T Nakamori

The central role of corticotrophin-releasing factor (CRF-41) in psychological stress in rats.

1. We investigated the central role of corticotrophin‐releasing factor (CRF‐41) in psychological stress‐induced responses, including cardiovascular, thermoregulatory and locomotive activity in free‐moving rats. 2. Psychological stress was induced by cage‐switch stress. After rats were placed in the novel environment, blood pressure, heart rate, body temperature and locomotive activity significantly increased. The intracerebroventricular (I.C.V.) injection of alpha‐helical CRF(9‐41), a CRF‐41 receptor antagonist, significantly attenuated the stress‐induced hypertension, tachycardia, hyperthermia and increase in locomotive activity. However, in unstressed rats, the I.C.V. injection of alpha‐helical CRF(9‐41) had no effect on physiological parameters measured in this study. 3. In unstressed rats, the I.C.V. injection of CRF‐41 (1 microgram and 10 micrograms) increased blood pressure, heart rate, body temperature and locomotive activity in a dose‐dependent manner. The changes in these responses were quite similar to those observed during cage‐switch stress. 4. The results suggest that central CRF‐41 plays an important role in psychological stress‐induced hypertension, hyperthermia, tachycardia and increase in locomotive activity. However, it is likely that central CRF‐41 does not contribute to normal cardiovascular and body temperature regulation when rats are free from stress.

Possible involvement of prostaglandin E in development of ACTH response in rats induced by human recombinant interleukin-1.

1. Intravenous (I.V.) injection of human recombinant interleukin‐1 alpha (IL‐1 alpha) produced dose‐dependent monophasic fevers in rats. Moreover, the I.V. injection of IL‐1 alpha produced dose‐dependent rises in the plasma concentrations of adrenocorticotrophic hormone (ACTH) 30 min after injections with dosages of 5 micrograms/kg and 15 micrograms/kg of IL‐1 alpha. 2. The febrile responses induced by the I.V. injection of IL‐1 alpha (15 micrograms/kg) were completely abolished, and conversely hypothermia occurred, when the animals were pre‐treated with a cyclo‐oxygenase inhibitor, indomethacin (INDO). Pre‐treatment with INDO also inhibited the increase in the plasma concentrations of ACTH induced by I.V. injection of IL‐1 alpha (15 micrograms/kg), indicating that enhancement of plasma concentrations of ACTH induced by I.V. injection of IL‐1 alpha is processed through the action of prostaglandins. 3. Intrapreoptic injection of prostaglandin E2 produced a dose‐dependent fever with a rapid onset at doses of 25 and 100 ng. Moreover, the intrapreoptic injection of prostaglandin E2 increased the plasma concentrations of ACTH in a dose‐dependent manner 30 min after injections. 4. The intrapreoptic injection of IL‐1 alpha (20 ng) caused slow monophasic fever. However, no significant elevation of plasma concentrations of ACTH was observed 30, 90 and 180 min after the intrapreoptic injection of IL‐1 alpha, as compared with the ACTH levels at each time in the control group which received an intrapreoptic injection of saline. 5. These results suggest that intrapreoptic prostaglandin E plays an important role in the ACTH response by inducing the release of corticotrophin‐releasing factor (CRF).

Possible involvement of prostaglandins in psychological stress-induced responses in rats.

1. We investigated the effect of pre‐treatment with intraperitoneal (I.P.) injection of indomethacin, an inhibitor of prostaglandin synthesis, on psychological stress‐induced responses including cardiovascular, thermoregulatory and hormonal responses in free‐moving rats. 2. Psychological stress was induced by cage‐switch stress. After the rats were placed in the novel environment, blood pressure, heart rate and body temperature significantly increased. Plasma levels of adrenocorticotrophic hormone (ACTH) and prostaglandin E2 were significantly higher 30 min after exposure to stress, in comparison to normal levels. 3. Pre‐treatment with I.P. indomethacin significantly suppressed the increases in body temperature induced by cage‐switch stress, but had no effect on increases in blood pressure and heart rate induced by this stress. Indomethacin also significantly suppressed the increases in the plasma levels of ACTH and prostaglandin E2 induced by cage‐switch stress. 4. The present results suggest that prostaglandins are involved in the development of hyperthermia and the ACTH response induced by psychological stress.

Multiple control of fever production in the central nervous system of rabbits.

