DIURNAL RHYTHM IN ORNITHINE DECARBOXYLASE ACTIVITY AND NORADRENERGIC AND CHOLINERGIC MARKERS IN RAT SUBMAXILLARY LYMPH-NODES

Diurnal variations in lymph node ornithine decarboxylase activity were examined in submaxillary lymph nodes of rats injected with Freund's c omplete adjuvant or its vehicle. After immunization, lymph node ornith ine decarboxylase activity increased by about 10-fold. Both in immuniz ed and non-immunized rats, a significant diurnal variation in ornithin e decarboxylase activity was found, with a maximal activity at early ( i.e. 13.00 h, vehicle) or late afternoon (i.e. 17.00 h, Freund's adjuv ant). Injection of Freund's adjuvant during daylight or at night resul ted in similar day-night differences in submaxillary lymph node ornith ine decarboxylase activity. In rats subjected to the sympathetic postg anglionic denervation (by ipsilateral superior cervical ganglionectomy ) or the preganglionic parasympathetic decentralization (by chorda tym pani section) of submaxillary lymph nodes, nyctohemeral variations in ornithine decarboxylase were still present, showing a maximum at 17.00 h. Superior cervical ganglionectomy augmented lymph node ornithine de carboxylase while chorda tympani section decreased it. When a unilater al superior cervical ganglionectomy plus chorda tympani section was pe rformed, the diurnal changes in ornithine decarboxylase were abolished . [H-3]Norepinephrine uptake and tyrosine hydroxylase activity attaine d their maxima in submaxillary lymph nodes at early night. After immun ization, these two presynaptic indicators of sympathetic activity in s ubmaxillary lymph nodes augmented significantly. Neuronal [H-3]choline uptake and [H-3]choline conversion into acetylcholine (two indicators of cholinergic activity) also augmented in Lymph nodes of rats inject ed with Freund's adjuvant. In immunized rats, maxima in [H-3]choline u ptake and [H-3]acetylcholine synthesis were found at 13.00-17.00 h whi le in non-immunized rats, a maximum in acetylcholine synthesis was fou nd at 17.00 h. The results are compatible with the view that the auton omic nervous system plays a role in circadian changes of immune respon siveness in lymphoid tissue and that a significant augmentation of pre synaptic autonomic activity takes place during immunization in lymphoi d tissue.