Résumé
The distribution of enkephalin, dynorphin, substance P and neurotensin in the periaqueductal gray[PAG] has been well established by immunohistochemical methods. However, there is little information about the regional distribution of these neuropeptide mRNA-containing neurons in the PAG. The present study was undertaken [1] to elucidate the distribution of these neuropeptide mRNA-containing neurons and to determine of the PAG, [2] to know how peptide expression relates to the proposed functional subdivisions of the PAG and [3] to know how neuropeptide mRNA levels in the PAG change following peripheral neuropathy The results obtained are as follows ; 1. Preproenkephalin[pENK] mRNA-containing neurons are found mostly in the ventrolateral portion at all levels of the PAG. 2. Prodynorphin[pDYN] mRNA-containing neurons are concentrated mostly in the ventrolateral portion at the caudal level of the PAG. 3. Preprotachykinin[pTAK] mRNA-containing neurons are localized mainly in the ventrolateral portion at all levels of the PAG. There is small numbers of pTAK mRNA-containing neurons in the dorsolateral and dorsal portion at all levels of the PAG. 4. Proneurotensin[pNT] mRNA-containing neurons are concentrated mostly in the medial part of ventrolateral portion of the caudal and mid PAG. 5. Peripheral neuropathy induces an increase of pNT mRNA levels in the PAG, while pENK, pDYN and pTAK mRNAs levels show no change. The present results indicate that the pENK, pDYN, pTAK or pNT mRNA-containing neurons are found mainly in the ventrolateral PAG, the area where analgesia is most easily produced and that neurotensin in the PAG may play an important role in modulating chronic neuropathic pain.