Anterograde tracing | EPFL Graph Search

In neuroscience, anterograde tracing is a research method that is used to trace axonal projections from their source (the cell body, or soma) to their point of termination (the synapse). A hallmark of anterograde tracing is the labeling of the presynaptic and the postsynaptic neuron(s). The crossing of the synaptic cleft is a vital difference between the anterograde tracers and the dye fillers used for morphological reconstruction. The complementary technique is retrograde tracing, which is used to trace neural connections from their termination to their source (i.e. synapse to cell body). Both the anterograde and retrograde tracing techniques are based on the visualization of the biological process of axonal transport. The anterograde and retrograde tracing techniques allow the detailed descriptions of neuronal projections from a single neuron or a defined population of neurons to their various targets throughout the nervous system. These techniques allow the "mapping" of connectio

Cortical Projection From the Premotor or Primary Motor Cortex to the Subthalamic Nucleus in Intact and Parkinsonian Adult Macaque Monkeys: A Pilot Tracing Study

Simon Pierre Jean Badoud, Jocelyne Bloch, Simon Borgognon

Besides the main cortical inputs to the basal ganglia, via the corticostriatal projection, there is another input via the corticosubthalamic projection (CSTP), terminating in the subthalamic nucleus (STN). The present study investigated and compared the CSTPs originating from the premotor cortex (PM) or the primary motor cortex (M1) in two groups of adult macaque monkeys. The first group includes six intact monkeys, whereas the second group was made up of four monkeys subjected to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication producing Parkinson's disease (PD)-like symptoms and subsequently treated with an autologous neural cell ecosystem (ANCE) therapy. The CSTPs were labeled with the anterograde tracer biotinylated dextran amine (BDA), injected either in PM or in M1. BDA-labeled axonal terminal boutons in STN were charted, counted, and then normalized based on the number of labeled corticospinal axons in each monkey. In intact monkeys, the CSTP from PM was denser than that originating from M1. In two PD monkeys, the CSTP originating from PM or M1 were substantially increased, as compared to intact monkeys. In one other PD monkey, there was no obvious change, whereas the last PD monkey showed a decrease of the CSTP originating from M1. Interestingly, the linear relationship between CSTP density and PD symptoms yielded a possible dependence of the CSTP re-organization with the severity of the MPTP lesion. The higher the PD symptoms, the larger the CSTP densities, irrespective of the origin (from both M1 or PM). Plasticity of the CSTP in PD monkeys may be related to PD itself and/or to the ANCE treatment.

