Imidazoline Binding Sites Research Articles

Farelerde Pentilenetetrazol ile İndüklenen Epilepsi Modelinde Agmatinin Etkilerinin ve Nitrik Oksitin Katkısının Araştırılması

Objective: Agmatine is an endogenous cationic amin and have been reported several neurotherapeutic effects through α2-adrenoceptors, imidazoline binding sites, inhibition of NMDA receptors and nitric oxide (NO) synthase. NO was reported to act as a neuromodulator and neurotransmitter in central nervous system and has proconvulsant/anticonvulsant activities in convulsion models. We aimed to compare the anticonvulsant activities of agmatine, sodium valproate, gabapentin and phenytoin, and to investigate the role of NO in effects of drugs. Material and Methods: Epilepsy seizures were induced in swiss-albino mice by single dose injection of penthylenetetrazole (PTZ) (60 mg/kg). Myoclonic-jerk (MJ) and generalized tonic-clonic seizures (GTCS) of mice were recorded. Agmatine (10 mg/kg), sodium valproate (150 mg/kg), gabapentin (20 mg/kg) and phenytoin (20 mg/kg) alone or in combinations with N(G)-Nitro-L-arginine-methyl-ester (L-NAME, 5 mg/kg), the precursor of NO, L-arginine (L-Arg, 60 mg/kg) and non-specific NO synthase inhibitor, were injected intraperitoneally. Results: While agmatine and sodium valproate significantly prevented GTCS%, phenytoin and gabapentin did not prevent. L-Arg significantly reduced activity of agmatine on MJ%. Both L-Arg and L-NAME did not affect activity of phenytoin on MJ% and GTCS%. L-Arg did not change the activity of gabapentin on MJ% and GTCS%. L-NAME significantly increased activity of gabapentin on MJ% and GTCS%. Conclusion: This study suggested that NO may have a role on anticonvulsant activity of agmatine and gabapentin but not those of sodium valproate and phenytoin.

Increased monoamine oxidase activity and imidazoline binding sites in insulin-resistant adipocytes from obese Zucker rats.

BACKGROUNDDespite overt insulin resistance, adipocytes of genetically obese Zucker rats accumulate the excess of calorie intake in the form of lipids.AIMTo investigate whether factors can replace or reinforce insulin lipogenic action by exploring glucose uptake activation by hydrogen peroxide, since it is produced by monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO) in adipocytes.METHODS 3H-2-deoxyglucose uptake (2-DG) was determined in adipocytes from obese and lean rats in response to insulin or MAO and SSAO substrates such as tyramine and benzylamine. 14C-tyramine oxidation and binding of imidazolinic radioligands [3H-Idazoxan, 3H-(2-benzofuranyl)-2-imidazoline] were studied in adipocytes, the liver, and muscle. The influence of in vivo administration of tyramine + vanadium on glucose handling was assessed in lean and obese rats.RESULTS2-DG uptake and lipogenesis stimulation by insulin were dampened in adipocytes from obese rats, when compared to their lean littermates. Tyramine and benzylamine activation of hexose uptake was vanadate-dependent and was also limited, while MAO was increased and SSAO decreased. These changes were adipocyte-specific and accompanied by a greater number of imidazoline I2 binding sites in the obese rat, when compared to the lean. In vitro, tyramine precluded the binding to I2 sites, while in vivo, its administration together with vanadium lowered fasting plasma levels of glucose and triacylglycerols in obese rats. CONCLUSIONThe adipocytes from obese Zucker rats exhibit increased MAO activity and imidazoline binding site number. However, probably as a consequence of SSAO down-regulation, the glucose transport stimulation by tyramine is decreased as much as that of insulin in these insulin-resistant adipocytes. The adipocyte amine oxidases deserve more studies with respect to their putative contribution to the management of glucose and lipid handling.

Nischarin Is Not the Functional I1 Imidazoline Receptor Involved in Blood Pressure Regulation.

Imidazoline receptor antisera selected/Nischarin was proposed several years ago as the functional entity for the I1 medullary receptors (I1Rs) targeted, together with α2-adrenoceptors, by the centrally acting antihypertensive drugs, such as clonidine. The objective of this study was to test this assumption using a pyrroline analog of clonidine, LNP599, which, unlike clonidine and related compounds, displays high selectivity toward I1Rs. Cardiovascular effects of LNP599 (3 mg/kg intravenous) were evaluated in anesthetized, artificially ventilated nischarin mutant rats expressing a truncated form of nischarin lacking the putative imidazoline binding site. LNP599 induced a rapid and pronounced fall in arterial blood pressure in wild-type animals (-42.7% ± 11.0% after 15 minutes), associated with a ≈30% heart rate reduction. Similar effects were obtained in homozygous and heterozygous nischarin mutant rats. The observation that the hypotensive response to I1R activation is not affected by the absence of the putative imidazoline binding site on nischarin strongly suggests that nischarin cannot be regarded as the functional I1R. Carbohydrate regulation was improved in nischarin mutant rats, further supporting the conclusion that nischarin and I1R are 2 distinct molecular entities.

