Minocycline treatment attenuates microglia activation and non-angiotensin II [125I] CGP42112 binding in brainstem following nodose ganglionectomy

We have previously shown that following unilateral nodose ganglionectomy, [125I] CGP42112 binds to a non-angiotensin II (Ang II) related binding site in rat dorsal motor nucleus of the vagus nerve, ambiguus nucleus and nucleus of the solitary tract. Furthermore, this up-regulated binding site localizes with activated microglia. Given that some tetracyclines may inhibit microglia activation in brain, we examined the effect of minocycline treatment on the binding of [125I] CGP42112 and [3H] PK11195 (an established radioligand for microglia), as well as OX-42 immunoreactivity (an immunomarker for activated microglia), following nodose ganglionectomy. Male Wistar Kyoto rats underwent unilateral nodose ganglionectomy or sham operation and were treated with saline or minocycline (50 mg/kg i.p.) 12 h before surgery and twice daily after surgery (each 50mg/kg i.p.) for 3 days. Subsequent to nodose ganglionectomy, [125I] CGP42112 binding (insensitive to PD123319 or Ang II) was increased approximately two-fold in the ipsilateral nucleus of the solitary tract and was also induced in the ipsilateral dorsal motor nucleus of the vagus nerve and ambiguus nucleus of saline-treated rats. Treatment with minocycline reduced this non-angiotensin II [125I] CGP42112 binding (40-50% reduction) in the nucleus of the solitary tract, dorsal motor nucleus of the vagus nerve and ambiguus nucleus. Analogous experiments using [3H] PK11195 also revealed up-regulated binding in the ipsilateral nucleus of the solitary tract ( approximately 205%), dorsal motor nucleus of the vagus nerve (approximately 80%) and ambiguus nucleus (approximately 210%) of saline-treated rats following nodose ganglionectomy, which was reduced by 40-100% with minocycline treatment. Immunoreactivity to OX-42 confirmed an increase in microglia activation and accumulation of macrophages in these brain stem nuclei following nodose ganglionectomy, which was also attenuated following treatment with minocycline. These data demonstrate that non-Ang II [125I] CGP42112 binding following nodose ganglionectomy is attenuated by minocycline treatment. This minocycline-induced effect was associated with reduced activation of microglia and an apparent reduction in the number of macrophages in the abovementioned nuclei. This evidence suggests that a non-Ang II [125I] CGP42112 binding site is located on, or associated with, activated microglia and macrophages, providing a useful tool with which to quantitate the neuroprotective effects of centrally acting anti-inflammatory compounds.