Hau-Jie Yau

Rescuing cocaine-induced prefrontal cortex hypoactivity prevents compulsive cocaine seeking

Loss of control over harmful drug seeking is one of the most intractable aspects of addiction, as human substance abusers continue to pursue drugs despite incurring significant negative consequences. Human studies have suggested that deficits in prefrontal cortical function and consequential loss of inhibitory control could be crucial in promoting compulsive drug use. However, it remains unknown whether chronic drug use compromises cortical activity and, equally important, whether this deficit promotes compulsive cocaine seeking. Here we use a rat model of compulsive drug seeking in which cocaine seeking persists in a subgroup of rats despite delivery of noxious foot shocks. We show that prolonged cocaine self-administration decreases ex vivo intrinsic excitability of deep-layer pyramidal neurons in the prelimbic cortex, which was significantly more pronounced in compulsive drug-seeking animals. Furthermore, compensating for hypoactive prelimbic cortex neurons with in vivo optogenetic prelimbic cortex stimulation significantly prevented compulsive cocaine seeking, whereas optogenetic prelimbic cortex inhibition significantly increased compulsive cocaine seeking. Our results show a marked reduction in prelimbic cortex excitability in compulsive cocaine-seeking rats, and that in vivo optogenetic prelimbic cortex stimulation decreased compulsive drug-seeking behaviours. Thus, targeted stimulation of the prefrontal cortex could serve as a promising therapy for treating compulsive drug use.

Scapuloperoneal spinal muscular atrophy and CMT2C are allelic disorders caused by alterations in TRPV4

Scapuloperoneal spinal muscular atrophy (SPSMA) and hereditary motor and sensory neuropathy type IIC (HMSN IIC, also known as HMSN2C or Charcot-Marie-Tooth disease type 2C (CMT2C)) are phenotypically heterogeneous disorders involving topographically distinct nerves and muscles. We originally described a large New England family of French-Canadian origin with SPSMA and an American family of English and Scottish descent with CMT2C. We mapped SPSMA and CMT2C risk loci to 12q24.1–q24.31 with an overlapping region between the two diseases. Further analysis reduced the CMT2C risk locus to a 4-Mb region. Here we report that SPSMA and CMT2C are allelic disorders caused by mutations in the gene encoding the transient receptor potential cation channel, subfamily V, member 4 (TRPV4). Functional analysis revealed that increased calcium channel activity is a distinct property of both SPSMA- and CMT2C-causing mutant proteins. Our findings link mutations in TRPV4 to altered calcium homeostasis and peripheral neuropathies, implying a pathogenic mechanism and possible options for therapy for these disorders.

Chronic neuropathic pain-like behavior correlates with IL-1β expression and disrupts cytokine interactions in the hippocampus.

Summary IL‐1β expression in the contralateral hippocampus coincides with neuropathic pain behavior in rats, and the correlations between hippocampal IL‐1β and IL‐1ra or IL‐6 are lost. ABSTRACT We have proposed that neuropathic pain engages emotional learning, suggesting the involvement of the hippocampus. Because cytokines in the periphery contribute to induction and maintenance of neuropathic pain but might also participate centrally, we used 2 neuropathic pain models, chronic constriction injury (CCI) and spared nerve injury (SNI), to investigate the temporal profile of hippocampal cytokine gene expression in 2 rat strains that show different postinjury behavioral threshold sensitivities. SNI induced long‐lasting allodynia in both strains, while CCI induced allodynia with time‐dependent recovery in Sprague Dawley (SD) and no allodynia in Wistar Kyoto (WK) rats. In WK rats, only SNI induced sustained upregulation of hippocampal interleukin (IL)‐1β, while IL‐6 expression was transiently increased and no significant changes in IL‐1ra expression were detected. Conversely, in SD rats, SNI resulted in sustained and robust increased hippocampal IL‐1β expression, which was only transient in rats with CCI. In this strain, IL‐6 expression was not affected in any of the 2 injury models and IL‐1ra expression was significantly increased in rats with SNI or CCI at late phases. We found that the degree and development of neuropathic pain depend on the specific nerve injury model and rat strain; that hippocampal IL‐1β mRNA levels correlate with neuropathic pain behavior; that, in contrast to sham‐operated animals, there are no correlations between hippocampal IL‐1β and IL‐1ra or IL‐6 in neuropathic rats; and that alterations in cytokine expression are restricted to the hippocampus contralateral to the injury side, again implying that the observed changes reflect nociception.

Methamphetamine downregulates striatal glutamate receptors via diverse epigenetic mechanisms.

