Functional and structural differences in febrile mechanism between rabbits and rats

Evaluation of antipyretic activity of Belladonna and Pyrogenium ultrahigh dilutions in induced fever model

Background Belladonna and Pyrogenium are commonly used to treat fever in homeopathy. But in vivo antipyretic activity of these medicines is not reported yet. The study was conducted to evaluate the effectiveness of ultrahigh dilutions of Belladonna (Bell) and Pyrogenium (Pyro) in fever model of rabbits induced by Baker's yeast. Methods Healthy, local strain rabbits (♂ and ♀) were divided into seven groups (n=42): Normal control, negative control, standard control, pyro 1000c, pyro 200c, Bell 1000c and Bell 200c. Fever was induced by intra peritoneal injection of 135 mg/kg Baker's yeast suspension. Rectal temperature was measured hourly. All the medicines were administered once a day. The results were expressed as mean ± SEM. ANOVA and least significant difference post hoc test were applied for checking the level of significance, p-value of ≤0.05 was considered significant statistically. Results Pyro in both potencies significantly reduced fever in rabbits compared to negative control group, while both potencies of Bell were ineffective. Paracetamol and Pyro 1000c reduced by 1.2 °C (39.7 ± 0.1 to 38.5 ± 0.1), while Pyro 200c reduced by 1 °C temperature (39.7 ± 0.5 to 38.7 ± 0.2). Conclusions Pyro possesses marked antipyretic activity in rabbit's Baker's yeast fever model. It would embolden its clinical use in fever with more guarantee of its efficacy. However, caveat of small sample size necessitates replication of experiment in large sample size.

In vivo evaluation of antipyretic effects of some homeopathic ultra-high dilutions on Baker's yeast-induced fever on Similia principle

BACKGROUND

Homeopathy is a controversial alternative system of medicine. The action of homeopathic medicines is considered slow and it is assumed that homeopathic medicines are ineffective in acute conditions such as fever.

OBJECTIVE

In the present study, effects of 3 homeopathic medicines on baker's yeast induced fever were investigated.

MATERIALS AND METHODS

42 local strain rabbits were equally divided into 7 groups. Normal saline was orally administered to group 1 (normal control) rabbits without fever induction. Group 2 underwent baker's yeast-induced fever (negative control). Groups 3, 4, 5, 6 and 7 underwent baker's yeast-induced fever and were thereafter treated orally with paracetamol, Nux vomica 200C and 1M, Calcarea phos 200C and Belladonna 200C respectively. Rectal temperature was checked hourly. The abdominal writhing and frequency of loose stools were also monitored. ANOVA was applied for checking statistical significance. p ≤ 0.05 was considered significant.

RESULTS

The rectal temperature increased significantly (p < 0.05) in the negative control group when compared to the normal control. Abdominal writhing and loose stools monitoring showed increased writhing and loose stools frequency of group 2, 3, 6 and 7 rabbits. However, treatment of paracetamol significantly reduced rectal temperature. Group 4 & 5 showed significant reduction of rectal temperature together with abatement of abdominal writhing and loose stools.

CONCLUSION

N. vomica ultra-high dilutions have normalized rectal temperature and prevented the abdominal writhing and loose stools in baker's yeast-induced fever model of rabbits. It could be due to antidotal activity of N. vomica ultra-high dilutions. Therefore, N. vomica ultra-high dilutions can be useful antipyretic agents and can treat conditions associated with gastrointestinal symptoms. However, fixed conclusion can't be asserted due to caveat of small sample size.

