Deafferentation-Induced Redistribution of MMP-2, but Not of MMP-9, Depends on the Emergence of GAP-43 Positive Axons in the Adult Rat Cochlear Nucleus

The matrix metalloproteinases MMP-9 and MMP-2, major modulators of the extracellular matrix (ECM), were changed in amount and distribution in the rat anteroventral cochlear nucleus (AVCN) following its sensory deafferentation by cochlear ablation. To determine what causal relationships exist between the redistribution of MMP-9 and MMP-2 and deafferentation-induced reinnervation, kainic acid was stereotaxically injected into the ventral nucleus of the trapezoid body (VNTB) prior to cochlear ablation, killing cells that deliver the growth associated protein 43 (GAP-43) into AVCN. Deafferentation-induced changes in the pattern of MMP-9 staining remained unaffected by VNTB lesions. By contrast, changes in the distribution of MMP-2 normally evoked by sensory deafferentation were reversed if GAP-43 positive axons were prevented to grow in AVCN. In conclusion, GAP-43-containing axons emerging in AVCN after cochlear ablation seem to be causal for the maintenance of MMP-2-mediated ECM remodeling

Synaptic Reorganization in the Adult Rat's Ventral Cochlear Nucleus following Its Total Sensory Deafferentation

Ablation of a cochlea causes total sensory deafferentation of the cochlear nucleus in the brainstem, providing a model to investigate nervous degeneration and formation of new synaptic contacts in the adult brain. In a quantitative electron microscopical study on the plasticity of the central auditory system of the Wistar rat, we first determined what fraction of the total number of synaptic contact zones (SCZs) in the anteroventral cochlear nucleus (AVCN) is attributable to primary sensory innervation and how many synapses remain after total unilateral cochlear ablation. Second, we attempted to identify the potential for a deafferentation-dependent synaptogenesis. SCZs were ultrastructurally identified before and after deafferentation in tissue treated for ethanolic phosphotungstic acid (EPTA) staining. This was combined with pre-embedding immunocytochemistry for gephyrin identifying inhibitory SCZs, the growth-associated protein GAP-43, glutamate, and choline acetyltransferase. A stereological analysis of EPTA stained sections revealed 1.11±0.09 (S.E.M.)×109 SCZs per mm3 of AVCN tissue. Within 7 days of deafferentation, this number was down by 46%. Excitatory and inhibitory synapses were differentially affected on the side of deafferentation. Excitatory synapses were quickly reduced and then began to increase in number again, necessarily being complemented from sources other than cochlear neurons, while inhibitory synapses were reduced more slowly and continuously. The result was a transient rise of the relative fraction of inhibitory synapses with a decline below original levels thereafter. Synaptogenesis was inferred by the emergence of morphologically immature SCZs that were consistently associated with GAP-43 immunoreactivity. SCZs of this type were estimated to make up a fraction of close to 30% of the total synaptic population present by ten weeks after sensory deafferentation. In conclusion, there appears to be a substantial potential for network reorganization and synaptogenesis in the auditory brainstem after loss of hearing, even in the adult brain

International Consensus Statement on Rhinology and Allergy: Rhinosinusitis

Background: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICAR‐RS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICAR‐RS‐2021 as well as updates to the original 140 topics. This executive summary consolidates the evidence‐based findings of the document. Methods: ICAR‐RS presents over 180 topics in the forms of evidence‐based reviews with recommendations (EBRRs), evidence‐based reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary. Results: ICAR‐RS‐2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidence‐based management algorithm is provided. Conclusion: This ICAR‐RS‐2021 executive summary provides a compilation of the evidence‐based recommendations for medical and surgical treatment of the most common forms of RS

Gap43 transcription modulation in the adult brain depends on sensory activity and synaptic cooperation.

Brain development and learning is accompanied by morphological and molecular changes in neurons. The growth associated protein 43 (Gap43), indicator of neurite elongation and synapse formation, is highly expressed during early stages of development. Upon maturation of the brain, Gap43 is down-regulated by most neurons with the exception of subdivisions such as the CA3 region of hippocampus, the lateral superior olive (LSO) and the central inferior colliculus (CIC). Little is known about the regulation of this mRNA in adult brains. We found that the expression of Gap43 mRNA in specific neurons can be modulated by changing sensory activity of the adult brain. Using the central auditory system of rats as a model, Gap43 protein and mRNA levels were determined in LSO and CIC of hearing-experienced rats unilaterally or bilaterally deafened or unilaterally stimulated by a cochlear implant (CI). Our data indicate that Gap43 is a marker useful beyond monitoring neuronal growth and synaptogenesis, reflecting also specific patterns of synaptic activities on specific neurons. Thus, unilateral loss of input to an adult auditory system directly causes asymmetrical expression of Gap43 mRNA between LSOs or CICs on both sides of the brainstem. This consequence can be prevented by simple-patterned stimulation of a dysfunctional ear by way of a CI. We suggest that as a function of input balance and activity pattern, Gap43 mRNA expression changes as cells associate converging afferent signals

Quantification of Gap43 mRNA staining intensities in LSO (A, B) and CIC (C, D).

