Effect of pinealectomy, superior cervical ganglionectomy, or melatonin treatment on 24‐hour rhythms in ornithine decarboxylase and tyrosine hydroxylase activities of rat spleen

Abstract

Diurnal variations in splenic ornithine decarboxylase and tyrosine hydroxylase activities were examined in rats subjected to pinealectomy, bilateral superior cervical ganglionectomy, or their respective sham operations. Rats were treated with Freund's complete adjuvant or its vehicle 2 days before sacrifice. After immunization, splenic ornithine decarboxylase activity was augmented 5-6-fold. In both immunized and nonimmunized sham-operated rats, significant diurnal variations in ornithine decarboxylase activity were detectable, with a maximum at early morning, acrophases after Cosinor analysis varying from 0845 to 1048h. In pinealectomized or superior cervical ganglionectomized, immunized rats, ornithine decarboxylase activity attained values 22-27% lower than those of immunized sham-operated controls, while amplitude decreased significantly by 27-30%. Administration of melatonin (30 microg/animal s.c. at late evening for 11 days in immunized rats) significantly augmented mesor levels of splenic ornithine decarboxylase activity and increased the amplitude of the diurnal rhythm both in pinealectomized and in superior cervical ganglionectomized rats. Melatonin treatment also augmented rhythm mesor in immunized, sham-ganglionectomized rats, as well as rhythm amplitude in immunized and nonimmunized, sham-ganglionectomized rats. Splenic tyrosine hydroxylase activity attained its maximum at late afternoon and early night, with acrophases varying from 1800 to 2023h. Immunization significantly increased mesor values of splenic tyrosine hydroxylase activity, whereas neither pinealectomy nor superior cervical ganglionectomy affected circadian rhythm parameters. Melatonin treatment augmented mesor values of tyrosine hydroxylase rhythm and increased its amplitude in pinealectomized, ganglionectomized, or sham-operated rats. The results are compatible with the view that the pineal gland plays a role in circadian changes of immune responsiveness in rat spleen via an immunopotentiating effect of melatonin on splenic cell proliferation.

Effect of Melatonin on 24-Hour Rhythms of Ornithine Decarboxylase Activity and Norepinephrine and Acetylcholine Synthesis in Submaxillary Lymph Nodes and Spleen of Young and Aged Rats

“…The single RZR/ROR melatonin responding gene identified, 5-lipoxygenase, was expressed in myeloid cells, as one of the key enzymes of allergic and inflammatory reactions, and thiazolidine diones, specific ligands for RZR/ROR receptors, exhibited a potent antiarthritic activity in the rat adjuvant arthritis model [54]. This could explain the improvement of circadian rhythmicity of immune cell proliferation found in the present and previous studies on rats injected with Freund’s adjuvant [18, 19, 20]. …”

“…Melatonin may serve the role of a potent time-related signal entraining circadian rhythmicity of immune responsiveness. For example, in recent studies exploring to what extent cell proliferation in rat submaxillary lymph nodes and spleen during the immune reaction (as assessed by ornithine decarboxylase activity) exhibited a pineal-dependent diurnal rhythmicity, we reported a significant 24-hour variation that was reduced by pinealectomy or pineal sympathetic denervation [19, 20]. This effect was counteracted by melatonin replacement.…”

“…Tissues were homogenized in chilled phosphate buffer (NaH 2 PO 4 and KH 2 PO 4 , 50 m M each (5:1, vol/vol), pH 7.2, containing 5 m M NaF, 0.1 m M pyridoxal-PO 4 , 0.1 m M EDTA-Na and 2 m M dithiothreitol, as described previously [18, 19, 20]. The homogenate was centrifuged (2,000  g for 10 min at 4°C) and 200-µl supernatant fractions were incubated in glass tubes fitted with rubber stopper and center wells containing a filter paper disk spotted with 20 µl of hyamine hydroxide: L -[1- 14 C]ornithine hydrochloride (1 µCi/tube) was then added, together with unlabeled L -ornithine to adjust the assay concentration to 0.25 m M .…”

Neuroimmunoendocrinology of the cervical autonomic nervous system

“…nicotinic cholinergic transmission in rat SCG, which is instrumental for stimulation of ganglion neurons and is triggered by acetylcholine release from preganglionic fibers, exhibited a circadian organization with a high activation during the first half of the night (2). Hence it was hypothesized that the nyctohemeral changes in submaxillary lymph node ODC activity could be related to a circadian signal conveyed via the sympathetic neurons arriving at the lymph nodes (83)(84)(85)(86). Diurnal rhythm of cell proliferation after Freund's adjuvant injection, as assessed by ODC, was measured in submaxillary lymph nodes of rats subjected to an ipsilateral SCGx and/or a chorda tympani section 10 days earlier.…”

“…Indeed, the interaction between the CNS and the immune system is a bidirectional process, immunocompetent cells affecting local neural processes by paracrine means through the release of cyto-kines and by endocrine means on the CNS via the bloodstream (90). During the immune reaction there was an increase of sympathetic and parasympathetic activity in local nerves, as indicated by the significant increase of tyrosine hydroxylase (TH) activity of submaxillary lymph nodes and spleen, and of 3H-choline conversion into acetylcholine and of norepinephrine and choline uptake in submaxillary lymph nodes of rat administered with Freund's adjuvant (85,86). Submaxillary lymph node Carotid Artery and splenic sympathetic activity attained their maximum at early night, while cholinergic activity in lymph nodes peaked during the afternoon.…”