Comparative study on the distribution patterns of P2X1–P2X6receptor immunoreactivity in the brainstem of the rat and the common marmoset (Callithrix jacchus): Association with catecholamine cell groups

The present study investigated the topographical distribution of P2X1–P2X6receptor subtypes in the rat and common marmoset hindbrain by immunohistochemistry. In addition, double‐labeling immunofluorescence was used to determine the extent of colocalization between catecholamine cell groups and the various P2X receptors. The data demonstrate a widespread distribution pattern for all six P2X receptors throughout both the rat hindbrain and the marmoset hindbrain, although distinctions between species, brain nuclei, and P2X receptor subtypes exist. In rat, dense staining for the P2X receptors was found in the nucleus of the solitary tract (NTS), medial vestibular nucleus, and medial and lateral parabrachial nuclei. Moderate staining was observed in the hypoglossal nucleus, cuneate nucleus, inferior olive, prepositus hypoglossi, rostral ventrolateral medulla (RVLM), and locus coeruleus. Staining was also observed in the gracile nucleus, the mesencephalic trigeminal nucleus, and the central pontine gray. In marmoset, prominent P2X receptor‐like immunoreactivity occurred in the NTS, medial cuneate nucleus, prepositus hypoglossi, and medial vestibular nucleus. Moderate staining was observed in the area postrema, dorsal motor nucleus of the vagus, lateral cuneate, lateral reticular, spinal trigeminal nucleus, RVLM, and inferior olive. Immunofluorescent double labeling of tyrosine hydroxylase (TH)‐containing cells revealed that all subtypes of P2X receptors show some degree of colocalization with TH. The highest proportion of TH and P2X receptor double labeling was in the A5 region (with the P2X2subunit), whereas the lowest proportion of double‐labeled cells occurred in the C2 region of the NTS for the P2X5subunit. These findings support a role for extracellular adenosine 5′‐triphosphate in fast synaptic neurotransmission within the brainstem. J. Comp. Neurol. 427:485–507, 2000. © 2000 Wiley‐Liss, Inc.