Electrophysiologic Characteristics of Basal Forebrain Neurons in vitro

Abstract

The medial septum (MS) and nucleus of the diagonal band (nDB) are nuclei of the basal forebrain that contain both cholinergic and non-cholinergic neurons. Since the work of Green and Arduini (1954), it has been established that the MS/nDB form a crucial link between the brainstem reticular formation and the hippocampus. In order to understand the function of the basal forebrain component of this pathway, much research has been directed toward categorizing MS/nDB cell types physiologically, primarily with extracellular unit recording techniques in vivo. Experiments in anesthetized or curarized animals have distinguished three types of MS/nDB neurons based on spontaneous firing patterns (Apostol and Creutzfeldt, 1974; Lamour et al., 1984; Segal, 1974; Vinogradova et al., 1987). One neuron type fires in an irregular, single spike pattern. A second type of neuron fires in bursts of 2 to 10 spikes and the burst frequency is synchronized with hippocampal slow rhythmic activity (theta rhythms). These neurons may switch under certain conditions between irregular and burst-type firing patterns. In addition, antidromically activated septo-hippocampal neurons are more likely to be bursting neurons (50%) than are unidentified MS/nDB neurons (30%; Lamour et al., 1984). A third type of neuron reported by a few laboratories has a pacemaker-like firing pattern that does not convert to other patterns (Apostol and Creutzfeldt, 1974; Lamour et al., 1984; Vinogradova et al., 1987).