Imaging and analysis of perivascular nerves in human mesenteric and coronary arteries: a comparison between epi-fluorescence and confocal microscopy

A comparison of confocal and epifluorescence microscopy for quantification of RNAScope and immunohistochemistry fluorescent images

BACKGROUND

Quantification of RNA expression and protein production in fluorescent stainings provides critical information concerning neurodevelopment. A trustable independent quantification technique requires acquisition of reliable images prior to image processing. There is uncertainty in existing literature regarding the use of confocal microscopy compared to standard epifluorescence microscopy, especially in the context of RNA in situ hybridization protocols.

NEW METHOD

The hindbrains of developing rat embryos from embryologic day 14 (E14) to E20 were sectioned and stained for expression of Hoxb1, Hoxb2, and Phox2b using both RNAScope and immunohistochemistry. Islet1 was used for identification of hindbrain motoneuron cell bodies. Slides were imaged using both confocal and epifluorescence microscopy.

RESULTS

Expression patterns of both mRNA and protein were similar in both imaging modalities. Analyses of Hoxb1 and Hoxb2 mRNA expression were particularly concordant between-scopes, with similar p-values and posthoc differences between timepoints. Confocal imaging of Hoxb2 protein yielded a significant peak at E18, but this level of significance was not reached using epifluorescence microscopy. Although similar trends were observed, only Phox2b RNAScope results were statistically significant when analyzed with confocal microscopy. In contrast, Phox2b immunostaining analyses showed significant differences using both microscopes.

COMPARISON WITH EXISTING METHODS

Researchers may save time and financial resources if epifluorescence microscopy provides comparable or equal results as confocal.

CONCLUSIONS

Epifluorescence microscopy appears sufficient for quantification of RNAScope experiments with relatively low puncta per cell, while confocal microscopy gives clearer definition to immunohistochemical protein relationships and may be preferable especially in targets with low protein production.

The role of C-afferents in mediating neurogenic vasodilatation in plantar skin after acute sciatic nerve injury in rats

Background

Vasomotor regulation of dermal blood vessels, which are critical in the function of the skin in thermoregulatory control, involves both neural and non-neural mechanisms. Whereas the role of sympathetic nerves in regulating vasomotor activities is comprehensively studied and well recognized, that of sensory nerves is underappreciated. Studies in rodents have shown that severance of the sciatic nerve leads to vasodilatation in the foot, but whether sympathetic or sensory nerve fibers or both are responsible for the neurogenic vasodilatation remains unknown.

Results

In adult Sprague–Dawley rats, vasodilatation after transection of the sciatic nerve gradually diminished to normal within 3–4 days. The neurotmesis-induced neurogenic vasodilatation was not detectable when the sciatic nerve was chronically deafferentated by selective resection of the dorsal root ganglia (DRGs) that supply the nerve. Specific activation of C-afferents by intra-neural injection of capsaicin resulted in neurogenic vasodilatation to a magnitude comparable to that by neurotmesis, and transection of the sciatic nerve pre-injected with capsaicin did not induce further vasodilatation.

Conclusions

Our results collectively indicate that vasodilatation after traumatic nerve injury in rats is predominantly mediated by C-fiber afferents.

Analysis of innervation of human mesenteric vessels in non-inflamed and inflamed bowel--a confocal and functional study

We investigated the distribution and density of perivascular nerves in human mesenteric arteries and veins and their responses to noradrenaline (NA), ATP and neuropeptide Y (NPY) in control (non-inflamed) and inflamed bowel, using confocal microscopy and in vitro pharmacology. The density of innervation at the adventitial-medial border of arteries and within the medial muscle coat of veins was increased in inflammatory bowel disease (IBD). Expression of markers for both sympathetic nerves and sensory-motor nerves was significantly increased in IBD. Calcitonin gene-related peptide-containing sensory-motor nerves were present in control arteries and IBD, but not in control veins. The density of 5-hydroxytryptamine-containing nerves was variable in controls, but consistently increased (three to four times) in IBD. Vasoactive intestinal peptide (VIP) expression increased (doubled) in arteries and veins. Arteries and veins contracted to NA and ATP, but only veins constricted to NPY. ATP contractions were reduced in arteries and veins in IBD, while contractions to NA were only slightly reduced. Neuropeptide Y induced significantly greater (20%) contractions of IBD veins. In summary, the density of sympathetic and sensory-motor innervation of both mesenteric arteries and veins was increased in IBD. Both 5-hydroxytryptamine and VIP immunoreactivity were also increased. The responses of both arteries and veins to ATP, and to a lesser extent NA, were reduced in IBD while responses to NPY were greater in veins. Decreased responses to ATP indicate changes in purinergic-mediated transmission in the pathological state.

Involvement of DRG11 in the development of the primary afferent nociceptive system

During development, dorsal root ganglia (DRG) neurons differentiate in various subpopulations, nociceptive neurons belonging in the small-diameter class. This study addresses the role played by DRG11, a transcription factor expressed in the spinal area of projection of small-diameter DRG neurons, in the development of the primary afferent system. The various subclasses of DRG neurons were compared between wild-type and Drg11(-/-) mice at embryonic and postnatal life. In Drg11(-/-) mice, numbers of small peptidergic and non-peptidergic DRG neurons were decreased at P7 concomitant with abnormal cell death. Innervation by small DRG neurons was impaired in cutaneous, visceral and deep tissues. Large DRG neurons were not affected. The data point to a role for DRG11 in early postnatal survival of normally generated small primary afferent neurons innervating various kinds of peripheral tissues, which would explain the nociceptive deficits observed in Drg11-null mutant mice.

Vanilloid receptor 1 expression in the rat urinary tract

Previous findings have shown that the capsaicin sensitivity of sensory fibres is due to the expression of a specific membrane protein, the vanilloid receptor type 1 (VR1). In the present work we studied the distribution, morphology and the neurochemical content of nerve fibres expressing this receptor in the rat urinary tract. Immunolabelling was performed against the VR1 and the positive fibres were examined by light and electron microscopy. Colocalisation of VR1 and substance P or calcitonin gene-related peptide immunoreactivities, and isolectin B4 binding, was evaluated under the confocal microscope. In addition, the effect of intravesical administration of resiniferatoxin, an ultra-potent vanilloid receptor agonist, in the receptor expression in the bladder was also studied. Numerous VR1-immunoreactive fibres were found in the mucosa and muscular layer of the entire urinary tract except the kidney. In the bladder, most fibres were also substance P- or calcitonin gene-related peptide-immunoreactive but did not bind isolectin B4. Under the electron microscope VR1 immunoreactivity was confined to unmyelinated axons and varicosities containing small clear and large dense-core synaptic vesicles. They occurred beneath or among epithelial cells or closely apposed to smooth muscle cells. Intravesical resiniferatoxin decreased VR1 immunoreactivity transiently. These data indicate that primary sensory fibres expressing VR1 are extremely abundant in the rat urinary tract and that, in contrast to the skin, they belong almost exclusively to the peptide-containing sub-population of primary afferents. As capsaicin-sensitive bladder afferents are involved in nociception and reflex micturition control, the numerous free terminal nerve endings expressing VR1 in the mucosa seem more adequate to accomplish the former function. However, the close apposition between VR1-expressing fibres and smooth muscle cells suggests that they may also encode the tonus of the muscular layer.