Brian N. Mathur

Proteinuria and Perinatal Lethality in Mice Lacking NEPH1, a Novel Protein with Homology to NEPHRIN

ABSTRACT A high-throughput, retrovirus-mediated mutagenesis method based on gene trapping in embryonic stem cells was used to identify a novel mouse gene. The human ortholog encodes a transmembrane protein containing five extracellular immunoglobulin-like domains that is structurally related to human NEPHRIN, a protein associated with congenital nephrotic syndrome. Northern analysis revealed wide expression in humans and mice, with highest expression in kidney. Based on similarity to NEPHRIN and abundant expression in kidney, this protein was designated NEPH1 and embryonic stem cells containing the retroviral insertion in the Neph1 locus were used to generate mutant mice. Analysis of kidney RNA fromNeph1 −/− mice showed that the retroviral insertion disrupted expression of Neph1 transcripts.Neph1 −/− pups were represented at the expected normal Mendelian ratios at 1 to 3 days of age but at only 10% of the expected frequency at 10 to 12 days after birth, suggesting an early postnatal lethality. The Neph1 −/−animals that survived beyond the first week of life were sickly and small but without edema, and all died between 3 and 8 weeks of age. Proteinuria ranging from 300 to 2,000 mg/dl was present in allNeph1 −/− mice. Electron microscopy demonstrated NEPH1 expression in glomerular podocytes and revealed effacement of podocyte foot processes inNeph1 −/− mice. These findings suggest that NEPH1, like NEPHRIN, may play an important role in maintaining the structure of the filtration barrier that prevents proteins from freely entering the glomerular urinary space.

Selective activation of cholinergic interneurons enhances accumbal phasic dopamine release: setting the tone for reward processing

Dopamine plays a critical role in motor control, addiction, and reward-seeking behaviors, and its release dynamics have traditionally been linked to changes in midbrain dopamine neuron activity. Here, we report that selective endogenous cholinergic activation achieved via in vitro optogenetic stimulation of nucleus accumbens, a terminal field of dopaminergic neurons, elicits real-time dopamine release. This mechanism occurs via direct actions on dopamine terminals, does not require changes in neuron firing within the midbrain, and is dependent on glutamatergic receptor activity. More importantly, we demonstrate that in vivo selective activation of cholinergic interneurons is sufficient to elicit dopamine release in the nucleus accumbens. Therefore, the control of accumbal extracellular dopamine levels by endogenous cholinergic activity results from a complex convergence of neurotransmitter/neuromodulator systems that may ultimately synergize to drive motivated behavior.

Proteomic Analysis Illuminates a Novel Structural Definition of the Claustrum and Insula

The claustrum is a prominent but ill-defined forebrain structure that has been suggested to integrate multisensory information and perhaps transform percepts into consciousness. The claustrums shape and vague borders have hampered experimental assessment of its functions. We used matrix-assisted laser desorption ionization-imaging mass spectrometry to reveal a novel protein marker, G-protein gamma2 subunit (Gng2), which is enriched in the claustrum but not adjacent structures of the rat forebrain. The spatial pattern of Gng2 expression suggests key differences from commonly held views of the claustrums structure. Using anatomical methods, we found that the rat claustrum is present only at striatal levels of the telencephalon and does not extend to frontal cortical territories. Moreover, the claustrum is surrounded on all sides by layer VI insular cortex cells in both the rat and primate. Using these defining characteristics of the claustrum, we found that the claustrum projects to cortical but not to subcortical sites. The definition of the claustrum as a cortical site is considered. The identification of a claustrum-specific protein opens the door to selective molecular lesions and the subsequent evaluation of the role of the claustrum in cognition.

Serotonin Induces Long-Term Depression at Corticostriatal Synapses

The striatum has important roles in motor control and action learning and, like many brain regions, receives multiple monoaminergic inputs. We have examined serotonergic modulation of rat and mouse corticostriatal neurotransmission and find that serotonin (5-HT) activates 5-HT1b receptors resulting in a long-term depression (LTD) of glutamate release and striatal output that we have termed 5-HT–LTD. 5-HT–LTD is presynaptically mediated, cAMP pathway dependent, and inducible by endogenous striatal 5-HT, as revealed by application of a selective 5-HT reuptake inhibitor. 5-HT–LTD is mutually occlusive with dopamine/endocannabinoid-dependent LTD, suggesting that these two forms of LTD act on the same corticostriatal terminals. Thus, serotonergic and dopaminergic mechanisms exist that may interact to persistently sculpt corticostriatal circuits, potentially influencing action learning and striatal-based disorders.

