Cholinergic Receptor Blockade in the VTA Attenuates Cue-Induced Cocaine-Seeking and Reverses the Anxiogenic Effects of Forced Abstinence

Drug relapse after periods of abstinence is a common feature of substance abuse. Moreover, anxiety and other mood disorders are often co-morbid with substance abuse. Cholinergic receptors in the ventral tegmental area (VTA) are known to mediate drug-seeking and anxiety-related behavior in rodent models. However, it is unclear if overlapping VTA cholinergic mechanisms mediate drug relapse and anxiety-related behaviors associated with drug abstinence. We examined the effects of VTA cholinergic receptor blockade on cue-induced cocaine seeking and anxiety during cocaine abstinence. Male Sprague-Dawley rats were trained to self-administer intravenous cocaine (~0.5 mg/kg/infusion, FR1 schedule) for 10 days, followed by 14 days of forced abstinence. VTA infusion of the non-selective nicotinic acetylcholine receptor antagonist mecamylamine (0, 10, and 30 μg/side) or the non-selective muscarinic receptor antagonist scopolamine (0, 2.4 and 24 μg /side) significantly decreased cue-induced cocaine seeking. In cocaine naïve rats, VTA mecamylamine or scopolamine also led to dose-dependent increases in open arm time in the elevated plus maze (EPM). In contrast, rats that received I.V. cocaine, compared to received I.V. saline rats, displayed an anxiogenic response on day 14 of abstinence as reflected by decreased open arm time in the EPM. Furthermore, low doses of VTA mecamylamine (10 μg /side) or scopolamine (2.4 μg /side), that did not alter EPM behavior in cocaine naive rats, were sufficient to reverse the anxiogenic effects of cocaine abstinence. Together, these data point to an overlapping role of VTA cholinergic mechanisms to regulate relapse and mood disorder-related responses during cocaine abstinence.

Activation of Membrane Estrogen Receptors Attenuates NOP-Mediated Tactile Antihypersensitivity in a Rodent Model of Neuropathic Pain

Women manifest a higher prevalence of several chronic pain disorders compared to men. We demonstrated earlier that estrogen rapidly attenuates nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP)-mediated thermal antinociception through the activation of membrane estrogen receptors (mERs). However, the effect of mER activation on NOP-mediated attenuation of tactile hypersensitivity in a neuropathic model of pain and the underlying mechanisms remain unknown. Following spared nerve injury (SNI), male and ovariectomized (OVX) female rats were intrathecally (i.t.) injected with a selective mER agonist and nociceptin/orphanin FQ (N/OFQ), the endogenous ligand for NOP, and their effects on paw withdrawal thresholds (PWTs) were tested. In addition, spinal cord tissue was used to measure changes in phosphorylated extracellular signal regulated kinase (ERK), protein kinase A (PKA), protein kinase C (PKC), and protein kinase B (Akt) levels. SNI significantly reduced PWTs in males and OVX females, indicating tactile hypersensitivity. N/OFQ restored PWTs, indicating an antihypersensitive effect. Selective mER activation attenuated the effect of N/OFQ in an antagonist-reversible manner. SNI led to a robust increase in the phosphorylation of ERK, PKA, PKC, and Akt. However, mER activation did not further affect it. Thus, we conclude that activation of mERs rapidly abolishes NOP-mediated tactile antihypersensitivity following SNI via an ERK-, PKA-, PKC-, and Akt-independent mechanism.

The L-type calcium channel blocker, isradipine, attenuates cue-induced cocaine-seeking by enhancing dopaminergic activity in the ventral tegmental area to nucleus accumbens pathway

