Morphological features are considered as markers of microglial functionality, and they show regional
heterogeneity in the brain. Recently the sleep-wake cycle was shown to affect microglial morphology
in mice and correlate with cortical sleep slow wave activity (SWA). Microglial sizes and ramification
increased during the dark period and decreased during the light period in cerebral areas associated
with SWA, suggesting that neuronal activation could be affecting microglial morphology through SWA.
I studied microglia in the hindbrain areas with and without functional connection to SWA to further
investigate the association between SWA and alterations in morphology, and to investigate if there are
differences in microglial morphology and their diurnal alterations in brain regions other than those
commonly investigated. I examined three hindbrain areas (cerebellar cortex (CC), deep cerebellar
nucleus (DCN) and medial vestibular nucleus (MVN)) and somatosensory cortex (SC) of mice (n=15) at
two timepoints: 6 hours after the light onset (high SWA) and offset (low SWA).
My aims were to answer if there are morphological differences in microglia between 1) the four brain
areas at both timepoints and 2) between the two timepoints in each brain area. My hypotheses were
that CC and DCN which have functional connections to cortical SWA, would show similar diurnal
morphology alterations as demonstrated in the cerebral areas, and MVN that has no known cortical
SWA connection, would lack significant alterations. As microglia are heterogenous throughout brain, I
expected microglia to differ between different brain areas, especially the hindbrain and the SC.
I found that microglial morphologies significantly differed between the hindbrain and the cortex, while
the hindbrain areas were more similar in morphology. Moreover, the brain areas demonstrated diurnal
morphology alterations of microglia with varying extent: CC and DCN microglial morphology did not
correlate with SWA as clearly as SC did, and interestingly, morphological features of MVN microglia
showed a pattern opposite to other areas, microglia being larger during the light period than the dark
period. These results highlight the importance of the diurnal time to microglial morphology and the
heterogeneity of microglia between different brain regions.