Novel monoamine oxidase inhibitors based on the privileged 2-imidazoline molecular framework

Series of structurally diverse 2-imidazoline derivatives have been synthesized by condensation of substituted aldehydes with ethylenediamine, Pd-catalyzed N-arylation of 2-imidazolines and by the formation of 1,2,4-oxadiazoles and benzoxazepines from 2-imidazoline-containing precursors. The 2-imidazoline derivatives were evaluated as potential inhibitors of human monoamine oxidase (MAO) A and B. Among the 2-imidazolines, good potency inhibitors were discovered with compound 9p (IC50 = 0.012 µM) being the most potent MAO-B inhibitor, while compound 9d (IC50 = 0.751 µM) was the most potent MAO-A inhibitor of the series. These potencies are in the same range as those of reference MAO inhibitors used in the clinic. Among 33 compounds evaluated, 13 exhibited IC50 values in the submicromolar range for the inhibition of an MAO isoform. It is postulated that the imidazoline moieties of some of these inhibitors may be recognized by the imidazoline I2-binding site of MAO. Good potency MAO inhibitors may be useful for the treatment of neuropsychiatric and neurodegenerative disorders such as depression and Parkinson’s disease, and future application for the treatment of prostate cancer, congestive heart failure and Alzheimer’s disease. In addition, high potency 2-imidazoline-derived MAO inhibitors may be used as potential probes for the imidazoline binding sites of the MAOs, as well as to determine alternative binding regions of imidazoline within the MAO active site.

Bis(2-aminoimidazolines) and Bisguanidines: Synthetic Approaches, Antiparasitic Activity and DNA Binding Properties.

Parasitic diseases caused by protozoan parasites of the genus Trypanosoma and Plasmodium cause some of the deadliest and disabling human infections in tropical and subtropical areas. Diphenyl-based bis(2-phenylimino)imidazolidines and bisguanidines are extremely potent antiparasitic agents against Trypanosoma brucei (etiological agent of African trypanosomiasis) and Plasmodium falciparum (etiological agent of severe malaria). Many of these compounds are also curative in mouse models of stage 1 African trypanosomiasis representing promising leads for the development of antitrypanosomal drugs. In addition, different classes of bis(2-iminoimidazolidines) and bisguanidines have been shown to have antimicrobial activity against other pathogens (e.g. bacteria, fungi, parasitic worms). Due to their structural and physicochemical properties, these dibasic compounds, which are dications at physiological pH, are prone to bind to the minor groove of DNA at AT-rich sites. In several cases, such interaction is thought to be responsible for their antimicrobial activity. In this review, we give a comprehensive view of the synthetic methods used to introduce the 2-aminoimidazoline scaffold in a molecule. Synthetic routes that give access to these cyclic guanidines (i.e. unsubstituted, 1-, 4-, and 5-substituted 2-aminoimidazolines) are detailed. The in vitro and in vivo antiprotozoal activity of bis(2-aminoimidazolines) and bisguanidines against kinetoplastid parasites (T. brucei, T. cruzi, Leishmania), Plasmodium spp. and other pathogens (e.g. ESKAPE bacteria, Candida spp., M. tuberculosis, E. multilocularia) is also reviewed. Finally, the targets that are involved in the antimicrobial activity (e.g. DNA) or other biological activities (e.g. α-adrenergic receptors, imidazoline binding sites, kinases) of this class of dicationic compounds are discussed.