BACKGROUND Chronic methamphetamine (METH) exposure causes neuroadaptations at glutamatergic synapses. METHODS To identify the METH-induced epigenetic underpinnings of these neuroadaptations, we injected increasing METH doses to rats for 2 weeks and measured striatal glutamate receptor expression. We then quantified the effects of METH exposure on histone acetylation. We also measured METH-induced changes in DNA methylation and DNA hydroxymethylation. RESULTS Chronic METH decreased transcript and protein expression of GluA1 and GluA2 alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) and GluN1 N-methyl-D-aspartate receptor subunits. These changes were associated with altered electrophysiological glutamatergic responses in striatal neurons. Chromatin immunoprecipitation-polymerase chain reaction revealed that METH decreased enrichment of acetylated histone H4 on GluA1, GluA2, and GluN1 promoters. Methamphetamine exposure also increased repressor element-1 silencing transcription factor (REST) corepressor 1, methylated CpG binding protein 2, and histone deacetylase 2 enrichment, but not of sirtuin 1 or sirtuin 2, onto GluA1 and GluA2 gene sequences. Moreover, METH caused interactions of REST corepressor 1 and methylated CpG binding protein 2 with histone deacetylase 2 and of REST with histone deacetylase 1. Surprisingly, methylated DNA immunoprecipitation and hydroxymethylated DNA immunoprecipitation-polymerase chain reaction revealed METH-induced decreased enrichment of 5-methylcytosine and 5-hydroxymethylcytosine at GluA1 and GluA2 promoter sequences. Importantly, the histone deacetylase inhibitor, valproic acid, blocked METH-induced decreased expression of AMPAR and N-methyl-D-aspartate receptor subunits. Finally, valproic acid also attenuated METH-induced decrease H4K16Ac recruitment on AMPAR gene sequences. CONCLUSIONS These observations suggest that histone H4 hypoacetylation may be the main determinant of METH-induced decreased striatal glutamate receptor expression.

Brief optogenetic inhibition of dopamine neurons mimics endogenous negative reward prediction errors

Correlative studies have strongly linked phasic changes in dopamine activity with reward prediction error signaling. But causal evidence that these brief changes in firing actually serve as error signals to drive associative learning is more tenuous. Although there is direct evidence that brief increases can substitute for positive prediction errors, there is no comparable evidence that similarly brief pauses can substitute for negative prediction errors. In the absence of such evidence, the effect of increases in firing could reflect novelty or salience, variables also correlated with dopamine activity. Here we provide evidence in support of the proposed linkage, showing in a modified Pavlovian over-expectation task that brief pauses in the firing of dopamine neurons in rat ventral tegmental area at the time of reward are sufficient to mimic the effects of endogenous negative prediction errors. These results support the proposal that brief changes in the firing of dopamine neurons serve as full-fledged bidirectional prediction error signals.

Optogenetic Inhibition of Dorsal Medial Prefrontal Cortex Attenuates Stress-Induced Reinstatement of Palatable Food Seeking in Female Rats

Relapse to maladaptive eating habits during dieting is often provoked by stress. Recently, we identified a role of dorsal medial prefrontal cortex (mPFC) neurons in stress-induced reinstatement of palatable food seeking in male rats. It is unknown whether endogenous neural activity in dorsal mPFC drives stress-induced reinstatement in female rats. Here, we used an optogenetic approach, in which female rats received bilateral dorsal mPFC microinjections of viral constructs coding light-sensitive eNpHR3.0–eYFP or control eYFP protein and intracranial fiber optic implants. Rats were food restricted and trained to lever press for palatable food pellets. Subsequently, pellets were removed, and lever pressing was extinguished; then the effect of bilateral dorsal mPFC light delivery on reinstatement of food seeking was assessed after injections of the pharmacological stressor yohimbine (an α-2 andrenoceptor antagonist) or pellet priming, a manipulation known to provoke food seeking in hungry rats. Dorsal mPFC light delivery attenuated yohimbine-induced reinstatement of food seeking in eNpHR3.0-injected but not eYFP-injected rats. This optical manipulation had no effect on pellet-priming-induced reinstatement or ongoing food-reinforced responding. Dorsal mPFC light delivery attenuated yohimbine-induced Fos immunoreactivity and disrupted neural activity during in vivo electrophysiological recording in awake rats. Optical stimulation caused significant outward currents and blocked electrically evoked action potentials in eNpHR3.0-injected but not eYFP-injected mPFC hemispheres. Light delivery alone caused no significant inflammatory response in mPFC. These findings indicate that intracranial light delivery in eNpHR3.0 rats disrupts endogenous dorsal mPFC neural activity that plays a role in stress-induced relapse to food seeking in female rats.

