Effects of repeated cocaine injections on cochlear function

Norepinephrine protects against cochlear outer hair cell damage and noise-induced hearing loss via α2A-adrenergic receptor

BACKGROUND

The cochlear sympathetic system plays a key role in auditory function and susceptibility to noise-induced hearing loss (NIHL). The formation of reactive oxygen species (ROS) is a well-documented process in NIHL. In this study, we aimed at investigating the effects of a superior cervical ganglionectomy (SCGx) on NIHL in Sprague-Dawley rats.

METHODS

We explored the effects of unilateral and bilateral Superior Cervical Ganglion (SCG) ablation in the eight-ten weeks old Sprague-Dawley rats of both sexes on NIHL. Auditory function was evaluated by auditory brainstem response (ABR) testing and Distortion product otoacoustic emissions (DPOAEs). Outer hair cells (OHCs) counts and the expression of α2A-adrenergic receptor (AR) in the rat cochlea using immunofluorescence analysis. Cells culture and treatment, CCK-8 assay, Flow cytometry staining and analysis, and western blotting were to explore the mechanisms of SCG fibers may have a protective role in NIHL.

RESULTS

We found that neither bilateral nor unilateral SCGx protected the cochlea against noise exposure. In HEI-OC1 cells, H2O2-induced oxidative damage and cell death were inhibited by the application of norepinephrine (NE). NE may prevent ROS-induced oxidative stress in OHCs and NIHL through the α2A-AR.

CONCLUSION

These results demonstrated that sympathetic innervation mildly affected cochlear susceptibility to acoustic trauma by reducing oxidative damage in OHCs through the α2A-AR. NE may be a potential therapeutic strategy for NIHL prevention.

Bilateral Sensorineural Hearing Loss in the Setting of Acute Methamphetamine Overdose

Substance abuse is a rare but known cause of sensorineural hearing loss (SNHL). We report a case of acute SNHL in a 28-year-old man following an overdose of methamphetamine and incidental ingestion of fentanyl. On initial encounter, he had moderate-to-severe hearing loss in the right ear and severe-to-profound hearing loss in the left ear in addition to acute kidney injury, liver failure, and lactic acidosis. The patient was treated with a two-week course of high-dose steroids and expressed a subjective improvement in hearing. This case highlights the importance of auditory testing following a drug overdose and is one of the only documented cases of hearing loss following methamphetamine use in recent years. There is a paucity of literature regarding the mechanism causing acute SNHL secondary to methamphetamines. Proposed etiologies include neurotransmitter depletion or reduced cochlear blood flow as possible causes of ototoxicity.

Drug-Induced Deafness: A Rare Case of Bilateral Sensorineural Hearing Loss Following Speedballing

Many users of recreational drugs use cocaine and opioids together, often called “speedballing.” Hearing loss is a rarely reported adverse effect following recreational drug abuse. Only one case has been reported in history with hearing loss caused by speedballing. Here, we present the case of a 38-year-old female who presented with speedball abuse and new-onset bilateral hearing loss to the emergency department. A computed tomography scan of the head was unremarkable. She was treated with thiamine, folate, multivitamins, and intravenous fluids. The hearing loss improved without any acute intervention. The significance of sudden hearing loss due to recreational drug use is highlighted by this case. Apart from a few animal studies, there is no detailed research explaining the pathophysiology of speedball-induced hearing loss. Further studies and trials are needed to better understand the effects of combined and separate cocaine and opioid use on audiologic physiology.

Limiares auditivos tonais, emissões otoacústicas e sistema olivococlear medial de ex-usuários de drogas