The claustrum in review

The claustrum is among the most enigmatic of all prominent mammalian brain structures. Since the 19th century, a wealth of data has amassed on this forebrain nucleus. However, much of this data is disparate and contentious; conflicting views regarding the claustrum’s structural definitions and possible functions abound. This review synthesizes historical and recent claustrum studies with the purpose of formulating an acceptable description of its structural properties. Integrating extant anatomical and functional literature with theorized functions of the claustrum, new visions of how this structure may be contributing to cognition and action are discussed.

Organophosphates dysregulate dopamine signaling, glutamatergic neurotransmission, and induce neuronal injury markers in striatum

J. Neurochem. (2011) 119, 303–313.

Endocannabinoid-dopamine interactions in striatal synaptic plasticity.

The nigrostriatal dopaminergic system is implicated in action control and learning. A large body of work has focused on the contribution of this system to modulation of the corticostriatal synapse, the predominant synapse type in the striatum. Signaling through the D2 dopamine receptor is necessary for endocannabinoid-mediated depression of corticostriatal glutamate release. Here we review the known details of this mechanism and discuss newly discovered signaling pathways interacting with this system that ultimately exert dynamic control of cortical input to the striatum and striatal output. This topic is timely with respect to Parkinson’s disease given recent data indicating changes in the striatal endocannabinoid system in patients with this disorder.

Voltage drives diverse endocannabinoid signals to mediate striatal microcircuit-specific plasticity

The dorsolateral striatum and cannabinoid type 1 receptor (CB1) signaling mediate habitual action learning, which is thought to require a balance of activity in the direct and indirect striatal output pathways. However, very little is known about how the high CB1–expressing striatal inhibitory microcircuitry might contribute to long-term plasticity capable of sculpting direct and indirect pathway output. Using optogenetic and molecular interrogation of striatal GABAergic microcircuits, we examined voltage-dependent long-term depression of inhibitory synapses (iLTD) onto mouse and rat medium spiny projection neurons (MSNs). The observed iLTD involved recruitment of different endocannabinoid types and showed both presynaptic and postsynaptic selectivity for MSN subtypes, ultimately resulting in a powerful disinhibition of direct pathway MSNs. These results suggest a new role for voltage states in gating circuit-specific forms of synaptic plasticity and illuminate possible circuit dynamics underlying action control.

Endocannabinoids in striatal plasticity.

Endocannabinoids (eCBs) are lipid metabolites found throughout the nervous system that modulate synaptic plasticity mainly via actions on the cannabinoid 1 (CB1) receptor. Within the striatum, eCBs and CB1Rs initiate both short- and long-lasting synaptic depression at intrinsic GABAergic synapses and glutamatergic synapses made by cortical afferents. Recent studies have explored the mechanisms underlying eCB-mediated synaptic depression, and the role of this plasticity in striatal function. Dopamine (DA) and its receptors promote eCB-mediated depression of glutamatergic synapses, and dopamine depletion in animal models alters corticostriatal synapses in ways that may contribute to Parkinsons disease (PD). A growing body of literature indicates that alterations in eCB signaling occur in PD patients, suggesting possible therapeutic approaches targeting this neuromodulatory system.

Genetic Inhibition of CaMKII in Dorsal Striatal Medium Spiny Neurons Reduces Functional Excitatory Synapses and Enhances Intrinsic Excitability

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is abundant in striatal medium spiny neurons (MSNs). CaMKII is dynamically regulated by changes in dopamine signaling, as occurs in Parkinsons disease as well as addiction. Although CaMKII has been extensively studied in the hippocampus where it regulates excitatory synaptic transmission, relatively little is known about how it modulates neuronal function in the striatum. Therefore, we examined the impact of selectively overexpressing an EGFP-fused CaMKII inhibitory peptide (EAC3I) in striatal medium spiny neurons (MSNs) using a novel transgenic mouse model. EAC3I-expressing cells exhibited markedly decreased excitatory transmission, indicated by a decrease in the frequency of spontaneous excitatory postsynaptic currents (sEPSCs). This decrease was not accompanied by changes in the probability of release, levels of glutamate at the synapse, or changes in dendritic spine density. CaMKII regulation of the AMPA receptor subunit GluA1 is a major means by which the kinase regulates neuronal function in the hippocampus. We found that the decrease in striatal excitatory transmission seen in the EAC3I mice is mimicked by deletion of GluA1. Further, while CaMKII inhibition decreased excitatory transmission onto MSNs, it increased their intrinsic excitability. These data suggest that CaMKII plays a critical role in setting the excitability rheostat of striatal MSNs by coordinating excitatory synaptic drive and the resulting depolarization response.