Naloxone blocks the interferon-alpha induced changes in hypothalamic neuronal activity

Molecular Effects of FDA-Approved Multiple Sclerosis Drugs on Glial Cells and Neurons of the Central Nervous System

Multiple sclerosis (MS) is characterized by peripheral and central inflammatory features, as well as demyelination and neurodegeneration. The available Food and Drug Administration (FDA)-approved drugs for MS have been designed to suppress the peripheral immune system. In addition, however, the effects of these drugs may be partially attributed to their influence on glial cells and neurons of the central nervous system (CNS). We here describe the molecular effects of the traditional and more recent FDA-approved MS drugs Fingolimod, Dimethyl Fumarate, Glatiramer Acetate, Interferon-β, Teriflunomide, Laquinimod, Natalizumab, Alemtuzumab and Ocrelizumab on microglia, astrocytes, neurons and oligodendrocytes. Furthermore, we point to a possible common molecular effect of these drugs, namely a key role for NFκB signaling, causing a switch from pro-inflammatory microglia and astrocytes to anti-inflammatory phenotypes of these CNS cell types that recently emerged as central players in MS pathogenesis. This notion argues for the need to further explore the molecular mechanisms underlying MS drug action.

Interferon modulates central nervous system function

The interferons (IFNs) are an endogenous pleiotropic family of cytokines that perform fundamental physiological functions as well as protecting host organisms from disease and in maintaining homeostasis. This review covers the effects of endogenous IFN on the nervous system. It starts with the description of its receptors, followed how it modulate neuronal activity, mood, sleep, temperature, the endocrine system, the opioid system and how it regulate food consumption and the immune system. Similar to other multifunctional cytokines, an excessive or inappropriate activity of IFNs can cause toxicity and even death. Furthermore, IFNs are currently the major treatment modality for several malignant and non-malignant diseases such as chronic hepatitis C and B, multiple sclerosis, hematological malignancies, malignant melanoma, renal cell carcinoma, etc.

Interferon and the central nervous system

Interferons (IFNs) were discovered as natural antiviral substances produced during viral infection and were initially characterized for their ability to "interfere" with viral replication, slow cell proliferation, and profound alteration of immunity. The IFNs are synthesized and secreted by monocytes, macrophages, T-lymphocytes, neurons, and glia cells. The different IFNs are classified into three classes: alpha, beta, and gamma. alpha-IFN produced in the brain exerts direct effects on the brain and endocrine system by activating the neurosecretory hypothalamic neurons and regulates the hypothalamic-pituitary-adrenocortical axis. IFNs modulate neurophysiological activities of many brain region involving in pain, temperature, and food intake regulation. alpha-IFN administration activates the sympathetic nerves innervating components of the immune system. IFNs may serve as regulatory mediators between the central nervous system, the immune system, and endocrine system. IFN is used as immunologic therapy to treat various hematologic malignancies and infectious ailments and autoimmune diseases.

Effects of interferon-α on cloned opioid receptors expressed in Xenopus oocytes

Interferon-alpha (IFNalpha) affects the opioid system. However, the direct action of IFNalpha on cloned opioid receptors remains unknown. Taking advantage of the functional coupling of cloned opioid receptors to G protein-activated inwardly rectifying K+ (GIRK) channels in a Xenopus oocyte expression system, we investigated the effects of recombinant IFNalpha on cloned mu-, delta- and kappa-opioid receptors. In oocytes co-injected with mRNAs for either the delta- or kappa-opioid receptor and for GIRK channel subunits, IFNalpha at high concentrations induced small GIRK currents that were abolished by naloxone, an opioid-receptor antagonist, compared with the control responses to each selective opioid agonist. Additionally, IFNalpha induced no significant current response in oocytes injected with mRNA(s) for either opioid receptor alone or GIRK channels. In oocytes expressing the mu-opioid receptor and GIRK channels, IFNalpha had little or no effect. Moreover, in oocytes expressing each opioid receptor and GIRK channels, GIRK current responses to each selective opioid agonist were not affected by the presence of IFNalpha, indicating no significant antagonism of IFNalpha toward the opioid receptors. Furthermore, IFNalpha had little or no effect on the mu/delta-, delta/kappa- or mu/kappa-opioid receptors expressed together with GIRK channels in oocytes. Our results suggest that IFNalpha weakly activates the delta and kappa-opioid receptors. The direct activation of the delta- and kappa-opioid receptors by IFNalpha may partly contribute to some of the IFNalpha effects under its high-dose medication.

