Novel Nanoparticles Based on N,O-Carboxymethyl Chitosan-Dopamine Amide Conjugate for Nose-to-Brain Delivery

A widely investigated approach to bypass the blood brain barrier is represented by the intranasal delivery of therapeutic agents exploiting the olfactory or trigeminal connections nose-brain. As for Parkinson’s disease (PD), characterized by dopaminergic midbrain neurons degeneration, currently there is no disease modifying therapy. Although several bio-nanomaterials have been evaluated for encapsulation of neurotransmitter dopamine (DA) or dopaminergic drugs in order to restore the DA content in parkinsonian patients, the premature leakage of the therapeutic agent limits this approach. To tackle this drawback, we undertook a study where the active was linked to the polymeric backbone by a covalent bond. Thus, novel nanoparticles (NPs) based on N,O-Carboxymethylchitosan-DA amide conjugate (N,O-CMCS-DA) were prepared by the nanoprecipitation method and characterized from a technological view point, cytotoxicity and uptake by Olfactory Ensheating Cells (OECs). Thermogravimetric analysis showed high chemical stability of N,O-CMCS-DA NPs and X-ray photoelectron spectroscopy evidenced the presence of amide linkages on the NPs surface. MTT test indicated their cytocompatibility with OECs, while cytofluorimetry and fluorescent microscopy revealed the internalization of labelled N,O-CMCS-DA NPs by OECs, that was increased by the presence of mucin. Altogether, these findings seem promising for further development of N,O-CMCS-DA NPs for nose-to-brain delivery application in PD.

Reduced synaptic activity and dysregulated extracellular matrix pathways are common phenotypes in midbrain neurons derived from sporadic and mutation-associated Parkinson's disease patients

Several mutations that cause Parkinson's disease (PD) have been identified over the past decade. These account for 15-25% of PD cases; the rest of the cases are considered sporadic. Currently, it is accepted that PD is not a single monolithic disease but rather a constellation of diseases with some common phenotypes. While rodent models exist for some of the PD-causing mutations, research on the sporadic forms of PD is lagging due to a lack of cellular models. In our study, we differentiated PD patient-derived dopaminergic (DA) neurons from induced pluripotent stem cells (iPSCs) of several PD-causing mutations as well as from sporadic PD patients. Strikingly, we observed a common neurophysiological phenotype: Neurons derived from PD patients had a severe reduction in the rate of synaptic currents compared to those derived from healthy controls. While the relationship between mutations in genes such as the SNCA and LRRK2 and a reduction in synaptic transmission has been investigated before, here we show evidence that the pathogenesis of the synapses in neurons is a general phenotype in PD. Analysis of RNA sequencing results displayed changes in gene expression in different synaptic mechanisms as well as other affected pathways such as extracellular matrix-related pathways. Some of these dysregulated pathways are common to all PD patients (monogenic or idiopathic). Our data, therefore, shows pathways and mechanisms that are central and convergent to PD and suggests a strong involvement of the tetra-partite synapse in PD pathology.

Diverse processing underlying frequency integration in midbrain neurons of barn owls

Emergent response properties of sensory neurons depend on circuit connectivity and somatodendritic processing. Neurons of the barn owl’s external nucleus of the inferior colliculus (ICx) display emergence of spatial selectivity. These neurons use interaural time difference (ITD) as a cue for the horizontal direction of sound sources. ITD is detected by upstream brainstem neurons with narrow frequency tuning, resulting in spatially ambiguous responses. This spatial ambiguity is resolved by ICx neurons integrating inputs over frequency, a relevant processing in sound localization across species. Previous models have predicted that ICx neurons function as point neurons that linearly integrate inputs across frequency. However, the complex dendritic trees and spines of ICx neurons raises the question of whether this prediction is accurate. Data from in vivo intracellular recordings of ICx neurons were used to address this question. Results revealed diverse frequency integration properties, where some ICx neurons showed responses consistent with the point neuron hypothesis and others with nonlinear dendritic integration. Modeling showed that varied connectivity patterns and forms of dendritic processing may underlie observed ICx neurons’ frequency integration processing. These results corroborate the ability of neurons with complex dendritic trees to implement diverse linear and nonlinear integration of synaptic inputs, of relevance for adaptive coding and learning, and supporting a fundamental mechanism in sound localization.

Temporary Unilateral Hearing Loss Impairs Spatial Auditory Information Processing in Neurons in the Central Auditory System

Temporary conductive hearing loss (CHL) can lead to hearing impairments that persist beyond resolution of the CHL. In particular, unilateral CHL leads to deficits in auditory skills that rely on binaural input (e.g., spatial hearing). Here, we asked whether single neurons in the auditory midbrain, which integrate acoustic inputs from the two ears, are altered by a temporary CHL. We introduced 6 weeks of unilateral CHL to young adult chinchillas via foam earplug. Following CHL removal and restoration of peripheral input, single-unit recordings from inferior colliculus (ICC) neurons revealed the CHL decreased the efficacy of inhibitory input to the ICC contralateral to the earplug and increased inhibitory input ipsilateral to the earplug, effectively creating a higher proportion of monaural responsive neurons than binaural. Moreover, this resulted in a ∼10 dB shift in the coding of a binaural sound location cue (interaural-level difference, ILD) in ICC neurons relative to controls. The direction of the shift was consistent with a compensation of the altered ILDs due to the CHL. ICC neuron responses carried ∼37% less information about ILDs after CHL than control neurons. Cochlear peripheral-evoked responses confirmed that the CHL did not induce damage to the auditory periphery. We find that a temporary CHL altered auditory midbrain neurons by shifting binaural responses to ILD acoustic cues, suggesting a compensatory form of plasticity occurring by at least the level of the auditory midbrain, the ICC.

