Differences in presynaptic hippocampal GABAergic terminals at the early stage of life in female and male mice: effect of an acute early inflammatory challenge

GABA dictates the efficiency of synaptic connection, influencing its developmental complexity, but its role is tuned by developmental sex differences which affect the efficiency of its innervation. We investigated the efficiency of mechanisms of GABA storage and exocytosis in hippocampal terminals of male and female mice during the juvenile period (PND21), adolescence (PND36) or adulthood (PND90). The expression of mRNA encoding for the presynaptic GABA transporter type 1, (GAT1) and the vesicular GABA transporter (VGAT1) was analysed. A significant scaling-down in the GAT1 mRNA levels (SLC6A1) was detected at PND21 in both sexes until adulthood, while the SLC32A1-VGAT mRNA level was conserved. We also analysed the density of GAT1 and VGAT proteins. Western blot analysis unveiled the presence of a monomeric and an oligomeric form of GAT1. The density of the monomeric form was conserved at the different stages of development in both sexes. Differently, the oligomeric assembly was significantly overexpressed in hippocampal synaptosomal lysates from PND21 male and female mice, but recovered at PND36. VGAT density was largely conserved in PND21 and PND36 male hippocampal synaptosomal lysates when compared to adult particles, but significantly lower in PND21 female particles. Notably, these changes are consistent and support the altered vesicular storage of newly taken-up [3H]GABA detected in PND21 male and female hippocampal synaptosomes as well as the different responsiveness of GABAergic male and female synaptosomes to increasing depolarizing stimuli (12, 20 and 30 mM KCl-enriched solutions) measured as efficiency of the [3H]GABA exocytosis. Interstingly, an acute LPS treatment affects the efficiency of GABA exocytosis at PND36 in a sex-dependent manner. These results add new knowledge on the role of GABA as effector of central inhibitory plasticity at the early stage of development and its relevance in dimorphic adaptation in physio pathological conditions.