Biomedical subjects

L R Watkins

Publications and source records attributed to L R Watkins.

At least 19 recordsLinked to original sources

PubMed1995

Blockade of cytokine induced conditioned taste aversion by subdiaphragmatic vagotomy: further evidence for vagal mediation of immune-brain communication.

Interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) are cytokines released by activated immune cells. IL-1 beta and TNF-alpha elicit various illness symptoms including avoidance of novel tastes with which they have been paired (conditioned taste aversion). Previous hypotheses to account for these actions have focused on blood-borne IL-1 beta and TNF-alpha exerting their effects directly at the brain. However, recent evidence suggests that these cytokines may activate subdiaphragmatic vagal afferents. The present experiments demonstrate that subdiaphragmatic vagal transection both attenuates acquisition and facilitates extinction of conditioned taste aversions induced by i.p. administration of either IL-1 beta or TNF-alpha.

Animals↗

PubMed1995

Blockade of interleukin-1 induced hyperthermia by subdiaphragmatic vagotomy: evidence for vagal mediation of immune-brain communication.

Interleukin-1 beta (IL-1 beta), a cytokine released by activated immune cells, elicits various illness symptoms including hyperthermia. Previous hypotheses to account for these actions have focused on blood-borne IL-1 beta exerting its effects directly at the level of the brain. However, recent behavioral and physiological evidence suggest that IL-1 beta can activate the subdiaphragmatic vagus. The present experiments demonstrate that subdiaphragmatic vagal transection disrupts the hyperthermia-inducing effects of recombinant human IL-1 beta and stress. These data provide evidence for a novel route of immune-brain communication, as well as a novel route whereby stress can influence physiological processes.

Animals↗

PubMed1995

Stressed rats fail to expand the CD45RC+CD4+ (Th1-like) T cell subset in response to KLH: possible involvement of IFN-gamma.

Exposure to stressors effects various aspects of immune function, including the in vivo antibody response. We have previously reported that rats exposed to an acute session of inescapable tail shock (IS) show long-term reductions in anti-KLH (keyhole limpet hemocyanin) IgM and IgG. The mechanisms responsible for this suppression are currently unknown. Previous work has suggested changes in CD4+ T cells could be important. We report here that exposure to IS results in a reduction in Con A-stimulated IFN-gamma levels in mesenteric lymphocytes and splenocytes taken immediately after IS termination. In addition, IS exposure prevents the KLH-induced increase in the number of CD45RC+CD4+ T cells (Th1-like) in both the mesenteric lymph nodes and the spleen 4 days after immunization. The failure of KLH to expand the CD45RC+CD4+ subset could be due to the stress-induced reduction in IFN-gamma levels reported in cells taken at the time of immunization. Implications of these findings as a mechanism for the decrease in the in vivo antibody response previously reported is discussed.

Animals↗

PubMed1995

Cytokine-to-brain communication: a review & analysis of alternative mechanisms.

It is becoming well accepted that products of the immune system (cytokines) can signal the brain that infection has occurred. This cytokine-to-brain communication can result in marked alterations in brain function and behavior. This review examines alternative mechanisms that have been proposed to explain how such immune products can reach the brain via the blood to cause centrally-mediated "illness" responses. Finally, we describe a new view which argues that cytokines signal brain in quite a different manner, by stimulating afferent terminals of peripheral nerves at local sites of synthesis and release.

Afferent Pathways↗

PubMed1995

Stress-induced reduction in the rat mixed lymphocyte reaction is due to macrophages and not to changes in T cell phenotypes.

