RESPONSE OF NAIVE CUTANEOUS AND MUSCLE AFFERENTS TO POTENTIAL TARGETSIN-VITRO

It is now well documented that motoneurons are specified to innervate particular target muscles prior to axon outgrowth. Here we investigate whether sensory neurons are similarly specified to innervate target s kin or muscle, taking advantage of the avian trigeminal system where c utaneous and muscle afferents are anatomically separate. Using this sy stem, we have previously shown that by embryonic day 10 (E10) (approxi mately 4-5 days after target innervation), regenerating cutaneous and muscle afferents differ in their response to various potential targets in vitro, in manners consistent with their normal innervation pattern s in vivo. Thus, by E10 these two populations of sensory neurons have distinct identities as skin and muscle afferents. In contrast, we repo rt here that the responses of younger, naive cutaneous and muscle affe rents that have not yet, or only recently, innervated peripheral targe ts are indistinguishable, regardless of the target tissue tested. Thes e findings suggest that at stages when innervation is being establishe d, cutaneous and muscle afferents, unlike motoneurons, may not yet hav e acquired rigidly specified identities and/or the ability to recogniz e and respond selectively to their appropriate peripheral targets. (C) 1998 Academic Press.