Diurnal rhythm in ornithine decar☐ylase activity and noradrenergic and cholinergic markers in rat submaxillary lymph nodes

Abstract

Diurnal variations in lymph node ornithine decar☐ylase activity were examined in submaxillary lymph nodes of rats injected with Freund's complete adjuvant or its vehicle. After immunization, lymph node ornithine decar☐ylase activity increased by about 10-fold. Both in immunized and non-immunized rats, a significant diurnal variation in ornithine decar☐ylase activity at early (i.e. 13.00 h, vehicle) or late afternoon (i.e. 17.00 h, Freund's adjuvant). Injection of Freund's adjuvant during daylight or at night resulted in similar day-night differences in submaxillary lymph node ornithine decar☐ylase activity. In rats subjected to the sympathetic postganglionic denervation (by ipsilateral superior cervical ganglionectomy) or the preganglionic parasympathetic decentralization (by chorda tympani section) of submaxillary lymph nodes, nyctohemeral variations in ornithine decar☐ylase were still present, showing a maximum at 17.00 h. Superior cervical ganglionectomy augmented lymph node ornithine decar☐ylase while chorda tympani section decreased it. When a unilateral superior cervical ganglionectomy plus chorda tympani section was performed, the diurnal changes in ornithine decar☐ylase were abolished. [ 3H]Norepinephrine uptake and tyrosine hydroxylase activity attained their maxima in submaxillary lymph nodes at early night. After immunization, these two presynaptic indicators of sympathetic activity in submaxillary lymph nodes augmented significantly. Neuronal [ 3H]choline uptake and [ 3H]choline conversion into acetylcholine (two indicators of cholinergic activity) also augmented in lymph nodes of rats injected with Freund's adjuvant. In immunized rats, maxima in [ 3H]choline uptake and [ 3H]acetylcholine synthesis were found at 13.00–17.00 h while in non-immunized rats, a maximum in acetylcholine synthesis was found at 17.00 h. The results are compatible with the view that the autonomic nervous system plays a role in circadian changes of immune responsiveness in lymphoid tissue and that a significant augmentation of presynaptic autonomic activity takes place during immunization in lymphoid tissue.