Spinal distribution and brainstem projection of lamina I neurons in the pigeon

Lamina I neurons of the spinal dorsal horn serve nociception both in mammals and in birds. The projection of these neurons to the brain is largely unknown in birds. Injections of retrogradely transported fluorescent tracers into various brainstem nuclei showed that these neurons, which are distributed throughout the spinal cord, heavily project to the nucleus of the solitary tract and the parabrachial area but not to the hypothalamus. Injections into the nucleus of the solitary tract revealed a group of neurons located in Lissauer's tract of thoracic segments. These results point to a functional role of spinal lamina I neurons in avian visceronociception.