Analysis of co-isogenic prion protein deficient mice reveals behavioral deficits, learning impairment, and enhanced hippocampal excitability

Background Cellular prion protein (PrPC) is a cell surface GPI-anchored protein, usually known for its role in the pathogenesis of human and animal prionopathies. However, increasing knowledge about the participation of PrPC in prion pathogenesis contrasts with puzzling data regarding its natural physiological role. PrPC is expressed in a number of tissues, including at high levels in the nervous system, especially in neurons and glial cells, and while previous studies have established a neuroprotective role, conflicting evidence for a synaptic function has revealed both reduced and enhanced long-term potentiation, and variable observations on memory, learning, and behavior. Such evidence has been confounded by the absence of an appropriate knock-out mouse model to dissect the biological relevance of PrPC, with some functions recently shown to be misattributed to PrPC due to the presence of genetic artifacts in mouse models. Here we elucidate the role of PrPC in the hippocampal circuitry and its related functions, such as learning and memory, using a recently available strictly co-isogenic Prnp0/0 mouse model (PrnpZH3/ZH3). Results We performed behavioral and operant conditioning tests to evaluate memory and learning capabilities, with results showing decreased motility, impaired operant conditioning learning, and anxiety-related behavior in PrnpZH3/ZH3 animals. We also carried in vivo electrophysiological recordings on CA3-CA1 synapses in living behaving mice and monitored spontaneous neuronal firing and network formation in primary neuronal cultures of PrnpZH3/ZH3 vs wildtype mice. PrPC absence enhanced susceptibility to high-intensity stimulations and kainate-induced seizures. However, long-term potentiation (LTP) was not enhanced in the PrnpZH3/ZH3 hippocampus. In addition, we observed a delay in neuronal maturation and network formation in PrnpZH3/ZH3 cultures. Conclusion Our results demonstrate that PrPC promotes neuronal network formation and connectivity. PrPC mediates synaptic function and protects the synapse from excitotoxic insults. Its deletion may underlie an epileptogenic-susceptible brain that fails to perform highly cognitive-demanding tasks such as associative learning and anxiety-like behaviors.

Repositioning Doxycycline for treating Parkinson’s Disease: evidence from a pre-clinical mouse model

Background Parkinson’s disease remains orphan of valuable therapies capable to interfere with the disease pathogenesis despite the large number of symptomatic approaches adopted in clinical practice to manage this disease. Treatments simultaneously affecting α-synuclein (α-syn) oligomerization and neuroinflammation may counteract Parkinson’s disease. Recent data demonstrated that Doxycycline an antibiotic of the tetracycline class, can inhibit α-syn aggregation and exert anti-inflammatory activity. We herein investigate, for the first time, the potential therapeutic properties of Doxy in a human α-syn A53T transgenic Parkinson’s disease mouse model by the evaluation of behavioural, biochemical and histopathological parameters. Methods human α-syn A53T transgenic mice were treated with Doxycycline (10 mg/Kg daily ip) for 30 days, the effect of treatment on motor and cognitive behaviour impairment and daily live activity of mice were examined, successively immunocytochemical, electrophysiological and biochemical analysis of cerebral tissue was performed. Results Doxy treatment abolished cognitive and daily life activity deficiencies in A53T mice. The effect on cognitive functions was associated with neuroprotection, inhibition of α-syn oligomerization and gliosis both in the cortex and hippocampus. Doxy treatment restored hippocampal long-term potentiation in association with inhibition of pro-inflammatory cytokines expression. Moreover, Doxy ameliorated motor impairment and reduced striatal glial activation in A53T mice. Conclusions Our findings promote Doxy as a valuable multi-target therapeutic approach counteracting both symptoms and neuropathology in the complex scenario of α-synucleinopathies

Enhanced long-term potentiation and impaired learning in mice lacking alternative exon 33 of CaV1.2 calcium channel

The CACNA1C (calcium voltage-gated channel subunit alpha 1 C) gene that encodes the CaV1.2 channel is a prominent risk gene for neuropsychiatric and neurodegenerative disorders with cognitive and social impairments like schizophrenia, bipolar disorders, depression and autistic spectrum disorders (ASD). We have shown previously that mice with exon 33 deleted from CaV1.2 channel (CaV1.2-exon 33−/−) displayed increased CaV1.2 current density and single channel open probability in cardiomyocytes, and were prone to develop arrhythmia. As Ca2+ entry through CaV1.2 channels activates gene transcription in response to synaptic activity, we were intrigued to explore the possible role of Cav1.2Δ33 channels in synaptic plasticity and behaviour. Homozygous deletion of alternative exon 33 resulted in enhanced long-term potentiation (LTP), and lack of long- term depression (LTD), which did not correlate with enhanced learning. Exon 33 deletion also led to a decrease in social dominance, sociability and social novelty. Our findings shed light on the effect of gain-of-function of CaV1.2Δ33 signalling on synaptic plasticity and behaviour and provides evidence for a link between CaV1.2 and distinct cognitive and social behaviours associated with phenotypic features of psychiatric disorders like schizophrenia, bipolar disorder and ASD.

