Neurotransmitter Modulation Relates with Tinnitus Signal Generation and Management

A regulatory pathway model of neuropsychological disruption in Havana syndrome

Introduction

In 2016 diplomatic personnel serving in Havana, Cuba, began reporting audible sensory phenomena paired with onset of complex and persistent neurological symptoms consistent with brain injury. The etiology of these Anomalous Health Incidents (AHI) and subsequent symptoms remains unknown. This report investigates putative exposure-symptom pathology by assembling a network model of published bio-behavioral pathways and assessing how dysregulation of such pathways might explain loss of function in these subjects using data available in the published literature. Given similarities in presentation with mild traumatic brain injury (mTBI), we used the latter as a clinically relevant means of evaluating if the neuropsychological profiles observed in Havana Syndrome Havana Syndrome might be explained at least in part by a dysregulation of neurotransmission, neuro-inflammation, or both.

Method

Automated text-mining of >9,000 publications produced a network consisting of 273 documented regulatory interactions linking 29 neuro-chemical markers with 9 neuropsychological constructs from the Brief Mood Survey, PTSD Checklist, and the Frontal Systems Behavior Scale. Analysis of information flow through this network produced a set of regulatory rules reconciling to within a 6% departure known mechanistic pathways with neuropsychological profiles in N = 6 subjects.

Results

Predicted expression of neuro-chemical markers that jointly satisfy documented pathways and observed symptom profiles display characteristically elevated IL-1B, IL-10, NGF, and norepinephrine levels in the context of depressed BDNF, GDNF, IGF1, and glutamate expression (FDR < 5%). Elevations in CRH and IL-6 were also predicted unanimously across all subjects. Furthermore, simulations of neurological regulatory dynamics reveal subjects do not appear to be "locked in" persistent illness but rather appear to be engaged in a slow recovery trajectory.

Discussion

This computational analysis of measured neuropsychological symptoms in Havana-based diplomats proposes that these AHI symptoms may be supported in part by disruption of known neuroimmune and neurotransmission regulatory mechanisms also associated with mTBI.

Comparative Analysis of Brainstem Auditory Evoked Potential Patterns between Menstruating and Menopausal North Indian Females

INTRODUCTION

Various studies suggest a significant impact of gonadal hormones on many neuronal functions, including auditory processing. Although a few researchers have independently investigated the brainstem auditory evoked potential (BAEP) patterns during various phases of menstrual cycle and also during menopause, there is an acute paucity of comparative data between their BAEP patterns. This study was conducted to compare the BAEP patterns between normally menstruating females and menopausal females from North India.

MATERIALS AND METHODS

A cross-sectional study was done on 90 females aged 17-21 years who were in the follicular phase of their menstrual cycle and 100 menopausal females aged 46-70 years. BAEP recording was done using standardized protocol. The data were analyzed using SPSS software. It contained mean wave latencies I, II, III, IV, V, and Interpeak Latencies (IPL) I-V, I-III, and III-V.

RESULTS

The mean values of latencies of waves I, III, and V and also of IPL I-III, I-V, and III-V were significantly higher (P > 0.05) in menopausal females. However, the difference between mean values of wave latencies II and IV of both groups was statistically non-significant (P > 0.05).

CONCLUSION

The increased latencies in menopausal females indicate subtle degenerative changes that start appearing within the central auditory pathway after menopause and are probably due to a decline in ovarian hormones, especially estrogen.

Mass spectrometry imaging of blast overpressure induced modulation of GABA/glutamate levels in the central auditory neuraxis of Chinchilla

Acoustic trauma damages inner ear neural structures including cochlear hair cells which result in hearing loss and neurotransmitter imbalances within the synapses of the central auditory pathway. Disruption of GABA/glutamate levels underlies, tinnitus, a phantom perception of sound that persists post-exposure to blast noise which may manifest in tandem with acute/chronic loss of hearing. Many putative theories explain tinnitus physiology based on indirect and direct assays in animal models and humans, although there is no comprehensive evidence to explain the phenomenon. Here, GABA/glutamate levels were imaged and quantified in a blast overpressure model of chinchillas using Fourier transform ion cyclotron resonance mass spectrometry imaging. The direct measurement from whole-brain sections identified the relative levels of GABA/glutamate in the central auditory neuraxis centers including the cochlear nucleus, inferior colliculus, and auditory cortex. These preliminary results provide insight on the homeostasis of GABA/glutamate within whole-brain sections of chinchilla for investigation of the pathomechanism of blast-induced tinnitus.

Molecular Aspects of Melatonin Treatment in Tinnitus: A Review

Tinnitus is a hearing disorder characterized by the perception of sound without external acoustic stimuli, which is caused by damage to the auditory system in response to excessive levels of noise, ototoxic agents and aging. Neural plasticity, oxidative/nitrosative stress and apoptosis play important roles in the pathogenesis of tinnitus. The expression of neural plasticity related to excessive glutamatergic neurotransmission leads to generation of abnormal sound in one's ears or head. Furthermore, hyperactivation and over-expression of NMDA receptors in response to excessive release of glutamate contribute to the calcium overload in the primary auditory neurons and subsequent cytotoxicity. Reactive oxygen/nitrogen species are endogenously produced by different type of cochlear cells under pathological conditions, which cause direct damage to the intracellular components and apoptotic cell death. Cochlear hair-cell death contributes to the progressive deafferentation of auditory neurons, which consequently leads to the aberrant activity in several parts of the auditory pathway. Therefore, targeting neural plasticity, oxidative/nitrosative stress, apoptosis and autophagy may ameliorate tinnitus. Melatonin is an endogenously produced indoleamine synchronizing circadian and circannual rhythms. Based on laboratory studies indicating the protective effect of melatonin against cochlear damage induced by acoustic trauma and ototoxic agents, and also clinical studies reporting the ability of melatonin to minimize the severity of tinnitus, melatonin is suggested to be a treatment option for the patient with tinnitus. Herein, we describe the ameliorative effect of melatonin on tinnitus, focusing on neural plasticity, oxidative/nitrosative stress, apoptotsis and autophagy.

A proof-of-principle study of the short-term effects of 3,4-methylenedioxymethamphetamine (MDMA) on tinnitus and neural connectivity

Background: This study was conducted to investigate the short-term behavioural and neurophysiological effects of 3,4-methylenedioxymethamphetamine (MDMA) on tinnitus perception.Methods: A double-blind randomized controlled cross-over design. Part 1. Behavioural measures of tinnitus following 30 mg MDMA or placebo administration (N = 5 participants) and Part 2. Behavioural measures of tinnitus and correlations between pairs of apriori regions of interest (ROI) using resting-state functional magnetic resonance imaging (rs-fMRI) before and after 70 mg of MDMA or placebo (N = 8 participants).Results: The results to MDMA were similar to placebo. For the 70 mg dose, there was a significant reduction after 4 h in annoyance and ignore ratings. RsMRI showed decreased connectivity compared with placebo administration between the left hippocampal, right hippocampal, left amygdala and right amygdala regions, and between the right posterior parahippocampal cortex and the left amygdala after two hours of 70 mg MDMA administration. Increased connectivity compared to placebo administration was found post MDMA between the right post-central gyrus and right posterior and superior temporal gyrus, and between the thalamus and frontoparietal network.Conclusions: Following 70 mg of MDMA two tinnitus rating scales significantly improved. There was, however, a placebo effect. Compared with placebo the rsMRI following the MDMA showed reductions in connectivity between the amygdala, hippocampus and parahippocampal gyrus. There is sufficient proof of concept to support future investigation of MDMA as a treatment for tinnitus.