Effect of peripheral nerve injury on cGMP and nitric oxide synthase levelsin rat dorsal root ganglia: time course and coexistence

Using the indirect immunofluorescence method, the distribution of cyclic GM P (cGMP) and nitric oxide synthase (NOS) was investigated in lumbar 5 dorsa l root ganglia (DRGs) of untreated rats 1, 3 and 7 days following sciatic n erve section (axotomy). Untreated and axotomized (7 days) rats were also st udied after perfusion with the NO donor sodium nitroprusside (SNP). Moreove r, rats were injected with carrageenan lambda into the unilateral hindpaw a nd studied after 6 h, 1 day or 2 days. An increase in the number of cGMP-po sitive satellite cell profiles was found in axotomized DRGs at 3 days with lower numbers after 7 days. In contrast, no change in cGMP-like immunoreact ivity (LI) in satellite cell profiles was detected 1 day after axotomy or 6 h, 1 day or 2 days after inflammation, as compared to controls. Axotomy in duced a marked increase in the percentage of NOS-immunoreactive (TR) neuron profiles in the ipsilateral DRGs as follows: 3.0% at 1 day, 15% at 3 days and 25% at 7 days, whereas no significant change was found in the expressio n of NOS-LI in the inflamed DRGs as compared to untreated DRGs. Between 15 and 20% of all NOS-positive neuron profiles were surrounded by, or in parti al contact with, cGMP-IR satellite cells in controls 1 and 3 days after axo tomy, whereas the corresponding figure was around 5% after 7 days. After SN P perfusion 60-70% of all DRG neuron profiles were partly or totally associ ated with cGMP-positive satellite cell profiles, with no significant differ ence between untreated and axotomized ganglia. The nerve injury-induced, pa rallel upregulation of NOS in DRG neurons and cGMP in satellite cells in th e initial phase after axotomy suggests an involvement of NO as a signalling molecule between neurons and satellite cells in DRGs, especially after per ipheral nerve injury, perhaps exerting a survival effect as recently propos ed by Thippeswamy and Morris (1997). (C) 1998 International Association for the Study of Pain. Published by Elsevier Science B.V.