Central mediators involved in the febrile response: effects of antipyretic drugs

Fever is a complex signal of inflammatory and infectious diseases. It is generally initiated when peripherally produced endogenous pyrogens reach areas that surround the hypothalamus. These peripheral endogenous pyrogens are cytokines that are produced by leukocytes and other cells, the most known of which are interleukin-1β, tumor necrosis factor-α, and interleukin-6. Because of the capacity of these molecules to induce their own synthesis and the synthesis of other cytokines, they can also be synthesized in the central nervous system. However, these pyrogens are not the final mediators of the febrile response. These cytokines can induce the synthesis of cyclooxygenase-2, which produces prostaglandins. These prostanoids alter hypothalamic temperature control, leading to an increase in heat production, the conservation of heat, and ultimately fever. The effect of antipyretics is based on blocking prostaglandin synthesis. In this review, we discuss recent data on the importance of prostaglandins in the febrile response, and we show that some endogenous mediators can still induce the febrile response even when known antipyretics reduce the levels of prostaglandins in the central nervous system. These studies suggest that centrally produced mediators other than prostaglandins participate in the genesis of fever. Among the most studied central mediators of fever are corticotropin-releasing factor, endothelins, chemokines, endogenous opioids, and substance P, which are discussed herein. Additionally, recent evidence suggests that these different pathways of fever induction may be activated during different pathological conditions.

Central mediators involved in the febrile response: effects of antipyretic drugs

Fever is a complex signal of inflammatory and infectious diseases. It is generally initiated when peripherally produced endogenous pyrogens reach areas that surround the hypothalamus. These peripheral endogenous pyrogens are cytokines that are produced by leukocytes and other cells, the most known of which are interleukin-1β, tumor necrosis factor-α, and interleukin-6. Because of the capacity of these molecules to induce their own synthesis and the synthesis of other cytokines, they can also be synthesized in the central nervous system. However, these pyrogens are not the final mediators of the febrile response. These cytokines can induce the synthesis of cyclooxygenase-2, which produces prostaglandins. These prostanoids alter hypothalamic temperature control, leading to an increase in heat production, the conservation of heat, and ultimately fever. The effect of antipyretics is based on blocking prostaglandin synthesis. In this review, we discuss recent data on the importance of prostaglandins in the febrile response, and we show that some endogenous mediators can still induce the febrile response even when known antipyretics reduce the levels of prostaglandins in the central nervous system. These studies suggest that centrally produced mediators other than prostaglandins participate in the genesis of fever. Among the most studied central mediators of fever are corticotropin-releasing factor, endothelins, chemokines, endogenous opioids, and substance P, which are discussed herein. Additionally, recent evidence suggests that these different pathways of fever induction may be activated during different pathological conditions.

Magnetic resonance imaging of soft tissue infection with iron oxide labeled granulocytes in a rat model

OBJECT

We sought to detect an acute soft tissue infection in rats by magnetic resonance imaging (MRI) using granulocytes, previously labeled with superparamagnetic particles of iron oxide (SPIO).

MATERIALS AND METHODS

Parasternal infection was induced by subcutaneous inoculation of Staphylococcus aureus suspension in rats. Granulocytes isolated from isogenic donor rats were labeled with SPIO. Infected rats were imaged by MRI before, 6 and 12 hours after intravenous injection of SPIO-labeled or unlabeled granulocytes. MR findings were correlated with histological analysis by Prussian blue staining and with re-isolated SPIO-labeled granulocytes from the infectious area by magnetic cell separation.

RESULTS

Susceptibility effects were present in infected sites on post-contrast T2*-weighted MR images in all animals of the experimental group. Regions of decreased signal intensity (SI) in MRI were detected at 6 hours after granulocyte administration and were more pronounced at 12 hours. SPIO-labeled granulocytes were identified by Prussian blue staining in the infected tissue and could be successfully re-isolated from the infected area by magnetic cell separation.

CONCLUSION

The application of SPIO-labeled granulocytes in MRI offers new perspectives in diagnostic specificity and sensitifity to detect early infectious processes.

Increased vascular permeability in the circumventricular organs of adult rat brain due to stimulation by extremely low frequency magnetic fields

It has been demonstrated that the exposure of biological systems to magnetic fields (MFs) can produce several beneficial effects: tissue recovery in chronic wounds, re-establishment of blood circulation after tissue ischemia or in necrotic tissues, improvement after epileptic episodes, angiogenesis, etc. In the current study, the effects of extremely low frequency (ELF) MF on the capillaries of some circumventricular organs (CVOs) are demonstrated; a vasodilator effect is reported as well as an increase in their permeability to non-liposoluble substances. For this study, 96 Wistar male rats (250 g body mass) were used and divided into three groups of 32 rats each: a control group (no treatment); a sham ELF-MF group; and an experimental group subjected to ELF-MF (120 Hz harmonic waves and 0.66 mT, root mean square) by the use of Helmholtz coils. All animals were administered colloidal carbon (CC) intravenously to study, through optical and transmission electron microscopy, the capillary permeability in CVOs and the blood-brain barrier (BBB) in brain areas. An increase in capillary permeability to CC was detected in the ELF-MF-exposed group as well as a significant increase in vascular area (capillary vasodilation); none of these effects were observed in individuals of the control and sham ELF-MF groups. It is important to investigate the mechanisms involved in the phenomena reported here in order to explain the effects of ELF-MF on brain vasculature.

