Peripheral and central anatomical organization of cutaneous afferent subtypes in a rat nociceptive intersegmental spinal reflex

The central projection patterns of cutaneous afferents from the forelimb and shoulder of mice were studied in the spinal dorsal horn after intracutaneous injection of AlexaFluor 488-conjugated and/or 594-conjugated cholera toxin subunit B (CTB). Based on their dermatomes, the following eight skin regions are thought to be innervated by spinal nerves from the sixth to eighth cervical spinal nerve roots: the dorsal surface of the shoulder, brachium, proximal forearm, distal forearm, hand, palmar surface of the second and third digits, and palm. The termination areas of afferents from the dorsal surface of the shoulder and forearm were narrow, distributed in a dorsoventral direction, and aligned in order from lateral to medial within the sixth to eighth cervical dorsal horns. By contrast, the termination areas of the palmar surface of the second and third digits largely overlapped. We also injected CTB into the dorsal surface of the hindlimb and pelvic regions. Skin regions there are thought to be innervated by nerves from the third to fifth lumbar spinal nerve roots. The observed projection patterns in the lumbar dorsal horn were similar to the cervical patterns. Injection of a mixture of CTB and wheat-germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), which are thought to label Aβ and Aδ/C fibers, respectively, showed segregated termination areas of CTB-and WGA-HRP-labeled afferents. Moreover, alignment of the termination areas was in the dorsoventral direction. These results suggest there is fine somatotopic (mediolateral axis) and modality-specific (dorsoventral axis) organization within the spinal dorsal horn.

Section: Methodssupporting

confidence: 84%

Mediolateral and dorsoventral projection patterns of cutaneous afferents within transverse planes of the mouse spinal dorsal horn

Odagaki

Kubo

Hayashi

et al. 2018

“…The anti‐CTB antibody is a commercial polyclonal antibody (List Biological Laboratories) raised in goats against the purified CTB from Vibrio cholerae type Inaba 569B. We observed CTB‐labeled afferents detected by this antibody being distributed in lamina (L) III to LIV, as previously reported (Florence, Wall, & Kaas, ; Lee, White, Chung, & Tansey, ; Maslany, Crockett, & Egger, ).…”

Section: Methodssupporting

confidence: 86%

Differential innervation within a transverse plane of spinal gray matter by sensorimotor cortices, with special reference to the somatosensory cortices

Kubo

Murabe

Odagaki

et al. 2019

The corticospinal (CS) neurons projecting to the cervical cord distribute not only in motor‐related cortical areas, but also in somatosensory areas, including the primary somatosensory cortex (S1). The exact functions of these widely distributed CS neurons are largely unknown, however. In this study, we injected mice with adeno‐associated virus encoding membrane‐binding fluorescent proteins to investigate the distribution of axons from CS neurons in different regions within a broad cortical area. We found that CS axons from the primary motor cortex (M1), the rostral part of S1 (S1r), and the caudal part of S1 (S1c) differentially project to specific compartments within the spinal gray matter of the seventh cervical cord segment: (a) M1 projects mainly to intermediate and ventral areas, (b) S1r to the mediodorsal area, and (c) S1c to the dorsolateral area. We also found that the projection from S1r, which corresponds to the forelimb area, largely overlaps the cutaneous afferent terminals from the forepaw (hand) in the dorsal horn, and we detected a similar relation between S1c and the trunk. Our findings suggest the existence of considerably fine somatotopic compartments within the dorsal horn that process somatosensation and descending information, which is provided mainly by S1 CS neurons and contribute to delicate control of sensory information in generation of movement.

“…The anti‐CTB antibody (#703; List Biological Laboratories) produced in goats with CTB (choleragenoid) has been frequently used to label injected CTB as a retrograde tracer. This tracing and detection method has been successfully applied in numerous previous studies (for example, Rosin, Chang, & Guyenet, ; Lee, White, Chung, & Tensey, ). Preabsorption of the antibodies from antiserum with excessive CTB molecules showed no labeling whereas adjacent tissue sections showed typical CTB labeling without preabsorbing the antibodies (Rosin et al, ).…”

Section: Methodsmentioning

confidence: 99%

Dorsal and ventral parts of thalamic nucleus submedius project to different areas of rat orbitofrontal cortex: A single neuron‐tracing study using virus vectors

Kuramoto

Iwai

Yamanaka

et al. 2017

The rodent orbitofrontal cortex is involved in a variety of cognitive and behavioral functions that require thalamic input to be successfully expressed. Although the thalamic nucleus submedius (Sm) is a major source of afferents to the orbitofrontal cortex, thalamocortical projection from the Sm has not been fully elucidated. In the present study, we first divided the rat Sm into dorsal and ventral parts according to the distribution of vesicular glutamate transporter 2-immunoreactive varicosities, which were somatosensory afferents from the brain stem. Subsequently we investigated dendritic and axonal arborizations of individual dorsal and ventral Sm neurons by visualizing the processes with Sindbis virus vectors expressing membrane-targeted fluorescent proteins. The number of dendritic processes of ventral Sm neurons was greater than that of dorsal Sm neurons. In the cerebral cortex, all the reconstructed Sm neurons sent axons primarily to layers 2-5. Interestingly, dorsal Sm neurons formed a single axon arbor exclusively within the ventrolateral orbital area, whereas ventral Sm neurons made two axon arbors in the lateral orbital and ventral orbital areas simultaneously. The spread of each axon arbor was 500-1000 µm in diameter in the direction tangential to the cortical surface. These results indicate that the dorsal and ventral Sm comprise two distinct thalamocortical pathways. The dorsal Sm pathway relay somatosensory information to the ventrolateral orbital area and may be involved in emotional and aversive aspects of nociceptive information processing, whereas the ventral Sm pathway seems to co-activate distant orbitofrontal cortical areas, and may link their functions under certain circumstances.