Regulation of calbindin-D28K gene expression in response to acute and chronic morphine administration

Addiction and the cerebellum with a focus on actions of opioid receptors

Increasing evidence suggests that the cerebellum could play a role in the higher cognitive processes involved in addiction as the cerebellum contains anatomical and functional pathways to circuitry controlling motivation and saliency. In addition, the cerebellum exhibits a widespread presence of receptors, including opioid receptors which are known to play a prominent role in synaptic and circuit mechanisms of plasticity associated with drug use and development of addiction to opioids and other drugs of abuse. Further, the presence of perineural nets (PNNs) in the cerebellum which contain proteins known to alter synaptic plasticity could contribute to addiction. The role the cerebellum plays in processes of addiction is likely complex, and could depend on the particular drug of abuse, the pattern of use, and the stage of the user within the addiction cycle. In this review, we discuss functional and structural modifications shown to be produced in the cerebellum by opioids that exhibit dependency-inducing properties which provide support for the conclusion that the cerebellum plays a role in addiction.

Assessment of individual differences in the rat nucleus accumbens transcriptome following taste-heroin extended access

Heroin addiction is a disease of chronic relapse that harms the individual through devaluation of personal responsibilities in favor of finding and using drugs. Only some recreational heroin users devolve into addiction but the basis of these individual differences is not known. We have shown in rats that avoidance of a heroin-paired taste cue reliably identifies individual animals with greater addiction-like behavior for heroin. Here rats received 5min access to a 0.15% saccharin solution followed by the opportunity to self-administer either saline or heroin for 6h. Large Suppressors of the heroin-paired taste cue displayed increased drug escalation, motivation for drug, and drug loading behavior compared with Small Suppressors. Little is known about the molecular mechanisms of these individual differences in addiction-like behavior. We examined the individual differences in mRNA expression in the nucleus accumbens (NAc) of rats that were behaviorally stratified by addiction-like behavior using next-generation sequencing. We hypothesized that based on the avoidance of the drug-paired cue there will be a unique mRNA profile in the NAc. Analysis of strand-specific whole genome RNA-Seq data revealed a number of genes differentially regulated in NAc based on the suppression of the natural saccharine reward. Large Suppressors exhibited a unique mRNA prolife compared to Saline controls and Small Suppressors. Genes related to immunity, neuronal activity, and behavior were differentially expressed among the 3 groups. In total, individual differences in avoidance of a heroin-paired taste cue are associated with addiction-like behavior along with differential NAc gene expression.

Detection of Purkinje cell loss following drug exposures to developing rat pups using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for calbindin-D28k mRNA expression

A technique is described that allows for the identification and quantification of Purkinje cell loss in cerebellum subsequent to developmental toxic exposures. This technique relies upon the extensively validated findings that the Purkinje cell is the only site of expression in the cerebellum of the calcium binding protein calbindin-D28k. Thus, analysis of mRNA expression specific to this protein by comparison to matched controls provides a reliable means of determining whether cell loss has occurred. Purkinje cell loss was induced in rat pups by ethanol exposure on postnatal day (PN) 4 or valproic acid administration to pregnant dams on gestational day 13. Analysis was conducted on PN5 or PN10 and the results compared to parallel groups of pups where the Purkinje cells were counted by traditional means. When compared to matched control rat pups the decrease in calbindin-D28k mRNA expression indicates Purkinje cell loss regardless of whether the cell loss was induced by prenatal valproic acid or postnatal ethanol exposure. The availability of a biochemical alternative to histological cell counting allows for more detailed analyses of the mechanisms of Purkinje cell death induced by these two toxicants, including analyses of the early alterations in signal transduction proteins.

