and baclofen (0.6 microg/microl), but differed from that of the specific GAT1 inhibitor, nipecotic acid (0.7 microg/microl). This difference could be accounted either for the parallel action of FrPbAII over glycinergic transporters or to an inspecific activity on GABAergic transporters. Data from the present investigation might be pointing to a novel compound with interesting and yet unexplored pharmacological potential.

GABA pharmacology—what prospects for the future?

Following the recognition of GABA as an inhibitory neurotransmitter, the discovery of high affinity GABA uptake, and the characterisation of GABA receptors great progress has been made in developing GABA pharmacology. Tiagabide, the first marketed GABA uptake inhibitor may be followed by new and more selective uptake inhibitors. Knowledge of the molecular pharmacology of GABA-A receptors, both synaptic and non-synaptic, may lead to improved anti-anxiety/anticonvulsant agents devoid of the sedative and dependence liabilities of earlier compounds and new hypnotics. Gaboxadol (THIP) is an example of a novel hypnotic that acts on GABA-A receptors by a non-benzodiazepine mechanism. Exploiting neurosteroid interactions with GABAergic mechanisms also holds much future promise.