Exposure to aversive events or stressors modulates various aspects of immune function. We have previously reported that exposure to an acute stressor, inescapable tail shock (IS), resulted in a shift in T cell subpopulations in rat mesenteric lymph nodes but not in cervical lymph nodes (Fleshner et al. (1992) J. Neuroimmunol. 41, 131-142). The mesenteric CD4+/CD8+ ratio was increased immediately after exposure to IS and was due primarily to an increase in the percent of CD4+ cells. The present experiments were designed to determine the relationship between the IS-associated phenotypic shift and its significance in the function of CD4+ T cells. The function assessed was the in vitro proliferative response to alloantigens coded for by the Major Histocompatibility Complex (MHC). Using the mixed lymphocyte reaction (MLR), we report that exposure to IS resulted in a decrease in the MLR response of cells from both cervical and mesenteric lymph nodes. Depletion of macrophages (nylon wool adherent cells) eliminated the IS-induced reduction and co-culture of macrophages (irradiation-insensitive cells) from shocked rats produced the suppression. One interpretation of these data is that exposure to IS resulted in the activation of macrophages and the release of a suppressive factor which reduced the MLR response of peripheral lymph node lymphocytes.

Animals↗

PubMed1995

Interleukin-1 beta induced corticosterone elevation and hypothalamic NE depletion is vagally mediated.

Processes occurring within the immune system can alter neural function. Cytokines released by cells of the immune system during illness are key messengers in immune-to-brain communication. Interleukin-1 beta (IL-1 beta) is particularly important in this regard and is known to stimulate a myriad of illness-related outcomes such as fever, sickness behavior, aphagia, adipsia, hypothalamic-pituitary-adrenal activation, and changes in pain reactivity. Thus peripherally released IL-1 beta has potent neural effects and is a critical mediator of the impact of immune processes on brain. There is, however, uncertainty concerning the communication pathways involved. We provide evidence that a primary route of peripheral cytokine signalling is through stimulation of peripheral vagal afferents rather than or in addition to direct cytokine access to brain. Subdiaphragmatic, but not hepatic vagotomy, blocked rhIL-1 beta-induced hypothalamic norepinephrine depletion and attenuated rhIL-1 beta-induced increases in serum corticosterone. These data suggest that rhIL-1 beta activates the hypothalamic-pituitary-adrenal axis via stimulation of peripheral vagal afferents and further support the hypothesis that peripheral cytokine signalling to the CNS is mediated primarily by stimulation of peripheral afferents.

Animals↗

PubMed1995

8-OH-DPAT microinjected in the region of the dorsal raphe nucleus blocks and reverses the enhancement of fear conditioning and interference with escape produced by exposure to inescapable shock.

Prior work suggests that inhibition of the dorsal raphe nucleus (DRN) either during exposure to inescapable electric shock (IS) or during later behavioral testing might block the usual behavioral consequences of IS. The 5-HT1A agonist 8-OH-DPAT was microinjected into the region of the DRN either before exposure to IS or before testing for fear conditioning and escape learning conducted 24 hr later. IS potentiated fear conditioning and interfered with escape performance. These effects were completely prevented by intra-DRN administration of 8-OH-DPAT at either point. Low but not high systemic doses of 8-OH-DPAT had a similar effect, supporting the idea that the effective site of action is presynaptic. The relation between these data and other effects of 8-OH-DPAT is discussed.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1995

The dorsal raphe nucleus is a site of action mediating the behavioral effects of the benzodiazepine receptor inverse agonist DMCM.

Systemic administration of benzodiazepine receptor inverse agonists leads to behavioral changes similar to those produced by inescapable shock (IS). The dorsal raphe nucleus (DRN) is a critical structure mediating IS effects. The present experiments determined whether the DRN is a site mediating the behavioral changes produced by benzodiazepine receptor inverse agonists. Microinjection of the inverse agonist Methyl 6,7-Dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) in the region of the DRN produced enhancement of fear conditioning as assessed by the amount of freezing in the presence of shock cues as well as interference with shuttlebox escape learning assessed 24 hr later. Furthermore, lesion of the DRN blocked the effects of systemic DMCM on fear conditioning and escape learning. These data suggest that the DRN is indeed critical in mediating these behavioral consequences of DMCM and further support a role for the DRN in producing the behavioral changes induced by IS.

Animals↗

PubMed1995

A long-term increase in basal levels of corticosterone and a decrease in corticosteroid-binding globulin after acute stressor exposure.

