Effects of intramuscular injection of botulinum toxin and doxorubicin on the survival of abducens motoneurons

PURPOSE. TO investigate in vivo the survival of abducens motoneurons (AMNS) at different periods of time after a single intramuscular injection of the neurotoxin botulinum toxin A (BTxA) or doxorubicin (DXR). METHODS. In Sprague-Dawley rats, the AMNs were labeled with fluorogold (FG) , which was applied intramuscularly in the lateral rectus muscle. The numbe rs of labeled neurons were determined in adult control animals; in young an imals that had received intramuscular injections of 0.125, 0.250, 1, or 2 U BTxA; and in adult rats that had received 100 mu g, 200 mu g or 300 mu g D XR, at various survival times. RESULTS. in control animals, the numbers of FG-labeled motoneurons were sim ilar to the numbers found by other investigators with the use of other retr ogradely transported tracers; motoneuron numbers diminished with time after FG application. The numbers of FG-labeled neurons in the animals that had been injected with BTxA were similar to those found in control animals, How ever, there were fewer FG-labeled neurons in the animals injected with DXR. CONCLUSIONS. Fluorogold injected into the lateral rectus muscle can be used to label the AMNs. However, this tracer does not persist within the cytopl asm of the labeled neurons for more than days. The intramuscular injection of 0.125, 0.250, I, or 2 U BTxA does not induce significant motoneuron deat h in young rats 30, 60, of 90 days after the injection. Doxorubicin infecte d intramuscularly causes variable amounts of motoneuron death that is relat ed both to the survival period and to the amount of DXR injected.