Jean-Claude Lacaille lectured at DHMC last Wednesday regarding persistent plasticity of inhibition in brain memory circuits.
His studies indicate that long-term neuroplasticity, which is the ability of neurons to be modified by experience, in hippocampal networks occurs not only at excitatory synapses of hippocampal granule and pyramidal cells, but also at excitatory synapses onto inhibitory interneurons.
The three aforementioned cell types are different neurons, which are involved in the formation of memories within the hippocampus.
Granule cells are miniscule neurons (less than 10 micrometers in diameter) that are found throughout the central nervous system (CNS). Pyramidal cells are a type of excitatory neuron located in the cerebral cortex, the hippocampus, and the amygdala.
Interneurons, the subject of Lacaille’s lecture, are connecting units that link afferent and efferent neurons and thus regulate incoming and outgoing signals. Most interneurons of the CNS are inhibitory, which means they are involved in reducing the chance that an action potential will occur in a post-synaptic neuron.
Lacaille reports that both long-term potentiation and depression occur at synapses of inhibitory interneurons in the dentate gyrus, which is part of the hippocampus. His findings indicate that not only are inhibitory interneurons of the hippocampus capable of displaying the plasticity of potentiation, which alters the efficacy of neurons based on their use or disuse, but also that changes in the efficacy of interneurons varies predictably among different types of interneurons.
According to Lacaille, hippocampal interneurons have highly diverse morphology, which consequently gives hippocampal neural networks a high degree of variability in terms of their plasticity. This variance of efficacy appears to correspond to the role of each interneuron in the hippocampus.
Thus, Lacaille’s research suggests that the extent of hippocampal plasticity that arises from inhibitory interneurons conforms to cell-type rules. This is important because inhibitory networks are essential for establishing feedback loops, which regulate neural function.
Consequently, understanding the ways in which the anatomy of interneurons impacts their varying degrees of plasticity is essential for modeling the actions of the hippocampus as a whole. This is essential for understanding the complexities of memory formation at the cellular level by widening the scope of neuroplasticity to include inhibitory neurons, a ubiquitous but otherwise excluded cell type.