Adrenal glucocorticoids play an important role in mediating many of the behavioral and physiological effects of exposure to stressors. Focus has been primarily on the acute stress-induced rise in glucocorticoids [corticosterone (CORT) in the rat]. There are reports, however, that exposure to chronic stressors can produce an increase in basal CORT and a decrease in corticotropin-binding globulin (CBG). These changes occur subsequent to the stress-induced rise in CORT. The following experiments examined whether exposure to an acute stressor (100 5-sec inescapable tail shocks; IS) could also produce long term changes in basal CORT and CBG. We report that a single session of IS results in an increase in basal total serum CORT that persists 48-96 h after IS termination. The increase is present only at the diurnal trough (morning). CBG levels ae also decreased for 24-48 h. The decrease is present at both the diurnal peak (evening) as well as the trough (morning). These changes result in an increase in the percent and amount of biologically active CORT (unbound or free). Thus, glucocorticoid-sensitive targets are exposed to high levels of free CORT for several days after IS termination. The long term increase in free CORT reported here may play an important role in mediating some of the effects produced by IS as well as those produced by other acute stressors.

Animals↗

PubMed1994

Illness-induced hyperalgesia is mediated by a spinal NMDA-nitric oxide cascade.

A variety of experimental manipulations produce enhanced pain responsivity. Recent work has demonstrated that activation of N-methyl-D-aspartate (NMDA) receptors in the spinal cord can produce persistent enhancement of pain via production of nitric oxide and/or prostaglandins. To date, the behavioral paradigms used to study NMDA mediated hyperalgesia have all involved direct excitation of spinal cord dorsal horn neurons via activation of primary nociceptive afferents. The present series of experiments examined whether the NMDA cascade would also be activated by events that do not produce direct pain input to the spinal cord dorsal horn. The hyperalgesia-inducing paradigm used was intraperitoneal lipopolysaccharide (LPS), which causes transient illness. Prior work has shown that LPS induces hyperalgesia via activation of hepatic vagal afferents to the brain, thereby activating a centrifugal pain facilitory circuit. The present study demonstrates that this centrifugal hyperalgesia is produced via activation of the NMDA-nitric oxide cascade at the level of the spinal cord.

2-Amino-5-phosphonovalerate↗

PubMed1994

Illness-induced hyperalgesia is mediated by spinal neuropeptides and excitatory amino acids.

The spinal cord dorsal horn contains neural mechanisms which can greatly facilitate pain. We have recently shown that 'illness'-inducing agents, such as intraperitoneally administered lipopolysaccharide (LPS; bacterial endotoxin), can produce prolonged hyperalgesia. This hyperalgesic state is mediated at the level of the spinal cord via activation of the NMDA-nitric oxide cascade. However, prolonged neuronal depolarization is required before such a cascade can occur. The present series of experiments were aimed at identifying spinal neurotransmitters which might be responsible for creating such a depolarized state. These studies show that LPS hyperalgesia is mediated at the level of the spinal cord by substance P, cholecystokinin and excitatory amino acids acting at non-NMDA sites. No apparent role for serotonin or kappa opiate receptors was found.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1994

A permissive role of corticosterone in an opioid form of stress-induced analgesia: blockade of opiate analgesia is not due to stress-induced hormone release.

The 100 inescapable tail-shock paradigm produces three sequential analgesic states as the number of shocks increases: an early opioid analgesia (after 2 shocks) that is attenuated by systemic naltrexone, a middle analgesia (after 5-40 shocks) that is unaffected by systemic naltrexone, and a late opioid analgesia (after 80-100 shocks) that is attenuated by systemic naltrexone. In order to determine whether the absence of adrenal hormones would affect any of these analgesias, we tested adrenalectomized (ADX) versus sham-operated control rats 2 weeks post-surgery. Pain threshold was assessed using the tail-flick (TF) test. ADX attenuated both the early (2 shock) and late (80-100 shock) opiate analgesias and failed to reduce the naltrexone-insensitive analgesia after 5-40 shocks. We demonstrated that a loss of adrenomedullary catecholamines does not underlie the ADX-induced attenuation of opioid analgesia since sympathetic blockade using systemic chlorisondamine (6 mg/kg) failed to reduce analgesia at any point in the shock session. It was further shown that stress levels of adrenal hormones are not critical since (a) analgesia was unaffected when animals were tested 48 h after ADX, (b) 2 shocks do not produce a surge in corticosterone (CORT) over and above levels observed in animals restrained and TF tested in preparation for shock, and (c) basal CORT replacement in drinking water fully restored analgesia in ADX rats. These experiments demonstrate that basal CORT, rather than adrenomedullary substances, is critical to the expression of analgesia. The function of CORT here is not linked to a shock-induced surge of the steroid. CORT appears to play a permissive role in the expression of analgesia. Potential effects of the absence of corticosteroids on neurotransmitter biosynthesis important in analgesia production are discussed.