Previous preclinical and clinical investigations have focused on the L-type calcium channel (LTCC) as a potential therapeutic target for substance abuse. While some clinical studies have examined the ability of LTCC blockers to alter cocaine's subjective effects, very few LTCC studies have examined cocaine relapse. Here, we examined whether ventral tegmental area (VTA)-specific or systemic administration of the LTCC inhibitor, isradipine, altered cocaine-seeking behavior in a rat model. Male Sprague-Dawley rats first received 10 days of cocaine self-administration training (2 h sessions), where active lever depression resulted in delivery of a ∼0.5 mg/kg cocaine infusion paired with a tone + light cue. Rats then underwent 10 days of forced abstinence, without access to cocaine or cocaine cues. Rats were then returned to the opertant chamber for the cue-induced cocaine-seeking test, where active lever depression in the original training context resulted in tone + light cue presentation. We found VTA specific or systemic isradipine administration robustly attenuated cocaine-seeking, without altering cocaine-taking nor natural reward seeking. Dopamine (DA) signaling in the nucleus accumbens (NAc) core is necessary and sufficient for cue-induced drug-seeking. Surprisingly in our study, isradipine enhanced tonic and phasic DA signaling in cocaine abstinent rats, with no change in sucrose abstinent nor naïve rats. Strikingly, isradipine's behavioral effects were dependent upon NAc core DA receptor activation. Together, our findings reveal a novel mechanism by which the FDA-approved drug, isradipine, could act to decrease cocaine relapse.

Ventral tegmental area muscarinic receptors modulate depression and anxiety-related behaviors in rats

Cholinergic and dopaminergic mechanisms within the mesolimbic dopamine system are suggested to play a role in the manifestation of depression and anxiety-related disorders. However, despite the fact that cholinergic mechanisms in the ventral tegmental area (VTA) highly regulate dopamine activity, the role of VTA cholinergic mechanisms in depression-related behaviors is relatively unknown. Here we sought to determine whether enhancing cholinergic tone in the VTA would alter depression and anxiety-related behavior in the forced swim test (FST), elevated plus maze (EPM) and sucrose preference test (SPT). Adult Sprague Dawley male rats received VTA infusion of the acetylcholinesterase inhibitor, physostigmine (0, 1, 2μg/side), immediately prior to the FST, EPM, or SPT. Physostigmine administration increased immobility time in the FST, decreased time spent on open arms in the EPM, and decreased sucrose preference. We also examined whether activation of VTA muscarinic receptors was sufficient to alter behavior in the FST and EPM. Similar to physostigmine, VTA infusion of the muscarinic receptor agonist, pilocarpine (0, 3, 30μg/side), increased immobility time in the FST and decreased time spent on open arms in the EPM. These data suggest that enhanced VTA cholinergic tone promotes pro-depressive and anxiogenic-like effects and demonstrate that specific activation of VTA muscarinic receptors is also sufficient to induce pro-depressive and anxiogenic responses. Together, these findings reveal a novel role of VTA cholinergic, and specifically muscarinic receptor, mechanisms in mediating responses to stress and anxiety.

Activation of membrane estrogen receptors attenuates opioid receptor-like1 receptor-mediated antinociception via an ERK-dependent non-genomic mechanism

To our knowledge, the present data are the first to demonstrate that activation of membrane estrogen receptors (mERs) abolishes opioid receptor-like 1 (ORL1) receptor-mediated analgesia via extracellular signal-regulated kinase (ERK)-dependent non-genomic mechanisms. Estrogen was shown previously to both attenuate ORL1-mediated antinociception and down-regulate the ORL1 gene expression. The present study investigated whether non-genomic mechanisms contribute to estrogen-induced attenuation of ORL1-mediated antinociception by the mERs GPR30, Gq-coupled mER, ERα, and ERβ. E2BSA [β-estradiol-6-(O-carboxymethyl)oxime: bovine serum albumin] (0.5mM), a membrane impermeant analog of estradiol, injected intrathecally immediately prior to orphanin FQ (OFQ;10 nmol), the endogenous ligand for the ORL1 receptor, abolished OFQ's antinociceptive effect in both male and ovariectomized (OVX) female rats, assessed using the heat-induced tail-flick assay. This effect was not altered by protein synthesis inhibitor, anisomycin (125 μg), given intrathecally 15 min prior to E2BSA and OFQ. Intrathecal application of selective receptor agonists permitted the relative contributions of various estrogen receptors in mediating this blockade of the antinociceptive response of OFQ. Activation of GPR30, Gq-mER, ERα, but not ERβ abolished ORL1-mediated antinociception in males and OVX females. E2BSA produced a parallel and significant increase in the phosphorylation of ERK 2 only in OVX females, and pre-treatment with MEK/ERK 1/2 inhibitor, U0126 (10 μg), blocked the mER-mediated abolition of ORL1-mediated antinociception in OVX females. Taken together, the data are consistent with the interpretations that mER activation attenuates ORL1-mediated antinociception through a non-genomic, ERK 2-dependent mechanism in females.

