Early antibiotic administration prevents cognitive impairment induced by meningitis in rats

A novel automated test battery reveals enduring behavioural alterations and cognitive impairments in survivors of murine pneumococcal meningitis

Pneumococcal meningitis, caused by Streptococcus pneumoniae infection, is a major form of lethal bacterial meningitis. Survivors are predisposed to developing lifelong disabling sequelae, including cognitive impairment, psychological problems and motor deficits. In our experimental model, ventricular inoculation of 10(5) colony-forming units of S. pneumoniae type 3 caused 90% of mice to develop life-threatening meningitis within 48 h. Antibiotic treatment with ceftriaxone 20 h post infection reduced the incidence of severe meningitis to <10%. At the time of treatment, upregulation of pro-inflammatory cytokines was detected, including interleukin-1β, interleukin-6 and tumour necrosis factor. We evaluated the long-term behavioural and cognitive sequelae in control mice and those surviving meningitis using an automated system (the IntelliCage) in which mice perform a range of behavioural and spatial tasks to obtain water rewards from conditioning units in their home cage. Surviving mice showed a number of altered behaviours relative to controls, including (i) hypoexploration when first exposed to the IntelliCage, (ii) altered activity patterns (fewer visits to conditioning stations during the light phase and more in the dark phase), (iii) avoidance of light (a constant or flashing LED stimulus), (iv) impaired spatial learning (a complex patrolling task), and (v) impaired discrimination reversal learning. Overall these results suggest photophobia and weakened learning ability in post-meningitic mice, particularly on tasks engaging hippocampal and prefrontal neural substrates. This study also demonstrates a standardised and comprehensive battery of tests that can be readily used to investigate neurological sequelae in undisturbed mice residing in a complex home cage environment.

Pathophysiology of neonatal acute bacterial meningitis

Neonatal meningitis is a severe acute infectious disease of the central nervous system and an important cause of morbidity and mortality worldwide. The inflammatory reaction involves the meninges, the subarachnoid space and the brain parenchymal vessels and contributes to neuronal injury. Neonatal meningitis leads to deafness, blindness, cerebral palsy, seizures, hydrocephalus or cognitive impairment in approximately 25-50 % of survivors. Bacterial pathogens can reach the blood-brain barrier and be recognized by antigen-presenting cells through the binding of Toll-like receptors. They induce the activation of NFκB or mitogen-activated protein kinase pathways and subsequently upregulate leukocyte populations and express numerous proteins involved in inflammation and the immune response. Many brain cells can produce cytokines, chemokines and other pro-inflammatory molecules in response to bacterial stimuli, and polymorphonuclear leukocytes are attracted, activated and released in large amounts of superoxide anion and nitric oxide, leading to peroxynitrite formation and generating oxidative stress. This cascade leads to lipid peroxidation, mitochondrial damage and breakdown of the blood-brain barrier, thus contributing to cell injury during neonatal meningitis. This review summarizes information on the pathophysiology and adjuvant treatment of acute bacterial meningitis in neonates.

Evaluation of energetic metabolism in the rat brain after meningitis induction by Klebsiella pneumoniae

BACKGROUND

Bacterial meningitis is an infection of the central nervous system characterised by strong inflammatory response. The brain is highly dependent on ATP, and the cell energy is obtained through oxidative phosphorylation, a process which requires the action of various respiratory enzyme complexes and creatine kinase (CK) as an effective buffering system of cellular ATP levels in tissues that consume high energy.

OBJECTIVES

Evaluate the activities of mitochondrial respiratory chain complexes I, II, III, IV and CK activity in hippocampus and cortex of the Wistar rat submitted to meningitis by Klebsiella pneumoniae.

METHODS

Adult Wistar rats received either 10 µl of sterile saline as a placebo or an equivalent volume of K. pneumoniae suspension. The animals were killed in different times at 6, 12, 24 and 48 h after meningitis induction. Another group was treated with antibiotic, starting at 16 h and continuing daily until their decapitation at 24 and 48 h after induction.

RESULTS

In the hippocampus, the meningitis group without antibiotic treatment, the complex I was increased at 24 and 48 h, complex II was increased at 48 h, complex III was inhibited at 6, 12, 24 and 48 h and in complex IV all groups with or without antibiotic treatment were inhibited after meningitis induction, in the cortex there was no alteration. Discussion Although descriptive, our results show that antibiotic prevented in part the changes of the mitochondrial respiratory chain. The meningitis model could be a good research tool to study the biological mechanisms involved in the pathophysiology of the K. pneumoniae meningitis.

Dissociation between learning and memory impairment and other sickness behaviours during simulated Mycoplasma infection in rats

To investigate potential consequences for learning and memory, we have simulated the effects of Mycoplasma infection, in rats, by administering fibroblast-stimulating lipopepide-1 (FSL-1), a pyrogenic moiety of Mycoplasma salivarium. We measured the effects on body temperature, cage activity, food intake, and on spatial learning and memory in a Morris Water Maze. Male Sprague-Dawley rats had radio transponders implanted to measure abdominal temperature and cage activity. After recovery, rats were assigned randomly to receive intraperitoneal (I.P.) injections of FSL-1 (500 or 1000 μg kg(-1) in 1 ml kg(-1) phosphate-buffered saline; PBS) or vehicle (PBS, 1 ml kg(-1)). Body mass and food intake were measured daily. Training in the Maze commenced 18 h after injections and continued daily for four days. Spatial memory was assessed on the fifth day. In other rats, we measured concentrations of brain pro-inflammatory cytokines, interleukin (IL)-1β and IL-6, at 3 and 18 h after injections. FSL-1 administration induced a dose-dependent fever (∼1°C) for two days, lethargy (∼78%) for four days, anorexia (∼65%) for three days and body mass stunting (∼6%) for at least four days. Eighteen hours after FSL-1 administration, when concentrations of IL-1β, but not that of IL-6, were elevated in both the hypothalamus and the hippocampus, and when rats were febrile, lethargic and anorexic, learning in the Maze was unaffected. There also was no memory impairment. Our results support emerging evidence that impaired learning and memory is not inevitable during simulated infection.

Antibiotic therapy prevents, in part, the oxidative stress in the rat brain after meningitis induced by Streptococcus pneumoniae

Bacterial meningitis is associated with intense inflammation and also linked to the production of reactive oxygen species. To this aim, animals underwent a magna cistern tap and received either sterile saline as a placebo or an equivalent volume of a Streptococcus pneumoniae suspension. The animals began antibiotic therapy 16h after induction. The animals were sacrificed at 24 or 48h post-infection and the hippocampus and cortex were harvested. The activity of the enzymes superoxide dismutase, catalase, and thiobarbituric acid reactive species, protein carbonyls, and free sulphydryl groups were altered, but reversed, in part, by the antibiotic treatment. Our results support the hypothesis that antibiotic treatment prevents, in part, the oxidative stress in the bacterial meningitis induced by Streptococcus pneumoniae.