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Male Wistar rats were injected intraventricularly with two doses of 250 μg of 6-hydroxydopamine (6-OHDA) at a 48 hr interval. Seven days after the second injection, 50 μg of norepinephrine (NE) or 100 μg of dibutyryl cyclic AMP (DCAMP) were injected intraventricularly. There were no differences in gross behavior but an increase in irritability was observed in rats treated with 6-OHDA compared with controls. NE increased locomotor activity and irritability of animals. Chemical sympathectomy intensified locomotor excitation and irratibility caused by NE. DCAMO caused an increase of locomotor activity, irritability and convulsions 30 min after injection. These behavioral phenomena were intensified in animals treated with 6-OHDA. It is suggested that 6-OHDA sensitizes the central nervous system to action of NE and DCAMP.

It was shown that dibutyryl cyclic AMP (DAMP) injected intraventricularly in doses of 100–200 μg in rats causes the increase of locomotor and exploratory activity and convulsions, depending on the dose. DAMP increased excitatory behavioural effects of noradrenaline (NA) injected intraventricularly in doses of 10 or 50 μg. NA in a dose of 200 μg abolished convulsions evoked by DAMP. Cyclic AMP (cAMP) injected intraventricularly in doses of 100–400 μg had no effect on the rat's behaviour. Pretreatment of rats with dimethylsulphoxide and with theophylline caused in some animals behavioural phenomena after injection of cAMP, similar to the behavioural symptoms evoked by DAMP.

1 A simple method of injecting soluble substances into the lateral ventricle of the brain of the conscious mouse is described. 2 The effect of various doses of noradrenaline, dopamine, acetylcholine, 5-hydroxytryptamine given into the right lateral brain ventricle were tested on locomotor and exploratory activities of mice. 3 Noradrenaline in a dose of 0.1 mug increased locomotor activity. This effect was prevented by phenoxybensamine but not by propranolol. 4 Higher doses of noradrenaline (1 or 10 mug) decreased locomotor and exploratory activities. Propranolol but not phenoxybenzamine abolished these effects. 5 Dopamine (0.1 or 1 mug) increased locomotor activity. The higher doses also induced tremor. 6 The highese dose of dopamine tested (10 mug) elicited stereotypical behaviour. 7 All the behavioural phenomena induced by 0.1 mug and 10 mug of dopamine were blocked by pimozide. 8 Acetylcholine (1 and 10 mug) and 5-hydroxytryptamine (1 mug) inhibited locomotor and exploratory activity. 9 The effects of 1 and 10 mug of acetylcholine were abolished by atropine (5 mg/kg i.p. Methysergide (5 mg/kg i.p.) had no influence on the effects of 5-hydroxytryptamine (1 mug).