Cellular plasticity induced by anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor encephalitis antibodies.

OBJECTIVE: Autoimmune-mediated anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis is a severe but treatment-responsive disorder with prominent short-term memory loss and seizures. The mechanisms by which patient antibodies affect synapses and neurons leading to symptoms are poorly understood. METHODS: The effects of patient antibodies on cultures of live rat hippocampal neurons were determined with immunostaining, Western blot, and electrophysiological analyses. RESULTS: We show that patient antibodies cause a selective decrease in the total surface amount and synaptic localization of GluA1- and GluA2-containing AMPARs, regardless of receptor subunit binding specificity, through increased internalization and degradation of surface AMPAR clusters. In contrast, patient antibodies do not alter the density of excitatory synapses, N-methyl-D-aspartate receptor (NMDAR) clusters, or cell viability. Commercially available AMPAR antibodies directed against extracellular epitopes do not result in a loss of surface and synaptic receptor clusters, suggesting specific effects of patient antibodies. Whole-cell patch clamp recordings of spontaneous miniature postsynaptic currents show that patient antibodies decrease AMPAR-mediated currents, but not NMDAR-mediated currents. Interestingly, several functional properties of neurons are also altered: inhibitory synaptic currents and vesicular γ-aminobutyric acid transporter (vGAT) staining intensity decrease, whereas the intrinsic excitability of neurons and short-interval firing increase. INTERPRETATION: These results establish that antibodies from patients with anti-AMPAR encephalitis selectively eliminate surface and synaptic AMPARs, resulting in a homeostatic decrease in inhibitory synaptic transmission and increased intrinsic excitability, which may contribute to the memory deficits and epilepsy that are prominent in patients with this disorder.

Acute mechanisms underlying antibody effects in anti-N-methyl-D-aspartate receptor encephalitis.

OBJECTIVE: A severe but treatable form of immune-mediated encephalitis is associated with antibodies in serum and cerebrospinal fluid (CSF) against the GluN1 subunit of the N-methyl-D-aspartate receptor (NMDAR). Prolonged exposure of hippocampal neurons to antibodies from patients with anti-NMDAR encephalitis caused a reversible decrease in the synaptic localization and function of NMDARs. However, acute effects of the antibodies, fate of the internalized receptors, type of neurons affected, and whether neurons develop compensatory homeostatic mechanisms were unknown and are the focus of this study. METHODS: Dissociated hippocampal neuron cultures and rodent brain sections were used for immunocytochemical, physiological, and molecular studies. RESULTS: Patient antibodies bind to NMDARs throughout the rodent brain, and decrease NMDAR cluster density in both excitatory and inhibitory hippocampal neurons. They rapidly increase the internalization rate of surface NMDAR clusters, independent of receptor activity. This internalization likely accounts for the observed decrease in NMDAR-mediated currents, as no evidence of direct blockade was detected. Once internalized, antibody-bound NMDARs traffic through both recycling endosomes and lysosomes, similar to pharmacologically induced NMDAR endocytosis. The antibodies are responsible for receptor internalization, as their depletion from CSF abrogates these effects in hippocampal neurons. We find that although anti-NMDAR antibodies do not induce compensatory changes in glutamate receptor gene expression, they cause a decrease in inhibitory synapse density onto excitatory hippocampal neurons. INTERPRETATION: Our data support an antibody-mediated mechanism of disease pathogenesis driven by immunoglobulin-induced receptor internalization. Antibody-mediated downregulation of surface NMDARs engages homeostatic synaptic plasticity mechanisms, which may inadvertently contribute to disease progression.

The chromatin remodeler ISWI acts during Drosophila development to regulate adult sleep.

Sleep disruptions are among the most commonly reported symptoms across neurodevelopmental disorders (NDDs), but mechanisms linking brain development to normal sleep are largely unknown. From a Drosophila screen of human NDD-associated risk genes, we identified the chromatin remodeler Imitation SWItch/SNF (ISWI) to be required for adult fly sleep. Loss of ISWI also results in disrupted circadian rhythms, memory, and social behavior, but ISWI acts in different cells and during distinct developmental times to affect each of these adult behaviors. Specifically, ISWI expression in type I neuroblasts is required for both adult sleep and formation of a learning-associated brain region. Expression in flies of the human ISWI homologs SMARCA1 and SMARCA5 differentially rescues adult phenotypes, while de novo SMARCA5 patient variants fail to rescue sleep. We propose that sleep deficits are a primary phenotype of early developmental origin in NDDs and point toward chromatin remodeling machinery as critical for sleep circuit formation.

Mechanisms underlying autoimmune synaptic encephalitis leading to disorders of memory, behavior and cognition: insights from molecular, cellular and synaptic studies.

Recently, several novel, potentially lethal and treatment-responsive syndromes that affect hippocampal and cortical function have been shown to be associated with auto-antibodies against synaptic antigens, notably glutamate or GABA-B receptors. Patients with these auto-antibodies, sometimes associated with teratomas and other neoplasms, present with psychiatric symptoms, seizures, memory deficits and decreased levels of consciousness. These symptoms often improve dramatically after immunotherapy or tumor resection. Here we review studies of the cellular and synaptic effects of these antibodies in hippocampal neurons in vitro and preliminary work in rodent models. Our work suggests that patient antibodies lead to rapid and reversible removal of neurotransmitter receptors from synaptic sites, leading to changes in synaptic and circuit function that in turn are likely to lead to behavioral deficits. We also discuss several of the many questions raised by these and related disorders. Determining the mechanisms underlying these novel anti-neurotransmitter receptor encephalopathies will provide insights into the cellular and synaptic bases of the memory and cognitive deficits that are hallmarks of these disorders, and potentially suggest avenues for therapeutic intervention.

Social Behavioral Deficits with Loss of Neurofibromin Emerge from Peripheral Chemosensory Neuron Dysfunction.

Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder associated with social and communicative disabilities. The cellular and circuit mechanisms by which loss of neurofibromin 1 (Nf1) results in social deficits are unknown. Here, we identify social behavioral dysregulation with Nf1 loss in Drosophila. These deficits map to primary dysfunction of a group of peripheral sensory neurons. Nf1 regulation of Ras signaling in adult ppk23+ chemosensory cells is required for normal social behaviors in flies. Loss of Nf1 attenuates ppk23+ neuronal activity in response to pheromones, and circuit-specific manipulation of Nf1 expression or neuronal activity in ppk23+ neurons rescues social deficits. This disrupted sensory processing gives rise to persistent changes in behavior beyond the social interaction, indicating a sustained effect of an acute sensory misperception. Together our data identify a specific circuit mechanism through which Nf1 regulates social behaviors and suggest social deficits in NF1 arise from propagation of sensory misinformation.

Identification of octopaminergic neurons that modulate sleep suppression by male sex drive.

Molecular and circuit mechanisms for balancing competing drives are not well understood. While circadian and homeostatic mechanisms generally ensure sufficient sleep at night, other pressing needs can overcome sleep drive. Here, we demonstrate that the balance between sleep and sex drives determines whether male flies sleep or court, and identify a subset of octopaminergic neurons (MS1) that regulate sleep specifically in males. When MS1 neurons are activated, isolated males sleep less, and when MS1 neurons are silenced, the normal male sleep suppression in female presence is attenuated and mating behavior is impaired. MS1 neurons do not express the sexually dimorphic FRUITLESS (FRU) transcription factor, but form male-specific contacts with FRU-expressing neurons; calcium imaging experiments reveal bidirectional functional connectivity between MS1 and FRU neurons. We propose octopaminergic MS1 neurons interact with the FRU network to mediate sleep suppression by male sex drive.