Abstract
The effects of this drug on brain electrophysioloy (Bradley and Elkes,1953) and on animal behavior (Bignami, 1966) have been likened to those of amphetamine. There are, however, several important differences. Like those of amphetamine, nicotine, and eserine, the effects of LSD vary with the dose. For the salve of the present discussion, and both for electrophysiological and behavioral experiments' the limit between "low" and high,, doses may be considered to be around 0.1 mg/g. 'Low doses of LSD stimulate the reticular formation, cause arousal (Bradley and Elkes, 1953;Brawley and Duffield, 1972).and enhance both the amplitude and the duration of hippocampal theta wave trains (Adey er al., 1962; Radulovacki and Adey, 1965). At high doses of LSD theta becomes depressed(Adey em al., 1962) and may be eventually replaced by fast activity At low doses LSD enhances hippocampal evolved responses to afferent stimulation (Revzin and Armstrong, 1966), and at high doses it depresses these responses This stimulative effect at low doses end depressant effect a. high doses of LSD is also seen on several other than hippocampal brain electrophysiological variables (Brawley and Duffield, 1972). Like amphetamine (Graham et al.,1974), LSD lowers susceptibility to audiogenic seizures (Boggan, 1973). LSD is a powerful antagonist of serotonin on smooth muscles (Jarvik, 1970). The hippocampus is fairly rich in serotonin, and this substance has effects both on hippocampal unit activity (it depresses, Biseoe and Straughan, 1966) and on hippocampal seizure threshold (it lowers it, lasello and Ivlarichich, 1973). As far as I know, LSD has iiot been tried as an antagonist in these two circumstances; but anyway it appears to be doubtful that the central actions of LSD in general can be explained by antagonism to serotonin (Jarvik, 1970): other anti-serotonin agents like BOL or methysergide do not share the central effects of LSD. Methysergide antagonizes the lowering of hippocampal seizure threshold caused by serotonin, although probably not in a competitive fashion (Nasello and Marichich, 1973). High doses Qf LSD such as those which depress electrical activity (and learning, ) cause an increase of brain serotonin content, by an unknown mechanism (G iannan and Freedman, 1965). Low doses of LSO enh.,nce learning of a variety of avoidance tasks: one-way active(Taeschler e to/., 1960),continuous(Janard, 1963),and two-way active (Bignanii at al., 19G:j; Binami, 1972). It also improves discrimination learning of various types
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