Internship: biology – neurosciences

Synapse formation is a key stage in development. Newly formed synapses are stabilized or eliminated. This requires an activity-dependent process, which remains obscure. Research from the laboratory has highlighted the key role of the ATP transformation product adenosine and its A2A receptor (A2AR) in the stabilization/destabilization of nascent inhibitory GABAergic and excitatory glutamatergic synapses. We showed that exposure to caffeine, a natural A2AR non-selective antagonist during the lactation period (between P3 and P16) which corresponds to the period of synaptogenesis in rodents, increased glutamatergic synapse density in the hippocampus at P21. This had deleterious consequences on animal behavior, with an increase in the sensitivity to epilepsy at P30 and cognitive deficits at P70-80. We showed that astrocytes contribute to the activity A2AR-dependant pruning of glutamatergic synapses.  We wish now to determine the impact of A2AR blockade on astrocyte activation, synapse pruning and cognition. Therefore, we will perform immunohistochemistry experiments to label mouse hippocampal slices (male and female) in saline vs caffeine treated mice for GFAP (a marker of reactive astrocytes), the astrocyte-specific phagocytic receptor Megf10 involved in synapse phagocytosis and the synaptic protein PSD95. After acquiring z-stack images on a confocal microscope, astrocytes will be reconstructed in 3D using Imaris software. The number of astrocytes in each layer of the hippocampus will be compared in saline vs caffeine treated animals. The fluorescence intensity of the different markers within the astrocyte will be quantified. As reactive astrocytes acquire a star-like shape, we will also study their morphology (total volume and the number, length and complexity of the processes). We expect that blocking A2AR activity with caffeine will decrease astrocyte reactivity (by decreasing GFAP protein content while preventing the star like shape of astrocytes) and increasing the number of glutamatergic synapses.

References:

1. Gomez Castro F*, Zappettini S*, Pressey J*, Silva CG, Russeau M, Gervasi N, Figueiredo M, Montmasson C, Renner M, Canas PM, Gonçalves FQ, Alçada-Morais S, Szabó E, Rodrigues RJ, Agostinho P, Tomé AR, Caillol G, Thoumine O, Nicol X, Letterrier C, Lujan R, Tyagarajan S, Cunha RA, Esclapez M, Bernard C†, Levi S†. (2021) Convergence of adenosine and GABA signaling for synapse stabilization during development. Science 374, abk2055 PMID: 34735259 DOI: 10.1126/science.abk2055

Rimbert S., Moreira J. B., Xapelli S, Lévi S. †. (2023) Role of purines in brain development, from neuronal proliferation to synaptic refinement. Neuropharmacology. 2023 237:109640. doi: 10.1016/j.neuropharm.2023.109640.