Flufenamic acid decreases neuronal excitability through modulation of voltage-gated sodium channel gating

The electrophysiological phenotype of individual neurons critically depends on the biophysical properties of the voltage‐gated channels they express. Differences in sodium channel gating are instrumental in determining the different firing phenotypes of pyramidal cells and interneurons; moreover, sodium channel modulation represents an important mechanism of action for many widely used CNS drugs. Flufenamic acid (FFA) is a non‐steroidal anti‐inflammatory drug that has been long used as a blocker of calcium‐dependent cationic conductances. Here we show that FFA inhibits voltage‐gated sodium currents in hippocampal pyramidal neurons; this effect is dose‐dependent with IC50= 189 μm. We used whole‐cell and nucleated patch recordings to investigate the mechanisms of FFA modulation of TTX‐sensitive voltage‐gated sodium current. Our data show that flufenamic acid slows down the inactivation process of the sodium current, while shifting the inactivation curve ∼10 mV toward more hyperpolarized potentials. The recovery from inactivation is also affected in a voltage‐dependent way, resulting in slower recovery at hyperpolarized potentials. Recordings from acute slices demonstrate that FFA reduces repetitive‐ and abolishes burst‐firing in CA1 pyramidal neurons. A computational model based on our data was employed to better understand the mechanisms of FFA action. Simulation data support the idea that FFA acts via a novel mechanism by reducing the voltage dependence of the sodium channel fast inactivation rates. These effects of FFA suggest that it may be an effective anti‐epileptic drug.

Neural Estimates of Imagined Outcomes in the Orbitofrontal Cortex Drive Behavior and Learning

Imagination, defined as the ability to interpret reality in ways that diverge from past experience, is fundamental to adaptive behavior. This can be seen at a simple level in our capacity to predict novel outcomes in new situations. The ability to anticipate outcomes never before received can also influence learning if those imagined outcomes are not received. The orbitofrontal cortex is a key candidate for where the process of imagining likely outcomes occurs; however, its precise role in generating these estimates and applying them to learning remain open questions. Here we address these questions by showing that single-unit activity in the orbitofrontal cortex reflects novel outcome estimates. The strength of these neural correlates predicted both behavior and learning, learning that was abolished by temporally specific inhibition of orbitofrontal neurons. These results are consistent with the proposal that the orbitofrontal cortex is critical for integrating information to imagine future outcomes.

Severe neurological phenotypes of Q129 DRPLA transgenic mice serendipitously created by en masse expansion of CAG repeats in Q76 DRPLA mice

We herein provide a thorough description of new transgenic mouse models for dentatorubral–pallidoluysian atrophy (DRPLA) harboring a single copy of the full-length human mutant DRPLA gene with 76 and 129 CAG repeats. The Q129 mouse line was unexpectedly obtained by en masse expansion based on the somatic instability of 76 CAG repeats in vivo. The mRNA expression levels of both Q76 and Q129 transgenes were each 80% of that of the endogenous mouse gene, whereas only the Q129 mice exhibited devastating progressive neurological phenotypes similar to those of juvenile-onset DRPLA patients. Electrophysiological studies of the Q129 mice demonstrated age-dependent and region-specific presynaptic dysfunction in the globus pallidus and cerebellum. Progressive shrinkage of distal dendrites of Purkinje cells and decreased currents through α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and γ-aminobutyrate type A receptors in CA1 neurons were also observed. Neuropathological studies of the Q129 mice revealed progressive brain atrophy, but no obvious neuronal loss, associated with massive neuronal intranuclear accumulation (NIA) of mutant proteins with expanded polyglutamine stretches starting on postnatal day 4, whereas NIA in the Q76 mice appeared later with regional specificity to the vulnerable regions of DRPLA. Expression profile analyses demonstrated age-dependent down-regulation of genes, including those relevant to synaptic functions and CREB-dependent genes. These results suggest that neuronal dysfunction without neuronal death is the essential pathophysiologic process and that the age-dependent NIA is associated with nuclear dysfunction including transcriptional dysregulations. Thus, our Q129 mice should be highly valuable for investigating the mechanisms of disease pathogenesis and therapeutic interventions.

Mesopontine median raphe regulates hippocampal ripple oscillation and memory consolidation

Sharp wave–associated field oscillations (∼200 Hz) of the hippocampus, referred to as ripples, are believed to be important for consolidation of explicit memory. Little is known about how ripples are regulated by other brain regions. We found that the median raphe region (MnR) is important for regulating hippocampal ripple activity and memory consolidation. We performed in vivo simultaneous recording in the MnR and hippocampus of mice and found that, when a group of MnR neurons was active, ripples were absent. Consistently, optogenetic stimulation of MnR neurons suppressed ripple activity and inhibition of these neurons increased ripple activity. Notably, using a fear conditioning procedure, we found that photostimulation of MnR neurons interfered with memory consolidation. Our results demonstrate a critical role of the MnR in regulating ripples and memory consolidation.