Neuroligin-3 in dopaminergic circuits promotes behavioural and neurobiological adaptations to chronic morphine exposure.

Chronic opioid exposure causes structural and functional changes in brain circuits, which may contribute to opioid use disorders. Synaptic cell-adhesion molecules are prime candidates for mediating this opioid-evoked plasticity. Neuroligin-3 (NL3) is an X-linked postsynaptic adhesion protein that shapes synaptic function at multiple sites in the mesolimbic dopamine system. We therefore studied how genetic knockout of NL3 alters responses to chronic morphine in male mice. Constitutive NL3 knockout caused a persistent reduction in psychomotor sensitization after chronic morphine exposure and change in the topography of locomotor stimulation produced by morphine. This latter change was recapitulated by conditional genetic deletion of NL3 from cells expressing the Drd1 dopamine receptor, whereas reduced psychomotor sensitization was recapitulated by conditional genetic deletion from dopamine neurons. Without NL3 expression, dopamine neurons in the ventral tegmental area exhibited diminished activation following chronic morphine exposure, by measuring in vivo calcium signals with fibre photometry. This altered pattern of dopamine neuron activity may be driven by aberrant forms of opioid-evoked synaptic plasticity in the absence of NL3: dopamine neurons lacking NL3 showed weaker synaptic inhibition at baseline, which was subsequently strengthened after chronic morphine. In total, our study highlights neurobiological adaptations in dopamine neurons of the ventral tegmental area that correspond with increased behavioural sensitivity to opioids and further suggests that NL3 expression by dopamine neurons provides a molecular substrate for opioid-evoked adaptations in brain function and behaviour.

Angiotensin-converting enzyme gates brain circuit-specific plasticity via an endogenous opioid.

Angiotensin-converting enzyme (ACE) regulates blood pressure by cleaving angiotensin I to produce angiotensin II. In the brain, ACE is especially abundant in striatal tissue, but the function of ACE in striatal circuits remains poorly understood. We found that ACE degrades an unconventional enkephalin heptapeptide, Met-enkephalin-Arg-Phe, in the nucleus accumbens of mice. ACE inhibition enhanced µ-opioid receptor activation by Met-enkephalin-Arg-Phe, causing a cell type-specific long-term depression of glutamate release onto medium spiny projection neurons expressing the Drd1 dopamine receptor. Systemic ACE inhibition was not intrinsically rewarding, but it led to a decrease in conditioned place preference caused by fentanyl administration and an enhancement of reciprocal social interaction. Our results raise the enticing prospect that central ACE inhibition can boost endogenous opioid signaling for clinical benefit while mitigating the risk of addiction.

Management of Suprachoroidal Hemorrhage in a Patient With Boston Type I Keratoprosthesis.

Purpose: Suprachoroidal hemorrhage (SCH) is a rare but vision-threatening complication in patients with keratoprosthesis devices (KPro), particularly in the setting of concurrent glaucoma tube shunts. Although there are many approaches to draining an SCH, surgery can be especially challenging in these patients because a crowded anterior chamber, and frequent anterior extension of the SCH. Methods: A case report is discussed. Results: We describe a novel approach to surgical drainage of SCH in a 64-year-old monocular patient with a Type I Boston KPro, an Ahmed valve, and aphakia. Conclusion: Successful repair of appositional SCH in the context of KPro can be safely and effectively achieved by injecting viscoelastic through the backplate holes of the KPro, thereby providing internal tamponade within the vitreous compartment while liquefied hemorrhage is drained by sclerotomy.

µ-Opioid Receptor (Oprm1) Copy Number Influences Nucleus Accumbens Microcircuitry and Reciprocal Social Behaviors.

The µ-opioid receptor regulates reward derived from both drug use and natural experiences, including social interaction, through actions in the nucleus accumbens. Here, we studied nucleus accumbens microcircuitry and social behavior in male and female mice with heterozygous genetic knockout of the µ-opioid receptor (Oprm1+/-). This genetic condition models the partial reduction of µ-opioid receptor signaling reported in several neuropsychiatric disorders. We first analyzed inhibitory synapses in the nucleus accumbens, using methods that differentiate between medium spiny neurons (MSNs) expressing the D1 or D2 dopamine receptor. Inhibitory synaptic transmission was increased in D2-MSNs of male mutants, but not female mutants, while the expression of gephyrin mRNA and the density of inhibitory synaptic puncta at the cell body of D2-MSNs was increased in mutants of both sexes. Some of these changes were more robust in Oprm1+/- mutants than Oprm1-/- mutants, demonstrating that partial reductions of µ-opioid signaling can have large effects. At the behavioral level, social conditioned place preference and reciprocal social interaction were diminished in Oprm1+/- and Oprm1-/- mutants of both sexes. Interaction with Oprm1 mutants also altered the social behavior of wild-type test partners. We corroborated this latter result using a social preference task, in which wild-type mice preferred interactions with another typical mouse over Oprm1 mutants. Surprisingly, Oprm1-/- mice preferred interactions with other Oprm1-/- mutants, although these interactions did not produce a conditioned place preference. Our results support a role for partial dysregulation of µ-opioid signaling in social deficits associated with neuropsychiatric conditions.SIGNIFICANCE STATEMENT Activation of the µ-opioid receptor plays a key role in the expression of normal social behaviors. In this study, we examined brain function and social behavior of female and male mice, with either partial or complete genetic deletion of µ-opioid receptor expression. We observed abnormal social behavior following both genetic manipulations, as well as changes in the structure and function of synaptic input to a specific population of neurons in the nucleus accumbens, which is an important brain region for social behavior. Synaptic changes were most robust when µ-opioid receptor expression was only partially lost, indicating that small reductions in µ-opioid receptor signaling can have a large impact on brain function and behavior.