Objetivos analisar se o uso de drogas ilícitas pode interferir nos sistemas auditivos periférico e central. Métodos a amostra foi composta por 17 indivíduos distribuídos conforme o tipo de droga mais consumida: 10 indivíduos no grupo maconha (G1) e sete no grupo crack/cocaína (G2). Os grupos foram subdivididos segundo o tempo de uso de drogas: um a cinco, seis a 10 e mais que 15 anos. Foram avaliados por meio de anamnese, audiometria tonal liminar, imitânciometria, emissões otoacústicas transientes (EOAT) e efeito supressor das EOAT. Resultados comparando os limiares tonais do G1 e G2, observaram-se limiares elevados para o G2, com diferença estatisticamente significante no grupo de um a cinco anos para 250, 500, 6000 e 8000Hz na orelha direita e de seis a 10 anos para 4000 e 8000Hz na orelha esquerda. Para usuários por mais que 15 anos, observou-se limiares superiores a 25dBNA de 3000 a 8000Hz na orelha direita. Nas EOAT e efeito supressor das EOAT não houve diferença estatisticamente significante entre G1 e G2 e entre os tempos de uso das drogas. O G1 apresentou relação sinal/ruído das EOAT superior ao G2. O efeito supressor das EOAT esteve presente em 79% das orelhas avaliadas. Conclusão na amostra estudada, o crack/cocaína apresentou efeito mais deletério sobre o sistema auditivo do que a maconha. O maior tempo de uso de drogas influenciou nos resultados do G1. O uso de drogas ilícitas não provocou alterações no SOCM.

Brain stem evoked response audiometry of former drug users

Illicit drugs are known for their deleterious effects upon the central nervous system and more specifically for how they adversely affect hearing.

Objective

This study aims to analyze and compare the hearing complaints and the results of brainstem evoked response audiometry (BERA) of former drug user support group goers.

Methods

This is a cross-sectional non-experimental descriptive quantitative study. The sample consisted of 17 subjects divided by their preferred drug of use. Ten individuals were placed in the marijuana group (G1) and seven in the crack/cocaine group (G2). The subjects were further divided based on how long they had been using drugs: 1 to 5 years, 6 to 10 years, and over 15 years. They were interviewed, and assessed by pure tone audiometry, acoustic impedance tests, and BERA.

Results

No statistically significant differences were found between G1 and G2 or time of drug use in absolute latencies and interpeak intervals. However, only five of the 17 individuals had BERA results with adequate results for their ages.

Conclusion

Marijuana and crack/cocaine may cause diffuse disorders in the brainstem and compromise the transmission of auditory stimuli regardless of how long these substances are used for.

The protective effect of the sympathetic nervous system against acoustic trauma

OBJECTIVE

the cochlea is innervated by the sympathetic nerve fibers. However, the functions of those fibers in the cochlea are still controversial. The present study was designed to determine whether the sympathetic nervous system (SNS) exerts a protective or enhancing effect on acoustic trauma.

METHODS

acoustic overstimulation (either of 110, 115, or 130 dB SPL for 10 min) was performed in guinea pigs during electrical stimulation of the ipsilateral cervical SNS, after its surgical elimination or in the non-treated condition. The threshold shift of the compound action potential (CAP) from the pre-exposure value was measured at 1 h and at 1 week after acoustic overstimulation. Two-way analyses of variance (ANOVAs) were completed for the SNS conditions and the frequencies.

RESULTS

although no significant difference was found at 1 h after overstimulation among these three groups, the CAP threshold shift at 1 week (110 and 115 dB SPL) was significantly smaller in the SNS stimulation group than in the other two groups.

CONCLUSION

a protective effect was observed in the SNS stimulation group 1 week after the exposure to acoustic overstimulation of moderate intensity (from 110 to 115 dB SPL for 10 min).

Alpha 1-adrenergic receptor antagonist blocks acute cocaine action on the compound action potential of the auditory nerve in the chinchilla

Acute systemic cocaine injection is known to significantly decrease the compound action potential (CAP) amplitude of the auditory nerve. In an attempt to elucidate the mechanism underlying this phenomenon, the present study investigated the influence of prazosin, an adrenergic alpha 1-receptor antagonist, on the effect of cocaine on the CAP. Amplitude-intensity functions at 1 and 8 kHz were obtained before and after treatment with cocaine (experimental group) or saline (control group) in prazosin pretreated subjects. The characteristic reduction in CAP amplitude after an acute cocaine injection was blocked by 0.05 mg/kg prazosin. When subjects were re-injected with cocaine or saline one h after prazosin, the reduction in CAP amplitude following cocaine injection had recovered.