Effects of stimulation of the locus coeruleus (LC) on evoked potential in the medial amygdala elicited by stimulation of the olfactory bulb (OB-AME potential) were studied in gallamine-immobilized rats. The amplitude of the OB-AME potential was inhibited 27.5%. by the conditioning stimulation of LC delivered 30 msec before the test stimulation. The inhibitory effect of LC was reduced by propranolol 5 mg/kg i.p., but not by phentolamine 10 mg/kg i.p․ This effect was also reduced by tetrabenazine 10 mg/kg i.p.․ Methamphetamine 5 mg/kg i.p. produced considerable potentiation of the LC inhibitory effect and a reduction of the OB-AME potential itself. These results suggest that the LC plays an inhibitory role in the electrical activity of the medial amygdala.
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