Effect of electrolytic and neurotoxic lesions of the median raphe nucleus on anxiety and stress

To study the role played by 5-HT mechanisms of the MRN, behavioural and phy siological parameters were presently measured in rats having either electro lytic or 5,7-dihydroxytryptamine (5,7-DHT) lesion of the MRN made 7 days be fore testing. Half the animals were submitted to 2-h restraint 24 h before the test. In the elevated plus-maze, the electrolytic lesion increased the percentage of open-arm entries and of time spent on open arms - an anxiolyt ic effect - in both restrained and nonrestrained rats. The neurotoxic lesio n had a similar effect, but only on restrained rats. Restraint had anxiogen ic effect. The electrolytic lesion increased transitions between the light and dark compartments and the time spent in the bright compartment of the l ight-dark box in both restrained and nonrestrained rats. The neurotoxic les ion only increased bright time in restrained rats. The incidence, number an d size of gastric ulcers were increased by either the electrolytic or the n eurotoxic lesion in both restrained and nonrestrained animals. Both types o f lesion depleted 5-HT in the hippocampus in restrained and nonrestrained r ats. Restraint increased 5-HT levels. These results implicate 5-HT mechanis ms of the median raphe nucleus in the regulation of anxiety and in the gene sis of gastric stress ulcers. (C) 2001 Elsevier Science Inc. All rights res erved.