Li T. Chen

Role and Mechanisms of Interleukin-1 in the Modulation of Neurotoxicity

Objective: Recent studies on cerebral ischemia in the rat have demonstrated that administration of interleukin-1 receptor antagonist (IL-1ra) markedly reduces the volumes of infarcts which are associated with N-methyl-D-aspartate (NMDA)-mediated neurotoxicity. These observations suggested that endogenous interleukin-1 (IL-1) may be involved in the mediation of excitotoxic neuronal injury following ischemia. Method: In the present studies, we examined the role of interleukin-1β (IL-1β) in NMDA-related and microglia-induced excitotoxicity in cocultures of mixed neurons and microglia. Results: Our observations in these mixed cultures indicated that addition of IL-1β exaggerated NMDA and glutamate-evoked hippocampal neuron death. Addition of microglia, activated by lipopolysaccharide (LPS) and interferon-γ (IFN-γ), to cocultures of cortical neurons and glia induced significantly greater neurotoxicity when compared with cocultures of cortical neurons and untreated microglia. This neurotoxicity did not require that activated glia be in cell-to-cell contact with neurons. Addition of either IL-1ra or the NMDA receptor antagonist MK-801 to cocultures of cortical neurons and activated glia partially reversed the neuronal damage mediated by activated microglia. Finally, IL-1β concentrations in the supernatant of cocultures of cortical neurons and microglia treated by LPS and IFN-γ were markedly increased when compared with coculture of neurons with untreated microglia. Conclusion: These results suggest that both the NMDA receptor and the IL-1 receptor are involved in microglia-mediated neurotoxicity.

Cytokine and adrenal axis responses to endotoxin.

The push-pull cannula (PPC) technique was applied to examine the kinetics of in vivo concentration changes in male rat brain extracellular fluid (ECF) of endogenous interleukin-1beta (IL-1beta) and corticotrophin releasing hormone (CRH) after a peripheral injection of lipopolysaccharide (LPS) (25 microg/100 g b.wt. intravenously). In addition, IL-1beta, adrenocorticotropin hormone (ACTH) and corticosterone concentrations in plasma were also measured at selected intervals after LPS challenge. Administration of LPS resulted in a progressive increase in the concentrations of IL-1beta in brain hypothalamic ECF. A significant increase from the zero time mean value of 77+/-10 to 393+/-88 pg/ml at the 15-min interval was recorded. The increase in IL-1beta concentration in hypothalamic ECF reached a peak of 883+/-237 pg/ml at 30 min post-LPS. CRH concentration in the same hypothalamic ECF was 41+/-17 pg/ml at time zero, 97+/-15 pg/ml at 15 min and at 30 min was significantly increased (215+/-56 pg/ml). A time course of significant increases at 30 min in plasma concentrations of IL-1beta, ACTH and corticosterone was also recorded in the same animals described above. The data show that a peripherally administered LPS bolus elicited an early (over 15 min post-injection) increase in brain ECF IL-1beta concentration; additional significant increases in hormones released from the hypothalamic-pituitary-adrenal (HPA) axis were recorded at 30 min post-LPS injection. These observations support the concept of an early change in hypothalamic ECF concentration of IL-1beta preceding LPS-induced activation of the HPA axis.

In vivo release of interleukin-1β into hypothalamic extracellular fluid in rats: effects of repeated sampling

Interleukin-1 beta (Il-1 beta) concentrations in extracellular fluid (ECF) withdrawn at 10-min intervals through a push-pull cannula (PPC) located in the hypothalamus were studied in freely behaving male rats for 1 h at 24 and 72 h and again at 7 days after PPC implantation. Il-1 beta concentrations in ECF were similar in the latter. However, when ECF was sampled at 3 h and again 7 days after PPC implantation, Il-1 beta concentrations were greatly elevated at 7 days when compared to all other intervals. These results demonstrate how the relationships between Il-1 beta measured in ECF and the conditions of measurement appear to be integral parts of a whole intracerebral system: cytokine concentrations appear to be inextricably bound to intrahypothalamic conditions created by the sampling device presence and frequency of use.

