The rewarding and locomotor-sensitizing effects of repeated cocaine administration are distinct and separable in mice

Repeated psychostimulant exposure progressively increases their potency to stimulate motor activity in rodents. This behavioral or locomotor sensitization is considered a model for some aspects of drug addiction in humans, particularly drug craving during abstinence. However, the role of increased motor behavior in drug reward remains incompletely understood. Intracranial self-stimulation (ICSS) was measured concurrently with locomotor activity to determine if acute intermittent cocaine administration had distinguishable effects on motor behavior and perception of brain stimulation-reward (BSR) in the same mice. Sensitization is associated with changes in neuronal activity and glutamatergic neurotransmission in brain reward circuitry. Expression of AMPA receptor subunits (GluR1 and GluR2) and CRE binding protein (CREB) was measured in the ventral tegmental area (VTA), dorsolateral striatum (STR) and nucleus accumbens (NAc) before and after a sensitizing regimen of cocaine, with and without ICSS. Repeated cocaine administration sensitized mice to its locomotor stimulating effects but not its ability to potentiate BSR. ICSS increased GluR1 in the VTA but not NAc or STR, demonstrating selective changes in protein expression with electrical stimulation of discrete brain structures. Repeated cocaine reduced GluR1, GluR2 and CREB expression in the NAc, and reductions of GluR1 and GluR2 but not CREB were further enhanced by ICSS. These data suggest that the effects of repeated cocaine exposure on reward and motor processes are dissociable in mice, and that reduction of excitatory neurotransmission in the NAc may predict altered motor function independently from changes in reward perception

Orexin-1 receptor antagonism does not reduce the rewarding potency of cocaine in Swiss–Webster mice

The orexin family of hypothalamic neuropeptides has been implicated in reinforcement mechanisms relevant to both food and drug reward. Previous behavioral studies with antagonists at the orexin A-selective receptor, OX1, have demonstrated its involvement in behavioral sensitization, conditioned place-preference, and self-administration of drugs of abuse. Adult male Swiss-Webster mice were implanted with stimulating electrodes to the lateral hypothalamus and trained to perform intracranial self-stimulation (ICSS). The effects of the OX1-selective antagonist SB 334867 on brain stimulation-reward (BSR) and cocaine potentiation of BSR were measured. SB 334867 (10 – 30 mg/kg, i.p.) alone had no effect on ICSS performance or BSR threshold. Cocaine (1.0 – 30 mg/kg i.p.) dose-dependently potentiated BSR, measured as lowering of BSR threshold. This effect was not blocked by 30 mg/kg SB 334867 at any cocaine dose tested. In agreement with previous reports, SB 334867 resulted in a reduction of body weight 24 hours after acute administration. Based on these data, it is concluded that orexins acting at OX1 do not contribute to BSR; and are not involved in the reward-potentiating actions of cocaine on BSR. The data are discussed in the context of prior findings of SB 334867 effects on drug-seeking and drug-consuming behaviors

Visual impairment in an optineurin mouse model of primary open-angle glaucoma

Primary open angle glaucoma (POAG) is characterized by progressive neurodegeneration of retinal ganglion cells (RGCs). Why RGCs degenerate in low pressure POAG remains poorly understood. To gain mechanistic insights, we developed a novel mouse model based on a mutation in human optineurin associated with hereditary, low-pressure POAG. This mouse improves the design and phenotype of currently available optineurin mice, which showed high global overexpression. While both 18-month old optineurin and nontransgenic control mice showed an age-related decrease in healthy axons and RGCs, the expression of mutant optineurin enhanced axonal degeneration and decreased RGC survival. Mouse visual function was determined using visual evoked potentials, which revealed specific visual impairment in contrast sensitivity. The E50K optineurin transgenic mouse described here exhibited clinical features of POAG, and may be useful for mechanistic dissection of POAG and therapeutic development

Ube3a is required for experience-dependent maturation of the neocortex

Experience-dependent maturation of neocortical circuits is required for normal sensory and cognitive abilities, which are distorted in neurodevelopmental disorders. We have tested whether experience-dependent neocortical modifications require Ube3a, an E3 ubiquitin ligase whose dysregulation has been implicated in autism and Angelman syndrome (AS). Using visual cortex as a model, we demonstrate that experience-dependent maturation of excitatory cortical circuits is severely impaired in AS mice deficient in Ube3a. This developmental defect is associated with profound impairments in neocortical plasticity. Remarkably, normal plasticity is preserved under conditions of sensory deprivation, but rapidly lost by sensory experiences. The loss of neocortical plasticity is reversible, as late-onset visual deprivation restores normal synaptic plasticity. Further, Ube3a-deficient mice lack ocular dominance plasticity in vivo when challenged with monocular deprivation. These results show that Ube3a is necessary to maintain plasticity during experience-dependent neocortical development, and suggest that loss of neocortical plasticity contributes to deficits associated with AS

Pathway-specific dopaminergic deficits in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a neurodevelopmental disorder caused by maternal deletions or mutations of the ubiquitin ligase E3A (UBE3A) allele and characterized by minimal verbal communication, seizures, and disorders of voluntary movement. Previous studies have suggested that abnormal dopamine neurotransmission may underlie some of these deficits, but no effective treatment currently exists for the core features of AS. A clinical trial of levodopa (l-DOPA) in AS is ongoing, although the underlying rationale for this treatment strategy has not yet been thoroughly examined in preclinical models. We found that AS model mice lacking maternal Ube3a (Ube3am–/p+ mice) exhibit behavioral deficits that correlated with abnormal dopamine signaling. These deficits were not due to loss of dopaminergic neurons or impaired dopamine synthesis. Unexpectedly, Ube3am–/p+ mice exhibited increased dopamine release in the mesolimbic pathway while also exhibiting a decrease in dopamine release in the nigrostriatal pathway, as measured with fast-scan cyclic voltammetry. These findings demonstrate the complex effects of UBE3A loss on dopamine signaling in subcortical motor pathways that may inform ongoing clinical trials of l-DOPA therapy in patients with AS

Ube3a is required for experience-dependent maturation of the neocortex

Photograph of a scene at the reconstructed Choctaw Chief's House

Visual impairment in an optineurin mouse model of primary open-angle glaucoma.

