Isolation and culture of rat sensory neurons having distinct sensory modalities

We have recently published papers in which sensory neurons that innervate either the tooth pulp or masseter muscle spindles were labelled in vivo and later identified and studied in primary tissue culture (Taddese et al., 1995; Cook et al., 1997). Here, we provide detailed descriptions of cell labelling and tissue culture methods that we used. The purpose of the preparations is to compare nociceptive and non-nociceptive sensory neurons in vitro. The spindles in mastication muscles are the only muscle afferents whose cell bodies reside in the mesencephalic nucleus (MeN5) of the fifth nerve (Corbin and Harrison, J Neurophysiol, 1940; Cody et al., J Physiol, 1972). Thus, labelling neurons projecting to the masseter muscle and dissecting the MeN5 isolates muscle spindle afferents. Pain is the only conscious sensation elicited by physiological stimulus of tooth pulp (Anderson and Matthews, 1967; Edwall and Olgart, 1977; Ahlquist et al., 1984; Narhi et al., 1994); there may be unconscious sensations that arise from the pulp, but these have never been demonstrated. Thus, tooth pulp afferents represent at least a highly enriched, and possibly a pure, population of nociceptors. In broad outline, the methods of labelling and tissue culture are standard, but we have honed many details in order to obtain practical yields.