Role of Posterior Medial Thalamus in the Modulation of Striatal Circuitry and Choice Behavior.

The posterior medial (POm) thalamus is heavily interconnected with sensory and motor circuitry and is likely involved in behavioral modulation and sensorimotor integration. POm provides axonal projections to the dorsal striatum, a hotspot of sensorimotor processing, yet the role of POm-striatal projections has remained undetermined. Using optogenetics with slice electrophysiology, we found that POm provides robust synaptic input to direct and indirect pathway striatal spiny projection neurons (D1- and D2-SPNs, respectively) and parvalbumin-expressing fast spiking interneurons (PVs). During the performance of a whisker-based tactile discrimination task, POm-striatal projections displayed learning-related activation correlating with anticipatory, but not reward-related, pupil dilation. Inhibition of POm-striatal axons across learning caused slower reaction times and an increase in the number of training sessions for expert performance. Our data indicate that POm-striatal inputs provide a behaviorally relevant arousal-related signal, which may prime striatal circuitry for efficient integration of subsequent choice-related inputs.

Gordon Holmes Syndrome Model Mice Exhibit Alterations in Microglia, Age, and Sex-Specific Disruptions in Cognitive and Proprioceptive Function.

Gordon Holmes syndrome (GHS) is a neurological disorder associated with neuroendocrine, cognitive, and motor impairments with corresponding neurodegeneration. Mutations in the E3 ubiquitin ligase RNF216 are strongly linked to GHS. Previous studies show that deletion of Rnf216 in mice led to sex-specific neuroendocrine dysfunction due to disruptions in the hypothalamic-pituitary-gonadal axis. To address RNF216 action in cognitive and motor functions, we tested Rnf216 knock-out (KO) mice in a battery of motor and learning tasks for a duration of 1 year. Although male and female KO mice did not demonstrate prominent motor phenotypes, KO females displayed abnormal limb clasping. KO mice also showed age-dependent strategy and associative learning impairments with sex-dependent alterations of microglia in the hippocampus and cortex. Additionally, KO males but not females had more negative resting membrane potentials in the CA1 hippocampus without any changes in miniature excitatory postsynaptic current (mEPSC) frequencies or amplitudes. Our findings show that constitutive deletion of Rnf216 alters microglia and neuronal excitability, which may provide insights into the etiology of sex-specific impairments in GHS.

Good vibrations.

The role of a mechanosensitive ion channel in sexual behavior is unveiled.

Erratum: The E3 ubiquitin ligase RNF216/TRIAD3 is a key coordinator of the hypothalamic-pituitary-gonadal axis.

[This corrects the article DOI: 10.1016/j.isci.2022.104386.].

The E3 ubiquitin ligase RNF216/TRIAD3 is a key coordinator of the hypothalamic-pituitary-gonadal axis.

Recessive mutations in RNF216/TRIAD3 cause Gordon Holmes syndrome (GHS), in which dysfunction of the hypothalamic-pituitary-gonadal (HPG) axis and neurodegeneration are thought to be core phenotypes. We knocked out Rnf216/Triad3 in a gonadotropin-releasing hormone (GnRH) hypothalamic cell line. Rnf216/Triad3 knockout (KO) cells had decreased steady-state GnRH and calcium transients. Rnf216/Triad3 KO adult mice had reductions in GnRH neuron soma size and GnRH production without changes in neuron densities. In addition, KO male mice had smaller testicular volumes that were accompanied by an abnormal release of inhibin B and follicle-stimulating hormone, whereas KO females exhibited irregular estrous cycling. KO males, but not females, had reactive microglia in the hypothalamus. Conditional deletion of Rnf216/Triad3 in neural stem cells caused abnormal microglia expression in males, but reproductive function remained unaffected. Our findings show that dysfunction of RNF216/TRIAD3 affects the HPG axis and microglia in a region- and sex-dependent manner, implicating sex-specific therapeutic interventions for GHS.

The Temporal Dynamics of Arc Expression Regulate Cognitive Flexibility.

Neuronal activity regulates the transcription and translation of the immediate-early gene Arc/Arg3.1, a key mediator of synaptic plasticity. Proteasome-dependent degradation of Arc tightly limits its temporal expression, yet the significance of this regulation remains unknown. We disrupted the temporal control of Arc degradation by creating an Arc knockin mouse (ArcKR) where the predominant Arc ubiquitination sites were mutated. ArcKR mice had intact spatial learning but showed specific deficits in selecting an optimal strategy during reversal learning. This cognitive inflexibility was coupled to changes in Arc mRNA and protein expression resulting in a reduced threshold to induce mGluR-LTD and enhanced mGluR-LTD amplitude. These findings show that the abnormal persistence of Arc protein limits the dynamic range of Arc signaling pathways specifically during reversal learning. Our work illuminates how the precise temporal control of activity-dependent molecules, such as Arc, regulates synaptic plasticity and is crucial for cognition.

A Comprehensive Atlas of E3 Ubiquitin Ligase Mutations in Neurological Disorders.

Protein ubiquitination is a posttranslational modification that plays an integral part in mediating diverse cellular functions. The process of protein ubiquitination requires an enzymatic cascade that consists of a ubiquitin activating enzyme (E1), ubiquitin conjugating enzyme (E2) and an E3 ubiquitin ligase (E3). There are an estimated 600-700 E3 ligase genes representing ~5% of the human genome. Not surprisingly, mutations in E3 ligase genes have been observed in multiple neurological conditions. We constructed a comprehensive atlas of disrupted E3 ligase genes in common (CND) and rare neurological diseases (RND). Of the predicted and known human E3 ligase genes, we found ~13% were mutated in a neurological disorder with 83 total genes representing 70 different types of neurological diseases. Of the E3 ligase genes identified, 51 were associated with an RND. Here, we provide an updated list of neurological disorders associated with E3 ligase gene disruption. We further highlight research in these neurological disorders and discuss the advanced technologies used to support these findings.

The microbiota influences cell death and microglial colonization in the perinatal mouse brain.

The mammalian fetus develops in a largely sterile environment, and direct exposure to a complex microbiota does not occur until birth. We took advantage of this to examine the effect of the microbiota on brain development during the first few days of life. The expression of anti- and pro-inflammatory cytokines, developmental cell death, and microglial colonization in the brain were compared between newborn conventionally colonized mice and mice born in sterile, germ-free (GF) conditions. Expression of the pro-inflammatory cytokines interleukin 1ß and tumor necrosis factor α was markedly suppressed in GF newborns. GF mice also had altered cell death, with some regions exhibiting higher rates (paraventricular nucleus of the hypothalamus and the CA1 oriens layer of the hippocampus) and other regions exhibiting no change or lower rates (arcuate nucleus of the hypothalamus) of cell death. Microglial labeling was elevated in GF mice, due to an increase in both microglial cell size and number. The changes in cytokine expression, cell death and microglial labeling were evident on the day of birth, but were absent on embryonic day 18.5, approximately one-half day prior to expected delivery. Taken together, our results suggest that direct exposure to the microbiota at birth influences key neurodevelopmental events and does so within hours. These findings may help to explain some of the behavioral and neurochemical alterations previously seen in adult GF mice.