Biochemical actions of sympathomimetic drugs which overcome cycloheximide-induced amnesia.
Earlier investigations of sympathomimetic drugs overcoming the amnesic action of cycloheximide (CXM) in day-old chickens were extended to biochemical studies in vitro. The effects of amphetamine, norepinephrine, alpha and beta noradrenergic stimulants and receptor blockers on Na+/K+ ATP'ase activity in total homogenate of chicken forebrain were investigated. Norepinephrine and the beta stimulant, isoprenaline significantly stimulated the activity of this enzyme, while the beta blocker, propranolol inhibited activity. Amphetamine, the alpha stimulant, methoxamine and the alpha receptor blocker, piperoxane had no effect on Na/K+ ATP'ase activity in total homogenate. In a purified synaptosomal preparation, both amphetamine (5 X 10(-5) M) and norepinephrine (1 X 10(-4) M) produced a slight stimulation of Na+/K+ ATP'ase activity. A similar concentration of amphetamine (1.12 X 10(-4) M) did not inhibit 14C-leucine uptake or incorporation into protein in the synaptosomal fraction. Nor was it able to alleviate CXM inhibition of 14C-leucine incorporation into synaptosomal protein. The results are interpreted in terms of amphetamine (via release of norepinephrine) norepinephrine and isoprenaline stimulating and maintaining the labile, sodium pump-dependent, phase of memory formation for a sufficient length of time until protein synthesis inhibition by CXM wears off.