Plasma Interleukin-1β, Prolactin, ACTH and Corticosterone Responses to Endotoxin after Damage of the Anterior Hypothalamic Area

This report concerns the use of an animal model described by us [J Submicrosc Cytol Pathol 1995;27:83–89] to investigate neural and endocrine sites for endotoxin (ENDO, E. coli 055:B5, 200 µg/100 g body weight in saline intravenously) effects on immunomodulatory hormone and cytokine release. Plasma interleukin-1β (IL-1β), prolactin (PRL), ACTH and corticosterone responses to ENDO after neurotoxic damage of neurons residing in the anterior hypothalamic area (AHA) were studied in freely behaving male rats. Excitotoxic cell damage in the AHA was produced by bilaterally injecting N-methyl-DL-aspartate (NMA) in artificial cerebrospinal fluid (aCSF) into this brain site. Injections of comparable volumes of aCSF alone served as controls for brain damage associated with the treatment. In both experimental brain manipulations before ENDO challenge the rise in plasma IL-1β concentrations in response to ENDO was reduced by 2-fold at 1 h and 3- to 5-fold at 3 h when compared to controls. Nevertheless, experimental and control brain manipulations did not modulate the expected rise in corticosterone concentrations after ENDO exposure which rose 5-fold above the baseline level in all animals. However, AHA manipulation did reduce plasma ACTH and prolactin concentrations differentially. Introduction of either NMA or the control injection of aCSF alone into AHA reduced plasma ACTH concentrations by 2-fold at 0.5 and 1 h after ENDO. However, there was a greater reduction in the rise of plasma PRL concentrations after ENDO found in NMA-treated groups versus rats receiving control aCSF. These results demonstrate that variable-size hypothalamic damage (a larger lesion produced in AHA by NMA treatment vs. a smaller lesion control after aCSF) can result in a differential blunting of PRL, IL-1β and ACTH release into blood in the face of robust, unmodulated corticosterone increases. In summary, these findings revealed a consistent predominant influence of ENDO on adrenal release of corticosterone as a concomitant to differential IL-1β, ACTH and PRL release after AHA cell loss. In conclusion, these results constitute further evidence for hypothalamic orchestration of a balance between immunotropic and immunosuppressive neuroendocrine-immune events during acute bacterial infection of mammals.

Dietary Docosahexanoic Acid (DHA) Effects upon the Rat Pup Auditory System|[bull]| 1526

Rats fed diets high in n3 fatty acids have lower whole brain levels of myelin basic protein, lower activities of 2′-3′cyclic nucleotide 3′-phosphodiesterase(an indicator of myelination) (DiBiase & Salvati, 1997), and longer auditory brainstem conduction times (ABCTs) (Saste et al., in press). We investigated the effects of varying levels of the n3 fatty acid DHA upon development of the rat pup auditory system.Methods: Dams were fed, from day 2 of gestation and throughout lactation, a purified diet whose fat source (22% of cals) was a vegetable oil blend supplemented with an algae oil containing 0% or 3% DHA. On postnatal day(pnd) 3, pups were culled to 10 per dam and were randomly cross fostered among dams of the same diet group to minimize litter effects (n=6 dams per diet group, 60 pups per diet group). Milk from culled pup stomachs was used for fatty acid analysis. On pnd 15, auditory electromyelographic reflexes (AEMR) to 130 db peak sound pressure level clicks were recorded from needle electrodes placed in the muscle of the thigh of 20 pups per diet group; pups were then sacrificed and brainstems removed for fatty acid analysis. For the remaining 40 pups per diet group, ABCTs were measured on pnd 24 and 31, and the postnatal day of appearance of the auditory startle reflex was determined. An additional group of dams fed 1% DHA diet had pups whose weight gains were 2/3 that of dams fed the 0% or 3% DHA diets; data from these pups are not presented. Results: Length of gestation, maternal weight gains and pup weights on pnd 3 did not differ between diet groups. Weight gains to pnd 12 were slightly lower among pups of dams fed the 3% DHA diet. The fatty acid composition of dam milk and pup brainstems reflected maternal diet. AEMRs were not different, however, ABCTs on pnd 24 were longer and the time of appearance of the auditory startle reflex was later in pups of dams fed 3% DHA.Conclusion: High levels of dietary DHA during development may be associated with delays in myelination of the central nervous system as suggested by longer ABCTs and a delay in appearance of the auditory startle reflex. Similar AEMRs between diet groups suggest minimal effects upon the peripheral nervous system. Table

AN ANIMAL MODEL FOR ASSESSMENT OF NEURODEVELOPMENT FOLLOWING NEONATAL HYPOXIC-ISCHEMIC INJURY † 1034

AN ANIMAL MODEL FOR ASSESSMENT OF NEURODEVELOPMENT FOLLOWING NEONATAL HYPOXIC-ISCHEMIC INJURY † 1034