Cell culture as models for studying neural functions.

Two cell culture systems were used for studies of neural functions in vitro. A neuronal hybrid cell line (neuroblastoma x glioma hybrid cells) and primary glial-rich cultures of newborn murine brain. The level of cyclic AMP in both systems is regulated by two groups of hormones, those that stimulate and those that inhibit formation of cyclic AMP. Among the inhibitory hormones active on the hybrid cells are opioids. Therefore the cells are being used in the elucidation of action of opioids. The list of stimulating and inhibitory hormones regulating the primary glial-rich cultures includes several peptide hormones such as the gastrointestinal peptides secretin and vasoactive intestinal peptide, the calcaemic hormones parathyrin and calcitonin, adrenocorticotropin and melanotropins, and somatostatin. Noradrenaline (via alpha- and beta-adrenergic receptors) and adenosine (via A1 and A2 receptors) inhibit and stimulate cyclic AMP synthesis in the primary glial-rich cultures. Bradykinin slowly hyperpolarizes the hybrid cells and elicits formation of cyclic GMP. Both responses desensitize rapidly. Substance P increases the permeability of hybrid cells for Na+, as measured by using 14C-guanidinium as substitute for Na+. Hybrid cells actively accumulate taurine, an amino acid that appears to fulfill important functions in the nervous system. The transport of taurine across the plasma membrane is highly specific for and strictly dependent on Na+. The pumped station hypothesis of taurine action in the nervous system views taurine gradient plus taurine carrier as a transport system for the elimination of sodium from neurons during phases of high neuronal activity.