Strong and specific connections between retinal axon mosaics and midbrain neurons revealed by large scale paired recordings

SUMMARYThe superior colliculus (SC) is a midbrain structure that plays important roles in visually guided behaviors. Neurons in the SC receive afferent inputs from retinal ganglion cells (RGC), the output cells of the retina, but how SC neurons integrate RGC activity in vivo is unknown. SC neurons might be driven by strong but sparse retinal inputs, thereby reliably transmitting specific retinal functional channels. Alternatively, SC neurons could sum numerous but weak inputs, thereby extracting new features by combining a diversity of retinal signals. Here, we discovered that high-density electrodes simultaneously capture the activity and the location of large populations of retinal axons and their postsynaptic SC target neurons, permitting us to investigate the retinocollicular circuit on a structural and functional level in vivo. We show that RGC axons in the mouse are organized in mosaics that provide a single cell precise representation of the retina as input to SC. This isomorphic mapping between retina and SC builds the scaffold for highly specific wiring in the retinocollicular circuit which we show is characterized by strong connections and limited functional convergence, established in log-normally distributed connection strength. Because our novel method of large-scale paired recordings is broadly applicable for investigating functional connectivity across brain regions, we were also able to identify retinal inputs to the avian optic tectum of the zebra finch. We found common wiring rules in mammals and birds that provide a precise and reliable representation of the visual world encoded in RGCs to neurons in retinorecipient areas.HIGHLIGHTSHigh-density electrodes capture the activity of afferent axons and target neurons in vivoRetinal ganglion cells axons are organized in mosaicsSingle cell precise isomorphism between dendritic and axonal RGC mosaicsMidbrain neurons are driven by sparse but strong retinal inputsFunctional wiring of the retinotectal circuit is similar in mammals and birds

Dopaminergic axon tracts within a hyaluronic acid hydrogel encasement for implantation to restore the nigrostriatal pathway

Parkinson′s disease (PD) affects 10 million patients worldwide, making it the second most prevalent neurodegenerative disease. Motor symptoms emerge from the loss of dopamine in the striatum after the death of dopaminergic neurons and the long-projecting axons of the nigrostriatal pathway. Current treatments, such as dopamine replacement, deep brain stimulation or cell therapies, disregard the loss of this pathway at the core of symptoms. We sought to address this by improving our tissue-engineered nigrostriatal pathway (TE-NSP) technology, which consists of a tubular hydrogel with a collagen/laminin core that encases an aggregate of dopaminergic neurons and their axons in a way that resembles the nigrostriatal pathway. These constructs can be implanted to replace the lost neurons and axons with fidelity to the pathway, and thus provide dopamine according to feedback from the host circuitry. While TE-NSPs have been traditionally fabricated with agarose, here we utilized a hyaluronic acid (HA) hydrogel to expand the functionality of the encasement and our control over its properties. Using rat ventral midbrain neurons, we found that TE-NSPs exhibited longer and faster neurite growth with HA relative to agarose, with no differences observed in electrically-evoked dopamine release. When transplanted, HA hydrogels reduced host neuron loss and inflammation around the implant compared to agarose, and the cells and axons within TE-NSPs survived and maintained their cytoarchitecture for at least 2 weeks.

Constant Resting Frequency and Auditory Midbrain Neuronal Frequency Analysis of Hipposideros pratti in Background White Noise

Acoustic communication signals are inevitably challenged by ambient noise. In response to noise, many animals adjust their calls to maintain signal detectability. However, the mechanisms by which the auditory system adapts to the adjusted pulses are unclear. Our previous study revealed that the echolocating bat, Hipposideros pratti, increased its pulse intensity in the presence of background white noise. In vivo single-neuron recording demonstrated that the auditory midbrain neurons tuned to the second harmonic (H2 neurons) increased their minimal threshold (MT) to a similar degree as the increment of pulse intensity in the presence of the background noise. Furthermore, the H2 neurons exhibited consistent spike rates at their best amplitudes and sharper intensity tuning with background white noise compared with silent conditions. The previous data indicated that sound intensity analysis by auditory midbrain neurons was adapted to the increased pulse intensity in the same noise condition. This study further examined the echolocation pulse frequency and frequency analysis of auditory midbrain neurons with noise conditions. The data revealed that H. pratti did not shift the resting frequency in the presence of background noise. The auditory midbrain neuronal frequency analysis highly linked to processing the resting frequency with the presence of noise by presenting the constant best frequency (BF), frequency sensitivity, and frequency selectivity. Thus, our results suggested that auditory midbrain neuronal responses in background white noise are adapted to process echolocation pulses in the noise conditions.

Midbrain dopaminergic inputs gate amygdala intercalated cell clusters by distinct and cooperative mechanisms in male mice

Dopaminergic signaling plays an important role in associative learning, including fear and extinction learning. Dopaminergic midbrain neurons encode prediction error-like signals when threats differ from expectations. Within the amygdala, GABAergic intercalated cell (ITC) clusters receive one of the densest dopaminergic projections, but their physiological consequences are incompletely understood. ITCs are important for fear extinction, a function thought to be supported by activation of ventromedial ITCs that inhibit central amygdala fear output. In mice, we reveal two distinct novel mechanisms by which mesencephalic dopaminergic afferents control ITCs. Firstly, they co-release GABA to mediate rapid, direct inhibition. Secondly, dopamine suppresses inhibitory interactions between distinct ITC clusters via presynaptic D1 receptors. Early extinction training augments both GABA co-release onto dorsomedial ITCs and dopamine-mediated suppression of dorso- to ventromedial inhibition between ITC clusters. These findings provide novel insights into dopaminergic mechanisms shaping the activity balance between distinct ITC clusters that could support their opposing roles in fear behavior.