Fever of recombinant human interferon-alpha is mediated by opioid domain interaction with opioid receptor inducing prostaglandin E2

We have reported that there are distinct domains in Interferon-alpha (IFNalpha) molecule mediating immune and opioid-like effects respectively. And the opioid effect of IFNalpha is mediated by mu opioid receptor. We report here the structural basis of fever induced by recombinant human IFNalpha. Two kinds of IFNalpha mutants were obtained and used to investigate the structural basis of fever of IFNalpha, which are 129Ser-IFNalpha and 38Leu-IFNalpha. The antiviral activity of 129Ser-IFNalpha almost disappeared, but there still retained the strong analgesic activity. The antiviral activity of 38Leu-IFNalpha remained, but the analgesic activity disappeared completely. It showed that IFNalpha and 129Ser-IFNalpha decreased cAMP production, induced the fever, and stimulated PGE2 to release from the hypothalamus slices, which could be blocked by naloxone, but 38Leu-IFNalpha failed. It is the first demonstration that fever induced by IFNalpha is mediated by opioid domain of IFNalpha interacting with opioid receptor. It is inferred that high-activity and low side-effect IFNalpha or other cytokines could be obtained after being changed the motifs in the tertiary structure.

Interferon alpha (IFNalpha) and psychiatric syndromes: a review

Interferon alpha (IFNalpha) is used for the treatment of several disorders, such as chronic hepatitis or malignant melanoma. During the therapy, IFNalpha may cause severe neuropsychiatric syndromes including depression with suicidal ideation, paranoid psychoses, or confusional states. The reasons and management of these side effects are widely unknown. Our aim is to review research evidence for the contribution of IFNalpha for the etiopathology of psychiatric syndromes. Therefore, research findings of neuropsychiatric syndromes induced by IFNalpha treatment, the putative mechanisms underlying those syndromes, and their treatment are-reviewed. Furthermore, neuropsychiatric syndromes in diseases with high IFNalpha levels such as systemic lupus erythematosus (SLE) are discussed. Finally, the question is addressed whether IFNalpha may contribute to the etiopathology of endogenous psychiatric disorders. IFNalpha may cause psychiatric syndromes in a subset of treated patients. The underlying pathogenetic mechanisms include various effects on neuroendocrine, cytokine, and neurotransmitter systems. Research data on the role of IFNalpha in the pathogenesis of endogenous psychiatric disorders are conflicting. Future research should improve our understanding of the role of IFNalpha for the etiopathology of psychiatric syndromes and has an impact on treatment of IFNalpha-induced psychiatric syndromes.

Analgesic effect of interferon-alpha via mu opioid receptor in the rat

Using the tail-flick induced by electro-stimulation as a pain marker, it was found that pain threshold (PT) was significantly increased after injecting interferon-alpha (IFN alpha) into the lateral ventricle of rats. This effect was dosage-dependent and abolished by monoclonal antibody (McAb) to IFN alpha. Naloxone could inhibit the analgesic effect of IFN alpha, suggesting that the analgesic effect of IFN alpha be related to the opioid receptors. Beta-funaltrexamine (beta-FNA), the mu specific receptor antagonist could completely block the analgesic effect of IFN alpha. The selective delta-opioid receptor antagonist, ICI174,864 and the kappa-opioid receptor antagonist, nor-BNI both failed to prevent the analgesic effect of IFN alpha. IFN alpha could significantly inhibit the production of the cAMP stimulated by forskolin in SK-N-SH cells expressing the mu-opioid receptor, not in NG108-15 cells expressing the delta-opioid receptor uniformly. The results obtained provide further evidence for opioid activity of IFN alpha and suggest that this effect is mediated by central opioid receptors of the mu subtype. The evidence is consistent with the hypothesis that multiple actions of cytokines, such as immunoregulatory and neuroregulatory effects, might be mediated by distinct domains of cytokines interacting with different receptors.

Structural and functional neuropathology in transgenic mice with CNS expression of IFN-alpha

