Vagal control of lymphocyte release from rat thymus

The effects of the efferent vagal innervation on the thymus gland of the rat were investigated in vivo by means of section and stimulation experiments. It has been shown that section of the right vagus produces a decrease in the number of lymphocytes released from the thymus into the venous circulation, an effect that disappears after section of the recurrent laryngeal nerve. Vagal stimulation produces a transient increase in the number of lymphocytes released from the thymus, an effect that also disappears after section of the recurrent nerve. The effects of vagotomy are mimicked by nicotinic blocking agents, which also suppress the effects of vagal stimulation, whereas muscarinic blocking agents were ineffective. It is concluded that the vagal fibres running in the recurrent laryngeal nerve exert a tonic and phasic facilitatory influence on the mechanisms responsible for lymphocyte release from the thymus, and that this action is mediated through nicotinic receptors.