Identification and functional characterization of alpha(2)-adrenoceptor polymorphisms

For each alpha(2)-adrenoceptor subtype (alpha(2A), alpha(2B) and alpha(2C)), sequence variations within the coding region of each gene have been identified in humans. These result in substitutions or deletions of amino acids in the third intracellular loops of each receptor. This article summarizes the genetics and molecular biology of alpha(2)-adrenoceptor polymorphisms, including the consequences of each polymorphism on receptor signaling, as determined in transfected cells. These effects include alterations in G-protein coupling, desensitization and G-protein receptor kinase-mediated phosphorylation. Studies so far provide the mechanistic basis for future studies to investigate genetic risk factors and pharmacogenetics in pathophysiological conditions linked to alpha(2)-adrenoceptor function.

Modification of the beta 2-adrenergic receptor to engineer a receptor-effector complex for gene therapy

Depressed G-protein-coupled receptor (GPCR) signaling has been implicated as a component of the pathophysiology of a number of complex diseases including heart failure and asthma, and augmentation or restoration of signaling by various means has been shown to improve organ function. Because some properties of native GPCRs are disadvantageous for ectopic therapeutic expression, we utilized the beta(2)-adrenergic receptor (beta(2)AR) as a scaffold to construct a highly modified therapeutic receptor-effector complex (TREC) suitable for gene therapy. Altogether, 19 modifications were made to the receptor. The ligand-binding site was re-engineered in TM-3 so that a beta-hydroxylmethyl side chain acts as a proton donor for the binding of a novel ligand. In addition, sites critical for agonist-promoted down-regulation in the amino terminus and for phosphorylation by GPCR kinases, and protein kinases A and C, in the third intracellular loop and the carboxyl terminus of the receptor were altered. These modifications of the receptor resulted in depressed agonist-stimulated adenylyl cyclase activity (26.8 +/- 2.1 versus 41.4 +/- 8 pmol/min/mg for wild-type beta(2)AR). This was fully restored by fusing the carboxyl terminus of the modified receptor to G alpha(s) (43.3 +/- 2.7 pmol/min/mg). The fully modified fused receptor was not activated by beta-agonists but rather by a nonbiogenic amine agonist that itself failed to activate the wild-type beta(2)AR. This two-way selectivity thus provides targeted activation based on physiologic status. Furthermore, the TREC did not display tachyphylaxis to prolonged agonist exposure (desensitization was 1 +/- 5% versus 55 +/- 4% for wild-type beta(2)AR). Thus, despite extensive alterations in regions of conformational lability, the beta(2)AR can be tailored to have optimal signaling characteristics for gene therapy. As a general paradigm, TRECs for enhancement of other G-protein signaling appear to be feasible for modification of other pathologic states.

Polymorphic deletion of three intracellular acidic residues of the alpha 2B-adrenergic receptor decreases G protein-coupled receptor kinase-mediated phosphorylation and desensitization

A polymorphic variant of the human alpha(2B)-adrenergic receptor (alpha(2B)AR), which consists of a deletion of three glutamic acids (residues 301-303) in the third intracellular loop was found to be common in Caucasians (31%) and to a lesser extent in African-Americans (12%). The consequences of this deletion were assessed by expressing wild-type and the Del301-303 receptors in Chinese hamster ovary and COS cells. Ligand binding was not affected, although a small decrease in coupling efficiency to the inhibition of adenylyl cyclase was observed with the mutant. The deletion occurs within a stretch of acidic residues that is thought to establish the milieu for agonist-promoted phosphorylation and desensitization of the receptor by G protein-coupled receptor kinases (GRKs). Agonist-promoted phosphorylation studies carried out in cells coexpressing the alpha(2B)ARs and GRK2 revealed that the Del301-303 receptor displayed approximately 56% of wild-type phosphorylation. Furthermore, the depressed phosphorylation imposed by the deletion was found to result in a complete loss of short term agonist-promoted receptor desensitization. Thus the major phenotype of the Del301-303 alpha(2B)AR is one of impaired phosphorylation and desensitization by GRKs, and thus the polymorphisms renders the receptor incapable of modulation by this key mechanism of dynamic regulation.

