Cholinergic function in cultures of mouse spinal cord neurons

Cholinergic synapses formed in cultures of fetal mouse spinal cord (SC) and superior cervical ganglion (SCG) were studied using intracellular and extracellular stimulation and recording as well as immunohistochemical staining for choline acetyltransferase (ChAT). Dissociated SC neurons and SC explants exhibited cholinergic terminals on SCG and SC neurons as demonstrated by ChAT immunoreactivity. Intracellular recordings showed that cholinergic inputs to SCG neurons were relatively common and that these synaptic inputs were blocked by the nicotinic acetylcholine (ACh) receptor blocker, tubocurarine. A comparison of three preparations indicated that the incidence of cholinergic activity recorded in SCG neurons was significantly higher in co-cultures of SCG with spinal cord ventral horn (VH) neurons grown on a substrate of non-neuronal cells from cerebral cortex, than in co-cultures with VH alone or with SC and dorsal root ganglion cells. Consistency between cholinergic physiology and staining for ChAT-positive terminals on SCG neuronal somata was obtained in cultures of SC explants grown with dissociated SCG. Application of acetylcholine, muscarine, and/or vasoactive intestinal polypeptide (VIP) produced slow excitation of SC neurons. Fast excitatory cholinergic interactions between SC neurons were not observed. Excitatory synaptic interactions between SC neurons were augmented by ACh or muscarine, while inhibitory synaptic interactions were diminished. Both types of synaptic modulation probably were produced by a presynaptic mechanism. Acetylcholine or muscarine affected synaptic interactions between SC neurons in only one-third of the synaptic connections tested, suggesting that the incidence of presynaptically cholinoceptive SC neurons is low in dissociated cell cultures. The experimental results show that a culture system incorporating dissociated fetal mouse SC neurons or explants of SC with sympathetic ganglion neurons expresses both nicotinic and muscarinic cholinergic function.