1. The effects of microinjection of prostaglandin D2, E2 and F2 alpha and of endogenous pyrogen on the rectal temperature of rabbits were extensively examined in sixty‐eight brain regions and in the third cerebral ventricle. 2. Intracerebroventricular injection of both prostaglandins E2 and F2 alpha produced dose‐dependent fever over a range of 100‐1000 ng. The selective brain regions, the nucleus broca ventralis, preoptic area, anterior hypothalamus and the ventromedial hypothalamus, responded to microinjections of a small dose (less than 200 ng) of prostaglandins E2 and F2 alpha by producing fever. Furthermore, the lateral hypothalamus, ventral thalamus, substantia nigra and the trigeminal nucleus were also sensitive to high concentrations of prostaglandins E2 and F2 alpha, fever being produced. It is likely that prostaglandin D2 is not involved in fever induction. 3. The ventricular injection of endogenous pyrogen also produced fever. However, brain regions sensitive to microinjection of endogenous pyrogen were exclusively localized to regions near the organum vasculosum laminae terminalis (OVLT), such as the nucleus broca ventralis and the preoptic area. In contrast to the monophasic fever induced by prostaglandins E2 and F2 alpha, about 30 min after ventricular or cerebral injection of endogenous pyrogen the rectal temperature gradually started to rise and the fever was prolonged over 4 h. 4. We investigated the effect of an inhibitor of prostaglandin synthesis, sodium salicylate, on biphasic fever induced by intravenous injection of bacterial endotoxin. The microinjections of sodium salicylate into the bilateral regions near the OVLT suppressed the second peak but had no effect on the first peak. 5. The present study clarifies that there exist two separate mechanisms of induction of biphasic fever. Correlating with the first peak of biphasic fever, prostaglandins synthesized outside the blood‐brain barrier act on multiple sites in the central nervous system to induce fever. Correlating with the second peak, endogenous pyrogen acts on regions near the OVLT to synthesize and release pyrogenic prostaglandins.

Evidence for separate mechanisms of induction of biphasic fever inside and outside the blood‐brain barrier in rabbits.

1. Intravenous bacterial endotoxin, or endogenous pyrogen, in high concentration both caused biphasic fever in rabbits. In low concentration they produced only the first phase of fever. 2. Subcutaneous indomethacin suppressed the first phase of fever produced by high concentration of intravenous endotoxin or endogenous pyrogen, but not the second phase. 3. Intraventricular cerebral injection of indomethacin reduced the second phase of fever produced by high concentration of intravenous endotoxin or endogenous pyrogen, but not the first phase. 4. Intraventricular cerebral injection of endotoxin or of endogenous pyrogen caused slow monophasic fever. This was suppressed by intraventricular, but not by subcutaneous, indomethacin. 5. It is concluded that the first phase of biphasic fever is caused by pyrogen acting via structures outside the blood‐brain barrier, presumably peripheral nerves, and the second phase by pyrogen acting via structures within the blood‐brain barrier, presumably hypothalamic neurones.

Interleukin‐1 beta production in the rabbit brain during endotoxin‐induced fever.

Interleukin‐1 beta (IL‐1 beta) production in the brain and the spleen was investigated in rabbits made febrile by intravenous (I.V.) injection of endotoxin, or human recombinant IL‐1 beta (hIL‐1 beta). The endotoxin used in the present study was the lipopolysaccharide (LPS) of Salmonella typhosa endotoxin. Monophasic fever was induced by I.V. injection of a low dose of LPS (0.02 micrograms kg‐1) and biphasic fever by I.V. injection of a large dose of LPS (4 micrograms kg‐1), a sublethal dose of LPS (40 micrograms kg‐1) or hIL‐1 beta (2 micrograms kg‐1). In situ hybridization and immunohistochemical studies revealed that, although no IL‐1 beta production was observed in the brain at 1 and 3 h after injection of a low dose of LPS (0.02 micrograms kg‐1) or of hIL‐1 beta (2 micrograms kg‐1), IL‐1 beta production was demonstrated in organum vasculosum laminae terminalis (OVLT) and some cells around the blood vessels in the parenchyma 1 h after 4 micrograms kg‐1 LPS. IL‐1 beta production was detected throughout the brain after 40 micrograms kg‐1 LPS. Pretreatment with indomethacin, an inhibitor of prostaglandin synthesis, did not affect IL‐1 beta production in the brain induced by 4 micrograms kg‐1 LPS. The cell type which produces IL‐1 beta in the OVLT following LPS injection was confirmed to be a macrophage by electron microscopy. The cells producing IL‐1 beta in the parenchyma were determined to be microglial cells. In the spleen, each dose of LPS induced a significant increase in IL‐1 beta production in polymorphonuclear cells and macrophages in the red pulp 1 h after injection. However, 2 micrograms kg‐1 hIL‐1 beta did not induce IL‐1 beta production in the spleen. The present results show clearly that systemic administration of LPS induces IL‐1 beta production in the OVLT which may be responsible for induction of the second phase of biphasic fever. The production of IL‐1 beta in the OVLT was not attributable to the action of peripherally synthesized IL‐1 beta or prostaglandins.