<p>Bilateral comparison of left-to-right or ipsilateral-to-contralateral staining intensities in LSO (A) and CIC (C) indicates that Gap43 mRNA was different between both sides of the brainstem if sensory stimulation was reduced on one side only (LSO: n = 19/92 rats/slices; F = 45.48, DFn = 2, DFd = 118; <i>ud</i>: 0.39±0.02; Co: 0.96±0.03; CIC: n = 19/89 rats/slices; F = 201.5, DFn = 2, DFd = 116; <i>ud</i>: 1.82±0.08; Co: 1.03±0.03; p<0.001 for both). EIS in the ear of one side with the other ear continuing transduction of acoustically signals maintained ipsilateral-to-contralateral balance as in controls (LSO: n = 6/29 rats/slices; <i>us</i>: 1.03±0.03; CIC: n = 6/30 rats/slices, <i>us</i>: 1.06±0.03; p>0.05 for both). Dotted line indicates bilateral symmetry (1.0). Significant differences against control level are indicated by asterisks above bars. Significant divergences between <i>ud</i> and <i>us</i> rats are indicated by lines with associated asterisks. (B) Staining results of <i>gap43</i> transcription in LSO (n = 29/142 rats/slices; F = 53.89, DFn = 5, DFd = 278) indicates that the staining intensity increased significantly against controls (Co) in LSOc due to unilateral deafness (<i>ud</i>; n = 19/89 rats/slices; p<0.001), and in bilateral LSO after unilateral stimulation (<i>us</i>; n = 14/55 rats/slices; p<0.001 for both). Additionally, staining intensity in <i>ud</i> rats on the contralateral side was significantly higher than for bilaterally deafened (<i>bd</i>) rats (n = 15/87 rats/slices; ###: p<0.001). Staining intensities of both LSOs of <i>us</i> rats were higher than the ipsilateral intensity of <i>ud</i> rats (n = 17/90 rats/slices; p<0.001 for both). (D) Staining results of <i>gap43</i> transcription in CIC (n = 29/145 rats/slices; F = 18.71, DFn = 5, DFd = 284) revealed that the level increased against controls in CICi due to <i>ud</i> (n = 19/91 rats/slices; p<0.001), and in bilateral CIC after <i>us</i> (n = 14/56 rats/slices; p = 0.0085 for Co vs. <i>us</i> i; p = 0.0385 for Co vs. <i>us</i> c). Mean staining intensity of CIC of <i>bd</i> rats was significantly different from CICi of <i>ud</i> rats (n = 15/89 rats/slices; ###: p<0.001), whereas both sides of <i>us</i> rats rose against CICc of <i>ud</i> rats (n = 17/95 rats/slices; p = 0.0007 for <i>us</i> i vs. <i>ud</i> c; p = 0.0049 for <i>us</i> c vs. <i>ud</i> c). Significance levels: (***/^###) for p<0.001, (**) for p<0.01, (*) for p<0.05. LSO: lateral superior olive; CIC: central inferior colliculus; i: ipsilateral; c: contralateral.</p

Experimental Design.

<p>T_i: time of implantation of a passive electrode dummy or onset of electrical intracochlear stimulation (EIS); d: day(s).</p

Gap43 mRNA and protein expression in auditory brainstem.

<p>(A) Anteroventral cochlear nucleus (AVCN, dashed line) was devoid of Gap43 mRNA staining on both sides under any experimental condition. (B) Faintly stained Gap43 protein-positive axonal boutons were present throughout AVCN in controls and all experimental conditions. Inset: higher magnification of immuno-positive presynaptic endings (arrowheads). (C) Gap43 protein expression in lateral olivocochlear neurons (arrows) within LSOi (dashed line) required at least 5 days (d) of electrode implantation independent of its activation. Inset: close-up of Gap43 protein-positive neurons (arrows) and boutons following 7d of <i>ud</i>. (D) Throughout CIC (dashed line), Gap43 immunoreactivity was always present. Inset: close-up of immuno-positive presynaptic endings (arrowheads). Scale bars for A to D: 0.2 mm. Scale bars of insets B to D: 20 μm. LSO: lateral superior olive; CIC: central inferior colliculus; nVIII: 8th cranial nerve; tb: trapezoid body; i: ipsilateral; c: contralateral; <i>ud</i>: unilateral deafness.</p

Expression level of Gap43 mRNA depends on synaptic cooperation in auditory brainstem nuclei.

<p>(A) Under control conditions, neurons in LSO and CIC of both sides of the brainstem receive stimulation-dependent excitatory (green) and inhibitory (red) inputs defining a functional balance with respect to metabotropic receptor activation to generate a basal level of Gap43 mRNA expression (light purple dots). (B) Induction of bilateral deafness silences all stimulation-dependent inputs (gray), leaving Gap43 mRNA levels unchanged. Question marks indicate a possible influence of spontaneous activity in MNTB neurons of unknown significance. (C) Unilateral deafness causes an imbalance of excitation and inhibition on neurons. Loss of excitation (gray) remained ineffective in modulating Gap43 mRNA levels in LSOi and CICc, whereas loss of stimulation-dependent inhibition for LSO via MNTB induces a significant increase of Gap43 mRNA staining level (dark purple dots) in LSOc and CICi. (D) Following unilateral EIS, excitatory afferents of neurons in LSOi and CICc as well as inhibitory afferents on neurons in LSOc and CICi were kept active even if the CI induced input is stronger-than-normal (thick lines). This resulted in a deviation from the normal excitatory-to-inhibitory input ratio and led to a rise of <i>gap43</i> transcription in neurons of these auditory regions (dark purple dots). nVII: 8th cranial nerve; MNTB: medial nucleus of the trapezoid body; LSO: lateral superior olive; CI: cochlear implant; CIC: central inferior colliculus; EIS: electrical intracochlear stimulation; VCN: ventral cochlear nucleus.</p

Experimental Groups.

<p>c: contralateral; i: ipsilateral; Co: control; <i>bd</i>: bilateral deaf; <i>ud</i>: unilateral deaf; <i>us:</i> unilateral stimulation; EIS: electrical intracochlear stimulation.</p