Biology subjects

Hovhannisyan, A. H.

Publications and source records attributed to Hovhannisyan, A. H..

6 recordsLinked to original sources

bioRxiv2025

Innervation of Retrodiscal Tissues in Patients with Temporomandibular Joint Disorder

Temporomandibular joint (TMJ) disorders (TMJDs) are a group of musculoskeletal conditions affecting the orofacial region and often associated with facial pain. Understanding the sensory innervation of TMJ structures, particularly the retrodiscal tissue, is essential for identifying pain mechanisms in TMJD because to study these mechanisms, we must first determine the sensory neuronal makeup of the TMJ. However, data on nerve types within TMJ tissues remain limited. This study examined the sensory and sympathetic nerve profiles in retrodiscal tissues from TMJD patients with osteoarthritis (OA), rheumatoid arthritis (RA), or condylar hyperplasia (CH) who underwent bilateral TMJ replacement (TMJR). Immunohistochemistry with specific nerve markers was used to visualize and quantify nerve subtypes. CH tissues had significantly lower densities of pgp9.5+ sensory fibers compared to RA and OA, which showed similar levels. Across all subtypes, the ratio of unmyelinated (pgp9.5+/NFH-) to myelinated (pgp9.5+/NFH+) fibers was approximately 70:30. Most sensory nerves were CGRP+ (peptidergic), while a smaller portion were CGRP- (non-peptidergic), some of which were parvalbumin-positive (PV+). Both myelinated and non-myelinated peptidergic as well as non-peptidergic fibers were present in the retrodiscal tissues. In addition to sensory innervation, all retrodiscal tissues contained tyrosine hydroxylase-positive (TH+) sympathetic fibers, primarily innervating blood vessels (alpha-smooth muscle actin (-SMA+)). These vessels were also predominantly innervated by unmyelinated sensory fibers, with limited input from myelinated sensory nerves. In summary, all TMJD subtypes shared similar nerve compositions, but CH tissues exhibited reduced sensory nerve density, a potential explanation for the lower association with pain compared to OA and RA. For all TMJD subtypes, retrodiscal tissue vasculature was mainly innervated by sympathetic and unmyelinated sensory nerves. These findings enhance understanding of the neural basis of TMJD-related pain.

neuroscience↗

bioRxiv2025

Modeling Masticatory Myalgia to Headache-like Referred Pain Triggers Local Gene Plasticity at Referred Pain Sites

Patients with myofascial pain in the head and neck area report widespread and referred pain, including headache. Existing preclinical models fail to replicate this clinical phenotype; therefore, we aimed to develop animal models mimicking referred pain phenomenon and investigate whether referred pain leads to gene plasticity at the referred sites. We modeled masticatory myalgia by stimulation of either the masseter (MM) or temporal muscle (TM) in mice. MM and TM were stimulated with a single high-dose injection of Collagenase-type II (Col), repetitive low-dose Col injections, repetitive gentle MM stimulation, or single or repetitive forceful mouth opening. Referred pain was assessed by measuring mechanical hypersensitivity in the periorbital area (representing headache-like behavior) and another masticatory muscle. Stimulation of the MM, whether through single or repetitive Col injections or mouth opening, produced inconsistent, short-lasting (1-2 days) headache-like behavior in both males and females. In contrast, stimulation of the TM, using different paradigms, triggered mechanical hypersensitivity in both the MM and the periorbital area. Referred headache-like behavior lasted longer in females compared to males, while referred myalgia in the MM was pronouncer in males. The referred pain in the MM and periorbital areas triggered by TM stimulation was associated with significant gene plasticity in the MM and dura mater. Transcriptional changes in the MM following Col injection into the TM resembled those observed after direct MM injections. Presented data imply that referred pain modeled by TM stimulation could be accounted by nociceptive signaling from multiple local sites involved in this referred pain network.

neuroscience↗

bioRxiv2024

Investigating Mechanically Activated Currents from Trigeminal Neurons of Non-Human Primates

IntroductionPain sensation has predominantly mechanical modalities in many pain conditions. Mechanically activated (MA) ion channels on sensory neurons underly responsiveness to mechanical stimuli. The study aimed to address gaps in knowledge regarding MA current properties in higher order species such as non-human primates (NHP; common marmosets), and characterization of MA currents in trigeminal (TG) neuronal subtypes. MethodsWe employed patch clamp electrophysiology and immunohistochemistry (IHC) to associate MA current types to different marmoset TG neuronal groups. TG neurons were grouped according to presumed marker expression, action potential (AP) width, characteristic AP features, after-hyperpolarization parameters, presence/absence of AP trains and transient outward currents, and responses to mechanical stimuli. ResultsMarmoset TG were clustered into 5 C-fiber and 5 A-fiber neuronal groups. The C1 group likely represent non-peptidergic C-nociceptors, the C2-C4 groups resembles peptidergic C-nociceptors, while the C5 group could be either cold-nociceptors or C-low-threshold-mechanoreceptors (C-LTMR). Among C-fiber neurons only C4 were mechanically responsive. The A1 and A2 groups are likely A-nociceptors, while the A3-A5 groups probably denote different subtypes of A-low-threshold-mechanoreceptors (A-LTMRs). Among A-fiber neurons only A1 was mechanically unresponsive. IHC data was correlated with electrophysiology results and estimates that NHP TG has [~]25% peptidergic C-nociceptors, [~]20% non-peptidergic C-nociceptors, [~]30% A-nociceptors, [~]5% C-LTMR, and [~]20% A-LTMR. ConclusionOverall, marmoset TG neuronal subtypes and their associated MA currents have common and unique properties compared to previously reported data. Findings from this study could be the basis for investigation on MA current sensitizations and mechanical hypersensitivity during head and neck pain conditions.

