Picrotoxin microinjections into the brain: a model of abrupt withdrawal 'jumping' behaviour in rats not exposed to any opiate?

Picrotoxin microinjections (0.5 microliter per side) given into the locus coeruleus, superior colliculus and central grey of freely moving Wistar rats produced an accelerating galloping locomotion, most often forwards but also upwards. Systemic administration of apomorphine (0.7-2.0 mg/kg s.c.) given 20 min earlier increased the number of rats that displayed the so-called 'running and jumping' behaviour after picrotoxin (0.1-0.2 microgram). The dose-effect curve, however, varied according to the brain structure selected. Systemic administration of morphine (1.0-10.0 mg/kg i.p.) was found to reduce the occurrence of running and jumping behaviour when it was elicited via the locus coeruleus, but not the superior colliculus and central grey. It is suggested that the running and jumping behaviour which is elicited via the locus coeruleus might be a suitable model of a partial morphine abstinence syndrome, i.e. withdrawal jumping, in experimental animals not exposed to any opiate. The superior colliculus and central grey appear to be involved in mediating an opiate-unrelated phenomenon of 'withdrawal' jumping in rats not exposed to any opiate.