Adrenal Medulla↗

PubMed1994

Characterization of cytokine-induced hyperalgesia.

Agents which induce symptoms of illness, such as lipopolysaccharide (LPS), cause diverse effects including hyperalgesia. While previous studies have examined central pathways mediating LPS hyperalgesia, the initial steps in activating this system remain unknown. Since LPS induces the release of various cytokines and eicosinoids from immune cells, the present series of experiments examined the potential involvement of these substances in LPS hyperalgesia. This work demonstrates that: (a) Interleukin-1 beta (IL-1 beta) can produce hyperalgesia following either intraperitoneal or intracerebroventricular injection. In contrast, IL-1 beta delivered intrathecally did not affect pain responsivity. (b) Liver macrophages (Kupffer cells) appear to be critically involved, and relay signals to the brain via hepatic vagal afferents. (c) Both IL-1 beta and tumor necrosis factor appear to be critical mediators of LPS hyperalgesia. In contrast, prostaglandins do not appear to be involved. Taken together, these studies suggest that substances classically thought of as products of the immune system may dynamically enhance pain responsivity via actions either on the hepatic vagus or at central sites.

Animals↗

PubMed1994

Subcutaneous formalin produces centrifugal hyperalgesia at a non-injected site via the NMDA-nitric oxide cascade.

Previous work has demonstrated that pain facilitation can occur following injection of subcutaneous irritants, such as formalin. Such studies have focused on apparent pain facilitation induced at the site of irritant injection. Changes in processing of incoming pain information have typically been assumed to result from activation of neurocircuitry intrinsic to the spinal cord. The present series of studies have examined hyperalgesia exhibited at a site distant from the site of irritant injection and have begun to define the neurocircuitry and neuropharmacology underlying this pain enhancement. This work demonstrates that s.c. formalin injected into the dorsum of one hindpaw in rats produces prolonged hyperalgesia as measured by the tailflick test. Hyperalgesia is not mediated solely by circuitry intrinsic to the spinal cord, but rather involves activation of centrifugal pathways originating within the brain and descending to the spinal cord via pathway(s) outside of the dorsolateral funiculus. At the level of the spinal cord, this hyperalgesic state is mediated by an NMDA-nitric oxide cascade, since hyperalgesia can be abolished by administration of either an NMDA antagonist (APV) or a nitric oxide synthesis inhibitor (L-NAME).

2-Amino-5-phosphonovalerate↗

PubMed1994

Neurocircuitry of illness-induced hyperalgesia.

We have previously demonstrated that illness-inducing agents such as lithium chloride (LiCl) and the bacterial cell wall endotoxin lipopolysaccharide (LPS) produce hyperalgesia on diverse pain measures. The present series of studies attempted to identify the neurocircuitry mediating these effects. These studies have demonstrated that illness-inducing agents produce hyperalgesia by activating: (a) peripheral nerves rather than by generating a blood-borne mediator (Expt. 1); (b) vagal afferents, specifically afferents within the hepatic branch of the vagus (Expt. 2); (c) as yet unidentified brain site(s) rostral to the mid-mesencephalon (Expt. 6); (d) a centrifugal pathway that arises from the nucleus raphe magnus, and not from the adjacent nucleus reticularis paragigantocellularis pars alpha (Expts. 4 and 5); (e) a centrifugal pathway in the dorsolateral funiculus of the spinal cord (Expt. 3); and (f) the same centrifugal pathways for diverse illness inducing agents (Expts. 3, 7 and 8). These data call for the re-evaluation of a number of assumptions inherent in previous studies of hyperalgesia.