Cytokines belonging to the type I interferon (e.g. interferon-alpha) family are important in the host response to infection and may have complex and broad ranging actions in the central nervous system (CNS) that may be beneficial or harmful. To better understand the impact of the CNS expression of the type I interferons (IFN), transgenic mice were developed that produce IFN-alpha(1) chronically from astrocytes. In two independent transgenic lines with moderate and low levels of astrocyte IFN-alpha mRNA expression respectively, a spectrum of transgene dose- and age-dependent structural and functional neurological alterations are induced. Structural changes include neurodegeneration with loss of cholinergic neurons, gliosis, angiopathy with mononuclear cell cuffing, progressive calcification affecting basal ganglia and cerebellum and the up-regulation of a number of IFN-alpha-regulated genes. At a functional level, in vivo and in vitro electrophysiological studies revealed impaired neuronal function and disturbed synaptic plasticity with pronounced hippocampal hyperexcitability. Severe behavioral alterations were also evident in higher expressor GFAP-IFNalpha mice which developed fatal seizures around 13 weeks of age precluding their further behavioral assessment. Modest impairments in discrimination learning were measured in lower expressor GFAP-IFNalpha mice at various ages (7-42 weeks). The behavioral and electrophysiological findings suggest regional changes in hippocampal excitability which may be linked to abnormal calcium metabolism and loss of cholinergic neurons in the GIFN mice. Thus, these transgenic mice provide a novel animal model in which to further evaluate the mechanisms that underlie the diverse actions of type I interferons in the intact CNS and to link specific structural changes with functional impairments.

Is interferon-alpha a neuromodulator?

Interferons were initially characterized for their ability to 'interfere' with viral replication, slow cell proliferation, and profoundly alter immunity. They are a group of hormone-like molecules synthesized and secreted by macrophages, monocytes, T lymphocytes, glia, and neurons. These cytokines have been shown to have several regulatory roles and diverse biological activities, including control of cellular and humoral immune responses, inflammation, and tumor regression. In addition, there are many reports indicating that interferon-alpha (IFN-alpha) participates in the regulation of various cellular and humoral processes such as the endocrine system modulates behavior, brain activity, temperature, glucose sensitive neurons, feeding pattern and opiate activity. Therefore, IFN-alpha can be considered as a physiological modulator, with only one of its functions being the ability to hinder viral replication intracellularly.

Naloxone differentially alters fevers induced by cytokines

Interferon-alpha (IFN-alpha), a cytokine acting as an endogenous pyrogen and a putative activator of the opioid system, binds to opiate receptors in vitro. The mu opioid receptor antagonist, naloxone hydrochloride (NLX), attenuates IFN-alpha-induced increases in the firing rate of cold-sensitive neurons within thermosensitive areas of the brain. The influence of NLX on fevers induced by central endogenous pyrogens was investigated in rats. Subcutaneous (SQ) injection of NLX (1 mg/kg) was made 30 min prior to intracerebroventricular (ICV) injection of IFN-alpha 2b (7900IU). Alternatively, NLX (10 or 80 micrograms) was microinjected ICV 30 min prior to administration of IFN-alpha 2b. Administered SQ, NLX attenuated the febrile response to IFN-alpha 2b. In contrast, central (ICV) NLX did not attenuate fevers induced by IFN-alpha 2b. Animals previously exposed to both IFN-alpha 2b and NLX (SQ or ICV) subsequently lost their sensitivity to this cytokine, and also showed diminished reactivity to human recombinant interleukin-1 beta (hrIL-1 beta; 10 ng) and prostaglandin E2 (PGE2; 250 ng). These results suggest that systemic and central elements of the opioid system may play differential roles in temperature regulation. Previous administration of NLX and IFN-alpha 2b may alter the sensitivity of the CNS to subsequent injections of different pyrogens.

The use of conditioning to probe for CNS pathways that regulate fever and NK cell activity

Immune and central nervous system (CNS) interactions are complicated because afferent signals from the immune system to the CNS in response to antigens or infections may elicit an immediate efferent response to the immune system. This communication loop is required for the homeostatic regulation of the immune system. Conditioning can be used as a tool to take the communication loop apart. In conditioned animals, the conditioned stimulus can be employed later to trigger the site of the association memory located within CNS, and set off the efferent pathway. Conditioning therefore allows one to isolate and identify the potential circuits in the brain that becomes conditioned. We have conditioned a pathway in the brain which can be used to modulate core body temperature (Tc) and natural killer (NK) cell activity. The Tc and NK cell activity are used as readouts to detect the expression of the conditioned response which is taking place in the brain. Since various cytokines (IFN, IL-1 etc) that are produced by antigenic stimulation invariably raise fever, it appears that the immune system could signal the CNS with nonspecific cytokines that activate the hypothalamic-pituitary pathway to modulate core body temperature. These observations infer that the thermoregulatory pathway in the brain becomes conditioned and points to a common pathway of communication in which interferon-beta, prostaglandin E2, CRH and ACTH appear to play a role in modulating both Tc and NK cell activity.

Interferon-alpha therapy for chronic myelogenous leukemia

PURPOSE

To provide a status report on the use of interferon (IFN)-alpha in patients with chronic myelogenous leukemia (CML).

