Behavioural brain research
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In the present study, the effects of post-training intra-dorsal hippocampal (intra-CA1) injection of an N-methyl-D-aspartate (NMDA) receptor agonist and competitive or noncompetitive antagonists, on memory retention of passive avoidance learning was measured in the presence and absence of physostigmine in rats. Intra-CA1 administration of lower doses of the NMDA receptor agonist NMDA (10(-5) and 10(-4) microg/rat) did not affect memory retention, although the higher doses of the drug (10(-3), 10(-2) and 10(-1) microg/rat) increased memory retention. The greatest response was obtained with 10(-1) microg/rat of the drug. ⋯ The competitive and noncompetitive NMDA receptor antagonists, DL-AP5 and MK-801, decreased the effect of physostigmine (2 microg/rat). Atropine decreased memory retention by itself and potentiated the response to DL-AP5 and MK-801. In conclusion, it seems that both NMDA and cholinergic systems not only play a part in the modulation of memory in the dorsal hippocampus of rats but also have demonstrated a complex interaction as well.
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Single pulse transcranial magnetic stimulation (TMS) was used to test the assumption that kinesthetic imagery of action is more 'motor' than visual imagery of action. We assessed corticospinal excitability during motor imagery of a thumb-palm opposition movement by recording potentials evoked by TMS from two hand muscles that would (opponens pollicis, OP, target) or would not (abductor digiti minimi, ADM, control) be activated during actual performance of the very same movement. Participants were asked to imagine the thumb-palm opposition movement while maintaining first person imagery that was either purely visual or predominately kinesthetic. ⋯ No significant effects were found in a control muscle (ADM) thus indicating that the effect was not related to spatial coding. Subjective reports obtained after the experiment indicate that the results cannot be ascribed to qualitative differences in the imagery experienced. For relatively simple motor tasks requiring no 'expertise' we found no detectable difference in the motor cortex due to imagery modality.
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Comparative Study
Evidence for the involvement of L-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effect of memantine in mice.
This study investigated the involvement of the L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the antidepressant-like effect of an acute administration of memantine in the forced swimming test (FST) in mice, since this signaling pathway is supposed to play a significant role in depression. The antidepressant-like effect of memantine (3 mg/kg, i.p.) was prevented by pretreatment with L-arginine (750 mg/kg, i.p.) or S-nitroso-N-acetyl-penicillamine (SNAP, 25 microg/site, i.c.v.), but not with d-arginine (750 mg/kg, i.p.). ⋯ Furthermore, the reduction in the immobility time elicited by memantine (3 mg/kg, i.p.) in the FST was prevented by pretreatment with sildenafil (5 mg/kg, i.p.). Taken together, the results demonstrate that memantine produced an antidepressant-like effect in the FST that seems to be mediated through an interaction with the L-arginine-NO-cGMP pathway.