The antidepressant tianeptine persistently modulates glutamate receptor currents of the hippocampal CA3 commissural associational synapse in chronically stressed rats.
Recent hypotheses on the action of antidepressants imply a modulation of excitatory amino acid transmission. Here, the effects of long-term antidepressant application in rats with the drug tianeptine were examined at hippocampal CA3 commissural associational (c/a) glutamate receptor ion channels, employing the whole-cell patch-clamp technique. The drug's impact was tested by subjecting rats to daily restraint stress for three weeks in combination with tianeptine treatment (10 mg/kg/day). Whereas stress increased the deactivation time-constant and amplitude of the N-methyl-d-aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs), it did not affect the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/kainate receptor-mediated EPSCs. Concomitant pharmacological treatment of stressed animals with tianeptine resulted in a normalized scaling of the amplitude ratio of NMDA receptor to AMPA/kainate receptor-mediated currents and prevented the stress-induced attenuation of NMDA-EPSCs deactivation. Both paired-pulse-facilitation and frequency-dependent plasticity remained unchanged. Both in control and stressed animals, however, tianeptine treatment strengthened the slope of the input-output relation of EPSCs. The latter was mimicked by exposing hippocampal slices in vitro with 10 micro m tianeptine, which rapidly increased the amplitudes of NMDA- and AMPA/kainate EPSCs. The enhancement of EPSCs could be blocked by the intracellular presence of the kinase inhibitor staurosporine (1 micro m), suggesting the involvement of a postsynaptic phosphorylation cascade rather then presynaptic release mechanisms at CA3 c/a synapses. These results indicate that tianeptine targets the phosphorylation-state of glutamate receptors at the CA3 c/a synapse. This novel signal transduction mechanism for tianeptine may provide a mechanistic resolution for its neuroprotective properties and, moreover, a pharmacological trajectory for its memory enhancing and/or antidepressant activity.
Kole
Maarten H P
MH
Division of Neurobiology, German Primate Center, Göttingen, Germany. mhpkoledpz.gwdg.de
Swan
Laura
L
Fuchs
Eberhard
E
D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000494:pharmacology*; D003345:Corticosterone / Q000097:blood; D004594:Electrophysiology; D006624:Hippocampus / Q000187:drug effects*; D008297:Male; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000187:drug effects; D017470:Receptors, Glutamate / Q000187:drug effects*; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects; D012149:Restraint, Physical; D015398:Signal Transduction; D013315:Stress, Psychological / Q000188:drug therapy / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects; D013841:Thiazepines / Q000494:pharmacology*
D000929:Antidepressive Agents, Tricyclic; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D013841:Thiazepines; C050504:tianeptine; D003345:Corticosterone