DATA SOURCES

Data on IFN-alpha therapy for CML collected from published articles identified in a MEDLINE computer search.

RESULTS

Previously untreated patients with low-risk factors and early-stage disease consistently had the best results in clinical trials. A dose response was seen, with patients treated with dosages of 5 million units (MU)/m2 per day showing the greatest incidence of cytogenetic remissions. In addition, randomized trials showed a survival advantage for IFN-alpha-treated patients. In studies comparing IFN-alpha therapy to chemotherapy, IFN-alpha produced significantly more major and durable cytogenetic responses than chemotherapy did. In studies combining IFN-alpha and chemotherapy, patients had significantly more cytogenetic responses, although more patient accrual and follow-up data are needed to offer conclusive statements concerning durability of response. IFN-alpha also showed activity in maintaining remissions after both chemotherapy and bone marrow transplantation.

CONCLUSIONS

IFN-alpha has significant activity in patients with CML, with best results at dosages of 5 MU/m2 per day. At these dosages, in patients with early-stage, Philadelphia+ CML, hematologic response rates of 70% to 80% and cytogenetic response rates of 50% (approximately 20% of which were complete) are seen. One randomized trial shows a survival advantage with cytogenetic response in IFN-alpha-treated patients, and this advantage appears to be unrelated to the degree of that response. These questions remain under study.

Microglial localization of alpha-interferon receptor in human brain tissues

The localization of the alpha-interferon receptor (alpha-IFNR) was examined in human brain tissues from neurologically normal, Alzheimer's disease (AD) and cerebral infarction cases, using one antibody (IFNaR3) which preferentially recognizes alpha 2-IFN receptor and a second antibody (anti-p40) which recognizes the soluble alpha-IFN alpha/beta receptor. In all cases, microglial cells were stained with the antibodies. In infarct brains, macrophages were intensely labeled for alpha-IFNR. The anti-p40 antibody also showed capillary staining which might be due to residual blood plasma. On Western blots, IFNaR3 recognized only a 210 kDa alpha-IFN/receptor complex, indicating its localization in microglial cells. The anti-p40 antibody recognized this complex as well as four other major materials of lower molecular weight. These results suggest that alpha-IFNR protein is constitutively expressed in microglial cells.

Neuroendocrine effects of interferon-alpha in the rat

We have previously found that recombinant human interferon-alpha 2A (rHu-IFN-alpha 2A) inhibits hypothalamo-pituitary-adrenocortical (HPA) axis activity following both peripheral and central administration. This effect is antagonized by mu-opioid receptor antagonists, suggesting transduction by this subtype of opioid receptors. We have now demonstrated that this effect is also observed with hybrid rHu-IFN-alpha A/D, rat kidney fibroblast-derived IFN-alpha, and recombinant rat IFN-alpha preparations. The inhibitory effects on HPA activity were observed after intraperitoneal (i.p.) injections of rHu-IFN-alpha2A(10(03)U), rHu-IFN-alpha A/D (10(4)U), and of Rat-IFN-alpha (1-10U). Similar effects were observed with intracerebroventricular (i.c.v.) administration of all four IFN-alpha preparations. No increases in plasma corticosterone concentrations were observed with doses of rHu-IFN-alpha A/D up to 10(6)U (i.p.) or 7x10(5)U (i.c.v.), but increases were found following i.c.v. administration of high doses of Rat-IFN-alpha (10(3) and 5x10(3)U). The inhibitory effects of all of the IFN-alpha preparations tested were antagonized by naloxone, but the stimulatory effects of 5x10(3)U Rat-IFN-alpha were not. Injections of rHu-IFN-alpha 2A(10(4)U, i.p.) to urethane-anesthetized rats decreased the electrical activity of the majority of hypothalamic paraventricular nucleus (PVN) neurons tested, including putative corticotropin-releasing factor-(CRF)-secreting neurons antidromically identified as projecting to the median eminence. Similarly, iontophoretic application of rHu-IFN-alpha 2A decreased the electrical activity of such cells. These electrophysiological data suggest that the decreases in HPA activity evoked by IFN-alpha are mediated, at least in part, by a rapid inhibitory effect at the level of the corticotropin-releasing factor-secreting neurons.

