TRIGEMINAL PROJECTIONS IN SNAKES POSSESSING INFRARED SENSITIVITY

The 1st order projections of the trigeminal nerve were studied in 4 spp. of snakes Boa constrictor, Corallus enydris cookii, Crotalus viridis helleri and Coluber constrictor], 3 of which were IR sensitive, utilizing Ag degeneration and Co2+ iontophoresis techniques. The trigeminal nerve projected ipsilaterally to a main sensory nucleus, descending spinal nucleus, ventral trigeminal field and solitary nucleus with a contralateral projection to the base of the descending spinal nucleus in all 4 spp. A major additional projection to the lateral nucleus of the trigeminal was present in all 3 IR sensitive species but absent in the other. Iontophoresis of CoCl2 into a trigeminal branch composed entirely of IR sensitive fibers and into a trigeminal branch containing no IR fibers indicated that the lateral nucleus of the trigeminal nerve was the sole 1st order target of the IR system.