Effects of methamphetamine-induced neurotoxicity on striatal long-term potentiation

Rationale Methamphetamine (METH) exposure is associated with damage to central monoamine systems, particularly dopamine signaling. Rodent models of such damage have revealed a decrease in the amplitude of phasic dopamine signals and significant striatal dysfunction, including changes in the molecular, system, and behavioral functions of the striatum. Dopamine signaling through D1 receptors promotes corticostriatal long-term potentiation (LTP), a critical substrate of these striatal functions. Objectives Therefore, the purpose of this study was to determine if METH-induced dopamine neurotoxicity would impair D1 receptor-dependent striatal LTP in mice. Methods Mice were treated with a METH binge regimen (4 × 10 mg/kg d,l-methamphetamine, s.c.) that recapitulates all of the known METH-induced neurotoxic effects observed in humans, including dopamine toxicity. Three weeks later, acute brain slices containing either the dorsomedial striatum (DMS) or dorsolateral striatum (DLS) were prepared, and plasticity was assessed using white matter, high-frequency stimulation (HFS), and striatal extracellular electrophysiology. Results Under these conditions, LTP was induced in brain slices containing the DMS from saline-pretreated mice, but not mice with METH-induced neurotoxicity. Furthermore, the LTP observed in DMS slices from saline-pretreated mice was blocked by the dopamine D1 receptor antagonist SCH23390, indicating that this LTP is dopamine D1 receptor-dependent. Finally, acute in vivo treatment of METH-pretreated mice with bupropion (50 mg/kg, i.p.) promoted LTP in DMS slices. Conclusions Together, these studies demonstrate that METH-induced neurotoxicity impairs dopamine D1 receptor-dependent LTP within the DMS and that the FDA-approved drug bupropion restores induction of striatal LTP in mice with METH-induced dopamine neurotoxicity.

Dissociating encoding of memory and salience by manipulating long-term synaptic potentiation

Neural codes are thought to be reorganized during memory formation by long-term potentiation (LTP) of synapses. Here, using a novel approach for selectively blocking LTP, we found that eliminating LTP in hippocampal or striatal circuits only produces limited effects on learning and memory. To reconcile the discrepancy between the large physiological effect of blocking LTP and the absent effect on learning, we studied how LTP impacts neuronal computations in the hippocampus using in-vivo Ca2+-imaging. Contrary to current conceptual frameworks, we found that hippocampal CA1-region LTP is not required for accurate representations of space in hippocampal neurons, but rather endows these neurons with reward- and novelty-coding properties. Thus, instead of driving formation of cognitive maps and memory engrams, CA1-region LTP incorporates salience information into cognitive representations.

Red Light Optogenetics in Neuroscience

Optogenetics, a field concentrating on controlling cellular functions by means of light-activated proteins, has shown tremendous potential in neuroscience. It possesses superior spatiotemporal resolution compared to the surgical, electrical, and pharmacological methods traditionally used in studying brain function. A multitude of optogenetic tools for neuroscience have been created that, for example, enable the control of action potential generation via light-activated ion channels. Other optogenetic proteins have been used in the brain, for example, to control long-term potentiation or to ablate specific subtypes of neurons. In in vivo applications, however, the majority of optogenetic tools are operated with blue, green, or yellow light, which all have limited penetration in biological tissues compared to red light and especially infrared light. This difference is significant, especially considering the size of the rodent brain, a major research model in neuroscience. Our review will focus on the utilization of red light-operated optogenetic tools in neuroscience. We first outline the advantages of red light for in vivo studies. Then we provide a brief overview of the red light-activated optogenetic proteins and systems with a focus on new developments in the field. Finally, we will highlight different tools and applications, which further facilitate the use of red light optogenetics in neuroscience.

Essential regulatory functions of CaMKII T286 phosphorylation in LTP and two distinct forms of LTD

The Ca2+/calmodulin-dependent protein kinase II (CaMKII) mediates both long-term potentiation and depression (LTP and LTD) of excitatory synapses, two opposing forms of synaptic plasticity induced by strong versus weak stimulation of NMDA-type glutamate receptors (NMDARs). NMDAR-dependent LTD is prevalent in juvenile hippocampus, but in mature hippocampus, LTD is still readily induced by stimulating metabotropic glutamate receptors (mGluRs). Here we show that mGluR-dependent LTD also requires CaMKII and its T286 autophosphorylation that induces Ca2+-independent autonomous kinase activity. This autophosphorylation (i) accelerated CaMKII movement to excitatory synapses after LTP stimuli and (ii) was required for the movement to inhibitory synapses after NMDAR-LTD stimuli. Similar to NMDAR-LTD, the mGluR-LTD stimuli did not induce any CaMKII movement to excitatory synapses. However, in contrast to NMDAR-LTD, the mGluR-LTD did not involve CaMKII movement to inhibitory synapses and did not require additional T305/306 autophosphorylation. Taken together, even though CaMKII T286 autophosphorylation has a longstanding prominent role in LTP, it is also required for both major forms of LTD in hippocampal neurons, albeit with differential requirements for the heterosynaptic communication of excitatory signals to inhibitory synapses.