The adult turtle spinal cord can generate multiple kinds of limb movements, including swimming, three forms of scratching, and limb withdrawal (flexion reflex), even without brain input and sensory feedback. There are many multifunctional spinal neurons, activated during multiple motor patterns, and some behaviorally specialized neurons, activated during only one. How do multifunctional and behaviorally specialized neurons each contribute to motor output? We analyzed in vivo intracellular recordings of multifunctional and specialized neurons. Neurons tended to spike in the same phase of the hip-flexor activity cycle during swimming and scratching, though one preferred opposite phases. During both swimming and scratching, a larger fraction of multifunctional neurons than specialized neurons were highly rhythmic. One group of multifunctional neurons was active during the hip flexor-on phase and another during the hip flexor-off phase. Thus, hip flexor-extensor alternation may be generated by a subset of mult...

Microglia carry out important functions as the resident macrophages of the brain. To study their role in health and disease, the research community needs tools to genetically modify them with maximum completeness in a manner that distinguishes them from closely related cell-types, such as monocytes. While currently available tamoxifen-inducible CreERT2 lines are able to achieve the differentiation from other cells, the field needs improved and publicly available constitutively active Cre lines, especially ones with favorable efficiency and specificity profiles for studies where high recombination efficiency is imperative and where tamoxifen administration is contraindicated. Here, we leverage the microglia-specific Fcrls gene to generate mice expressing Cre. Using genomic methods, we show correct positioning of the transgene and intact microglia homeostasis in Fcrls-2A-Cre mice. Crossing Fcrls-2A-Cre mice to four different reporters, we demonstrate highly efficient recombination in microglia across differe...

Midbrain dopamine neurons receive convergent synaptic input from multiple brain areas, which perturbs rhythmic pacemaking to produce the complex firing patterns observed in vivo. This study investigated the impact of single and multiple inhibitory inputs on ventral tegmental area (VTA) dopamine neuron firing in mice of both sexes using novel experimental measurements and modeling. We first measured unitary inhibitory postsynaptic currents (uIPSCs) produced by single axons using both minimal electrical stimulation and minimal optical stimulation of rostromedial tegmental nucleus (RMTg) and ventral pallidum (VP) afferents. We next determined the phase resetting curve (PRC), the reversal potential for GABAA receptor-mediated IPSCs, and the average inter-spike membrane potential trajectory during pacemaking. We combined these data in a phase oscillator model of a VTA dopamine neuron, simulating the effects of unitary inhibitory postsynaptic conductances (uIPSGs) on spike timing and rate. The effect of a uIPSG ...

Cognitive dysfunction is associated with methamphetamine use disorder. Here, we used genetic and pharmacological approaches to examine the involvement of either mGlu2 or mGlu3 receptors in memory deficit induced by methamphetamine in mice. Methamphetamine treatment (1 mg/kg, i.p., once a day for 5 days followed by 7 days of withdrawal) caused an impaired performance in the novel object recognition (NOR) test in wild-type mice, but not in mGlu2-/- or mGlu3-/- mice. Memory deficit in wild-type mice challenged with methamphetamine was corrected by systemic treatment with selectively negative allosteric modulators of mGlu2 or mGlu3 receptors (compounds VU6001966 and VU0650786, respectively). Methamphetamine treatment in wild-type mice caused large increases in levels of mGlu2/3 receptors, the type-3 activator of G protein signaling (AGS3), Rab3A and the vesicular glutamate transporter, vGlut1 in the prefrontal cortex (PFC). Methamphetamine did not alter mGlu2/3-mediated inhibition of cAMP formation, but abolis...

The cerebellum is a conserved structure of the vertebrate brain involved in the timing and calibration of movements. Its function is supported by the convergence of fibers from granule cells (GCs) and inferior olive neurons (IONs) onto Purkinje cells (PCs). Theories of cerebellar function postulate that IONs convey error signals to PCs that, paired with the contextual information provided by GCs, can instruct motor learning. Here, we use the larval zebrafish to investigate (i) how sensory representations of the same stimulus vary across GCs and IONs and (ii) how PC activity reflects these two different input streams. We use population calcium imaging to measure IONs and GCs responses to flashes of diverse luminance and duration. First, we observe that GCs show tonic and graded responses, as opposed to IONs, whose activity peaks mostly at luminance transitions, consistently with the notion that GCs and IONs encode context and error information, respectively. Secondly, we show that GC activity is patterned ...

