Coping and immunosuppression: inescapable but not escapable shock suppresses lymphocyte proliferation

Inescapable shock, neurotransmitters, and addiction to trauma: toward a psychobiology of post traumatic stress

Chronic post traumatic stress has been described as a "physioneurosis" (Kardiner 1941), that is, a mental disorder with both psychological and physiological components. The behavioral sequelae of inescapable shock in animals and of massive psychic trauma in people show a striking parallel. Inescapable shock in animals leads to both transient catecholamine depletion and subsequent stress-induced analgesia. We postulate that the numbing and catatenoid reactions following trauma in humans correspond to the central nervous system (CNS) catecholamine depletion that follows inescapable shock in animals. We further explore the evidence for a human equivalent of "stress-induced analgesia" in animals, which is known to be mediated by endogenous opioids. Although reexposure to trauma may produce a paradoxical sense of calm and control due to endogenous opioid release, a cessation of traumtic stimulation will be followed by symptoms of opioid withdrawal and physiological hyperreactivity mediated by CNS noradrenergic hypersensitivity. This hyperreactivity can, in turn, be temporarily modified by reexposure to trauma. This factor could account for voluntary reexposure to trauma in many traumatized individuals and would provide a complementary formulation to the conventional psychodynamic concept of attempted mastery of the psychosocial meaning of the trauma.

Conditioned taste aversion suppresses induction of delayed-type hypersensitivity immune reactions

Conditioned taste aversion was induced in mice by pairing saccharin drinking with an intraperitoneal injection of lithium chloride, a toxic but nonimmunosuppressive drug. Conditioned mice showed not only suppressed saccharin drinking but also a 75% reduction in the induction of delayed-type hypersensitivity immune responses to low doses of sheep erythrocytes. This effect was observed with doses of lithium chloride which had no effect of their own on immune functions. In addition, a reduction in water consumption was not responsible for the reduced immune response of conditioned mice since the immune responses of water deprived mice did not differ from those of nondeprived mice. Conditioned mice exposed to saccharin had higher plasma levels of glucocorticoids than nonconditioned mice, suggesting that the experience of being reexposed to a taste paired with lithium chloride was perceived as aversive. These data demonstrate that alterations in immune functions can be induced by a conditioned taste aversion procedure independently of any immunosuppressive drug.

The anterior cingulate cortex and stress: effects of chlordiazepoxide on unit-activity and stimulation-induced gastric pathology in rats

Multiple unit-activity in the anterior cingulate cortex of rats indicated that during immobilization-stress some units increased responding, and others decreased their response rates. Changes in unit-behavior were also found when a stimulus was presented that previously had been paired with the restraint treatment. Pretreatment with chlordiazepoxide prevented the stress-induced increases in unit-activity, whereas, suppressed units were not affected by the drug treatment. Injections of chlordiazepoxide also attenuated the gastric pathology which was found following low-level electrical stimulation of the area of the units which had been identified to respond to restraint-stress.

Intrinsic mechanisms of pain inhibition: activation by stress

Portions of the brain stem seem normally to inhibit pain. In man and laboratory animals these brain areas and pathways from them to spinal sensory circuits can be activated by focal stimulation. Endogenous opioids appear to be implicated although separate nonopioid mechanisms are also evident. Stress seems to be a natural stimulus triggering pain suppression. Properties of electric footshock have been shown to determine the opioid or nonopioid basis of stress-induced analgesia. Two different opioid systems can be activated by different footshock paradigms. This dissection of stress analgesia has begun to integrate divergent findings concerning pain inhibition and also to account for some of the variance that has obscured the reliable measurement of the effects of stress on tumor growth and immune function.

Evidence for the activation of the endogenous opiate system in hamsters infected with human blood flukes, Schistosoma mansoni

Nociceptive thresholds were investigated in golden hamsters infected with the human blood fluke, Schistosoma mansoni. Increases in thermal thresholds suggestive of analgesia were evident by 20-25 days of infection. These increased further during a 40-42 day period. The altered responses were suppressed by the opioid antagonist naloxone. Non-invasive inhibition of the activity of the pineal gland by exposure to light also reduced nocturnal analgesia in schistosome infected animals. Naloxone antagonism and pineal inhibition of morphine- induced analgesia was obtained similarly in control, uninfected animals. Taken together, these findings suggest strongly that infection with S. mansoni results in a chronic activation of the endogenous opiate system.

Sympathetic innervation of lymph nodes in mice

Noradrenergic innervation of popliteal and mesenteric lymph nodes in mice was examined with fluorescence histochemistry. Dense varicose plexuses entered the nodes with the vasculature in the hilar region and continued with the vasculature into the medullary region. Fine, delicate varicosities and small vascular plexuses continued into the cortical and paracortical regions surrounding the germinal centers; some varicosities ended among lymphocytes. A subcapsular plexus contributed fibers into the cortical and paracortical regions. Chemical measurements revealed the presence of norepinephrine in lymph nodes that was depletable with 6-hydroxydopamine. Depletion of norepinephrine from lymph nodes with this agent resulted in a diminished primary immune response in draining lymph nodes following subcutaneous injection of an antigen in two mouse strains, but had no effect in two other strains. These findings suggest that noradrenergic fibers innervate both the vasculature and parenchymal regions of lymph nodes, and may participate in the modulation of immune responses in these organs.

A decrease in thymus-mediated immune responses as a result of treatment of neonatal rats with glutamate

We investigated whether administration of monosodium 1-glutamate (MSG) to neonatal rats would disrupt immune responses in intact and orchidectomized adult male rats. Neonatal male rats were treated with saline or MSG which causes severe endocrine abnormalities. Half of each group of animals were orchidectomized as adults and killed one week later along with intact rats. MSG treatment resulted in suppressed serum LH levels in intact rats. Thymus weight and spleen cellularity in intact animals were not affected by MSG treatment, but thymus weight increased within one week after orchidectomy in both saline- and MSG-treated groups. In intact rats, lymphocyte stimulation by the T cell specific mitogens (concanavalin A or phytohemagglutinin) or the B cell specific mitogen (lipopolysaccharide) was unaffected by prior treatment with MSG. However, MSG treatment blocked the decrease attributable to orchidectomy in concanavalin A and phytohemagglutinin stimulation of lymphocyte blastogenesis. The results suggest that administration of MSG to neonatal male rats can alter some immune responses in the adult animal.

Opioid peptides mediate the suppressive effect of stress on natural killer cell cytotoxicity

The cytotoxic activity of natural killer cells was investigated in rats subjected to one of two inescapable footshock stress paradigms, both of which induce analgesia, but only one via activation of opioid mechanisms. Splenic natural killer cell activity was suppressed by the opioid, but not the nonopioid, form of stress. This suppression was blocked by the opioid antagonist naltrexone. Similar suppression of natural killer activity was induced by high doses of morphine. These results suggest that endogenous opioid peptides mediate the suppressive effect of certain forms of stress on natural killer cell cytotoxicity.

Apparent involvement of opioid peptides in stress-induced enhancement of tumor growth

Exposure to stress has been associated with alterations in both immune function and tumor development in man and laboratory animals. In the present study, we investigated the effect of a particular type of inescapable footshock stress, known to cause an opioid mediated form of analgesia, on survival time of female Fischer 344 rats injected with a mammary ascites tumor. Rats subjected to inescapable footshock manifested an enhanced tumor growth indicated by a decreased survival time and decreased percent survival. This tumor enhancing effect of stress was prevented by the opiate antagonist, naltrexone, suggesting a role for endogenous opioid peptides in this process. In the absence of stress, naltrexone did not affect tumor growth.