Morphological and functional characterization of cholinergic interneurons in the dorsal horn of the mouse spinal cord

Abstract

Endogenous acetylcholine is an important modulator of sensory processing, especially at the spinal level, where nociceptive (pain-related) stimuli enter the central nervous system and are integrated before being relayed to the brain. To decipher the organization of the local cholinergic circuitry in the spinal dorsal horn, we used transgenic mice expressing enchanced green fluorescent protein specifically in cholinergic neurons (ChAT::EGFP) and characterized the morphology, neurochemistry, and firing properties of the sparse population of cholinergic interneurons in this area. Three-dimensional reconstruction of lamina III ChAT::EGFP neurons based either on their intrinsic fluorescence or on intracellular labeling in live tissue demonstrated that these neurons have long and thin processes that grow preferentially in the dorsal direction. Their dendrites and axon are highly elongated in the rostrocaudal direction, beyond the limits of a single spinal segment. These unique morphological features suggest that dorsal horn cholinergic interneurons are the main contributors to the plexus of cholinergic processes located in lamina IIi, just dorsal to their cell bodies. In addition, immunostainings demonstrated that dorsal horn cholinergic interneurons in the mouse are γ-aminobutyric acidergic and express nitric oxide synthase, as in rats. Finally, electrophysiological recordings from these neurons in spinal cord slices demonstrate that two-thirds of them have a repetitive spiking pattern with frequent rebound spikes following hyperpolarization. Altogether our results indicate that, although they are rare, the morphological and functional features of cholinergic neurons enable them to collect segmental information in superficial layers of the dorsal horn and to modulate it over several segments.

Boundary cap neural crest stem cells homotopically implanted to the injured dorsal root transitional zone give rise to different types of neurons and glia in adult rodents

“…Calbindin is expressed in both excitatory and inhibitory segmental and intersegmental interneurons [32]. ChAT-positive neurons are sparsely distributed but form a widely distributed network of fibers, which are proposed to modulate sensory transmission in the dorsal horn [33]. Neurons expressing the tyrosine kinase receptor RET include interneurons as well as neurons in lamina I giving rise to the spinothalamic tract [34].…”

Normal and abnormal coding of somatosensory stimuli causing pain

“…As an adjunct to electrophysiology, for example, optogenetics enables targeted patch clamp recordings in slices with dramatically enhanced throughput by allowing visual identification of subpopulation of neurons, especially when these represent a small minority of the overall population 71, 72 . But the ability to combine single-cell electrophysiology with single-cell optical sensing and activation in vivo using novel micro-optrodes will be particularly instrumental to determine the role of specific subpopulation of cells within the intact circuit and in contextual environment 73 .…”

Relief of Hypersensitivity after Nerve Injury from Systemic Donepezil Involves Spinal Cholinergic and γ-Aminobutyric Acid Mechanisms

“…33,34 Stimulation of M2, M3, and M4 muscarinic receptors results in presynaptic GABA release in the spinal cord and γ-aminobutyric acid type B receptor-mediated analgesia. 13,16,35 Stimulation of spinal nicotinic receptors has been reported to produce presynaptic GABA release and γ-aminobutyric acid type A receptor-mediated analgesia.…”