neuroscience↗

bioRxiv2023

Transcriptional Profiles of Non-neuronal and Immune Cells in Mouse Trigeminal Ganglia

Non-neuronal cells constitute 90-95% of sensory ganglia. These cells play critical roles in modulation of nociceptive signal transmissions by sensory neurons. Accordingly, the aim of this review-study was to identify, profile and summarize TG non-neuronal cell types in naive male mice using published and our own data generated by single-cell RNA sequencing (scRNA-seq), flow cytometry (FC) and immunohistochemistry (IHC). TG contains 5 types of non-neuronal cells: glial, fibroblasts, smooth muscle, endothelial and immune cells. There is agreement among publications for glial, fibroblasts, smooth muscle and endothelial cells. Based on gene profiles, glial cells were classified as Schwann cells and satellite glial cells (SGC). Mpz had dominant expression in Schwann cells, and Fabp7 is specific for SCG. Two types of Col1a2+ fibroblasts located throughout TG were distinguished using gene profiles. TG smooth muscle and endothelial cells representing blood vessels were detected with well recognized markers. Our study split reported single TG immune cell group into 3 types of macrophages and 4 types of neutrophils. Macrophages were located among neuronal bodies and nerve fibers, and were sub-grouped by unique transcriptomic profiles and using Ccr2, Cx3cr1 and Iba1 as markers. S100a8+ neutrophils were located in dura surrounding TG and were sub-grouped by clustering and expressions of Csf3r, Ly6G, Ngp, Elane and Mpo. Overall, generated and summarized here dataset on non-neuronal TG cells could provide essential and fundamental information for studies on cell plasticity, interactomic network between neurons and non-neuronal cells and function during variety of pain conditions in the head and neck region.

neuroscience↗

bioRxiv2023

Association of inflammation and tissue damage inducedbiological processes in masseter muscle with the resolution of chronic myalgia

Biological processes linked to intramuscular inflammation during myogenous temporomandibular disorder (TMDM) are largely unknown. We mimicked this inflammation by intra-masseteric muscle (MM) injections of complete Freunds adjuvant (CFA) or collagenase type 2 (Col), which emulates tissue damage. CFA triggered mechanical hypersensitivity at 1d post-injection was mainly linked to processes controlling chemotactic activity of monocytes and neutrophils. At 5d post-CFA, when hypersensitivity was resolved, there was minimal inflammation whereas tissue repair processes were pronounced. Low dose Col (0.2U) also produced acute orofacial hypersensitivity that was linked to tissue repair, but not inflammatory processes. High dose Col (10U) triggered prolonged orofacial hypersensitivity with inflammatory processes dominating at 1d post-injection. At pre-resolution time point (6d), tissue repair processes were underway and a significant increase in pro-inflammatory gene expressions compared to 1d post-injection were detected. RNA-seq and flow cytometry showed that immune processes in MM were linked to accumulation of macrophages, natural killer and natural killer T cells, dendritic cells and T-cells. Altogether, CFA and Col treatments induced different immune processes in MM. Importantly, orofacial hypersensitivity resolution was preceded with repairs of muscle cell and extracellular matrix, an elevation in immune system gene expression and accumulation of distinct immune cells in MM.

neuroscience↗

bioRxiv2023

Sensory innervation of masseter, temporal and lateral pterygoid muscles in common marmosets

Myogenous temporomandibular disorders (TMDM) is associated with an increased responsiveness of nerves innervating the masseter (MM), temporal (TM), medial pterygoid (MPM) and lateral pterygoid muscles (LPM). This study aimed to examine sensory nerve types innervating MM, TM and LPM of adult non-human primate - common marmosets. Sensory nerves are localized in specific regions of these muscles. Pgp9.5, marker for all nerves, and NFH, a marker for A-fibers, showed that masticatory muscles were predominantly innervated with A-fibers. The proportion of C- to A-fibers was highest in LPM, and minimal (6-8%) in MM. All C-fibers (pgp9.5+/NFH-) observed in masticatory muscles were peptidergic (CGRP+) and lacked mrgprD, trpV1 and CHRNA3, a silent nociceptive marker. All fibers in masticatory muscles were labeled with GFAP+, a myelin sheath marker. There were substantially more peptidergic A-fibers (CGRP+/NFH+) in TM and LPM compared to MM. Almost all A-fibers in MM expressed trkC, with some of them having trkB and parvalbumin. In contrast, a lesser number of TM and LPM nerves expressed trkC, and lacked trkB. Tyrosine hydroxylase antibodies, which did not label TG, highlighted sympathetic fibers around blood vessels of the masticatory muscles. Overall, masticatory muscle types of marmosets have distinct and different innervation patterns.

neuroscience↗