FRONTIERS MEDIA SA2020

The role of medial amygdala inhibitory neurons in regulating social behavior

Aiste Baleisyte

Aggression is an evolutionary conserved social behavior that is necessary for an animalÂŽs survival. The neural substrates coordinating aggression are known to exist in the amygdala and the hypothalamus. While the medial amygdala (MeA) and the ventrolateral subdivision of the ventromedial hypothalamus (VMHvl) have been implicated in aggression control and are known to be anatomically inter-connected, it has not yet been described at the circuit-level whether an interaction between these nuclei plays a role in aggression control.Posteriodorsal MeA (MeApd) is a majorly GABAergic nucleus (~70%), however the role of heterogeneous sub-populations of the MeA-GABA neurons in aggression is poorly understood. Since we were interested to identify the inhibitory cell types in the MeApd that control aggression, we first attempted to stimulate all the GABA neurons in the MeApd. Using a fast variant of channelrhodopsin-2E123T,H134R (ChETA) in VGATCre mice, we found that optogenetic stimulation of MeA-GABA neurons in the resident males interrupted intruder-directed aggression, contrary to the previous findings by Hong et al., where stimulation of MeApd-GABA neurons using channelrhodopsin-2H134R (ChR2) evoked aggression. An in-depth investigation of this discrepancy, using two AAV serotypes, revealed that optogenetic stimulation with ChETA suppressed aggression, whereas optogenetic stimulation with ChR2 increased aggression, irrespective of the AAV serotype. Recordings of the membrane potential changes reported larger plateau depolarizations, smaller action potential amplitudes, and larger local inhibition when using ChR2 as compared to ChETA. Thus, in the first part I showed that optogenetic stimulation of the brain areas with heterogenous population of interconnected GABA neurons such as the MeApd, can strongly depend on the properties of optogenetic tools.In the second part, we further explored how the MeApd-GABA neurons control aggression via long-range projections to their target nuclei in hypothalamus. Anterograde tracing revealed synapses from the MeApd-GABA neurons in the ventral premammillary (PMv) and the lateral ventromedial hypothalamic nuclei (VMHvl); both nuclei were previously identified in positive control of aggression (Lin et al., 2011; Stagkourakis et al., 2018). Ex-vivo optogenetic mapping of synaptic outputs from the MeApd-GABA projecting axons revealed evoked IPSCs in glutamatergic neurons in the VMHvl and the PMv, suggesting likely mechanism for inhibiting aggression. In-vivo optogenetic activation of the MeApd-GABA axonal terminals above the VMHvl or the PMv had no effect on aggression and instead led to an increased mounting, likely caused by optic fiber implantation in the hypothalamus. To avoid this artifact, we have combined retrograde AAV with Cre ON/Flip ON approach and specifically stimulated the VMHvl projecting MeApd-GABA neurons. This approach revealed that in aggressive mice, stimulation of this pathway tends to reduce aggression. Finally, we performed in-vivo Ca2+ imaging of the VMHvl projecting MeApd-GABA neurons during the RI test, which showed that these neurons are largely multimodal and get activated during different sub-types of social behaviours including aggression.This study shows that direct inhibitory path from the MeApd-GABA neurons to the VMHvl might suppress aggressive behaviour. Altogether, this work provides a step forward in our understanding of the neural substrates underlying aggression.

EPFL2021

Elezanumab, a human anti-RGMa monoclonal antibody, promotes neuroprotection, neuroplasticity, and neurorecovery following a thoracic hemicompression spinal cord injury in non-human primates

Quentin Barraud, Grégoire Courtine, Lili Huang, Xiaomeng Zhang

Spinal cord injury (SCI) is a devastating condition characterized by loss of function, secondary to damaged spinal neurons, disrupted axonal connections, and myelin loss. Spontaneous recovery is limited, and there are no approved pharmaceutical treatments to reduce ongoing damage or promote repair. Repulsive guidance molecule A (RGMa) is upregulated following injury to the central nervous system (CNS), where it is believed to induce neuronal apoptosis and inhibit axonal growth and remyelination. We evaluated elezanumab, a human anti-RGMa monoclonal antibody, in a novel, newly characterized non-human primate (NHP) hemicompression model of thoracic SCI. Systemic intravenous (IV) administration of elezanumab over 6 months was well tolerated and associated with significant improvements in locomotor function. Treatment of animals for 16 weeks with a continuous intrathecal infusion of elezanumab below the lesion was not efficacious. IV elezanumab improved microstructural integrity of extralesional tissue as reflected by higher fractional anisotropy and magnetization transfer ratios in treated vs. untreated animals. IV elezanumab also reduced SCI-induced increases in soluble RGMa in cerebrospinal fluid, and membrane bound RGMa rostral and caudal to the lesion. Anterograde tracing of the corticospinal tract (CST) from the contralesional motor cortex following 20 weeks of IV elezanumab revealed a significant increase in the density of CST fibers emerging from the ipsilesional CST into the medial/ventral gray matter. There was a significant sprouting of serotonergic (5-HT) fibers rostral to the injury and in the ventral horn of lower thoracic regions. These data demonstrate that 6 months of intermittent IV administration of elezanumab, beginning within 24 h after a thoracic SCI, promotes neuroprotection and neuroplasticity of key descending pathways involved in locomotion. These findings emphasize the mechanisms leading to improved recovery of neuromotor functions with elezanumab in acute SCI in NHPs.