Glial Response and Neuroinflammation in Cerebrocortical Atrophy in a Young Irish Wolfhound Dog

A two-year-old, Irish Wolfhound dog presented with a history of progressive neurological signs. Neurological exam revealed disorientation, absence of menace response, reduction of right nasal sensation, hypermetria and ataxia with reduction of proprioception in all four limbs. MRI findings were compatible with laminar neuronal necrosis and possible bilateral cortical cerebral atrophy. Grossly, a severe bilateral reduction of the gray matter with flattening of gyri, mainly in frontal and parietal cerebral areas, was observed. Histologically, multiple, segmental, bilateral, and symmetric areas of neuronal loss, necrosis and degeneration, in a laminar pattern, associated with a reactive gliosis were observed. Immunohistochemical studies showed severe reduction of neuronal bodies, proliferation and hypertrophy of astrocytes and microglia. Few perivascular B and T cells were demonstrated. Based on these data, we show some of the neuroinflammatory events that occur during CNS repair in a chronic phase of this condition.

Comprehensive Topographical Map of the Serotonergic Fibers in the Mouse Brain

It is well established that serotonergic fibers distribute throughout the brain. Abnormal densities or patterns of serotonergic fibers have been implicated in neuropsychiatric disorders. Although many classical studies have examined the distribution pattern of serotonergic fibers, most of them were either limited to specific brain areas or had limitations in demonstrating the fine axonal morphology. In this study, we utilize transgenic mice expressing GFP under the SERT promoter to map the topography of serotonergic fibers across the rostro-caudal extent of each brain area. We demonstrate previously unreported regional density and fine-grained anatomy of serotonergic fibers. Our findings include: 1) SERT fibers distribute abundantly in the thalamic nuclei close to the midline and dorsolateral areas, in most of the hypothalamic nuclei with few exceptions such as the median eminence and arcuate nuclei, and within the basal amygdaloid complex and lateral septal nuclei, 2) the source fibers of innervation of the hippocampus traverse through the septal nuclei before reaching its destination, 3) unique, filamentous type of straight terminal fibers within the nucleus accumbens, 4) laminar pattern of innervation in the hippocampus, olfactory bulb and cortex with heterogenicity in innervation density among the layers, 5) cortical labelling density gradually decreases rostro-caudally, 6) fibers traverse and distribute mostly within the gray matter, leaving the white fiber bundles uninnervated, and 7) most of the highly labelled nuclei and cortical areas have predominant anatomical connection to limbic structures. In conclusion, we provide novel, regionally specific insights on the distribution map of serotonergic fibers using transgenic mouse.

Stochastic Single Cell Behaviour Leads to Robust Horizontal Cell Layer Formation in the Vertebrate Retina

ABSTRACTDevelopmental programs that arrange cells and tissues into patterned organs are remarkably robust. In the developing vertebrate retina for example, neurons reproducibly assemble into distinct layers giving the mature organ its overall structured appearance. This stereotypic neuronal arrangement, termed lamination, is important for efficient neuronal connectivity. While retinal lamination is conserved in many vertebrates including humans, how it emerges from single cell behaviour is not fully understood. To shed light on this question, we here investigated the formation of the retinal horizontal cell layer. Using in vivo light sheet imaging of the developing zebrafish retina, we generated a comprehensive quantitative analysis of horizontal single cell behaviour from birth to final positioning. Interestingly, we find that all parameters analyzed including cell cycle dynamics, migration paths and kinetics as well as sister cell dispersal are very heterogeneous. Thus, horizontal cells show individual non-stereotypic behaviour before final positioning. Yet, these initially stochastic cell dynamics always generate the correct laminar pattern. Consequently, our data shows that lamination of the vertebrate retina contains a yet underexplored extent of single cell stochasticity.

Distribution and Cellular Localization of KCC2 in the Ferret Neocortex

KCC2 (a brain-specific potassium-chloride cotransporter) affects development of the cerebral cortex, including aspects of neuronal migration and cellular maturation and differentiation. KCC2 also modulates chloride homeostasis by influencing the switch of GABA from depolarizing in young neurons to hyperpolarizing in mature neurons. We describe the expression pattern, regional distribution, and cellular colocalization of KCC2 in the ferret cortex in normal kits and those treated with methylazoxymethanol acetate (MAM). We earlier developed a model of impaired cortical development by injecting MAM during mid-cortical gestation, which briefly interferes with neuronal production and additionally results in increased levels of KCC2 at P0. Using immunohistochemistry, we show a shift in KCC2 expression during development, being high in the subplate at P0, repositioning into a subtle laminar pattern in the neocortex at P7-P14, and becoming homogeneous at P35. KCC2 colocalizes with neuronal markers in the developing and mature cerebral cortex of normal ferrets and those treated with MAM, but shows a differential pattern of expression at different ages and locates in distinct cellular compartments during development. Subcellular localization shows that KCC2 predominantly situates in the membrane fraction of neocortical samples. These findings reveal that KCC2 colocalizes differentially with neurons and its expression pattern alters during development.

Acetylcholine excites neocortical pyramidal neurons via nicotinic receptors

The neuromodulator acetylcholine (ACh) shapes neocortical function during sensory perception, motor control, arousal, attention, learning, and memory. Here we investigate the mechanisms by which ACh affects neocortical pyramidal neurons in adult mice. Stimulation of cholinergic axons activated muscarinic and nicotinic ACh receptors on pyramidal neurons in all cortical layers and in multiple cortical areas. Nicotinic receptor activation evoked short-latency, depolarizing postsynaptic potentials (PSPs) in many pyramidal neurons. Nicotinic receptor-mediated PSPs promoted spiking of pyramidal neurons. The duration of the increase in spiking was membrane potential dependent, with nicotinic receptor activation triggering persistent spiking lasting many seconds in neurons close to threshold. Persistent spiking was blocked by intracellular BAPTA, indicating that nicotinic ACh receptor activation evoked persistent spiking via a long-lasting calcium-activated depolarizing current. We compared nicotinic PSPs in primary motor cortex (M1), prefrontal cortex (PFC), and visual cortex. The laminar pattern of nicotinic excitation was not uniform but was broadly similar across areas, with stronger modulation in deep than superficial layers. Superimposed on this broad pattern were local differences, with nicotinic PSPs being particularly large and common in layer 5 of M1 but not layer 5 of PFC or primary visual cortex (V1). Hence, in addition to modulating the excitability of pyramidal neurons in all layers via muscarinic receptors, synaptically released ACh preferentially increases the activity of deep-layer neocortical pyramidal neurons via nicotinic receptors, thereby adding laminar selectivity to the widespread enhancement of excitability mediated by muscarinic ACh receptors.