Response of nigral dopamine neurons to acute and prolonged morphine treatment

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Abstract
The effects of morphine and acute exposure to cold on nigral dopamine (DA) neurons and possible interactions with cholinergic systems were studied by histochemical microfluorimetry in normal and partially morphinetolerant mice. Morphine (40 mg/kg), cold (4°C), nicotine (1 mg/kg) and physiostigmine (0.25 mg/kg) elicited a rapid rise and subsequent decrease in the fluorescence intensity of DA nerve cells with certain differences in time course. Fastest changes with a peak at 5 min, a marked subsequent drop below control levels and return towards control intensity after 40 min were seen after physostigmine. Antagonisms between various treatments were noted. DA responses correlated well with the time course of behavioural effects, especially after physostigmine.