Ceramide mediates the rapid phase of febrile response to IL-1beta

IL-1beta was identified after a long search for the endogenous pyrogen. It acts by inducing synthesis of prostaglandin E2, which mediates the late phase of IL-1beta-induced fever. Here we show by radiotelemetry that the early phase of the fever response to IL-1beta is mediated by ceramide. Hypothalamic application of the cell-penetrating C2-ceramide mimics the rapid phase of the IL-1beta-induced fever. Inhibition of ceramide synthesis blocks the rapid phase of fever but does not affect the slower prostaglandin E2-dependent phase, which is blocked by indomethacin or by null mutation of the EP3 prostanoid receptor. Electrophysiological experiments on preoptic area/anterior hypothalamic neurons show that C2-ceramide, but not dihydroceramide, mimics the rapid hyperpolarizing effects of IL-1beta on the activity of warm-sensitive hypothalamic neurons. IL-1beta-mediated hyperpolarization is blocked by PP2, the selective inhibitor of the protein tyrosine kinase Src, which is known to be activated by ceramide. These in vivo and in vitro data suggest that ceramide fulfills the criteria for an endogenous pyrogen.

Baker yeast-induced fever in young rats: Characterization and validation of an animal model for antipyretics screening

In this study we describe a low-cost and reliable method for inducing fever in young male rats (28-30 days of age, 75-90 g), which seems suitable for the screening of new antipyretics. The effects of temperature measuring procedure-induced stress on the basal rectal temperature and on Baker yeast-induced hyperthermia was assessed. Rectal temperature (T) was recorded every hour for 12 h (07:00-19:00 h) with a lubricated thermistor probe. The animals were injected intraperitoneally with baker yeast (0.25, 0.135, 0.05 g/kg) or the equivalent volume of saline at 7:00 h. The administration of 0.135 g/kg baker yeast induced a sustained increase in rectal temperature for 4 h. Classical (dipyrone and acetaminophen) and novel (MPCA and FPCA) antipyretics, at doses that had no effect per se, reverted baker yeast-induced fever. The method presented induces a clear-cut fever, which is reverted by antipyretics commonly used in human beings and selected novel antipyretics in small animals. The method also allows antipyretic evaluation with low amount of drugs, due to the use of small animals and to the small variability of the pyretic response, which ultimately causes a significant reduction in the number of animals necessary for antipyretic evaluation. Therefore, this study describes an animal model of fever that is not only advantageous from the economical and technical point of view, but that also bears ethical concerns.

Altered frequency responses of sympathetic nerve discharge bursts after IL-1beta and mild hypothermia

Although interleukin-1beta (IL-1beta) administration produces nonuniform changes in the level of sympathetic nerve discharge (SND), the effect of IL-1beta on the frequency-domain relationships between discharges in different sympathetic nerves is not known. Autospectral and coherence analyses were used to determine the effect of IL-1beta and mild hypothermia (60 min after IL-1beta, colonic temperature from 38 degrees C to 36 degrees C) on the relationships between renal-interscapular brown adipose tissue (IBAT) and splenic-lumbar sympathetic nerve discharges in chloralose-anesthetized rats. The following observations were made. 1) IL-1beta did not alter renal-IBAT coherence values in the 0- to 2-Hz frequency band or at the cardiac frequency (CF). 2) Peak coherence values relating splenic-lumbar discharges at the CF were significantly increased after IL-1beta and during hypothermia. 3) Hypothermia after IL-1beta significantly reduced the coupling (0-2 Hz and CF) between renal-IBAT but not splenic-lumbar SND bursts. 4) Combining IL-1beta and mild hypothermia had a greater effect on renal-IBAT SND coherence values than did mild hypothermia alone. These data demonstrate functional plasticity in sympathetic neural circuits and suggest complex relationships between immune products and SND regulation.

