Irradiation influences the expression of substance P and enkephalin in the rat larynx.

The effects of radiotherapy on neuropeptide expression in the rat larynx were studied. Irradiation was given for five days, 6 or 8 Gray daily. Ten days after the end of irradiation, the larynx, the laryngeal nerves and different ganglia related to the larynx were dissected out from irradiated and control animals and processed for neuropeptide immunohistochemistry. There was an increased immunolabelling for two of the neuropeptides tested, substance P and enkephalin, in the innervation of the subglottic glands and in the acetylcholinesterase-positive ganglionic cells of the local ganglia. These cells were interpreted as representing postganglionic parasympathetic ganglionic cells. The changes seen in the subglottic glands were interpreted as most likely being related to the changing pattern of staining seen in the local ganglia. No changes in substance P- and enkephalin expression were observed in other laryngeal structures, the nodose ganglia, superior cervical ganglia or laryngeal nerve paraganglia. Thus, in certain respects neuropeptide expression in the larynx is modulated by radiotherapy. Since neuropeptides have both neurotransmitter and/or neuromodulator effects in airway tissue and since they show effects as growth factors, the occurrence of this plasticity in neuropeptide expression should be taken into consideration in future studies examining the effects of irradiation on normal/diseased airway tissues.