The projection linkage between the spinal dorsal horn neurons and both the solitary tract and dorsal column nuclei

Electrical stimulation of the solitary tract nucleus (SN) and dorsal column nuclei (DCN) as well as microelectrode recording from the lumbal spinal dorsal horn have been used to find and identify the axonal projection of and the afferent innervation on the spinal neurons of pentobarbital-anesthetized rats. A total of 92 neurons was recorded and identified mainly in laminae III-V of the lumbar spinal dorsal horn. Of them, 38 neurons were activated antidromically from stimulation of both the SN and DCN. The other 54 neurons responded synaptically to both the SN and DCN stimulations. The initial antidromic responses of 8 neurons in the first group were followed by one or more responses synaptically driven from the SN and/or DCN stimulation. Conduction velocities were in the range of A delta fibers, but faster in the antidromic responses and slower in the synaptic responses. These results indicate that (i) some spinal neurons issue branched axons of larger-sized A delta fibers and double project to both the SN and DCN; (ii) some of these double projection neurons receive in turn smaller A delta fiber innervation from the SN and/or DCN; and (iii) some other neurons in the spinal cord are dually innervated by smaller A delta fibers originating from both nuclei.