Astrocytic factors down-regulate the expression of major histocompatibility complex-class-II and intercellular adhesion molecule-1 on human monocytes

Several factors contribute to the maintenance of central nervous system immune privilege and astrocytes have been identified as a major source of immunomodulatory cytokines. To investigate whether hematogenous monocytes are immunologically deactivated by astrocyte-derived factors human monocytes were stimulated with lipopolysaccharide or interferon (IFN)-gamma and treated with the supernatant from pure astrocyte cultures, interleukin (IL)-4, IL-10, or with IL-1-receptor antagonist (1L-1-RA). Flow cytometry demonstrated that the supernatant from astrocyte cultures was the most potent agent in reducing the levels of major histocompatibility complex (MHC)-class-II- as well as intercellular adhesion molecule-1-expression, whereas IL-4, IL-10, and IL-1-RA had only marginal effects. The expression of leukocyte function antigen-1 and very late antigen-4 was not modulated by either factor. In conclusion, astrocytes seem to provide soluble factors that have the capacity to deactivate hematogenous monocytes.

Brain eicosanoids and LPS fever: species and age differences

The results of the present study, summarized in Table 2, demonstrate that different species and strains of rodents (rats and mice) and birds (chickens) exhibit rather specific fever response. Systemic administration of LPS caused monophasic elevation in Tb of chickens, biphasic changes in Tb of rats (initial drop followed by an increase in Tb), whereas mice failed to develop hyperthermia and responded by a decreased Tb. The LPS-induced alterations in hypothalamic prostanoid synthesis were also rather species-specific and differ markedly even between the two strains of mice. We failed to find a common direct correlation between LPS-induced changes in Tb and hypothalamic prostanoid production in rodents (rats and mice). This observation is supported by our recent study on age-related changes in fever response in rats, where we found that hypothalami of LPS-treated old and young adult rats produced similar amounts of PGE2 and PGI2, in spite of more pronounced and prolonged hypothermia, and a delayed elevation in Tb of old rats, as compared with young (Fraifeld et al., 1995b). Moreover, the hypothalamus of febrile chickens did not display any detectable activation of PGE2 production, suggesting that PGE2 is not a common central mediator of fever in homeotherms (Fraifeld et al., 1995a). Apparently, the actual body temperature not always reflects the functional state of central thermostat, and increased PGE2 production in hypothalamus would not directly, at least in rodents, lead to body temperature elevation. Furthermore, peripheral effects, including PG-mediated ones, of pyrogens can interfere and even overcome their centrally-mediated effects (Morimoto et al., 1991; Burysek et al., 1993). Previously, we have shown that no additional elevation in hypothalamic PGE2 production occurs in response to doses of LPS over 10 micrograms in rats and 25 micrograms in mice, while the increased doses led to further changes in Tb response (Kaplanski et al., 1993). Morimoto et al. (1991) have considered that PGE2 acts centrally to cause fever and peripherally to cause hypothermia, and, hence, these opposing actions, both being induced by LPS, may act together to determine the final thermoregulatory response. Other possibilities could be related to counterbalance of endogenous antipyretics (Kluger, 1991; Kozak et al., 1995), that may occur not only at the level of thermoregulatory center but also outside the CNS (Klir et al., 1995), and to the existence of PG-independent mechanisms of LPS fever. The latter have been shown for IL-8 (Rothwell et al., 1990; Zampronio et al., 1994) and MIP-1 (Davatelis et al., 1989; Minano et al., 1990; Hayashi et al., 1995; Lopez-Valpuesta and Myers, 1995), which are, apparently, mediated via CRF (Strijbos et al., 1992; Zampronio et al., 1994), and INF-alpha, mediated via the opioid receptor mechanisms (Hori et al., 1991, 1992). However, it has been shown recently that in different species the same pyrogenic cytokines (IL-8) may induced fever via different, PG-independent (in rats; Zampronio et al., 1994) or PG-dependent (in rabbits; Zampronio et al., 1995) mechanisms. It should be noted that fever response is not always accompanied by an elevation in Tb. The final effect of pyrogens on body temperature depends upon the balance between heat production and heat loss, which in turn is highly dependent upon body size and ambient temperature, especially in small animals. Perhaps, the hypothermic response observed in our mice and rats at 22 degrees C may be in part attributed to ambient temperature, which was below a thermoneutral zone. The reduced febrile response is considered, at least in part, to contribute to an increased mortality and prolonged recovery from infections (Kluger, 1986). From this point, it is difficult to suggest whether the hypothermia observed in our mice and rats could be of somewhat adaptive significance. It has been shown that at the ambient temperature of 30 degrees C, Swiss Webster mice can re

