The role of noradrenaline in learned behaviors: studies using DSP4.

Abstract

DSP4 (N‐2‐chloroethyl‐N‐ethyl‐2‐bromobenzylamine) is a novel noradrenaline (NA) neurotoxin sufficiently selective, following systemic administration, to be a pharmacological tool of much potential; this possibility has warranted the extensive use of DSP4 to study the role of noradrenaline in learned behaviors. Thus, after DSP4 treatment (50 mg/kg) a very robust two‐way active avoidance impairment is incurred and this deficit remained over a wide range of stimulus conditions and parameters. On the other hand, the acquisition of relatively simple tasks such as one‐way active avoidance, fear conditioning, step‐down passive avoidance and taste‐aversion conditioning, was only slightly affected or not affected at all. DSP4 administration caused a retardation of the rate of acquisition of a “right‐turn” running response for food reward in a modified T‐maze, and an attenuation of the exteroceptive context effect in taste‐aversion conditioning and extinction. In spite of a few similar results, NA‐depletions following DSP4 generally do not produce the same behavioral effects as the 6‐Hydroxydopamine lesions but are more akin to the locus coeruleus lesion. An hypothesis of the role of central NA, based mainly upon the shuttle box procedure, incorporates a function in establishing the Signal‐Response association, in adapting to situations that require a correct response to stress and in maintaining an adequate span of attention to the range of environmental events presented in any given learning situation.