Cyclohexane Produces Behavioral Deficits Associated with Astrogliosis and Microglial Reactivity in the Adult Hippocampus Mouse Brain

Abstract

Cyclohexane is a volatile substance that has been utilized as a safe substitute of several organic solvents in diverse industrial processes, such as adhesives, paints, paint thinners, fingernail polish, lacquers, and rubber industry. A number of these commercial products are ordinarily used as inhaled drugs. However, it is not well known whether cyclohexane has noxious effects in the central nervous system. The aim of this study was to analyze the effects of cyclohexane inhalation on motor behavior, spatial memory, and reactive gliosis in the hippocampus of adult mice. We used a model that mimics recreational drug use in male Balb/C mice (P60), divided into two groups: controls and the cyclohexane group (exposed to 9,000 ppm of cyclohexane for 30 days). Both groups were then evaluated with a functional observational battery (FOB) and the Morris water maze (MWM). Furthermore, the relative expression of AP endonuclease 1 (APE1), and the number of astrocytes (GFAP+ cells) and microglia (Iba1+ cells) were quantified in the hippocampal CA1 and CA3 areas. Our findings indicated that cyclohexane produced severe functional deficits during a recreational exposure as assessed by the FOB. The MWM did not show statistically significant changes in the acquisition and retention of spatial memory. Remarkably, a significant increase in the number of astrocytes and microglia cells, as well as in the cytoplasmic processes of these cells were observed in the hippocampal CA1 and CA3 areas of cyclohexane-exposed mice. This cellular response was associated with an increase in the expression of APE1 in the same brain regions. In summary, cyclohexane exposure produces functional deficits that are associated with an important increase in the APE1 expression as well as the number of astrocytes and microglia cells and their cytoplasmic complexity in the CA1 and CA3 regions of the adult hippocampus.

Cyclohexane, a Potential Drug of Abuse with Pernicious Effects on the Brain

“…Solvents such as toluene and trichloroethylene (TCE) exhibit biphasic dose-response curves, characterized by motor excitation at low exposure levels, and motor impairment, sedation and anesthesia at high exposure levels (Bowen et al, 2006 ). Interestingly, a similar biphasic dose-response effect has been described in mice exposed to cyclohexane, and is associated with neurohistological changes (Campos-Ordonez et al, 2015 ). Furthermore, these volatile solvents produce dramatic structural changes in the brain, including atrophy of the cerebral cortex, white matter, corpus callosum, hippocampus, brainstem, cerebellum, basal ganglia, red nuclei, and substantia nigra (Fan et al, 2014 ; Ramcharan et al, 2014 ).…”

“…Cyclohexane at concentrations typical of those used by recreational drug users (9000 ppm) also induces a glial cell response in the hippocampus (Campos-Ordonez et al, 2015 ). The astrocyte and microglial responses may have dual and opposing effects on the CNS.…”

“…However, a recent study found that cyclohexane promotes the overexpression of AP endonuclease 1 (APE1) in the hippocampus. This protein activates the cellular response to oxidative stress and regulates the transcription of genes involved in neuronal survival and DNA repair (Campos-Ordonez et al, 2015 ). This suggests that cyclohexane perturbs the redox balance in cells and affects the ability of tissue to detoxify ROS.…”

Phenytoin enhances the phosphorylation of epidermal growth factor receptor and fibroblast growth factor receptor in the subventricular zone and promotes the proliferation of neural precursor cells and oligodendrocyte differentiation

“…Membranes were then revealed with diaminobenzidine. Protein expression was quantitatively determined by densitometry (Campos-Ordonez et al, 2015).…”