Conditioned-reflex learning of normal juvenile and adult rats exposed to action of substance P and of an SP analogue.

The actions of both Substance P, a potential neurotransmitter or modulator and of a shortened analogue on learning and memorizing processes are reported in this paper. Sixty male rats, aged 22, 14, and 10 weeks, were exposed to Substance P (Arg-Pro-Gln-Gln-Phe-Gly-Leu-MetNH2) and to a shortened hexapeptide analogue (Lys-Phe-Ile-Gly-Leu-MetNH2), doses being 250 microgram/kg and 500 microgram/kg, to test their action upon learning and memorizing processes, such as acquisition, retention, and ecphoration, by means of a conditioned-reflex locomotor defense method. Response time of all three age groups as well their retention and ecphoration were normal under the impact of hexapeptide. The effects of Substance P were decline of retention in juvenile animals (10 weeks of age) and coupling between the processes of central-nervous afference synthesis, on the one hand, and the efference integral related to motoricity, on the other, in both juvenile and adult animals. A retention test was conducted and showed that discontinuation of application of either peptide over 4 d was followed by complete inhibition of ecphoration. Learning and memorising processes were restorable by reapplication of the peptides. These findings were defined as "state-dependent learning". Only slight variation under the impact of both Substance P and the analogue was recordable by non-invasive measurement of systolic blood pressure.