Primary open-angle glaucoma (POAG) is characterized by progressive neurodegeneration of retinal ganglion cells (RGCs). Why RGCs degenerate in low-pressure POAG remains poorly understood. To gain mechanistic insights, we developed a novel mouse model based on a mutation in human optineurin associated with hereditary, low-pressure POAG. This mouse improves the design and phenotype of currently available optineurin mice, which showed high global overexpression. Although both 18-month-old optineurin and nontransgenic control mice showed an age-related decrease in healthy axons and RGCs, the expression of mutant optineurin enhanced axonal degeneration and decreased RGC survival. Mouse visual function was determined using visual evoked potentials, which revealed specific visual impairment in contrast sensitivity. The E50K optineurin transgenic mouse described here exhibited clinical features of POAG and may be useful for mechanistic dissection of POAG and therapeutic development. Neurobiol Aging 2015 Jun; 36(6):2201-12

AhR-deficiency as a cause of demyelinating disease and inflammation

Abstract The Aryl hydrocarbon Receptor(AhR) is among the most important receptors which bind pollutants; however it also regulates signaling pathways independently of such exposure. We previously demonstrated that AhR is expressed during development of the central nervous system(CNS) and that its deletion leads to the occurrence of a congenital nystagmus. Objectives of the present study are to decipher the origin of these deficits, and to identify the role of the AhR in the development of the CNS. We show that the AhR-knockout phenotype develops during early infancy together with deficits in visual-information-processing which are associated with an altered optic nerve myelin sheath, which exhibits modifications in its lipid composition and in the expression of myelin-associated-glycoprotein(MAG), a cell adhesion molecule involved in myelin-maintenance and glia-axon interaction. In addition, we show that the expression of pro-inflammatory cytokines is increased in the impaired optic nerve and confirm that inflammation is causally related with an AhR-dependent decreased expression of MAG. Overall, our findings demonstrate the role of the AhR as a physiological regulator of myelination and inflammatory processes in the developing CNS. It identifies a mechanism by which environmental pollutants might influence CNS myelination and suggest AhR as a relevant drug target for demyelinating diseases

Pathway-specific dopaminergic deficits in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a neurodevelopmental disorder caused by maternal deletions or mutations of the ubiquitin ligase E3A (UBE3A) allele and characterized by minimal verbal communication, seizures, and disorders of voluntary movement. Previous studies have suggested that abnormal dopamine neurotransmission may underlie some of these deficits, but no effective treatment currently exists for the core features of AS. A clinical trial of levodopa (l-DOPA) in AS is ongoing, although the underlying rationale for this treatment strategy has not yet been thoroughly examined in preclinical models. We found that AS model mice lacking maternal Ube3a (Ube3a(m–/p+) mice) exhibit behavioral deficits that correlated with abnormal dopamine signaling. These deficits were not due to loss of dopaminergic neurons or impaired dopamine synthesis. Unexpectedly, Ube3a(m–/p+) mice exhibited increased dopamine release in the mesolimbic pathway while also exhibiting a decrease in dopamine release in the nigrostriatal pathway, as measured with fast-scan cyclic voltammetry. These findings demonstrate the complex effects of UBE3A loss on dopamine signaling in subcortical motor pathways that may inform ongoing clinical trials of l-DOPA therapy in patients with AS

Orexin-1 receptor antagonism does not reduce the rewarding potency of cocaine in Swiss–Webster mice

The orexin family of hypothalamic neuropeptides has been implicated in reinforcement mechanisms relevant to both food and drug reward. Previous behavioral studies with antagonists at the orexin A-selective receptor, OX(1), have demonstrated its involvement in behavioral sensitization, conditioned place-preference, and self-administration of drugs of abuse. Adult male Swiss-Webster mice were implanted with stimulating electrodes to the lateral hypothalamus and trained to perform intracranial self-stimulation (ICSS). The effects of the OX(1)-selective antagonist SB 334867 on brain stimulation-reward (BSR) and cocaine potentiation of BSR were measured. SB 334867 (10 – 30 mg/kg, i.p.) alone had no effect on ICSS performance or BSR threshold. Cocaine (1.0 – 30 mg/kg i.p.) dose-dependently potentiated BSR, measured as lowering of BSR threshold. This effect was not blocked by 30 mg/kg SB 334867 at any cocaine dose tested. In agreement with previous reports, SB 334867 resulted in a reduction of body weight 24 hours after acute administration. Based on these data, it is concluded that orexins acting at OX(1) do not contribute to BSR; and are not involved in the reward-potentiating actions of cocaine on BSR. The data are discussed in the context of prior findings of SB 334867 effects on drug-seeking and drug-consuming behaviors