Alterations in neuronal survival and glial reactions after axotomy by ceftriaxone and minocycline in the mouse hypoglossal nucleus

Some antibiotics are suggested to exert neuroprotective effects via regulation of glial responses. Attenuation of microglial activation by minocycline prevents neuronal death in a variety of experimental models for neurological diseases, such as cerebral ischemia, Parkinson's and Huntington's disease. Ceftriaxone delays loss of neurons in genetic animal models of amyotrophic lateral sclerosis through upregulation of astrocytic glutamate transporter expression (GLT-1). However, it remains largely unknown whether these antibiotics are able to protect neurons in axotomy models for progressive motor neuron diseases. Recent studies have shown that the axotomized motoneurons of the adult rat can survive, whereas those of the adult mouse undergo neuronal degeneration. We thus examined the possible effects of ceftriaxone and minocycline on neuronal loss and glial reactions in the mouse hypoglossal nucleus after axotomy. The survival rate of lesioned motoneurons at 28 days after axotomy (D28) was significantly improved by ceftriaxone and minocycline treatment. There were no significant differences in the cellular densities of astrocytes between ceftriaxone-treated and saline-treated animals. Ceftriaxone administration increased the expression of GLT-1 in the hypoglossal nucleus, while it suppressed the reactive increase of glial fibrillary acidic protein (GFAP) expression to control level. The cellular densities of microglia at D28 were significantly lower in minocycline-treated mice than in saline-treated mice. The time course analysis showed that immediate increase in microglia at D3 and D7 was not suppressed by minocycline. The present observations show that minocycline and ceftriaxone promote survival of lesioned motoneurons in the mouse hypoglossal nucleus, and also suggest that alterations in glial responses might be involved in neuroprotective actions of antibiotics.