Interneuron precursors transplanted into visual cortex induce network plasticity during their heterochronic maturation. Such plasticity can have a significant impact on the function of the animal, and is normally present only during a brief critical period in early postnatal development. Elucidating the synaptic and physiological properties of interneuron precursors as they mature is key to understanding how long-term circuit changes are induced by transplants. We studied the development of transplant-derived interneurons and compared it to endogenously-developing interneurons (those which are born and develop in the same animal) at parallel developmental time points using patch-clamp recordings in acute cortical slices. We found that transplant-derived interneurons develop into fast-spiking and nonfast-spiking neurons characteristic of the MGE lineage. Transplant-derived interneurons matured more rapidly than endogenously-developing interneurons, as shown by more hyperpolarized membrane potentials, smaller input resistances, and narrower action potentials at a juvenile age. In addition, transplant-derived fast-spiking interneurons have more quickly saturating input-output relationships and lower maximal firing rates in adulthood, indicating a possible divergence in function. Transplant-derived interneurons both form inhibitory synapses onto host excitatory neurons and receive excitatory synapses from host pyramidal cells. Unitary connection properties are similar to those of host interneurons. These transplant-derived interneurons, however, were less densely functionally connected onto host pyramidal cells than were host interneurons and received fewer spontaneous excitatory inputs from host cells. These findings suggest that many physiological characteristics of interneurons are autonomously determined, while some factors impacting their circuit function may be influenced by the environment in which they develop.
- medial ganglionic eminence
- low-threshold spiking
- interneuron transplantation
- Copyright © 2017, Journal of Neurophysiology