Naloxone suppresses the rising phase of fever induced by interferon-alpha

Interferon-alpha (IFN-alpha, 2.0 x 10(4) units) was bilaterally microinjected into the medial preoptic area and anterior hypothalamus in conscious rats treated 10 min prior with an opioid receptor antagonist, naloxone (NLX, 2 mg/kg, IM) or a prostaglandin synthetase inhibitor, acetaminophen (ACAP, 25 mg/kg, IM). The IFN-alpha-induced rise of rectal temperature (Tre) was suppressed from 20 to 60 min in NLX pretreated rats and from 30 to 180 min in ACAP pretreated rats. The rate of rise in Tre during the initial 20 min observed in NLX pretreated rats was significantly smaller than that in ACAP or saline pretreated rats. ACAP suppressed the fever when it was given 50 or 100 min after injection of IFN-alpha. In contrast, NLX did not affect the fever when given 25 or 50 min after IFN-alpha. The results suggest that an opioid that its involvement may last only in the early phase of the fever, but not after the plateau has been reached.

Treatment of neurotoxic side effects of interferon-alpha with naltrexone

Interferon-alpha (IFN-alpha) has potential dose-limiting neurotoxic side effects when used in cancer therapy. The nature of this neurotoxicity is speculative, and there is no definitive treatment. Because animal studies suggest that IFN-alpha acts at opioid receptor sites, we gave naltrexone, a long-acting opioid antagonist, to 9 patients who had hematological malignancies and who suffered from IFN-alpha side effects. Seven of these patients experienced complete or moderate relief of side effects. Five of the patients tested before and during naltrexone treatment showed improvement of cognitive functioning. Two patients could not tolerate naltrexone side effects. This study suggests an intervention against IFN-alpha side effects and provides support for the role of opioid receptor interaction in IFN-alpha neurotoxicity.

Alpha-interferon inhibits adrenocortical secretion via mu 1-opioid receptors in the rat

The effect of recombinant human alpha-interferon on plasma corticosterone concentrations was investigated in adult male rats. Intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration of alpha-interferon (10-10(4) U i.p., and 1-10(3) U i.c.v.) decreased basal plasma corticosterone concentrations. This effect was evident at both the peak and nadir in the circadian rhythm of hypothalamo-pituitary-adrenocortical secretory activity. The same inhibitory effect was obtained with intra-paraventricular nucleus administration of the cytokine. Furthermore, alpha-interferon attenuated the effects of stressors such as handling, 1 min of forced swimming, and sound stress in a novel environment. The effect of alpha-interferon (10(2) U i.c.v.) was blocked by prior injection of the opioid receptor antagonist, naloxone (1 mg/kg i.p.). Similarly, the effect of 10(3) U alpha-interferon administered i.p. was blocked by i.c.v. injection of naloxone (1 microgram/kg), or of the mu 1-specific receptor antagonist, naloxonazine (1 microgram). The selective delta-opioid receptor antagonist, naltrindole (1 microgram i.c.v.) and the kappa-opioid receptor antagonist, nor-binaltorphimine (1 microgram i.c.v.) both failed to prevent the inhibitory effect of alpha-interferon (10(3) U i.p.) on adrenocortical secretion. The results obtained provide further evidence for a neuromodulatory effect of alpha-interferon and that this effect is mediated by central opioid receptors of the mu 1-subtype, delta- and kappa-opioid receptors not being involved.

Behavioral effects of mouse interferons-alpha and -gamma and human interferon-alpha in mice

Behavioral effects of murine interferon-alpha and -gamma were explored using a well-characterized system for detecting interferon effects. In addition, the effectiveness of human interferon-alpha was determined. Mouse gamma-interferon decreased activity and food-related behavior, effects that were similar to the effects of mouse alpha-interferon. Equivalent doses of the human preparation had little effect upon these measures in mice. Some common action of alpha- and gamma-interferon is likely responsible for the similar effects seen for the two molecules. Low effectiveness of the human preparation in mice was predicted due to the differences in receptors between species.

Opioid-dopaminergic mechanisms in the potentiation of d-amphetamine discrimination by interferon-alpha

In rats trained to discriminate 0.8 mg/kg IP d-amphetamine from 1 ml/kg saline, 4 x 10(6) U/kg of recombinant human interferon-alpha (rIFN-alpha) given intramuscularly 1 h prior to tests potentiated responses elicited by 0.4 mg/kg d-amphetamine. Coadministration of the opioid receptor antagonist naloxone (1 mg/kg IP) with rIFN-alpha suppressed the potentiation of d-amphetamine by the cytokine. Opioid-dopaminergic mechanisms are proposed to explain the action of rIFN-alpha.

