Structural and neurochemical changes in the brainstem of vagotomized rats: Are they the cause of a disturbed control of pain sensitivity during fever?

Four weeks after subdiaphragmatic vagotomy (SV) a significantly smaller decrease in the level of lactate and succinate dehydrogenases (LD and SD) in the medial preoptic area of the hypothalamus of the hypothalamus at 90 min after intraperitoneal application of 3 µg/kg LPS was found as compared with sham SV. In the supraoptic hypothalamic nucleus the SD activity remained stable both in sham SV and SV rats irrespective of i.p. injection of saline or LPS, while the LD level decreased only in sham SV rats after LPS administration. Neurons of the NST and CVLM showed changes indicating both apoptosis and necrosis in the CNS. After intraperitoneal injection of 3 µg/kg LPS the pain sensitivity threshold did not significantly change in SV rats, in contrast to sham SV rats who exhibited hyperalgesia in the initial period of observation. It is suggested that the levelling effect of vagotomy on the central mechanisms of pain sensitivity control and on the changes in LD and SD in the hypothalamic nuclei upon systemic application of LPS is underlain by disorders of synaptic relations in the brainstem which occur due to destructive processes after SV. If one considers the results more broadly the consequences of the structural alterations in the CNS after injury of peripheral nerves because of traumas or ritual manipulations may be quite varied and determined, e.g., by the ontogenetic period