An asn to lys polymorphism in the third intracellular loop of the human alpha 2A-adrenergic receptor imparts enhanced agonist-promoted Gi coupling

alpha(2A)-Adrenergic receptors (alpha(2A)AR) are presynaptic autoinhibitory receptors of noradrenergic neurons in the central and peripheral sympathetic nervous systems, which act to dynamically regulate neurotransmitter release. Signaling through the G(i)/G(o) family of G-proteins, the receptor subserves numerous homeostatic and central nervous system functions. A single nucleotide polymorphism of this receptor, which results in an Asn to Lys substitution at amino acid 251 of the third intracellular loop, was identified in the human population. The frequency of Lys-251 was 10-fold greater in African-Americans than in Caucasians, but was not associated with essential hypertension. To determine the consequences of this substitution, wild-type and Lys-251 receptors were expressed in CHO and COS-7 cells. Expression, ligand binding, and basal receptor function were unaffected by the substitution. However, agonist-promoted [(35)S]GTPgammaS binding was approximately 40% greater with the Lys-251 receptor. This enhanced agonist function was observed with catecholamines, azepines, and imidazolines albeit to different degrees. In studies of agonist-promoted functional coupling to G(i), the polymorphic receptor displayed enhanced inhibition of adenylyl cyclase (60 +/- 4. 4 versus 46 +/- 4.1% inhibition) and markedly enhanced stimulation of MAP kinase (57 +/- 9 versus 15- +/- 2-fold increase over basal) compared with wild-type alpha(2A)AR. The potency of epinephrine in stimulating inositol phosphate accumulation was increased approximately 4 fold with the Lys-251 receptor. Unlike previously described variants of G-protein-coupled receptors, where the minor species causes either a loss of function or increased non-agonist function, Lys-251 alpha(2A)AR represents a new class of polymorphism whose phenotype is a gain of agonist-promoted function.

alpha 2A/alpha 2C-adrenergic receptor third loop chimera show that agonist interaction with receptor subtype backbone establishes G protein-coupled receptor kinase phosphorylation

The alpha(2A)-adrenergic receptor (AR) undergoes rapid agonist-promoted desensitization due to phosphorylation by G protein-coupled receptor kinases (GRKs) 2 and 3 at serines in the third intracellular loop of the receptor. In contrast, the alpha(2C)AR fails to display such desensitization or phosphorylation, which has been presumed to be due to this receptor lacking GRK phosphorylation sites. However, the alpha(2C)AR has multiple serines and threonines in putative favorable motifs within its third intracellular loop. We considered that the conformation of the third intracellular loop imposed by agonists binding to the transmembrane-spanning domains could be the basis of this subtype-specific property, rather than the presence or absence of phosphoacceptors per se. To address this, alpha(2A)/alpha(2C) third loop chimeric receptors were constructed. In whole cell phosphorylation studies, the alpha(2A) with the alpha(2C) third loop receptor underwent agonist-promoted phosphorylation while the alpha(2C) with the alpha(2A) third loop receptor did not, indicating that the agonist interaction with the parent receptor backbone establishes the phosphorylation phenotype. We postulated then that agonists with diverse structures that distinctly interact with alpha(2)AR should display different degrees of phosphorylation independent of receptor activation. Indeed, several full and partial agonists were identified, which evoked phosphorylation that was not related to intrinsic activity as established by [(35)S]guanosine 5'-3-O-(thio)triphosphate binding. Taken together, it appears that phosphorylation of the alpha(2)AR evoked by agonist is highly sensitive to the conformation of the third intracellular loop induced/stabilized by agonist to such an extent that these properties dictate the extent of phosphorylation of the loop when phosphoacceptors are present, and are the basis for subtype-specific phosphorylation.

