DISTRIBUTION AND SITES OF SYNTHESIS OF NTT4, AN ORPHAN MEMBER OF THE NA+ CL--DEPENDENT NEUROTRANSMITTER TRANSPORTER FAMILY, IN THE RAT CNS/

The distribution and sites of synthesis in rat CNS of NTT4, a novel or phan member of the Na+/Cl--dependent neurotransmitter transporter fami ly, were determined by immunohistochemistry and hybridization histoche mistry. Antibodies raised against recombinant fusion proteins, corresp onding to residues of NTT4, and S-35-labelled oligodeoxyribonucleotide probes, were used to delineate the cellular distribution of the trans porter at the protein and mRNA levels. High levels of immunoreactivity (mainly in the neuropil) were found in the olfactory bulb, cerebral c ortex, striatum, hippocampus, thalamus, substantia nigra, pontine nucl ei, cerebellum and spinal cord. The lowest levels were associated with the lateral hypothalamic area and deep mesencephalic nuclei. In situ hybridization signals correlated well with the immunoreactivity, and d emonstrated a widespread distribution of NTT4 transcripts exclusively in neurons. NTT4 transcripts appeared widely codistributed with the N- methyl-D-aspartate receptor subunit 1 (1-4b), i.e. spliced variants ch aracterized by a common 5' 63 bp insertion. These results indicate tha t the transporter was associated with neuronal processes in specific g lutamate innervated CNS regions. Although the substrate transported by NTT4 remains unknown, our findings suggest a possible role for this c arrier protein in glutamate/glycine neurotransmission.