Unraveling of important neurobiological mechanisms by the use of pure, fully differentiated neurons obtained from adult animals.

An important, and often overlooked, problem in the neurochemical approach to neurobiological problems is that analysis of tissue involves almost always a heterogeneous population of cells (neurons, glia and other types of tissue cells). The use of cell cultures has obvious limitations such as that they derive from embryonic or immediately postnatal animals; in addition, the cell culture conditions most certainly are quite different from the real tissue environment for the nerve cells. We underline here an alternative strategy, which is not new, but which, in our view, has already given formidable contributions to neurobiological studies and still is giving results of great importance. This is the technique proposed and used since the late fifties and early sixties by the senior author (H. Hydén). The method involves the isolation of the big vestibular neurons from the adult rabbit vestibular nucleus. The neurons, fully differentiated and performing a precisely defined function, are obtained rapidly and completely free from surrounding glial cells. The separate microbiochemical study of these cells and their surrounding glia has yielded already in 1962, the information that modifications in gene expression are associated with plastic modifications of the function of the relevant neurons, which take place in the behavioral event of learning. Another important concept was formulated in the same time period following determination of the activities of energy metabolism related enzymes separately in vestibular neurons and their glia under vestibular stimulation. This is the concept that, under increased functional activity glia increases its anaerobic metabolism and passes then on the resulting metabolites to the neurons for aerobic metabolism. Both these concepts (RNA and memory; metabolic cooperation between glia and neurons) are nowadays widely accepted. In addition, this approach with pure big nerve cells has allowed in recent years the discovery of a novel mechanism for chloride extrusion in these cells. This mechanism utilizes structures similar to GABA activated chloride channels in cyclic modifications resulting in the final extrusion of chloride ions. The energy for the process is provided by a protein phosphorylation step. Future approaches are warranted such as the possibility of recognizing by RT-PCR specific neuronal mRNAs and their modification in expression in relation to function and plastic modifications (learning). Another possible interesting application appears to be the recognition of the mRNAs for GABA(A) receptor subunits expressed here in these neurons in relation to the physiological and pharmacological characteristics of these native neuronal GABA(A) receptors.