Recovery of function from septal damage and the growth of sympathohippocampal fibers: a quantitative study in the rat

Abstract

A lesion to the septal area in rats results in a syndrome of behavioral changes, some of which are transient. The same lesion also results in a growth of sympathetic nerve fibers into the hippocampal formation. Although the two events--behavioral and neural--covary in time, their interrelationships have not been quantified. The purpose of this study was to quantify these interrelationships. Two primary objectives were: (1) to develop quantitative measures of catecholamine fluorescence; and (2) to describe the correlations between the behavioral changes and the indices of catecholamine changes. Glyoxylic acid histofluorescence procedures were used to induce fluorescence in the catecholamine containing sympathetic nerve endings. Catecholamine fibers of central origin are also sensitive to this procedure, so that one subgoal was to discriminate quantitatively between fluorescent fibers of central and sympathetic origins. Two indices of fluorescent fibers were identified, one relating to the intensity of fibers and one relating to the areal density of fibers in a field of fluorescence. Densities in several subareas of the hippocampus were shown to be colinear with time. Interestingly, density in pineal and intensity in habenula--two areas receiving a normal complement of sympathetic fibers--were also shown to increase linearly over time. Indices of fluorescence intensity in hippocampus were shown to correlate most highly with behavioral changes following the septal lesion. These results were discussed specifically relating behavioral activity and reactivity to hippocampal catecholamine fluctuations, and generally relating lesion-induced neural sprouting to recovery of function after brain damage.