The Gaze Following Patch (GFP) is located in the posterior temporal cortex and has been described as a cortical module dedicated to processing other people's gaze direction in a domain-specific manner. Thus, it appears to be the neural correlate of Baron-Cohen’s Eye-Direction Detector (EDD) which is one of the core modules in his Mindreading System - a neurocognitive model for the Theory of Mind concept. Inspired by Jerry Fodor’s ideas on the modularity of the mind, Baron-Cohen proposed that, among other things, the individual modules are domain-specific. In the case of the EDD this means that it exclusively processes eye-like stimuli to extract gaze direction and that other stimuli, that may carry directional information as well, are processed elsewhere. If the GFP is indeed EDD’s neural correlate it must meet this expectation. To test this, we compared the GFP’s BOLD activity during gaze-direction following with the activity during arrow-direction following in the present human fMRI study. Contrary to th...

Parvalbumin-expressing (PV) neurons, classified by their expression of the calcium-binding protein parvalbumin, play crucial roles in the function and plasticity of the lateral habenular nucleus (LHb). This study aimed to deepen our understanding of the LHb by collecting information about the heterogeneity of LHb PV neurons in mice. To achieve this, we investigated the proportions of the transmitter machinery in LHb PV neurons, including GABAergic, glutamatergic, serotonergic, cholinergic, and dopaminergic neurotransmitter markers, using transcriptome analysis, mRNA in situ hybridization chain reaction, and immunohistochemistry. LHb PV neurons comprise three subsets: glutamatergic, GABAergic, and double-positive for glutamatergic and GABAergic machinery. By comparing the percentages of the subsets, we found that the LHb was topographically organized anteroposteriorly; the GABAergic and glutamatergic PV neurons were preferentially distributed in the anterior and posterior LHb, respectively, uncovering the a...

Synapsins are highly abundant presynaptic proteins that play a crucial role in neurotransmission and plasticity via the clustering of synaptic vesicles. The synapsin III isoform is usually downregulated after development, but in hippocampal mossy fiber boutons, it persists in adulthood. Mossy fiber boutons express presynaptic forms of short- and long-term plasticity, which are thought to underlie different forms of learning. Previous research on synapsins at this synapse focused on synapsin isoforms I and II. Thus, a complete picture regarding the role of synapsins in mossy fiber plasticity is still missing. Here, we investigated presynaptic plasticity at hippocampal mossy fiber boutons by combining electrophysiological field recordings and transmission electron microscopy in a mouse model lacking all synapsin isoforms. We found decreased short-term plasticity, i.e., decreased facilitation and post-tetanic potentiation, but increased long-term potentiation in male synapsin triple knock-out (KO) mice. At th...

Previous studies have shown that ligands that bind to sigma-2 receptor/TMEM97 (s2R/TMEM97), a transmembrane protein, have anxiolytic/antidepressant-like properties and relieve neuropathic pain-like effects in rodents. Despite medical interest in s2R/TMEM97, little affective and pain behavioral characterization has been done using transgenic mice, which limits the development of s2R/TMEM97 as a viable therapeutic target. Using wild-type (WT) and global Tmem97 knock-out (KO) mice, we sought to identify the contribution of Tmem97 in modulating affective and pain-like behaviors using a battery of affective and pain assays, including open field, light/dark preference, elevated plus maze, forced swim test, tail suspension test, and the mechanical sensitivity tests. Our results demonstrate that female Tmem97 KO mice show less anxiety-like and depressive-like behaviors in light/dark preference and tail suspension tests but not in an open field, elevated plus maze, and forced swim tests at baseline. We next perform...

Glutamatergic synapses exhibit significant molecular diversity, but circuit-specific mechanisms that underlie synaptic regulation are not well characterized. Prior reports show that Rho-guanine nucleotide exchange factor (RhoGEF) Tiam1 regulates perforant path→dentate gyrus granule neuron synapses. In the present study, we report Tiam1's homolog Tiam2 is implicated in glutamatergic neurotransmission in CA1 pyramidal neurons. We find that Tiam2 regulates evoked excitatory glutamatergic currents via a postsynaptic mechanism mediated by the catalytic Dbl-homology domain. Overall, we present evidence for RhoGEF Tiam2's role in glutamatergic synapse function at Schaffer collateral→CA1 pyramidal neuron synapses.