Human recombinant interferon alpha inhibits naloxone binding to rat brain membranes

Regulation of certain central nervous system (CNS) functions by the immune system may involve interferons (IFNs) acting through opioid receptors. Human recombinant interferon alpha (hrIFN alpha), as well as natural IFN alpha, have been reported to modulate a variety of physiological CNS functions both in vivo and in vitro. If the mechanism is via opioid receptors then IFN alpha should inhibit the binding of certain opioid radioligands to brain membranes. This study reports the inhibitory effect of hrIFN alpha on the binding of 3H-naloxone to rat brain membranes in vitro. The inhibitory effect at 37 degrees C is hrIFN alpha concentration dependent over the range of 500 to 6000 antiviral units per ml (U/ml) with 500 micrograms of membrane protein. The presence of NaCl (100mM) increases specific binding of naloxone and attenuates the inhibitory effect of hrIFN alpha. The inhibitory effect of hrIFN alpha is sensitive to temperature with maximum inhibition observed at 37 degrees C, and less as incubation temperature is reduced. These data suggest that IFN alpha may modulate certain physiologic functions via opioid pathways in the brain.

Neurotoxicity of intraventricularly administered alpha-interferon for leptomeningeal disease

Nine patients with leptomeningeal disease are reported who were treated with intraventricular alpha-interferon (alpha-IFN). In seven of these patients, a progressive vegetative state developed during treatment. The patients became unresponsive to verbal commands but opened their eyes with auditory or tactile stimulation. It took an average of 3 weeks for these patients to become verbally responsive after treatment was discontinued. Electroencephalographic findings showed evidence of irritative involvement of the deep midline nuclei in 80% of patients. Periventricular white matter changes developed during treatment in three of six patients who underwent computed tomographic scans. All patients with this severe neurotoxicity received whole-brain irradiation before treatment. Possible mechanisms for the development of this neurotoxic syndrome are discussed. The neurotoxicity of alpha-IFN and brain irradiation may be additive, suggesting a cautious approach when using this combination for treatment.

Immunoregulators in the nervous system

The nervous system, through the production of neuroregulators (neurotransmitters, neuromodulators and neuropeptides) can regulate specific immune system functions, while the immune system, through the production of immunoregulators (immunomodulators and immunopeptides) can regulate specific nervous system functions. This indicates a reciprocal communication between the nervous and immune systems. The presence of immunoregulators in the brain and cerebrospinal fluid is the result of local synthesis--by intrinsic and blood-derived macrophages, activated T-lymphocytes that cross the blood-brain barrier, endothelial cells of the cerebrovasculature, microglia, astrocytes, and neuronal components--and/or uptake from the peripheral blood through the blood-brain barrier (in specific cases) and circumventricular organs. Acute and chronic pathological processes (infection, inflammation, immunological reactions, malignancy, necrosis) stimulate the synthesis and release of immunoregulators in various cell systems. These immunoregulators have pivotal roles in the coordination of the host defense mechanisms and repair, and induce a series of immunological, endocrinological, metabolical and neurological responses. This review summarizes studies concerning immunoregulators--such as interleukins, tumor necrosis factor, interferons, transforming growth factors, thymic peptides, tuftsin, platelet activating factor, neuro-immunoregulators--in the nervous system. It also describes the monitoring of immunoregulators by the central nervous system (CNS) as part of the regulatory factors that induce neurological manifestations (e.g., fever, somnolence, appetite suppression, neuroendocrine alterations) frequently accompanying acute and chronic pathological processes.

Neuromodulation of fever: apparent involvement of opioids

It was recently reported that the opiate antagonist, naloxone (Nal), blocks the changes induced by the endogenous pyrogen, interferon-alpha 2 (IFN), in the electrical activity of hypothalamic thermosensitive neurons in rat brain slice preparations. This study was undertaken to determine whether the pyrogenic response to this cytokine might, therefore, be modulated through Nal-reversible opiate receptors. To examine this possibility, conscious guinea pigs were injected IV with recombinant human (rh) IFN (10 MU/animal), or, for comparison, with S. enteritidis endotoxin (lipopolysaccharide, LPS; 2 micrograms/kg), rh tumor necrosis factor-alpha (TNF; 20 micrograms/kg), or rh interleukin-6 (IL6; 50 micrograms/kg); Nal (10 mg/kg, SC) was administered immediately before the pyrogens. And also for comparison, in separate experiments, indomethacin (Indo; 10 mg/kg, IM) was injected 20 min before the pyrogens. Both Nal and Indo abolished the febrile rises evoked by IFN, TNF, and IL6. Nal reduced the first and suppressed the second of the characteristically bimodal febrile response to LPS; Indo depressed both peaks. Neither blocker had any significant thermal effect by itself. These results suggest that two processes may mediate the pyrogenic effects of these substances, viz., an endogenous opioid- and a PGE-dependent mechanism.

