Brain tissue and serum from mice intracerebrally injected with 1 mu g
of staphylococcal alpha-toxin contained elevated amounts of a naturall
y occurring brain tissue component(s) called muscle-relaxing factor (M
RF). MRF induced reversible, generalized, flaccid paralysis of mice af
ter intracerebral but not intraperitoneal or intravenous administratio
n. MRF (i) was soluble in Hanks balanced salt solution and in acidifie
d (pH 2) Hanks balanced salt solution, in which it partitions into eth
yl acetate, acetone, and methanol; (ii) was separated from some pigmen
ts by thin-layer chromatography on silica gel plates; (iii) did not co
migrate with prostaglandin and leukotriene standards during high-press
ure liquid chromatography with a mu Bondapak fatty acid column; and (i
v) did not contain amino acids, exhibit absorption maxima at a wavelen
gth range of 210 to 600 nm, or fluoresce when exposed to W light. MRF
has been detected in rabbit brain that has been stored frozen at - 70
degrees C and has been enhanced in vitro in slices of both mouse and r
abbit brain following incubation of the brain slices with staphylococc
al alpha-toxin. Studies to identify the chemical nature of MRF and the
mechanism by which, in mice, it induces reversible, flaccid paralysis
of voluntary muscle are continuing.