Response of newborn and adult sheep to pyrogens: relation between fever and brain eicosanoid changes

We investigated whether the weak febrile response to pyrogens in newborns is due to a diminished activation of the putative pyrogen mediator, prostaglandin (PG)E2. Indwelling cannulas in the third ventricle of lambs (age, 5-31 days) and adult ewes were used to collect cerebrospinal fluid (CSF) for radioimmunoassay of PGE2. Intravenous (i.v.) endotoxin caused a smaller increase in body temperature but a larger increase in CSF PGE2 in lambs compared to adults. PGE2 by intracarotid infusion raised body temperature in 5 of 7 trials in 3 lambs and in 4 of 4 trials in 1 adult. Endotoxin given intracerebroventricularly (i.c.v.) induced a rise in temperature and CSF PGE2 in the lamb but, in the adult, these responses were delayed and smaller. Interleukin-1 i.c.v. and PGE2 i.c.v. were weak pyretic agents at both ages. We conclude that the lamb's diminished febrile response to endotoxin i.v. is not caused by a lesser rise in CSF PGE2, rather it may be due, at least in part, to reduced responsiveness to this putative mediator. Regardless of age, the sheep differs from other species in that pyrogen/PGE2 coupling occurs primarily at a site in brain that is better accessible from blood than CSF.

Participation of cAMP and cAMP-dependent protein kinase in beta-adrenoceptor-mediated interleukin-1 beta mRNA induction in cultured microglia

We previously reported evidence of beta-adrenoceptor-mediated induction of IL-1 beta mRNA in the rat hypothalamus. The present in vitro studies using northern blot analysis showed that the beta-adrenoceptor agonist isoproterenol (1 x 10(-8) to 1 x 10(-5) M) caused a marked induction of IL-1 beta mRNA in microglia, but not in astrocytes. This induction was remarkably suppressed by pretreatment of cells with the beta-adrenoceptor antagonist propranolol. These phenomena were confirmed by in situ hybridization with digoxigenin-labelled IL-1 beta RNA probe. Furthermore, dibutyryl cyclicAMP (dbcAMP) (5 x 10(-4) and 5 x 10(-5) M) markedly induced IL-1 beta mRNA in microglia. The intracellular level of cAMP in microglia was elevated in a dose-dependent manner when they were treated with isoproterenol, and this elevation was completely blocked by propranolol. The induction of IL-1 beta mRNA by either isoproterenol or dbcAMP was strongly inhibited by a cAMP-dependent protein kinase inhibitor, H8. These results, taken together, suggest that (1) microglia primarily induce IL-1 beta mRNA by stimulation of beta-adrenoceptors, and (2) cAMP and cAMP-dependent protein kinase presumably participate in a signal transduction mechanism involved in the induction of IL-1 beta mRNA via beta-adrenoceptors.

What roles does the organum vasculosum laminae terminalis play in fever in rabbits?

Experiments were designed to clarify the role of the brain's organum vasculosum laminae terminalis (OVLT) in the development of fever in rabbits. Rectal and ear skin temperatures were recorded in conscious animals in which the OVLT had been electrolytically destroyed or in which the preoptic anterior hypothalamus (PO/AH) had been transected bilaterally. When the OVLT had been ablated the febrile responses to intravenous injection of interleukin-1 beta (IL-1 beta) or tumour necrosis factor alpha were significantly attenuated, while those to intracerebroventricular injection of IL-1 beta were not affected. Fever induced by intracerebroventricular injection of prostaglandin E2 (PGE2) was prolonged significantly. The febrile responses to intravenous injection of IL-1 beta and to intracerebroventricular injection of PGE2 were attenuated when the transection was located caudally to the anterior wall of the third ventricle and extended laterally more than about 3 mm in the ventricular wall. The results show that the OVLT region is a site through which signals to increase body temperature are transferred from the blood to the brain in rabbits.

