Hippocampal Gαq/₁₁ but not Gαo-coupled receptors are altered in aging

Normal aging may limit the signaling efficacy of certain GPCRs by disturbing the function of specific Gα-subunits and leading to deficient modulation of intracellular functions that subserve synaptic plasticity, learning and memory. Evidence suggests that Gαq/₁₁ is more sensitive to the effects of aging relative to other Gα-subunits, including Gαo. To test this hypothesis, the functionality of Gαq/₁₁ and Gαo were compared in the hippocampus of young (6 months) and aged (24 months) F344 × BNF₁ hybrid rats assessed for spatial learning ability. Basal GTPγS-binding to Gαq/₁₁ was significantly elevated in aged rats relative to young and but not reliably associated with spatial learning. mAChR stimulation of Gαq/₁₁ with oxotremorine-M produced equivocal GTPγS-binding between age groups although values tended to be lower in the aged hippocampus and were inversely related to basal activity. Downstream Gαq/₁₁ function was measured in hippocampal subregion CA₁ by determining changes in [Ca(2+)]i after mAChR and mGluR (DHPG) stimulation. mAChR-stimulated peak change in [Ca(2+)]i was lower in aged CA₁ relative to young while mGluR-mediated integrated [Ca(2+)]i responses tended to be larger in aged. GPCR modulation of [Ca(2+)]i was observed to depend on intracellular stores to a greater degree in aged than young. In contrast, measures of Gαo-mediated GTPγS-binding were stable across age, including basal, mAChR-, GABABR (baclofen)-stimulated levels. Overall, the data indicate that aging selectively modulates the activity of Gαq/₁₁ within the hippocampus leading to deficient modulation of [Ca(2+)]i following stimulation of mAChRs but these changes are not related to spatial learning.