A four amino acid deletion polymorphism in the third intracellular loop of the human alpha 2C-adrenergic receptor confers impaired coupling to multiple effectors

The alpha(2)-adrenergic receptors (alpha(2)ARs) play a critical role in modulating neurotransmitter release in the central and peripheral sympathetic nervous systems. A polymorphism of the alpha(2)AR subtype localized to human chromosome 4 (the pharmacologic alpha(2C)AR subtype) within an intracellular domain has been identified in normal individuals. The polymorphism (denoted Del322-325) is because of an in-frame 12-nucleic acid deletion encoding a receptor lacking Gly-Ala-Gly-Pro in the third intracellular loop. To delineate the functional consequences of this structural alteration, Chinese hamster ovary cells were permanently transfected with constructs encoding wild-type human alpha(2C)AR and the polymorphic receptor. The Del322-325 variant had decreased high affinity agonist binding (K(H) = 7.3 +/- 0.95 versus 3.7 +/- 0.43 nm; %R(H) = 31 +/- 4 versus 49 +/- 4) compared with wild-type indicating impaired formation of the agonist-receptor-G protein complex. The polymorphic receptor displayed markedly depressed epinephrine-promoted coupling to G(i), inhibiting adenylyl cyclase by 10 +/- 4.3% compared with 73 +/- 2.4% for wild-type alpha(2C)AR. This also was so for the endogenous ligand norepinephrine and full and partial synthetic agonists. Depressed agonist-promoted coupling to the stimulation of MAP kinase ( approximately 71% impaired) and inositol phosphate production ( approximately 60% impaired) was also found with the polymorphic receptor. The Del322-325 receptor was approximately 10 times more frequent in African-Americans compared with Caucasians (allele frequencies 0.381 versus 0.040). Given this significant loss of function phenotype in several signal transduction cascades and the skewed ethnic prevalence, Del322-325 represents a pharmacoethnogenetic locus and may also be the basis for interindividual variation in cardiovascular or central nervous system pathophysiology.

Fusion of beta 2-adrenergic receptor to G alpha s in mammalian cells: identification of a specific signal transduction species not characteristic of constitutive activation or precoupling

The forward and antegrade interactions that comprise the agonist receptor-G protein complex were studied in Chinese hamster fibroblasts transfected to express the beta(2)-adrenergic receptor (beta(2)AR), the beta(2)AR and the alpha-subunit of its cognate G protein (G(s)), and a protein consisting of the beta(2)AR fused at its carboxy terminus with G(alpha)(s) (beta(2)AR-G(s)). Expression levels were matched at approximately 600 fmol/mg. Basal adenylyl cyclase activities were increased with the fusion receptor membranes compared to coexpressed receptor plus G(alpha)(s), and to wild-type beta(2)AR (20.5 +/- 1.8 vs 9.0 +/- 0.88 vs 8.7 +/- 0.93 pmol min(-)(1) mg(-)(1)), confirming in mammalian cells that the fusion of beta(2)AR and G(alpha)(s) results in a state not attained by expression of unfused components. However, agonist-stimulated activities were not increased proportionally, such that the stimulation over basal of the beta(2)AR-G(s) fusion protein (1. 5-fold) was less than wild-type beta(2)AR (2.1-fold). Agonist competition studies performed in the absence of guanine nucleotide exhibited high-affinity binding sites with a lower K(H) (1.75 vs 8. 47 nM) and greater %R(H) (51% vs 44%) for beta(2)AR-G(s), but GppNHp failed to convert most of these to the low-affinity state. Functional studies with the inverse agonist ICI 118551 did not show enhanced efficacy or potency with the fusion protein. Adenylyl cyclase studies with three partial agonists with diverse structures (dobutamine, ritodrine, and phenylephrine) showed no enhancement of efficacy with beta(2)AR-G(s) and a minor trend toward enhanced potency. Taken together, these results indicate that the tethering of G(alpha)(s) to the beta(2)AR causes a conformational change in the receptor that stabilizes a species "trapped" between the non-guanine nucleotide-bound state and the GTP-bound form. Functionally the receptor is not characterized by a consistent pattern of properties ascribed to other states such as constitutive activation or precoupling, but rather represents a unique state in the transition from high- to low-affinity forms.

