RAPID SHIFTS IN RECEPTIVE-FIELDS OF CELLS IN TRIGEMINAL SUBNUCLEUS INTERPOLARIS FOLLOWING INFRAORBITAL NERVE TRANSECTION IN ADULT RATS

Transection of the infraorbital nerve in adult rats results in an arra y of chronic functional anomalies in trigeminal brainstem subnucleus i nterpolaris, including changes in normal receptive field organization. This work examined whether long-term maintenance of acute modificatio ns, such as unmasking or strengthening of normally ineffective inputs to interpolaris cells, might contribute to the previously described ch ronic abnormalities. Using glass micropipettes, extracellular isolatio n of 37 interpolaris cells, with infraorbital receptive fields, was ma intained following intraorbital transection of the infraorbital nerve. Receptive fields and dynamic response properties were characterized i mmediately before and after the cut and throughout the post-transectio n isolation period. Orthodromic latencies to trigeminal ganglion shock s and antidromic activation from thalamus or cerebellum were also exam ined. Of the 37 cells, 21.6% exhibited receptive field shifts to non-i nfraorbital regions after cutting the infraorbital nerve. Using the no rmal probability of observing an interpolaris cell with more than one trigeminal division in its receptive field, the probability of observi ng this shift by chance was 0.0013. No such changes were observed for 12 control cells, recorded for durations equal to or greater than tota l recording times for the shifting cells, with the nerve intact. The r epresentation of local circuit, thalamic-projecting and cerebellar-pro jecting cells was similar in the total sample; however, all neurons ex hibiting transection-induced receptive field shifts were projection ne urons. In comparing the sample of cells that exhibited receptive field shifts with those that did not, prior to infraorbital nerve cut, ther e was no difference in mean latencies and thresholds for activation fr om the stimulating electrodes or in mean depth at which the cells were isolated. In addition, no difference was evident in receptive field s ize, effective receptor surface, dynamic response characteristics or s pontaneous activity. These data suggest that maintenance of acute rece ptive field changes, following infraorbital nerve cut, may contribute to some types of chronic functional alterations observed after such da mage. (C) 1998 Elsevier Science B.V.