Acute neuroinflammation provokes intracellular acidification in mouse hippocampus.
Maintaining pH levels within the physiological norm is an important component of brain homeostasis. However, in some pathological or physiological conditions, the capacity of the pH regulatory system could be overpowered by various factors resulting in a transient or permanent alteration in pH levels. Such changes are often observed in pathological conditions associated with neuroinflammation. We hypothesized that neuroinflammation itself is a factor affecting pH levels in neural tissue. To assess this hypothesis, we examined the effects of acute LPS-induced neuroinflammation on intra- and extracellular pH (pHi and pHo) levels in the CA1 region of mouse hippocampus.



Acute neuroinflammation was induced using two approaches: (1) in vivo by i.p. injections of LPS (5 mg/kg) and (2) in vitro by incubating hippocampal slices of naïve animals in the LPS-containing media (1 μg/mL, 1 h at 35 °C). Standard techniques were used to prepare hippocampal slices. pHi was measured using ratiometric pH-sensitive fluorescent dye BCECF-AM. pHo was assessed using calibrated pH-sensitive micropipettes. The presence of neuroinflammation was verified with immunohistochemistry (IL-1β and Iba1) and ELISA (IL-1β and TNF-α).



A significant reduction of pHi was observed in the slices of the LPS-injected 3-month-old (LPS 7.13 ± 0.03; Sal 7.22 ± 0.03; p = 0.043, r = 0.43) and 19-month-old (LPS 6.78 ± 0.08; Sal 7.13 ± 0.03; p = 0.0001, r = 0.32) mice. In contrast, the levels of pHo within the slice, measured in 19-month-old animals, were not affected (LPS 7.27 ± 0.02; Sal 7.26 ± 0.02; p = 0.6, r = 0.13). A reduction of pHi was also observed in the LPS-treated slices during the interval 3.5-7 h after the LPS exposure (LPS 6.92 ± 0.07; Veh 7.28 ± 0.05; p = 0.0001, r = 0.46).



Acute LPS-induced neuroinflammation results in a significant intracellular acidification of the CA1 neurons in mouse hippocampus, while the pHo remains largely unchanged. Such changes may represent a specific protective reaction of neural tissue in unfavorable external conditions or be a part of the pathological process.
Department of Neurosciences, University of California San Diego, 9500 Gilman Drive, La Jolla, CA, 92093, USA.|School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok, 690950, Russian Federation.
Anna A
AA
Tyrtyshnaia
Department of Neurosciences, University of California San Diego, 9500 Gilman Drive, La Jolla, CA, 92093, USA.|Academy of Biology and Biotechnology of Southern Federal University, 194/1 Stachki Str, Rostov-na-Donu, 344090, Russian Federation.
Larisa V
LV
Lysenko
Department of Neurosciences, University of California San Diego, 9500 Gilman Drive, La Jolla, CA, 92093, USA.
Francisco
F
Madamba
School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok, 690950, Russian Federation.
Igor V
IV
Manzhulo
School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok, 690950, Russian Federation.
Maxim Y
MY
Khotimchenko
Department of Neurosciences, University of California San Diego, 9500 Gilman Drive, La Jolla, CA, 92093, USA. akleschevnikov@ucsd.edu.|School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok, 690950, Russian Federation. akleschevnikov@ucsd.edu.
Alexander M
AM
Kleschevnikov
D000367:Age Factors; D000818:Animals; D004195:Disease Models, Animal; D004660:Encephalitis / Q000139:chemically induced / Q000473:pathology*; D004797:Enzyme-Linked Immunosorbent Assay; D045604:Extracellular Fluid / Q000187:drug effects / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000473:pathology*; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D066298:In Vitro Techniques; D053583:Interleukin-1beta / Q000378:metabolism; D007424:Intracellular Fluid / Q000187:drug effects / Q000502:physiology*; D008070:Lipopolysaccharides / Q000633:toxicity; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D013997:Time Factors
D053583:Interleukin-1beta; D008070:Lipopolysaccharides
Acidification; BCECF; Extracellular pH; Hippocampus; IL-1β; Iba1; Intracellular pH; LPS; Mice; Neuroinflammation