Acute nicotine exposure attenuates neurological deficits, ischemic injury and brain inflammatory responses and restores hippocampal long-term potentiation in ischemic stroke followed by lipopolysaccharide-induced sepsis-like state

Abstract

Ischemic stroke is followed by an increased susceptibility to bacterial infections, which exacerbate histological stroke outcome, neurological deficits and memory impairment due to increased neuroinflammation and neurotransmitter dysfunction. Pharmacological activation of nicotinic acetylcholine receptors was suggested to mitigate brain inflammatory responses in ischemic stroke. The functional responses associated with nicotinic acetylcholine receptor activation were unknown. In this study, male NMRI mice subjected to transient intraluminal middle cerebral artery occlusion (MCAO) were intraperitoneally exposed to vehicle treatment or Escherichia coli lipopolysaccharide (LPS; 4 mg/kg)-induced sepsis-like state 24 h post-MCAO, followed by intraperitoneal administration of vehicle or nicotine (0.5 mg/kg) 30 min later. Over 96 h, rectal temperature, neurological deficits, spontaneous locomotor activity, working memory, ischemic injury, synaptic plasticity, and brain inflammatory responses were evaluated by temperature measurement, behavioral analysis, infarct volumetry, electrophysiological recordings, and polymerase-chain reaction analysis. LPS-induced sepsis induced hypothermia, increased general and focal neurological deficits, reduced spontaneous exploration behavior, reduced working memory, and increased infarct volume post-MCAO. Additional treatment with nicotine attenuated LPS-induced hypothermia, reduced neurological deficits, restored exploration behavior, restored working memory, and reduced infarct volume. Local field potential recordings revealed that LPS-induced sepsis decreased long-term potentiation (LTP) in the dentate gyrus post-MCAO, whereas concomitant nicotine exposure restored LTP in the contralateral dentate gyrus. LPS-induced sepsis increased microglial/ macrophage Iba-1 mRNA and astrocytic GFAP mRNA levels post-MCAO, whereas add-on nicotine treatment reduced astrocytic GFAP mRNA. Taken together, these findings indicate that acute nicotine exposure enhances functional stroke recovery. Future studies will have to evaluate the effects of (1) chronic nicotine exposure, a clinically relevant vascular risk factor, and (2) the cessation of nicotine exposure, which is widely recommended post-stroke, but might have detrimental effects in the early stroke recovery phase.