Cytoskeletal genes regulation by chronic morphine treatment in rat striatum

It has been previously suggested that morphine can regulate the expression and function of some proteins of the cytoskeleton. In the present study, we used real-time quantitative polymerase chain reaction to examine the effects of chronic morphine administration, in rat striatum, on 14 proteins involved in microtubule polymerization and stabilization, intracellular trafficking, and serving as markers of neuronal growth and degeneration. Chronic morphine treatment led to modulation of the mRNA level of seven of the 14 genes tested. Glial fibrillary acidic protein (Gfap) and activity-regulated cytoskeleton-associated protein (Arc) mRNA were upregulated, while growth associated protein (Gap43), clathrin heavy chain (Cltc), alpha-tubulin, Tau, and stathmin were downregulated. In order to determine if the regulation of an mRNA correlates with a modulation of the expression of the corresponding protein, immunoblot analyses were performed. With the exception of Gap43, the levels of Cltc, Gfap, Tau, stathmin, and alpha-tubulin proteins were found to be in good agreement with those from mRNA quantification. These results demonstrate that neuroadaptation to chronic morphine administration in rat striatum implies modifications of the expression pattern of several genes and proteins of the cytoskeleton and cytoskeleton-associated components.

Microarray analysis of genes expressed in the frontal cortex of rats chronically treated with morphine and after naloxone precipitated withdrawal

Opioid dependence may be associated with adaptive changes in gene expression in the brain. In the present study we used DNA microarrays (U34A; Affymetrix) to analyze the expression of about 8000 genes in the frontal cortex of rats chronically treated with morphine and in rats after naloxone precipitated withdrawal. Chronic treatment for 10 days with ascending doses of morphine (10-50 mg/kg twice daily) resulted in a more than twofold induction of 14 genes after the last injection of morphine. The majority of these genes code for heat shock proteins (hsp70, hsp 27, hsp 40, hsp105, GRP78, etc.). The expression of the heat shock genes in the morphine-treated animals was reversed by naloxone (10 mg/kg). The opioid antagonist, in turn, precipitated withdrawal and increased the expression of a set of genes which are predominantly transcription factors (krox20, CREM, NGFI-B, IkappaB, etc). Only a few genes remained increased after naloxone application. Such persistently changed genes code for arc, a cytoskeleton-associated protein which is induced by synaptic activity, ania-3, a splice variant of the Homer 1 protein which is critically involved in activity-dependent alterations of synaptic function and rPer2, a protein regulating circadian rhythms. For selected genes the changes in gene expression were confirmed by real time PCR and by in situ hybridization. These findings indicate that the persistent changes in long-lasting plasticity during opiate dependence do not primarily depend on the increased expression levels of genes encoding for neurotransmitter, receptor and/or ion channel proteins, but rather on altered pattern of synaptic connectivity.

Gene expression following acute morphine administration

The long-term response to neurotropic drugs depends on drug-induced neuroplasticity and underlying changes in gene expression. However, alterations in neuronal gene expression can be observed even following single injection. To investigate the extent of these changes, gene expression in the medial striatum and lumbar part of the spinal cord was monitored by cDNA microarray following single injection of morphine. Using robust and resistant linear regression (MM-estimator) with simultaneous prediction confidence intervals, we detected differentially expressed genes. By combining the results with cluster analysis, we have found that a single morphine injection alters expression of two major groups of genes, for proteins involved in mitochondrial respiration and for cytoskeleton-related proteins. RNAs for these proteins were mostly downregulated both in the medial striatum and in lumbar part of the spinal cord. These transitory changes were prevented by coadministration of the opioid antagonist naloxone. Data indicate that microarray analysis by itself is useful in describing the effect of well-known substances on the nervous system and provides sufficient information to propose a potentially novel pathway mediating its activity.

Molecular cloning of a novel protein regulated by opioid treatment of NG108-15 cells

A new cDNA clone, NGD5, has been identified from a subtraction cDNA library constructed with mRNA isolated from control neuroblastoma x glioma NG108-15 cells and cells treated for 48 h with the delta-opioid agonist, D-Ala2, D-Leu5 enkephalin (DADLE). NGD5 mRNA is decreased, in a naloxone-reversible manner, upon long-term treatment of NG108-15 cells with DADLE, indicating that this clone may be related to opioid receptor function. Northern analysis indicates that NGD5 mRNA is expressed in rat brain. Two similar nearly full-length NGD5 clones, NGD5A and NGD5B, were isolated from a lambda gt10 NG108-15 cDNA library and sequenced. The predicted 40-kDa peptide encoded for by the NGD5 cDNA has no significant homology to the recently cloned mu, delta or kappa opioid receptors nor to any other known proteins.

Endogenous opiates: 1994

This article is the 17th installment of our annual review of research concerning the opiate system. It includes papers published during 1994 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics covered this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.