Sequential alteration of microglia and astrocytes in the rat thalamus following spinal nerve ligation.
J Neuroinflammation. 2018-12-15; 15(1):
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1. J Neuroinflammation. 2018 Dec 20;15(1):349. doi: 10.1186/s12974-018-1378-z.
Sequential alteration of microglia and astrocytes in the rat thalamus following
spinal nerve ligation.
Blaszczyk L(1)(2), Maître M(1)(2), Lesté-Lasserre T(1)(2), Clark S(1)(2), CotaD(1)(2), Oliet SHR(1)(2), Fénelon VS(3)(4).
(1)Bordeaux University, Bordeaux, France.
(2)Neurocentre Magendie, INSERM U1215, Bordeaux, France.
(3)Bordeaux University, Bordeaux, France. .
(4)Neurocentre Magendie, INSERM U1215, Bordeaux, France.
BACKGROUND: Spinal reactive astrocytes and microglia are known to participate to
the initiation and maintenance of neuropathic pain. However, whether reactive
astrocytes and microglia in thalamic nuclei that process sensory-discriminative
aspects of pain play a role in pain behavior remains poorly investigated.
Therefore, the present study evaluated whether the presence of reactive glia
(hypertrophy, increased number and upregulation of glial markers) in the ventral
posterolateral thalamic nucleus (VPL) correlates with pain symptoms, 14 and
28 days after unilateral L5/L6 spinal nerve ligation (SNL) in rats.
METHODS: Mechanical allodynia and hyperalgesia (von Frey filament stimulation) as
well as ambulatory pain (dynamic weight bearing apparatus) were assessed. Levels
of nine glial transcripts were determined by quantitative real-time PCR on laser
microdissected thalamic nuclei, and levels of proteins were assessed by Western
blot. We also studied by immunohistofluorescence the expression of glial markers
that label processes (GFAP for astrocytes and iba-1 for microglia) and cell body
(S100β for astrocytes and iba-1 for microglia) and quantified the immunostained
surface and the number of astrocytes and microglia (conventional counts and
optical dissector method of stereological counting).
RESULTS: Differential, time-dependent responses were observed concerning
microglia and astrocytes. Specifically, at day 14, iba-1 immunostained area and
number of iba-1 immunopositive cells were decreased in the VPL of SNL as compared
to naïve rats. By contrast, at day 28, GFAP-immunostained area was increased in
the VPL of SNL as compared to naïve rats while number of GFAP/S100β
immunopositive cells remained unchanged. Using quantitative real-time PCR of
laser microdissected VPL, we found a sequential increase in mRNA expression of
cathepsin S (day 14), fractalkine (day 28), and fractalkine receptor (day 14),
three well-known markers of microglial reactivity. Using Western blot, we
confirmed an increase in protein expression of fractalkine receptor at day 14.
CONCLUSIONS: Our results demonstrate a sequential alteration of microglia and
astrocytes in the thalamus of animals with lesioned peripheral nerves.
Furthermore, our data report unprecedented concomitant molecular signs of
microglial activation and morphological signs of microglial decline in the
thalamus of these animals.