Endothelial and neuronal nitric oxide synthases are present in the suprachiasmatic nuclei of Syrian hamsters and rats

Nitric oxide (NO) is involved in the transmission of light information to s uprachiasmatic nuclei (SCN). By immunocytochemistry, we showed that both ne uronal and endothelial NO synthase isoforms (nNOS and eNOS) were present in the SCN of rats and hamsters. nNOS-immunoreactive neurons were located mai nly around the SCN with only a few nNOS neurons within the nucleus. By doub le-label immunocytochemistry, we also found, within the population of SCN g lial fibrillary acidic protein (GFAP)-immunoreactive astrocytes, a subpopul ation of eNOS-immunoreactive astrocytes. Using Western blot analysis, we de tected in SCN protein extracts eNOS and nNOS proteins having the expected 1 40 and 150 kDa molecular weights, respectively. By in situ hybridization of a 2.4-kb murine eNOS probe, mRNA for eNOS was located in the SCN of rats a nd hamsters. The transcript was further identified by detection of a RT-PCR product of the predicted size, after amplification of total RNA with prime rs specific for eNOS. In the SCN and cerebellum, the size of the mRNA for n NOS, detected with a rat probe on Northern blot, was similar to 10.5 kb, co rresponding to that previously published. In the same tissues, we found two transcripts, one weakly expressed at similar to 4.0 kb and another more st rongly expressed at similar to 2.6 kb, both hybridizing with two non-overla pping murine and rat eNOS probes. These results suggested the existence in the SCN of alternate transcripts for eNOS. We propose that two pathways cou ld link light stimuli and NO release in the SCN: one involving N-methyl-D-a spartate (NMDA) receptors and nNOS in neurons; the other linking alpha-amin o-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and eNOS in astrocytes.