effects of lidocaine reversible inactivation of the dorsal raphe nucleus on passive avoidance learning in rats

Introduction: The role of serotonergic fibers in avoidance learning is controversial. Involvement of the dorsal raphe nucleus [DRN], the main source of hippocampal projecting serotonergic fibers in acquisition, consolidation and retrieval of passive avoidance [PA] learning, was investigated by functional suppression of this area. Materials and Methods: DRN functional inactivation was done by lidocaine [0.5µl, 2%] injection into the DRN, 5 min before training [n=10]; and 5 [n=9], 90 [n=10] and 360 min [n=9] after acquisition trial. In the last experiment, lidocaine was injected into the DRN 5 min before the retrieval test, which was 48 h after the training [n=10]. Results: Our results showed that PA learning was not impaired by DRN inactivation 5 min before training nor 5 and 360 min after training. Lidocaine injected 90 min after the acquisition trial significantly reduced avoidance of the dark compartment [P<0.001]. Intra-DRN injection of lidocaine before retrieval significantly increased PA retention [P<0.001]. Therefore, it seems that DRN has opposite effects on consolidation and retrieval of passive avoidance learning, but it has no effect on PA acquisition. Discussion: It is suggested that functional ablation of DRN may disrupt integrity of subcortical circuits participating in PA consolidation, but DRN inactivation by increasing brain awareness may affect PA retrieval in rats

Vitamin E derivative alpha-tocotrienol failed to show neuroprotective effects after embolic stroke in rats

Previous studies have demonstrated that pretreatment with alpha-tocotrienol [a-TCT] can reduce ischemic damage in mice following middle cerebral artery [MCA] occlusion. It is also reported to decrease stroke dependent brain tissue damage in 12-Lox-deficient mice and spontaneously hypertensive rats. In the present study, the neuroprotective effects of a-TCT and rosiglitazone [RGZ] at 3 hr after cerebral ischemia were investigated. Stroke was induced by embolizing a preformed clot into the MCA. Rats were assigned to vehicle, a-TCT [1 or 10 mg/kg], RGZ and sham-operation. Compared to the control group, only RGZ decreased infarct volume [P<0.05], neurological deficits [P<0.05] and sensory impairments [P<0.01] but low and high doses of a-TCT did not show any significant neuroprotective effect. Our data showed that a-TCT was not neuroprotective at 3 hr after the embolic model of stroke. Further studies should be undertaken to clarify the neuroprotective effects of a-TCT after stroke

Reversible inactivation and excitation of nucleus raphe magnus can modulate tail blood flow of male wistar rats in response to hypothermia

The nucleus raphe magnus [NRM] is involved in thermoregulatory processing. There is a correlation between changes in the firing rates of the cells in the NRM and the application of the peripheral thermal stimulus. We examined the effect of reversible inactivation and excitation of NRM on mechanisms involved in tail blood flow [TBF] regulation in hypothermia. Hypothermia was induced in Male Wistar rats and cannula was implanted above the NRM. To evaluate the effect of nucleus inactivation on TBF, the amount of TBF was measured by Laser Doppler in hypothermic rats, before and after lidocaine microinjection into NRM. TBF was also measured after glutamate microinjection to assess the effect of nucleus excitation in hypothermic rats. Results indicated that after dropping TBF by hypothermia, microinjection of lidocaine into NRM significantly decreased TBF from 54.43 +/- 5.7 to 46.81 +/- 3.4, whereas glutamate microinjection caused a significant increase from 44.194 +/- 0.6 to 98 +/- 10.0 Conclusion: These data suggest that NRM have thermoregulatory effect in response to hypothermia