Altered forebrain and hindbrain development in mice mutant for the Gsh-2 homeobox gene

The patterning of the mammalian brain is orchestrated by a large battery of regulatory genes. Here we examine the developmental function of the Gsh-2 nonclustered homeobox gene. Whole-mount and serial section in situ hybridizations have been used to better define Gsh-2 expression domains within the developing forebrain, midbrain, and hindbrain. Gsh-2 transcripts are shown to be particularly abundant in the hindbrain and within the developing ganglionic eminences of the forebrain. In addition, mice carrying a targeted mutation of Gsh-2 have been generated and characterized. Homozygous mutants uniformly failed to survive more than 1 day following birth. At the physiologic level the mutants experienced apnea and reduced levels of hemoglobin oxygenation. Histologically, the mutant brains had striking alterations of discrete components. In the forebrain the lateral ganglionic eminence was reduced in size. In the hindbrain, the area postrema, an important cardiorespiratory chemosensory center, was absent. The contiguous nucleus tractus solitarius, involved in integrating sensory input to maintain homeostasis, was also severely malformed in mutants. Immunohistochemistry was used to examine the mutant brains for alterations in the distribution of markers specific for serotonergic and cholinergic neurons. In addition, in situ hybridizations were used to define expression patterns of the Dlx 2 and Nkx 2.1 homeobox genes in Gsh-2 mutant mice. The mutant lateral ganglionic eminences showed an abnormal absence of Dlx 2 expression. These results better define the genetic program of development of the mammalian brain, support neuromeric models of brain development, and further suggest similar patterning function for homeobox genes in phylogenetically diverse organisms.

Malignant glaucoma following laser iridotomy

BACKGROUND

A 69-year-old man presented with malignant glaucoma 10 days after an iridotomy for acute angle-closure glaucoma.

METHODS

The case notes are reviewed, describing his presentation and treatment, including the technique of extracapsular cataract extraction with anterior vitrectomy.

RESULTS

An excellent visual outcome was achieved with no recurrence of the malignant glaucoma.

CONCLUSIONS

This case illustrates the recently established link between laser iridotomy and malignant glaucoma. Miotics and other possible causes are excluded, a surgical option is described and the importance of assessing central anterior chamber depth in cases of angle closure is emphasised.

Homeotic transformations and limb defects in Hox A11 mutant mice

Hox A11 is one of the expanded set of vertebrate homeo box (Hox) genes with similarities to the Drosophila homeotic gene, Abdominal-B (Abd-B). These Abd-B-type Hox genes have been shown to be expressed in the most caudal regions of the developing vertebrate embryo and in overlapping domains within the developing limbs, suggesting that these genes play important roles in pattern formation in both appendicular and axial regions of the body. In this report whole-mount in situ hybridization in mouse embryos gave a precise description of Hox A11 gene expression in the developing limbs and in the axial domain of the developing body. In addition, we generated a targeted mutation in Hox A11 and characterized the resulting phenotype to begin to dissect developmental functions of the Abd-B subfamily of Hox genes. Hox A11 mutant mice exhibited double homeotic transformations, with the thirteenth thoracic segment posteriorized to form an additional first lumbar vertebra and with the sacral region anteriorized, generating yet another lumbar segment. Furthermore, skeletal malformations were observed in both forelimbs and hindlimbs. In mutant forelimbs, the ulna and radius were misshapen, the pisiform and triangular carpal bones were fused, and abnormal sesamoid bone development occurred. In mutant hindlimbs the tibia and fibula were joined incorrectly and malformed at their distal ends. Also, an enlarged sesamoid developed ventral to the tibiale bone. Both heterozygous and homozygous mice displayed mutant phenotypes adding an additional level of complexity to the Hox code hypothesis.

Evaluation of the efficacy and acceptability to patients of a physiotherapist working in a health centre

The records of the first 805 patients who had been referred by general practitioners at this health centre to the attached physiotherapist were examined in November 1985, three years after the physiotherapy department was opened. Seventy per cent (549) of the patients had been treated within one week, treatment having started on the same day for 8.5% (67) of the patients. This compares with a mean of six weeks for direct access to a district general hospital that is eight miles away and between six and 13 months for the three nearest orthopaedic consultants who are 13 miles away. The most common conditions treated were knee injuries (16.5%), followed by cervical (15.5%) and shoulder (13.8%) injuries. Surprisingly, only 9% were back injuries. The non-attendance rate was 2.2% and only 7% of patients failed to complete treatment. Nearly all the patients were able to attend the clinic, only 4% requiring home treatment. By March 1986, 90 treatments a week were being carried out at a cost of 6.11 pounds per patient. Compared with official hospital figures, this represents a savings of 21,500 pounds a year for a practice of 12,000 patients.