The present study was designed to investigate the coupling mechanisms linking the immune and the neuroendocrine corticotropic systems in an integrated defense response triggered by an infectious aggression. The experimental paradigm used consisted of the exploration in individual conscious rats of the temporal pattern of increased plasma concentrations of the two stress hormones, adrenocorticotropic hormone (ACTH) and corticosterone (Cort), and of three cytokines known as ACTH stimulators, tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 beta, and IL-6, after intra-arterial infusions of lipopolysaccharide (LPS) given at three doses, 5 micrograms/kg (LPS-5), 25 micrograms/kg (LPS-25), and 1 mg/kg (LPS-1,000). Blood samples were taken 30 min and immediately before LPS injection (t0) and at 15, 30, 60, 120, 300, and 480 min post-LPS. The three doses of LPS induced ACTH and Cort surges, starting after 30 min for LPS-5 and LPS-25 or 15 min for LPS-1,000 and peaking with a similar amplitude at 60 min before receding slowly to baseline at 480 min for the two lower LPS doses. On the other hand, whatever the LPS dose, none of the three cytokines rose above undetectable basal levels before 60 min. They increased thereafter to culminate 10- to 30-fold above baseline at 60 min (TNF-alpha) or 120 min (IL-1 beta and IL-6) after LPS and declined back to basal levels at 300 min (TNF-alpha, all doses, and IL-6 for LPS-5 and LPS-25). After LPS-25, only IL-1 beta had not regressed to baseline levels at 480 min.(ABSTRACT TRUNCATED AT 400 WORDS)

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Alzheimer's disease (AD) is a neurodegenerative pathology characterized by the presence of senile plaques and neurofibrillary tangles, accompanied by synaptic and neuronal loss. The major component of senile plaques is an amyloid ␤ protein (A␤) formed by pathological processing of the A␤ precursor protein. We assessed the time-course and regional effects of a single intracerebroventricular injection of aggregated A␤ fragment 25-35 (A␤ 25-35 ) in rats. Using a combined biochemical, behavioral, and morphological approach, we analyzed the peptide effects after 1, 2, and 3 weeks in the hippocampus, cortex, amygdala, and hypothalamus. The scrambled A␤ 25-35 peptide was used as negative control. The aggregated forms of A␤ peptides were first characterized using electron microscopy, infrared spectroscopy, and Congo Red staining. Intracerebroventricular injection of A␤ 25-35 decreased body weight, induced short-and long-term memory impairments, increased endocrine stress, cerebral oxidative and cellular stress, neuroinflammation, and neuroprotective reactions, and modified endogenous amyloid processing, with specific time-course and regional responses. Moreover, A␤ 25-35 , the presence of which was shown in the different brain structures and over 3 weeks, provoked a rapid glial activation, acetylcholine homeostasis perturbation, and hippocampal morphological alterations. Alzheimer's disease (AD) is a chronic neurodegenerative pathology characterized by the presence of senile plaques and neurofibrillary tangles, accompanied by synaptic and neuronal loss in brain areas responsible for learning and memory impairments. 1 The major component of senile plaques is an amyloid ␤ protein (A␤) derived from amyloid precursor protein (APP). Genetic, cell biological, and postmortem studies on AD brain, together with A␤ neurotoxicity findings, gave rise to the amyloid cascade hypothesis to explain A␤-associated neurodegenerative processes. 2 In normal healthy individuals, A␤ peptides are present only in small quantities, as soluble monomers that circulate in cerebrospinal fluid and blood. In AD patients, A␤ peptides, which vary in length from 40 to 43 amino acids, accumulate as insoluble fibrillar deposits. 3 When cultured rat hippocampal neurons are exposed to aggregated A␤ peptides, their neurites adopt a dystrophic appearance and become comparable to those observed surrounding and infiltrating senile plaques. This observation suggested that A␤ is responsible for the neuritic abnormalities in AD pathology. 4 Structure-activity studies revealed that peptides containing the highly hydrophobic 25-35 region formed stable aggregates and mediated neuronal death by necrosis or apoptosis. 5,6,7 The truncated A␤ 25-35 fragment includes extracellular and intramembrane residues that have been reported to represent an active region of A␤. 8

ABSTRACT:Brain-derived neurotrophic factor (BDNF) is strongly expressed in the hippocampus, where it has been associated with memory processes. In the central nervous system, some learning processes, as well as brain insults, including stress, induce modifications in BDNF mRNA expression. Because stress and memory appear to share some neuronal pathways, we studied BDNF mRNA and BDNF peptide variations in response to short times of immobilization stress. Using an RNase protection assay, we demonstrated that short-time stress application induced a significant increase (at 60 min) in BDNF mRNA levels in the whole rat hippocampus. Changes in BDNF mRNA content appear to reflect increased expression of BDNF transcripts containing exons I, II, and III, that were also significantly modified at this time. The time course of stress-induced changes in BDNF transcript levels revealed that mRNA containing exon III was the first increased, significantly elevated by 15 min, attaining maximal levels at 60 min, as BDNF transcripts containing exons I and II. However, at longer times of stress (180 min), BDNF mRNA levels were decreased as well as mRNA containing exon IV. In situ hybridization analysis of discrete hippocampal layers demonstrated that BDNF mRNA expression increased as early as 15 min in most hippocampal regions, with no modification in the number of labeled cells. The same signal pattern, although less pronounced, was determined at 60 min, but at this time a significant increase in BDNF-positive cells was visualized in the CA3 layer. The peptide, measured by immunoassay, was significantly augmented after 180 min of stress exposure whereas at 300 min, levels were similar to those measured in control animals. These data suggest that rapid changes in BDNF expression may be part of a compensatory response to preserve hippocampal homeostasis or a form of neuronal plasticity to cope with new stimuli. Hippocampus 2003;13:646 -655.