Animals↗

PubMed1994

The nature of conditioned anti-analgesia: spinal cord opiate and anti-opiate neurochemistry.

The central nervous system contains circuitry that inhibits pain sensitivity (analgesia), as well as circuitry that opposes pain inhibition (anti-analgesia). Activation of analgesia systems and anti-analgesia systems can each be brought under environmental control using classical conditioning procedures. Analgesia can be produced by cues present before and during aversive events such as electric shock, while active inhibition of analgesia comes to be produced by cues never present immediately before or during shock and therefore signal safety. We have recently reported that these analgesia and anti-analgesia systems interact at the level of the spinal cord. A series of 3 experiments were performed to examine how such interactions occur. First, potential opioid mediation of conditioned analgesia was investigated using systemic and intrathecal (i.t.) delivery of opiate antagonists. Conditioned analgesia was found to be mediated by activation of spinal mu and delta opiate receptors. Second, analgesia produced by each of these receptor subtypes was challenged by environmental signals for safety. Analgesias produced by mu and delta opiate agonists were each abolished by safety signals. Third, antagonists/antisera directed against several putative anti-opiate neurotransmitters were tested i.t. to identify which mediate conditioned anti-analgesia at the level of the spinal cord. A cholecystokinin antagonist abolished conditioned anti-analgesia. In contrast, neuropeptide FF antiserum and a kappa opiate antagonist were without effect.

Analgesia↗

PubMed1994

Morphine-induced decreases in in vivo antibody responses.

Endogenous opioids have been shown to be released during acute stress and could play a role in immune modulation and activation of the hypothalamo-pituitary-adrenal axis. We investigated the ability of morphine sulfate to mimic stressor effects on decreases in in vivo antibody responses. Sprague-Dawley and Fischer 344 rats were given an intraperitoneal injection of an antigen, Keyhole limpet hemocyanin (KLH), followed by a single intravenous injection of either saline or varying doses of morphine sulfate. The corticosterone and anti-KLH IgG antibody responses to morphine were measured. A dose-dependent increase in corticosterone was observed. Significantly lower levels of anti-KLH IgG antibodies were observed in morphine-treated animals but these effects were strain and dose dependent. In Sprague-Dawley rats, 3 and 10 mg/kg doses of morphine decreased antibody levels while 1.5, 5, and 15 mg/kg did not change antibody responses. In Fischer 344 rats a dose of 5 mg/kg of morphine decreased antibody levels while 10 and 15 mg/kg did not change antibody responses. These results indicate that morphine can decrease antibody levels and that these decreases are not correlated with elevated levels of corticosterone. To determine if opioid binding is critical to these changes, animals received naltrexone prior to the administration of morphine. Naltrexone partially attenuated corticosterone levels, but completely blocked morphine-induced changes in immune function.

Animals↗

PubMed1994

Route of morphine administration modulates conditioned analgesic tolerance and hyperalgesia.

The present experiments investigated the effects of route of drug injection on two of the phenomena associated with repeated, cued, morphine administration. Experiment 1 examined the degree of situational specificity of analgesic tolerance following 5 days of morphine (5 mg/kg) delivered either subcutaneously (SC) or intravenously (i.v.). Situationally specific tolerance was only observed following i.v. morphine, although nonspecific tolerance was evident in both instances. Experiment 2 indicated that this difference was not due to dose, as neither 2.5 or 7.5 mg/kg SC morphine produced demonstrable situationally specific tolerance. Experiment 3 examined the putative existence of compensatory responses underlying the observed tolerance. Hyperalgesia in response to the environment in which morphine was experienced was evident in animals trained with i.v. morphine, but not in those receiving repeated SC injections. Potential explanations for these effects of route of administration are discussed.

Analgesics↗