Sensory Activity-Dependent and Sensory Activity-Independent Properties of the Developing Rodent Trigeminal Principal Nucleus

Abstract

The whisker-sensory trigeminal central pathway of rodents is an established model for studies of activity-dependent neural plasticity. The first relay station of the pathway is the trigeminal principal nucleus (PrV), the ventral part of which receives sensory inputs mainly from the infraorbital branch of the maxillary trigeminal nerve (ION). Whisker-sensory afferents play an important role in the development of the morphological and physiological properties of PrV neurons. In neonates, deafferentation by ION transection leads to the disruption of whisker-related neural patterns (barrelettes) and cell death within a specific time window (critical period), as revealed by morphological studies. Whisker-sensory inputs control synaptic elimination, postsynaptic AMPA receptor trafficking, astrocyte-mediated synaptogenesis, and receptive-field characteristics of PrV cells, without a postnatal critical period. Sensory activity-dependent synaptic plasticity requires the activation of NMDA receptors and involves the participation of glia. However, the basic physiological properties of PrV neurons, such as cell type-specific ion channels, presynaptic terminal function, postsynaptic NMDA receptor subunit composition, and formation of the inhibitory circuitry, are independent of sensory inputs. Therefore, the first relay station of the whisker sensation is largely mature-like and functional at birth. Delineation of activity-dependent and activity-independent features of the postnatal PrV is important for understanding the development and functional characteristics of downstream trigeminal stations in the thalamus and neocortex. This mini review focuses on such features of the developing rodent PrV.

Position-independent functional refinement within the vagus motor topographic map

“…But their central axons in the brainstem are segregated into distinct domains called barrelettes, where they synapse on different postsynaptic neurons 38 . While molecular differences play a major role in topographically sorting the central axons of whisker-innervating sensory neurons in prenatal mice, sensory experience from the periphery refines the topographic organization and instructs point-to-point synaptic connections postnatally 50,51 . Sensory experience gives correlated activity to sensory neurons innervating the same whisker and directs their central axons to converge into the same circuit through the Hebbian mechanism, enabling “neurons that fire together to wire together” 52,53 .…”

Development of tactile sensory circuits in the CNS

“…Finally, for the vPrV, a recent review identified and discussed activity-dependent and independent developmental features [27]. Several properties of the vPrV neurons develop independent of peripherally evoked activity.…”