Vasodilator dysfunction and oligodendrocyte dysmaturation in aging white matter.

OBJECTIVE: Microvascular brain injury (mVBI) is a common pathological correlate of vascular contributions to cognitive impairment and dementia (VCID) that leads to white matter (WM) injury (WMI). VCID appears to arise from chronic recurrent white matter ischemia that triggers oxidative stress and an increase in total oligodendrocyte lineage cells. We hypothesized that mVBI involves vasodilator dysfunction of white matter penetrating arterioles and aberrant oligodendrocyte progenitor cell (OPC) responses to WMI. METHODS: We analyzed cases of mVBI with low Alzheimer's disease neuropathological change in prefrontal cortex WM from rapid autopsies in a population-based cohort where VCID frequently occurs. Arteriolar vasodilator function was quantified by videomicroscopy. OPC maturation was quantified using lineage specific markers. RESULTS: Acetylcholine-mediated arteriolar dilation in mVBI was significantly reduced in WM penetrators relative to pial arterioles. Astrogliosis-defined WMI was positively associated with increased OPCs and was negatively associated with decreased mature oligodendrocytes. INTERPRETATION: Selectively impaired vasodilator function of WM penetrating arterioles in mVBI occurs in association with aberrant differentiation of OPCs in WMI, which supports that myelination disturbances in VCID are related to disrupted maturation of myelinating oligodendrocytes. Ann Neurol 2018;83:142-152.

Opposite Effects of mGluR1a and mGluR5 Activation on Nucleus Accumbens Medium Spiny Neuron Dendritic Spine Density.

The group I metabotropic glutamate receptors (mGluR1a and mGluR5) are important modulators of neuronal structure and function. Although these receptors share common signaling pathways, they are capable of having distinct effects on cellular plasticity. We investigated the individual effects of mGluR1a or mGluR5 activation on dendritic spine density in medium spiny neurons in the nucleus accumbens (NAc), which has become relevant with the potential use of group I mGluR based therapeutics in the treatment of drug addiction. We found that systemic administration of mGluR subtype-specific positive allosteric modulators had opposite effects on dendritic spine densities. Specifically, mGluR5 positive modulation decreased dendritic spine densities in the NAc shell and core, but was without effect in the dorsal striatum, whereas increased spine densities in the NAc were observed with mGluR1a positive modulation. Additionally, direct activation of mGluR5 via CHPG administration into the NAc also decreased the density of dendritic spines. These data provide insight on the ability of group I mGluRs to induce structural plasticity in the NAc and demonstrate that the group I mGluRs are capable of producing not just distinct, but opposing, effects on dendritic spine density.

Unbiased Stereological Analysis of Reactive Astrogliosis to Estimate Age-Associated Cerebral White Matter Injury.

Cerebral white matter injury (WMI) contributes to cognitive dysfunction associated with pathological aging. Because reactive astrocyte-related factors contribute to remyelination failure after WMI, we sought accurate, cost-effective, and reproducible histopathological approaches for quantification of morphometric features of reactive astrogliosis in aged human white matter in patients with vascular brain injury (VBI). We compared 7 distinct approaches to quantify the features of glial fibrillary acidic protein (GFAP)-labeled astrocytes in the prefrontal white matter of brains from patients with VBI (n = 17, mean age 88.8 years) and controls that did not exhibit VBI (n = 11, mean age 86.6 years). Only modern stereological techniques (ie, optical fractionator and spaceballs) and virtual process thickness measurements demonstrated significant changes in astrocyte number, process length, or proximal process thickness in cases with VBI relative to controls. The widely employed methods of neuropathological scoring, antibody capture assay (histelide), area fraction fractionator, and Cavalieri point counting failed to detect significant differences in GFAP expression between the groups. Unbiased stereological approaches and virtual thickness measurements provided the only sensitive and accurate means to quantify astrocyte reactivity as a surrogate marker of WMI in human brains with VBI.