The mammillary body, a potential site of action of neurotensin in passive avoidance behavior in rats.

Sites of action of neurotensin (NT) in passive avoidance behavior were investigated by intracerebral injection in male Wistar rats, which were trained in a step-down type one-trial learning passive avoidance test. An unavoidable foot shock was delivered through the grid floor of a dark compartment (learning trial) and passive avoidance latencies were tested 24 h after the learning trial (retention test). NT at small doses, 0.2 and 0.5 microgram, injected into the mammillary body increased the latency of the retention test in passive avoidance behavior, without affecting locomotor activity or rectal temperature. However, NT injected into the central amygdaloid nucleus did not influence either passive avoidance behavior or rectal temperature. When injected into the preoptic area, the nucleus accumbens or the substantia nigra, NT did not alter the passive avoidance behavior either. Responsiveness to electric foot shock was reduced after injection of NT into the mammillary body. Thus, the change in the responsiveness to electric foot shock did not comply with that in the passive avoidance behavior following intramammillary body injection of NT. These results suggest that the mammillary body is a site of action of NT in passive avoidance behavior and may play an important role in learning the behavior.