The immune effects of neuropeptides

In vitro and in vivo TNFalpha synthesis modulation by methylguanidine, an uremic catabolyte

This study was performed in order to examine whether the uraemic toxin, methylguanidine (MG), can modulate tumor necrosis factor alpha (TNF alpha) release by activated macrophages. In this study we have evaluated the ability of MG to influence TNF alpha release in vitro, in Escherichia coli lypopolysaccharide- (LPS)-stimulated J774 cells preincubated overnight with MG, and in vivo in rats treated with MG before and after LPS challenge. Parallel experiments employing N(G)-nitro-L-arginine methyl esther (L-NAME) were also carried out for comparison. The effect of LPS (6 x 10(3) u/ml) on TNF alpha release by J774, following overnight incubation with MG or L-NAME (1 mM), was examined 3 hours after LPS challenge. LPS-stimulated J774 released 287.83+/-88 u/ml TNF alpha into the culture medium. MG (1 mM) significantly inhibited TNF alpha release by 73% (P<0.05). L-NAME (1 mM) significantly inhibited TNF alpha release too by 72.88% (P<0.05). The effect of MG and L-NAME have been also studied in vivo. Serum TNF alpha levels in LPS treated rats 2 h after LPS challenge were 88.33+/-31.7 u/ml as compared to the serum TNF alpha levels of control rats (undetectable). Treatment of rats with MG (30 mg/kg, i.p.) strongly and significantly reduced TNF alpha release (98.71% inhibition; with P<0.001); in the same experimental setting L-NAME (10 mg/kg, i.p.) also significantly reduced TNF alpha serum levels (76.47% inhibition; with P<0.01). These results could indicate that immune disfunction related to uremia may be related to the inhibitory capability of uremic catabolyte, MG, on TNF alpha synthesis and release.

Adrenal and pituitary hormone patterns after spinal cord injury

Current evidence indicates that the neuroendocrine system is the highest regulator of immune/inflammatory reactions. We hypothesized that immune alterations, which were related to the level of injury, found in a cohort of spinal cord-injured subjects may be influenced by altered hormonal patterns postinjury. Therefore, we investigated aspects of both pituitary and adrenal function in the same cohort of spinal cord-injured subjects. We found significant elevations in both cortisol and dehydroepiandrosterone sulfate in chronic spinal cord-injured survivors compared with their able-bodied age- and gender-matched controls. Levels of dehydroepiandrosterone, adrenocorticotropin, and prolactin were not different in spinal cord-injured subjects overall compared with their controls. Both dehydroepiandrosterone sulfate and dehydroepiandrosterone were higher in tetraplegics compared with their controls, but we found no such differences in paraplegics compared with their controls. When the two groups of spinal cord-injured subjects were compared with each other, we also found differences between these two subject groups in dehydroepiandrosterone sulfate and dehydroepiandrosterone (higher in the tetraplegics compared with paraplegics). We found no differences between either group of spinal cord-injured subjects and their controls for adrenocorticotropin, prolactin, or cortisol. These data suggest that some hormonal differences between subjects and their controls may be further related to the level of injury (specifically dehydroepiandrosterone and dehydroepiandrosterone). Finally, we investigated correlations within subjects for the above hormones. Dehydroepiandrosterone sulfate and prolactin were highly correlated (the higher the dehydroepiandrosterone sulfate, the higher the prolactin) but only in the tetraplegic subjects.

Calcitonin gene-related peptide immunoreactivity in the hippocampus and its relationship to cellular changes following exposure to trimethyltin

Calcitonin gene-related peptide (CGRP) is a neuropeptide that is regionally regulated following peripheral insult and in central nervous system (CNS) damage models targeting limbic structures. Functional studies have shown this neuropeptide to be involved in neuronal protection and remodeling, vasodilation, immunomodulation, and apoptosis, thus making it an important constituent of the acute phase response. In the present study, we characterized the anatomic expression and distribution of CGRP immunoreactivity (CGRP-IR) after exposure to the toxin, trimethyltin (TMT). We chose this model because TMT causes dramatic changes in the endocrine system, the limbic system, particularly the hippocampus, as well as in the immune response. We have specifically focused on comparing the changes in CGRP-IR with the pattern of apoptosis (via TUNEL staining), cell-cycle activation (Ki67-IR), and in alteration in microglia (OX-42-IR) and astrocyte (gGFAP-IR) immunocytochemistry in TMT-treated hippocampus. Our results show a marked change in CGRP-IR in regions of the hippocampus that are temporally and anatomically correlated with the induction of apoptosis and activation of microglia, astrocyte, and the cell-cycle marker. Given the known effects of CGRP on these cell types and on programmed cell death elsewhere, these findings are consistent with a regional immunoregulatory/injury response role for CGRP following organotin poisoning.

