At weaning, Hooded Lister pups were singly (isolates) or group (n=5) housed (grouped). Eight weeks later, the startle and PPI response of isolates and grouped rats was investigated using conditions of fixed inter-stimulus interval (ISI) (pulse=110 dB/50 ms; prepulse=80 dB/30 ms; ISI=100 ms) or variable

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Nicotine (0.13 and 0.4 mg kg−1, s.c.) increased the ambulatory component of locomotor activity in rats previously exposed to the drug. Nicotine did not increase repeated movements reliably. An infusion of either nicotine (8 μg) or the potent nicotinic agonist cytisine (4 μg) into the ventral tegmental area of the forebrain increased ambulation but not repeated movements. An infusion of nicotine or cytisine into the nucleus accumbens, striatum, dorsal hippocampal formation or motor thalamus did not increase ambulatory or repeated movements. Mecamylamine (0.1–1.0 mg kg−1, s.c.) blocked increases in locomotor activity produced by an infusion of nicotine or cytisine into the ventral tegmental area. The locomotor activity produced by systemically administered nicotine may be mediated, in part, through nicotinic receptors located in the ventral tegmental area of the mesolimbic dopamine system.

Atypical neuroleptics produce fewer extrapyramidal side-e ects (EPS) than typical neuroleptics. The pharmacological pro®le of atypical neuroleptics is that they have equivalent or higher antagonist a nity for 5-HT 2 than for dopamine D 2 receptors. Our aim was to identify which 5-HT 2 receptor contributed to the atypical pro®le. Catalepsy was de®ned as rats remaining immobile over a horizontal metal bar for at least 30 s, 90 min after dosing.

Behavioural effects of d- and l-nicotine, d- and l-nornicotine and l-cotinine were studied in two paradigms. In experiment 1, rats responded under a multiple fixed-interval (FI) 5 min, fixed-ratio (FR) 20 schedule of food presentation. Aside from differences in potency and time course, l-nicotine and the stereoisomers of nornicotine produced qualitatively similar effects on rates of responding. With increasing doses of drugs, FI response rates first increased and then decreased, while FR response rates only decreased. In contrast, d-nicotine did not significantly increase FI response rates at lower doses, and only decreased FI and FR response rates at higher doses. At doses up to 100 mg/kg, cotinine produced only dose-dependent increases in FI response rates and had no effect on FR response rates. Rate-increasing effects of cotinine were not blocked by mecamylamine. In experiment 2, rats were trained to discriminate between l-nicotine (0.1 mg/kg SC) and saline (0.1 ml/kg SC) in a two-bar, operant conditioning procedure under a tandem variable-interval (VI) 1 min, FR 10 schedule of food presentation. Full generalization was obtained to d-nicotine and to l- and d-nornicotine. Generalization to cotinine occurred only with large doses that contained significant amounts of nicotine present as an impurity. There was no generalization to non-nicotinic drugs (morphine and clenbuterol), even at doses that reduced response rates.(ABSTRACT TRUNCATED AT 250 WORDS)