Absence of neural responses following suppression of the immune response by cyclophosphamide

Injection of sheep red blood cells (SRBC) as an antigenic stimulus, causes significant increases (up to 300%) in multiunit neural activity in the preoptic area/anterior hypothalamus of conscious rats. This increase occurs on the fifth or sixth day after immunization, at the time of first appearance of circulating antibodies at a serum titer of 1:32, increasing to 1:128 by day 10 following sensitization. Treatment with the immunosuppressive drug cyclophoshamide was able to prevent both antibody production and the expected increases in electrical activity in 5 of 6 rats; the one remaining animal showed a low level of circulating anti-SRBC antibodies on day 10 (1:32) and also, a small increase (36%) in neural activity at the expected time. These results provide further evidence that activation of the immune system is able to alter neuronal activity in an area of the brain important in the regulation of both neuroendocrine and neuroimmunomodulatory mechanisms, and that such activity is probably due to soluble secretory products released from components of the immune system.

Alpha-interferon modifies cortical EEG activity: dose-dependence and antagonism by naloxone

Activation of the immune system is believed to provide signals in the form of chemical messengers that are able to change neural activity in a variety of regions of the central nervous system. In studies designed to examine the effects of alpha-interferon (alpha-IFN) upon the central nervous system, recordings of cortical EEG were made following intracerebroventricular injection of various doses of the cytokine. Administration of 25 U of alpha-IFN increased the amount of wake and decreased the amount of desynchronized sleep in the first hour following injection; an increase in synchronization being seen in the third hour. alpha-IFN at 250 U increased the amount of synchronization and decreased the amount of desynchronized sleep in the EEG, principally in the second hour, with 2,500 U having similar but more potent effects, mostly in the first hour. The (mu) opiate receptor antagonist, naloxone, was found to decrease the amount of EEG synchronization and blocked the increases in synchronized sleep produced by 250 U alpha-IFN. The data suggest that alpha-interferon increases EEG synchronization in a dose-dependent and specific manner, probably via central mu-opiate receptors. The increased wake in the EEG following 25 U suggests, however, that another discrete effect of alpha-IFN may also exist.

Human psychoneuroimmunology today

Studies in human psychoneuroimmunology began around 1919, but a systematic approach wasn't used until the work of Solomon in the 1960s. Recently, the new specialty has achieved relative independence due to considerable data acquisition. Stress research has revealed relationships between neuroendocrine and immune changes. In parallel, increasing evidence of immunological alterations in psychiatric diseases has expanded the field; presently, immunological correlates of psychosomatic diseases and personality are sought. On the other hand, while immunological disease has been psychologically assessed for many years, a clear-cut link between psyche and immunological changes has yet to be shown. This fact, along with the therapeutic implications of advancing knowledge, will influence strongly the future trends of psychoneuroimmunology. Concepts emerging from the study of this field will be of heuristic value to both psychiatry and immunology and will help define new and expanded limits for both disciplines.

Naltrexone blocks the expression of the conditioned elevation of natural killer cell activity in BALB/c mice

An elevation of natural killer (NK) cell activity was conditioned by the association of a camphor odor conditioning stimulus (CS) with an injection of 20 micrograms polyinosinic:poly-cytidylic acid (poly I:C), the unconditioned stimulus (US). Poly I:C elicits the production and secretion of interferon (IFN), which induces an increase in NK cell activity. Reexposure to the CS occurred on Days 3 and 5 after the association trial on Day 0. Immediately following the CS exposure on Day 5, 1 microgram poly I:C was administered to all animals. This procedure resulted in an increased NK cell activity in the conditioned (CND), but not the nonconditioned (NC), mice. In this study we have shown that the expression of the conditioned response was blocked by an injection of naltrexone (NTX) at 10 mg/kg ip when given immediately prior to the two test CS odor exposures. Peripheral treatment (ip) with a quaternary form of naltrexone (QNTX), which is a less potent opiate antagonist, at the same dose and at the same time relative to the CS odor reexposure did not block the conditioned response. The formation of the conditioned association did not appear to be disrupted by NTX at the 10 mg/kg dose when given immediately prior to the trial odor exposure on Day 0. No modulation of NK cell activity was observed in any of the control groups treated with naltrexone or the quaternary analog. Because of the inability of the QNTX to block the conditioned response, we hypothesize that the opiate receptors involved in the conditioned response and blocked by NTX were within the central nervous system (CNS). Whether this response is peripherally or centrally mediated, we have shown that opiate receptors represent part of the mechanism which mediates the conditioned augmentation of NK cell activity.