Repressive/defensive coping, endogenous opioids and health: how a life so perfect can make you sick

Hyperactivity of endogenous opioid systems has been postulated to mediate the associations between defensive/repressive coping styles, enhanced stress responsivity, and reduced immunocompetence. Study 1 examined whether repressive/defensive coping would be associated with greater sensitivity to opioid antagonism. Judgments of the painfulness of ascending series of electrocutaneous stimulation applied to the forearm were determined before and after the administration of naloxone and placebo in 38 men and 42 women. All subjects were healthy with a mean age of 32.9 years. Naloxone (10 mg i.v.) and placebo were administered in double-blind fashion and counterbalanced. Subjects were classified as High- and Low-defensive and repressive copers on the basis of scores on the Marlowe-Crowne Social Desirability Scale and the Balanced Inventory of Desirable Responding, respectively. High Self-Deception was associated with naloxone-induced hyperalgesia, whereas no effects of naloxone on pain ratings were observed in low-Self-Deceptive subjects. In Study 2, resting plasma beta-endorphin levels were found to be positively correlated with defensiveness in men (n = 26), but not women (n = 44). Study 3 examined 82 healthy subjects (mean age = 28.7 years). Beta-endorphin/defensiveness correlations were found to be greater following, compared to prior to, electrical nociceptive stimulation in men (n = 49), but unrelated in women (n = 33). These findings are consistent with the hypothesized endorphinergic dysregulation associated with repressive/defensive coping styles and are discussed in terms of the immuno-regulatory implications of such a dysregulation.

Induction of calcitonin gene-related peptide-like immunoreactivity in hippocampal neurons following ischemia: a putative regional modulator of the CNS injury/immune response

Calcitonin gene-related peptide (CGRP) is a potent vasodilator and immune cell modulator. In two studies within the hippocampal formation (HF), CGRP-like immunoreactivity (CGRP-LI) was increased in the inner molecular layer of the dentate gyrus after adrenalectomy and in mossy cells after colchicine-induced destruction of granule neurons. Given the increase in CGRP-LI following damage to the granule cell region of the HF, we investigated another trauma model, ischemia, that targeted different areas of the HF, CA1 region, and subiculum to ascertain the regional expression of this peptide after insult. Following ischemia, light microscopic evaluation showed CGRP-LI in basket cell-like neuronal perikarya within the dorsal subiculum and CA1 region of the hippocampus and in varicose fibers within the CA2 region of the hippocampus. Control rats rarely expressed CGRP-LI within neurons in these regions. In ischemic brains, double-labeled immunocytochemistry with antibodies to various neural markers demonstrated co-localization of CGRP-LI primarily within surviving subicular and CA1 cells resembling interneurons containing parvalbumin-LI or calbindin-LI. Electron microscopic analysis of the CA1 region from ischemic brains showed that CGRP-LI was contained in terminals with numerous small synaptic vesicles that formed symmetric synapses with perikarya and large dendrites of pyramidal cells, some of which were degenerating. Collectively, the data from this study and our previous study indicate that damage induces CGRP-LI expression in interneurons and nonprincipal cells in the area of damage, and we hypothesize that CGRP expression in surviving neurons within damage-related regions of the hippocampus is likely to be an important, and possibly a protective, component of the response of the nervous system to injury.

Pituitary hormones and immune function

The pituitary gland plays a key role in the regulation of growth, differentiation and function of all cells in the body, including immunocytes. Immune reactions are generated through the proliferation of antigen-specific lymphocyte clones. Growth hormone and prolactin are required for the development of mature lymphocytes and for the maintenance of immunocompetence. These hormones enable lymphocytes to respond to antigen, which is delivered as an adherence signal in the context of major histocompatibility surface molecules of antigen-presenting cells. Numerous other adhesion molecules play a role in the regulation of lymphocyte activation. The activation process is completed by cytokine signalling, after which lymphocyte proliferation, differentiation and functional maturation take place. Interleukins, hormones and growth factors may all function as cytokines. Many lymphocytes exist in the body in a quiescent state, with minimal metabolic activities. These cells are maintained by competence hormones and insulin-like growth factor 1, which are present in the systemic and local environment. Apparently, some steroid hormones, opioid peptides and catecholamines are capable of modulating delivery of the signal from the lymphocyte membrane receptor to the nucleus. Steroid and thyroid hormones control nuclear transcription factors as their receptors, and thus are powerful regulators of lymphocyte signalling at the nuclear level. The bioactive forms of thyroid hormone and of several steroid hormones are generated locally by immunocytes. These important hormonal immunoregulators function both at systemic and local levels. Glucocorticoids are major regulators of cytokine production, and alpha-melanocyte-stimulating hormone functions as a powerful cytokine antagonist. The hormones secreted or regulated by the pituitary gland therefore regulate every level of immune activity, including the competence of lymphocytes to respond to immune/inflammatory stimuli, signal transduction, gene activation, the production and activity of cytokines and other immune effector functions.