Effects of Peripheral monoamines on the monosynaptic reflex neuronal activity of acute spinal cats

The monosynaptic reflex (MSR) neuronal activity of acute spinal cats was affected not only by monoamine levels in the central nervous system (CNS) but also by peripheral physiological changes, i.e. blood pressure and the temperature of the paraffin pool. Therefore, this report discusses the effects of peripheral monoamines, especially dopamine (DA) or norepinephrine (NE), on the MSR amplitude of acute spinal cats. The results were as follows: 1. Intravenous injections of DA or NE, which did probably not enter the CNS because of the blood-brain barrier, increased MSR neuronal activity. 2. These effects were blocked by the DA receptor antagonist, haloperidol, and the alpha-receptor antagonist, phenoxybenzamine, but not by the beta-receptor antagonist, propranolol. 3. This effect of NE was about 20-fold stronger that that of DA. 4. Larger doses of both amines caused increases in the blood pressure. These results suggested that most hypertensive drugs which cause increases in levels of NE influence the stimulation MSR neuronal activity.