Intracerebroventricular injection of interleukin-1 beta enhances nociceptive neuronal responses of the trigeminal nucleus caudalis in rats

To assess the effect of interleukin-1 (IL-1) in the brain on nociception electrophysiologically, recombinant human IL-1 beta (rhIL-1 beta) (1 pg/kg to 1 microgram/kg, i.e., 0.29 pg-0.33 microgram/rat) was microinjected into the lateral cerebral ventricle of urethane-anesthetized rats and the changes of responses in the wide dynamic range (WDR) neurons in the trigeminal nucleus caudalis to noxious pinching of facial skin were observed. A significant enhancement in the responses of the WDR neurons to noxious stimuli was observed after the injection of rhIL-1 beta between 10 pg/kg and 1 ng/kg, which showed a maximal response at a dose of 100 pg/kg (29-33 pg/rat) which began to appear 5 min after injection, reached a peak within 25 min and then gradually subsided. However, this dose of rhIL-1 beta did not affect the responses of low threshold mechanoreceptive neurons to skin brushing. An increase in the dose of rhIL-1 beta by more than 10 ng/kg (up to 1 microgram/kg) had no effect on the nociceptive responses of the WDR neurons. The rhIL-1 beta-induced enhancement of nociceptive responses of WDR neurons was completely abolished by pretreatment with either IL-1 receptor antagonist, Na salicylate or alpha-melanocyte stimulating hormone. These results therefore provide electrophysiological evidence that IL-1 beta which is produced in the brain induces hyperalgesia in the rat.

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.

Effects of endotoxin, interleukin-1 beta and prostaglandin injections on fever response in broilers

1. The effect of endotoxin, interleukin-1 beta and prostaglandin on fever response was studied in 80 broilers (Hubbard strain). Endotoxin (E. coli, LPS) was injected i.v. (1.5 micrograms/kg) and icv (1.5 micrograms/bird); interleukin-1 (human recombinant IL-1 beta, 80 pg/bird) and prostaglandin E2 (5 micrograms/bird) were injected icv. Indomethacin (10 mg/kg, i.v.) pretreatment was also used before i.v. endotoxin injection. 2. The results showed that indomethacin was able to block the fever response induced by i.v. endotoxin injection, and IL-1 beta and PGE2 were both effective in producing fever when injected icv. These data suggest a prostaglandin-mediated fever response by broilers, and also a strong evidence of the involvement of endogenous pyrogen (interleukin-1) in fever response in birds.

Organum vasculosum laminae terminalis (OVLT) is a brain site to produce interleukin-1 beta 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.

Organum vasculosum laminae terminalis (OVLT) in rabbit and rat: topographic studies

The microcirculation and fine structure of the rabbit and rat organum vasculosum laminae terminalis (OVLT) were examined by light microscopy and scanning and transmission electron microscopy. In both animals, the microcirculation is composed of a superficial and a deep vascular bed but the system is more complex and extensive in the rabbit. This was particularly true of the deep vascular bed. In the rabbit, the deep bed is composed of fenestrated capillaries, which are arranged in glomerular tufts surrounded by very wide perivascular spaces (PVS). In contrast, the deep vascular bed of the rat OVLT usually consists of only one or two small vessels. These are either fenestrated and surrounded by a PVS or lined by continuous endothelium with only a few fenestrae and without a dilated PVS. A corresponding difference was seen in the contours of the ventricular surface. It is much more irregular in the rabbit than in the rat and numerous bulges reflect the underlying vascular tufts and pockets of PVS in the rabbit. Supraependymal cells are present in both species and two sizes of them occur in the rabbit. The results demonstrate that the microcirculation of the OVLT is more elaborate and more highly developed in the rabbit than in the rat. We suggest that this might result in a different neurohemal microenvironment and, ultimately, in functional differences.