Age‐associated Downregulation of GABAergic and Glutamatergic Synapse‐related Gene Expression in the Rostral Ventrolateral Medulla of Male Rats

Abstract

The rostral ventrolateral medulla (RVLM), a part of the medullary reticular formation, plays a major role in several physiological responses, including cardiovascular and sympathetic nervous system functions. Although aging causes disturbances in the responses of these physiological systems, RVLM involvement in these age-related changes is not clear. Previous work on high-throughput gene expression analysis of the RVLM in aged animals suggested that neurotransmission- and synapse-related genes might be downregulated in these animals (Balivada S et al., 2017. Physiol Genomics. 49, 400). To identify the synapse-related genes, we hypothesized that aging leads to downregulation of GABAergic and glutamatergic synapse-related gene expression in the RVLM of aged rats. To test this hypothesis, we micropunched an RVLM-containing area from young (3 months), middle-aged (12 months), and aged (24 months) F344 male rats. Sampled sites were mapped onto the Brain Maps 4.0 rat brain reference atlas (Swanson LW, 2018. J. Comp. Neurol. 526, 935) to localize and validate the spatial location of the RVLM-containing micropunch. RNA purified from these micropunches was analyzed using GABA and Glutamate RT2 Profiler PCR arrays (n= 8–10). In addition, the expression of selected genes was analyzed at the protein level using western blotting (n=10). Genes that displayed significant differential expression (1.5-fold, p < .05, FDR < .05) were identified to be downregulated in the RVLM of aged and middle-aged rats. Compared to GABAergic synapse-related genes, more glutamatergic synapse-related genes were observed to be downregulated in the aged (76.6%) and middle-aged (77.7%) RVLM. Slc1a6 showed the highest fold downregulation (—1.8) at the RNA level in the RVLM of aged as compared to young rats, and its protein product, Excitatory Amino Acid Transporter-4, showed a downregulatory trend in the RVLM of aged rats. These results suggest that certain molecular constituents of both GABAergic and glutamatergic synapses might be altered in the RVLM of aged and middle-aged rats, and that the changes in glutamatergic synapse composition might be more prominent. Investigating the anatomical and functional changes associated with these glutamatergic synapses might help understand the effects of aging on the RVLM.