Neurophysiological and endocrine consequences of immune activity

The studies presented herein demonstrate the potency with which activity of the immune system is able to influence the central nervous system. Electrophysiological recordings have demonstrated significant changes in preoptic area/anterior hypothalamic (PO/AH) multiunit electrical activity (MUA) following sensitization with sheep red blood cells. The peak of activity occurred on the fifth day after immunization, the same day that serum antibodies were first detected. A significant increase in paraventricular nucleus MUA was also demonstrated, but this appeared to be delayed with respect to that in the PO/AH, occurring on the sixth day. Further changes thought to be associated with the immune response also were found: Serum corticosterone levels were elevated on the eighth day of the response, and PO/AH tissue levels of norepinephrine were reduced between the sixth and tenth days. During induction of a secondary response, PO/AH MUA showed a different profile of activity from that recorded during the first response. Chronic administration of the immunosuppressive drug, cyclophosphamide, prevented the recorded changes in PO/AH MUA. These results suggest that some secretory product(s) of the activated immune system may be able to exert effects on the central nervous system. Various immunoactive substances therefore were administered intra-cerebroventricularly in order to examine their effects upon PO/AH MUA, cortical EEG and adrenocortical hormone secretory activity. alpha-Interferon and thymic humoral factor were both found to decrease PO/AH MUA, increase EEG synchronization, and decrease basal levels of circulating corticosterone. In contrast, histamine and interleukin-1 did not alter PO/AH MUA but did cause decreased EEG synchronization and increased serum corticosterone levels. With another preparation, a specific activating effect of interleukin-1 upon putative corticotropin-releasing factor-secreting neurones has also been found, identified vasopressinergic neurones not being affected.

Endogenous opiates: 1987

This paper is the tenth installment of our annual review of the research during the past year involving the endogenous opiate system. It covers the nonanalgesia and behavioral studies of the opiate peptides published in 1987. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal activity; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical activity; locomotor activity; sex, pregnancy, and development; immunology and cancer; and other behavior.

Effects of interferon-alpha on the activity of preoptic thermosensitive neurons in tissue slices

Effects of recombinant interferon-alpha (IFN-alpha) on the single activity of thermosensitive and thermally insensitive neurons in the preoptic and anterior hypothalamus (PO/AH) were investigated in rat's brain tissue slices. IFN-alpha, in doses of less than 5 x 10(3) U/ml, decreased the activity in 34 of 52 warm-sensitive neurons and increased the activity in 3 of 5 cold-sensitive neurons, but had no effect on the majority (12 of 17) of thermally insensitive neurons. The neuronal responses to local IFN-alpha could be observed in a Ca2+-free/high Mg2+ solution, suggesting the direct action of IFN-alpha. The actions of IFN-alpha on thermosensitive neurons were blocked by concurrent application of naloxone, but not by sodium salicylate in doses which effectively blocked the neuronal responses to endotoxin and leukocytic pyrogen in the previous studies. The fever induced by IFN-alpha may be explained, at least partly, by the direct actions of IFN-alpha on the PO/AH thermosensitive neurons, which involve the opiate receptor mechanisms.

Convergence of thermal, osmotic and cardiovascular signals on preoptic and anterior hypothalamic neurons in the rat

Responsiveness of thermosensitive neurons in the preoptic and anterior hypothalamus (PO/AH) to osmotic and cardiovascular signals have been shown to be responsible, at least partly, for the reduced thermoregulation during dehydration and the hypothermia after acute blood loss. The responsiveness to local and peripheral (hepatoportal) osmotic stimuli were found in about 60% of PO/AH thermosensitive neurons and 12% of thermally insensitive neurons in tissue slices in vitro and in urethane-anesthetized rats. Since hyperosmotic stimuli predominantly decreased the activity of both warm-sensitive and cold-sensitive neurons, the reduced heat loss and heat production during dehydration may be explained by altered activity of PO/AH thermosensitive neurons induced by hyperosmolality. About 42% of 250 PO/AH neurons (66.3% of thermosensitive neurons and 30% of thermally insensitive neurons) exhibited the responsiveness to changes in blood pressure by less than 15 mmHg, which was found to be mediated by baro/volume receptors. Hypotensive stimuli predominantly increased the activity of warm-sensitive neurons and decreased the activity of cold-sensitive neurons. The neuronal responses may explain, at least in part, the hypothermia after acute bleeding.