Association between learning and cortical catecholamines in non-drug-treated rats

Seventeen male Sprague-Dawley rats were trained to eight to nine correct responses on a delayed spatial alternation test performed on alternate days in a T-maze. Locomotor activity in an observation box was scored on 2 consecutive days. The animals were killed 2 weeks after the end of behavioural testing and dopamine (DA), noradrenaline (NA), 5-hydroxytryptamine (5HT), the DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and the 5HT metabolite, 5-hydroxyindoleacetic acid (5HIAA) determined in cortex, hippocampus, striatum and hypothalamus. Cortical concentrations of both DA and NA correlated negatively and significantly with the number of errors made in learning the alternation task, though the latter correlation was less striking and became negligible after the correlation between DA and NA was partialled out. Concentrations of DA and NA in the other regions did not correlate significantly with errors. None of the other neurochemical variables correlated significantly with either errors or locomotor activity, except for hypothalamic HVA concentration which showed a marginally significant correlation with locomotor activity. The above results, together with effects of brain lesions reported by other authors, strongly indicate that cortical catecholamines facilitate learning in the normal non-drug-treated rat.