Direct projections from the spinal cord to the trigeminal sympathetic ganglion of the puffer fish, Takifugu niphobles

The sympathetic trunk of teleosts extends into the cranial levels, forming the cranial sympathetic ganglia. When horseradish peroxidase was applied to the trigeminal sympathetic ganglion (a sympathetic ganglion at the level of the trigeminal nerve) of the puffer fish, Takifugu niphobles, retrogradely labeled neurons were found in the central autonomic nucleus (a distinct cell column in the rostral part of the spinal cord). The central autonomic nucleus has been known to contain preganglionic neurons projecting to the sympathetic ganglia at the spinal levels. Thus, the present results indicate that the central autonomic nucleus in the spinal cord of teleosts contains not only preganglionic neurons projecting to the sympathetic ganglia at the spinal levels, but also neurons projecting to the sympathetic ganglia at the cranial levels.