Organum vasculosum laminae terminalis (OVLT) is a brain site to produce interleukin-1β during fever

The present study was carried out to determine whether interleukin-1 (IL-1) production occurs in the rabbit organum vasculosum laminae terminalis (OVLT) during fever induced by endotoxin. The intravenous (i.v.) injection of endotoxin (4 micrograms/kg) caused significant fever in rabbits. Through the use of in situ hybridization and immunohistochemical techniques, the synthesis of IL-1 was observed in the OVLT during the fever. The present results support the hypothesis that IL-1 is produced in the brain during fever.

Cardiovascular responses induced in free-moving rats by immune cytokines.

1. We investigated the effect of intraperitoneal (I.P.) injections of the immune cytokines, interleukin‐1 beta (IL‐1 beta) and tumour necrosis factor (TNF) on cardiovascular responses in free‐moving rats, using a biotelemetry system. 2. The I.P. injection of a small dose of IL‐1 beta (1 microgram/kg) induced a monophasic increase in the heart rate, and that of a large dose (10 micrograms/kg) induced biphasic increases in the blood pressure and heart rate. However, the I.P. injection of any of several doses of TNF (1, 10 and 50 micrograms/kg) had no effect on cardiovascular responses in rats. 3. Pre‐treatment with I.P. injection of indomethacin (10 mg/kg), an inhibitor of cyclo‐oxygenase, significantly suppressed the cardiovascular responses and the increase in the plasma noradrenaline (NA) concentration induced by I.P. injection of IL‐1 beta. 4. Microinjection of IL‐1 beta (1 and 10 ng) into the preoptic and anterior hypothalamic (PO‐AH) region induced dose‐dependent increases in the blood pressure and heart rate in rats. These responses were also suppressed by pretreatment with I.P. indomethacin (10 mg/kg). In addition, microinjection of prostaglandin E2 (20 and 100 ng) into the PO‐AH region increased blood pressure and heart rate, but that of prostaglandin D2 (100 ng) had no effect. 5. The present results suggest that IL‐1 beta stimulates the release of prostaglandins, presumably E series, near regions of the hypothalamus, which act on the hypothalamus to induce activation of the sympathetic nervous system. Subsequently, the blood pressure, heart rate and the plasma level of NA increase.

ACTH response induced in capsaicin-desensitized rats by intravenous injection of interleukin-1 or prostaglandin E.

1. We investigated whether afferent nerves are involved in the development of adrenocorticotrophic hormone (ACTH) responses induced either by systemic administration of interleukin‐1 beta (IL‐1 beta) and prostaglandin E2, or by psychological stress. The capsaicin desensitization method was used to impair afferent C fibres and we compared the ACTH responses between capsaicin desensitized and vehicle pretreated control rats. 2. The present results showed that the capsaicin desensitized rats had significantly smaller increases in plasma ACTH than the control rats in response to intravenous injection of IL‐1 beta or prostaglandin E2. 3. There were no significant differences between the capsaicin desensitized and control rats in the ACTH responses induced by cage switch stress. 4. The capsaicin desensitized rats responded to intravenous injection of corticotrophin releasing factor (CRF) with a greater increase in the plasma level of ACTH than the control rats, indicating that capsaicin pretreatment resulted in augmentation of pituitary gland sensitivity to CRF. 5. These results suggest that afferent neurons play an important role in the ACTH responses induced by systemic injection of IL‐1 beta or prostaglandin E2.

ACTH release induced in rats by noradrenaline is mediated by prostaglandin E2.

1. We investigated the involvement of prostaglandin E2 in the development of the adrenocorticotrophic hormone (ACTH) response induced by noradrenaline (NA) in rats. 2. Intravenous (i.v.) injection of NA produced dose‐dependent increases in the plasma concentration of ACTH and prostaglandin E2. However, pre‐treatment with systemic administration of indomethacin, an inhibitor of prostaglandin synthesis, significantly suppressed this increase in plasma ACTH. 3. The i.v. injection of prostaglandin E2 significantly increased the plasma concentration of ACTH in a dose‐dependent manner. In contrast, ACTH responses induced by the i.v. injection of prostaglandin E2 were significantly suppressed by systemic pre‐treatment with anti‐corticotrophin‐releasing factor antibody (anti‐CRF), although the plasma level of ACTH still increased in comparison to the basal level. 4. These results suggest that NA‐stimulated prostaglandin release is involved in the ACTH response induced by NA. In addition, it is likely that CRF may be responsible for a portion of the ACTH response induced by i.v. injection of prostaglandin E2.