The hippocampus is a region of the brain that's thought to play a role in many different neurological and psychiatric disorders. It's a complex structure that sits deep in the brain, and is related to memory, the regulation of emotions, and spatial navigation. The hippocampus has traditionally been considered to be a uniform structure, but it's been suggested that different parts of the hippocampus may have different functions; the anterior portion of the hippocampus, for example, may be more involved in mood and emotion while the posterior hippocampus might be more about to cognition.
New work has revealed more about the gene activity in these different parts of the hippocampus. The findings, which have been reported in Neuron, may help scientists learn more about treating disorders that affect the hippocampus.
"These new data reveal molecular-level differences that allow us to view the anterior and posterior hippocampus in a whole new way," said study leader Genevieve Konopka, Ph.D., an associate professor of neuroscience at the University of Texas Southwestern.
Konopka, study co-leader Bradley C. Lega, M.D., associate professor of neurological surgery, neurology, and psychiatry, and colleagues analyzed samples of the anterior and posterior hippocampus from five epilepsy patients who had hippocampus surgery; Lega did the surgical work. He noted that seizures can originate in the hippocampus and while they are typically caused by abnormalities, the assessment of the tissues that were removed suggested that they were anatomically normal.
The researchers also used single nuclei RNA sequencing (snRNA-seq) to identify the cell types and determine which genes were active in these hippocampal tissues at the time the sample was extracted. This research revealed the presence of neurons and support cells in both parts of the hippocampus. But the level of excitatory neurons, which trigger activity in other neurons, was very different in the anterior versus posterior regions.
The gene expression analysis showed that there was more activity in some genes that have been linked to mood disorders in the anterior hippocampus. But in the posterior hippocampus, there tended to be more activity in genes that have been linked to cognitive disorders.
Lega suggested that when we learn more about these differences, we'll gain a better understanding of disorders related to the hippocampus.
"The idea that the anterior and posterior hippocampus represent two distinct functional structures is not completely new, but it's been underappreciated in clinical medicine," he said. "When trying to understand disease processes, we have to keep that in mind."