[D-TRP11]-neurotensin, unlike alpha-flupenthixol, may not block amphetamine-induced hyperactivity in rats

Recent reports have suggested that neurotensin (NT) and some of its analogues resemble neuroleptics, for example alpha-flupenthixol (FLU), in their ability to suppress locomotor activity. The results obtained support this conclusion, but only if total photocell counts (the "traditional" index) are considered. An improved method of measuring activity--where subjects have to interrupt photocell beams in sequence before a ("conditional") count is registered--suggested, in direct contrast to the total counts index, that the stable analogue of neurotensin [D-Trp11]-neurotensin (DTNT) increased activity slightly (Sahgal and Keith, 1986). The present report is on the effects of DTNT (0-8 microgram/rat, i.c.v.) and FLU (0-1 mg/kg, i.p.) on hyperactivity induced by D-amphetamine (1.5 mg/kg, i.p.). The usual total counts index of activity suggested that FLU and DTNT blocked the increase. On the other hand, conditional count data suggested that only FLU was effective. Both measures indicated that FLU and amphetamine, administered separately, suppressed and enhanced activity, respectively. In contrast, DTNT at these doses had no significant effect on the conditional counts but markedly suppressed total counts. Subsequent observation of DTNT-treated rats placed in small open fields, suggested that the peptide induced marked circling (ambulatory) behaviour, at the cost of other behavioural categories, especially rearing and grooming. It is argued that (a) DTNT may not resemble neuroleptics in its effects on motor behaviour and (b) conditional activity counts, and also measures relating to brief interruptions of photocell beams, can provide useful additional information concerning motor activity.