Minocycline reduces lipopolysaccharide-induced neurological dysfunction and brain injury in the neonatal rat

Abstract

Preferential brain white matter injury and hypomyelination induced by intracerebral administration of the endotoxin lipopolysaccharide (LPS) in the neonatal rat brain has been characterized as associated with the activation of microglia. To examine whether inhibition of microglial activation might provide protection against LPS-induced brain injury and behavioral deficits, minocycline (45 mg/kg) was administered intraperitoneally 12 hr before and immediately after an LPS (1 mg/kg) intracerebral injection in postnatal day 5 (P5) Sprague-Dawley rats and then every 24 hr for 3 days. Brain injury and myelination were examined on postnatal day 21 and the tests for neurobehavioral toxicity were carried out from P3 to P21. LPS administration resulted in severe white matter injury, enlarged ventricles, deficits in the hippocampus, loss of oligodendrocytes and tyrosine hydroxylase neurons, damage to axons and dendrites, and impaired myelination as indicated by the decrease in myelin basic protein immunostaining in the P21 rat brain. LPS administration also significantly affected physical development (body weight) and neurobehavioral performance, such as righting reflex, wire hanging maneuver, cliff avoidance, locomotor activity, gait analysis, and responses in the elevated plus-maze and passive avoidance task. Treatment with minocycline significantly attenuated the LPS-induced brain injury and improved neurobehavioral performance. The protective effect of minocycline was associated with its ability to attenuate LPS-induced microglial activation. These results suggest that inhibition of microglial activation by minocycline may have long-term protective effects in the neonatal brain on infection-induced brain injury and associated neurologic dysfunction in the rat.

α-Phenyl-n-tert-butyl-nitrone attenuates lipopolysaccharide-induced neuronal injury in the neonatal rat brain

“…In this model we found that LPS resulted in preferential white matter injury in the neonatal rat brain and the injury was closely associated with increased oxidative stress following LPS exposure (Fan et al, 2005a). Although we did not find any cortical neuron death in hematoxylin and eosin stained brain sections following LPS exposure, we did observe that LPS injection caused alterations in dopamine neurons in the substantia nigra (SN) by tyrosine hydroxylase (TH) immunostaining and that LPS injection resulted in neurological dysfunction, suggesting possible neuronal involvement in this neonatal rat model of infection/inflammation-induced white matter injury (Fan et al, 2005b).α-Phenyl-n-tert-butyl-nitrone (PBN) is one of the most widely used nitrone-based antioxidants to trap and stabilize free radicals in biological systems (Floyd et al, 2002). The neuroprotective action of PBN has been observed in the LPS-mediated septic shock model, hypoxia-ischemia model, and other neuronal degenerative diseases through its ability to trap free radicals and inhibit oxidative damage or through cessation of enhanced signal transduction processes associated with neuroinflammation (Endoh et al, 2001;Floyd et al, , 2002Sang et al, 1999).…”

“…Our previous studies and data reported by other investigators indicate that perinatal LPS exposure reduces the number of TH positive neurons in these areas (Fan et al, 2005b;Ling et al, 2002), but it is unknown whether the reduction in the number of TH positive cells is a consequence of phenotypic suppression of TH expression or actual neuronal cell death. To answer this question, double labeling with TH and NeuN antibodies was performed and all TH positive and NeuN positive cells in the three midbrain sections for each animal (at a level 1/3 rostral from the lambda to the bregma) were counted bilaterally.…”

Viral-like brain inflammation during development causes increased seizure susceptibility in adult rats

“…Microglia are increasingly being targeted as one of the main immunotherapeutic targets for other neurological diseases (Villoslada et al, 2008), as they represent one of the most important cell types in the cascade of cytokine release within the brain (Lokensgard et al, 2002). The dose of minocycline used in the present study has been shown effective in attenuating LPS-induced white matter injury (periventricular leukomalacia) via reduction in pro-inflammatory cytokine (IL-1β and TNFα) release in young rats (Fan et al, 2005). Dosages in this range are known to be well-tolerated by patients (Kloppenburg et al, 1995), and cost effective (Michaelis et al, 2007).…”

“…POLY I:C (10 μg in 3 μL) or pyrogen-free saline (SAL; 3 μL) was slowly infused into the ventricle over a 1 min period. Similar doses of lipopolysaccharide (LPS) have been used to induce brain inflammation in neonatal rats (Fan et al, 2005). The incision was sutured and animals were returned to the heating pad until all male rats from that litter were injected.…”

“…Minocycline (90 mg/kg) was dissolved in phosphate-buffered-saline (PBS; pH=7.4) and administered intraperitoneally (Fan et al, 2005), concurrently with the ICV injections of POLY I:C at P14 in an attempt to interfere with inflammation and attenuate any long-term changes induced by POLY I:C.…”