Anatomically discrete functional effects of adenoviral clostridial light chain gene-based synaptic inhibition in the midbrain

Chronic Primary Tinnitus: A Management Dilemma

Tinnitus often described as sound in the ear in absence of any external stimulus. It poses a challenge to the psychological and mental wellbeing of the patient and professional unsatisfaction to the clinician. The patient often an old aged individual usually approaches the outpatient department with various sounds in the ear, making him feel ill or unable to have a sound sleep. The middle-aged patient often complains of professional incapability and lack of concentration due to tinnitus. Despite vast academic research and advances, the efficiency of available treatment is debatable, often compelling the clinician to convey the message that “you may have to learn to live with it”. In the present overview of reviews, we tend to look into the management of tinnitus and present a comprehensive outlook of various evidence-based reviews from Cochrane and augmented with various studies from PubMed.

Botulinum Neurotoxin Light Chains Expressed by Defective Herpes Simplex Virus Type-1 Vectors Cleave SNARE Proteins and Inhibit CGRP Release in Rat Sensory Neurons

A set of herpes simplex virus type 1 (HSV-1) amplicon vectors expressing the light chains (LC) of botulinum neurotoxins (BoNT) A, B, C, D, E and F was constructed. Their properties have been assessed in primary cultures of rat embryonic dorsal root ganglia (DRG) neurons, and in organotypic cultures of explanted DRG from adult rats. Following infection of primary cultures of rat embryonic DRG neurons, the different BoNT LC induced efficient cleavage of their corresponding target Soluble N-ethylmaleimide-sensitive-factor Attachment protein Receptor (SNARE) protein (VAMP, SNAP25, syntaxin). A similar effect was observed following infection by BoNT-A LC of organotypic cultures of adult rat DRG. To quantify and compare the functional activities of the different BoNT LC, the inhibition of calcitonin gene-related protein (CGRP) secretion was assessed in DRG neurons following infection by the different vectors. All BoNT-LC were able to inhibit CGRP secretion although to different levels. Vectors expressing BoNT-F LC displayed the highest inhibitory activity, while those expressing BoNT-D and -E LC induced a significantly lower CGRP release inhibition. Cleavage of SNARE proteins and inhibition of CGRP release could be detected in neuron cultures infected at less than one transducing unit (TU) per neuron, showing the extreme efficacy of these vectors. To our knowledge this is the first study investigating the impact of vector-expressed transgenic BoNT LC in sensory neurons.

Pain in amyotrophic lateral sclerosis: a neglected aspect of disease

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder marked by progressive loss of motor neurons, muscle wasting, and respiratory dysfunction. With disease progression, secondary symptoms arise creating new problematic conditions for ALS patients. Amongst these is pain. Although not a primary consequence of disease, pain occurs in a substantial number of individuals. Yet, studies investigating its pathomechanistic properties in the ALS patient are lacking. Therefore, more exploratory efforts into its scope, severity, impact, and treatment should be initiated. Several studies investigating the use of Clostridial neurotoxins for the reduction of pain in ALS patients suggest the potential for a neural specific approach involving focal drug delivery. Gene therapy represents a way to accomplish this. Therefore, the use of viral vectors to express transgenes that modulate the nociceptive cascade could prove to be an effective way to achieve meaningful benefit in conditions of pain in ALS.

Reversible unilateral nigrostriatal pathway inhibition induced through expression of adenovirus-mediated clostridial light chain gene in the substantia nigra

Clostridial light chain (LC) inhibits synaptic transmission by digesting a vesicle-docking protein, synaptobrevin, without killing neurons. We here report the feasibility of creating a rat hemiparkinsonism model through LC gene expression in the substantia nigra (SN), inhibiting nigrostriatal transmission. 40 adult Sprague Dawley rats were divided into four groups for SN injections of PBS, 6-hydroxydopamine (6-OHDA), or adenoviral vectors for the expression of LC (AdLC), or GFP (AdGFP). Amphetamine and apomorphine induced rotations were assessed before and after SN injection, revealing significant rotational alterations at 8 or 10 days after injection in both AdLC and 6-OHDA but not PBS and AdGFP groups. Induced rotation recovered by one month in AdLC rats but persisted in 6-OHDA rats. Histological analysis of the SN revealed LC and GFP expression with corresponding synaptobrevin depletion in the LC, but not the GFP groups. Tyrosine hydroxylase (TH) and dopamine transporter (DAT) immunohistochemistry (IHC) showed markedly decreased staining in ipsilateral SN and striatum in 6-OHDA but not AdLC or AdGFP rats. Similarly, compared with contralateral, ipsilateral striatal dopamine level only decreased in 6-OHDA but not AdLC, AdGFP, or PBS treated rats. Thus, LC expression induces nigral synaptobrevin depletion with resulting inhibition of nigrostriatal synaptic transmission. Unlike 6-OHDA, LC expression inhibits synaptic activity without killing neurons. This approach, therefore, represents a potentially reversible means of nigrostriatal pathway inhibition as a model for Parkinson's disease. Such a model might facilitate transient and controlled nigral inhibition for studying striatal recovery, dopaminergic re-innervation, and normalization of striatal receptors following the recovery of nigrostriatal transmission.

Viral clostridial light chain gene-based control of penicillin-induced neocortical seizures

Restraining excitatory neurotransmission within a seizure focus provides a nondestructive treatment strategy for intractable neocortical epilepsy. Clostridial toxin light chain (LC) inhibits synaptic transmission by digesting a critical vesicle-docking protein, synaptobrevin, without directly altering neuronal health. This study tests the treatment efficacy of adenoviral vector delivered LC (AdLC) on a model of seizures in rats induced by motor cortex penicillin (PCN) injection. LC expression significantly reduced electroencephalogram (EEG) frequency, amplitude, duration, and latency compared to control groups injected with either an adenoviral vector bearing green fluorescent protein (AdGFP) or phosphate buffered solution (PBS). Correspondingly, LC gene expression improved behavioral manifestations including seizure severity and latency. There was no statistical difference in motor function before and after vector administration between treatment and control groups. Histological analysis revealed spatially discrete LC expression with corresponding synaptobrevin depletion in the cortex surrounding the injection site. Thus, vector-mediated LC gene delivery is capable of improving both the EEG and behavioral manifestations of PCN-induced focal neocortical seizures through synaptobrevin depletion.