Immobilization stress and direct glucocorticoid effects on rat septohippocampus

The rat septohippocampal cholinergic system to a large extent regulates the adaptive physiological and behavioral response to stress. The mesoseptal dopaminergic (DA) system, one of the converging inputs to the lateral septum, exerts a tonic inhibitory action on the septohippocampal cholinergic neurons. High concentrations of pituitary-adrenocortical hormones in plasma may activate the septohippocampal cholinergic system. We have sought to determine whether this mode of activation may be directly initiated by hormonal action on the cholinergic terminals, or indirectly induced through an alteration in the DA septal inputs. The results indicate that stress initiates rapid and transient changes in DA uptake by septal DA terminals, changes which probably contribute to the initial transient activation of the hippocampal cholinergic system. While the effects of glucocorticoids, observed in vitro, may mimic the enhanced ACh release in stress, they do not mimic the increased choline uptake. Nevertheless, high glucocorticoid concentrations may act directly on septal dopaminergic terminals to reduce their DA uptake capacity. These results imply that the septohippocampal cholinergic activity represents an integrative pathway for neuronal and hormonal signals of stress.