ABSTRACT
The C1 cell group in the rat is characterized by neurones which contain both adrenaline and phenylethanolamine-N-methyltransferase, and usually also neuropeptide Y (NPY). The former two substances are lacking in Guinea pig brainstem and spinal cord. We have examined the distribution of NPY- and tyrosine hydroxylase-immunoreactivity in the ventrolateral medulla and thoracolumbar intermediate zone of Guinea pig, as well as the distribution of catecholamine-containing neurone somata and spinal terminals visualized after formaldehyde-glutaraldehyde fixation. The results are compared with comparable immunohistochemical data obtained from rats and rabbits. Catecholaminergic neurones in the Guinea pig with locations and terminations that correspond to those of the C1 cell group in rat and its analogue in the rabbit appear to consist of two subgroups, with only the more caudal group containing NPY. The more rostral group requires pretreatment with monoamine oxidase inhibitor to permit visualization of catecholamine fluorescence, a property previously though to be characteristic of adrenergic neurones. This observation raises the possibility that the catecholaminergic cell group in the C1 region of rabbits may not contain adrenaline either.
