Synapse formation and spontaneous activity in rat brainstem neurons in primary culture

The correlation between synaptogenesis and onset of spontaneous action pote ntials was assessed in rat brainstem cells up to 29 days in primary culture . Cells exhibited different stages of maturation followed by electron micro scopy and patch clamp recordings. Terminal boutons with no preferential ori entation of presynaptic vesicles appeared after 2 days in culture. After 5 days, preferential orientation of presynaptic vesicles and thickening of po stsynaptic membranes were observed. The spontaneous discharge of action pot entials, single or bursting, was observed after 7 days in vitro. This was f ollowed by the expression of a 128-pS K+ channel starting at 13 days in vit ro. A 69-pS K+ channel was also present throughout the duration of the cult ures. These results suggest that spontaneous discharge of action potentials does not occur before synapses are formed and K+ channel types develop dif ferentially in brainstem neurons in vitro. (C) 1999 Elsevier Science B.V. A ll rights reserved.