DEMENTIA PLATFORM U.K. EXPERIMENTAL MEDICINE: HUMAN IN VIVO ASTROGLIAL ACTIVATION IN EARLY ALZHEIMER’S DISEASE

Astrocyte activation and atrophy influence the synaptic health and progression of Alzheimer's disease(AD). A novel PET radioligand at Imperial College London (in collaboration with GlaxoSmithKline and Imanova, Ltd.) has shown favourable characteristics in preclinical models. [11C]BU99008 is selective for I2-imidazoline binding sites (I2BS) expressed on the mitochondrial membranes of astrocytes. These I2 imidazoline binding sites (I2BS) increase with astroglial activation in the brain. The primary objective is to assess the uptake of [11C]BU99008 in mild to moderate AD compared to healthy volunteers (HV). We also are exploring the relationship between increased uptake, brain amyloid load and glucose metabolism. Thus far, in two separate cohorts, we have completed analysis of a total of 18 HVs. Non-linear registration of the CIC atlas into native space for each subject's dynamic PET data and generation of regional time-activity data, time-activity curves for frontal, temporal, parietal occipital and hippocampus are being modelled using two-tissue (2TCM) compartmental models using MIAKATTM. Cohort 1 consists of 13 subjects age (54±7yr; mean±SD), data previously presented (Tyacke et al, NRM 2016). The new Cohort 2 consists of a significantly more elderly group of 5 subjects (70±7yr). They showed uptake (VT, ml.cm-3) highest in: nucleus accumbens (152±24), globus pallidus (141±45) and striatum (119±33); intermediate in the insular cortex (87±10), and cingulate cortex (76±12); and lowest in the occipital cortex (63±5) and cerebellum (57±3). These data are in good agreement with those in Cohort 1. However, in cohort 2 there was significantly greater (Student t-test; P<0.05) increase in the regions showing lowest binding in both cohorts. A correlation using all 18 subjects for whole brain binding showed a trend towards a significant increase with age (P=0.06; Spearmans). The [11C]BU99008 PET tracer has demonstrated that the tracer has good brain uptake in humans. More AD, MCI and healthy control subjects are being scanned to evaluate its possible use as a marker of pathology progression in AD. The Medical Research Council Dementias Platform UK (DPUK) is a multi-million pound public-private partnership developed by the MRC. This study was conducted as a component of a developing DPUK Imaging Network experimental medicine programme.

Neuroprotective Effects of Dexmedetomidine against Thapsigargin-induced ER-stress via Activity of α&lt;sub&gt;2&lt;/sub&gt;-adrenoceptors and Imidazoline Receptors

Dexmedetomidine is a potent and highly selective α2-adrenoceptor agonist with sedative, analgesic, and sympatholytic properties, though it also exhibits some affinity for imidazoline binding sites. In addition to its sedative effects, dexmedetomidine exerts neuroprotective effects under ischemic conditions. Invasive incidents such as ischemia or hypoxia induce dysfunctions in energy production or depletion of ATP as well as accumulation and aggregation of abnormal proteins in the endoplasmic reticulum (ER), leading to an ER-stress response. In the present study, we examined whether dexmedetomidine exerts inhibitory effects on apoptosis mediated by thapsigargin-induced ER-stress in SH-SY5Y cells, and proposed a possible underlying mechanism for its neuroprotective effects. We used thapsigargin (TG) to generate an ER-stress response in SH-SY5Y cells. SH-SY5Y cells were pretreated with Dex (1–1000 nM) or receptor antagonists (atipamezole, efaroxan, BU99006, and 2’,5’-dideoxyadenosine) for 1 hour before co-treatment with 1 mM TG for 20 hours. Co-incubation with dexmedetomidine suppressed thapsigargin-induced increases in cytosolic Ca2+, caspase-4 and -3 activity, eIF2α phosphorylation, and expression of ER-stress biomarkers. Dexmedetomidine treatment also decreased cAMP levels. In the presence of atipamezole or efaroxan, but not BU99006, inhibition of eIF2α phosphorylation and CHOP expression significantly increased following treatment with dexmedetomidine in thapsigargin-treated cells. However, pretreatment with BU99006 enhanced the increase in mitochondrial membrane potential associated with dexmedetomidine treatment. The results of the present study demonstrate that dexmedetomidine at clinically relevant concentrations suppresses ER-stress-induced apoptosis in SH-SY5Y cells. Some neuroprotective effects of dexmedetomidine may be mediated by α2-adrenoceptor and I1- and I2-receptors.

Antihypertensive drugs

Antihypertensive drugs

Harmane: An atypical neurotransmitter?

Harmane is an active component of clonidine displacing substance and a candidate endogenous ligand for imidazoline binding sites. The neurochemistry of tritiated harmane was investigated in the present study examining its uptake and release properties in the rat brain central nervous system (CNS) in vitro. At physiological temperature, [3H]harmane was shown to be taken up in rat brain cortex. Further investigations demonstrated that treatment with monoamine uptake blockers (citalopram, nomifensine and nisoxetine) did not alter [3H]harmane uptake implicating that the route of [3H]harmane transport was distinct from the monoamine uptake systems. Furthermore, imidazoline ligands (rilmenidine, efaroxan, 2-BFI and idazoxan) showed no prominent effect on [3H]harmane uptake suggesting the lack of involvement of imidazoline binding sites. Subsequent analyses showed that disruption of the Na+ gradient using ouabain or choline chloride did not block [3H]harmane uptake suggesting a Na+-independent transport mechanism. Moreover, higher temperatures (50°C) failed to impede [3H]harmane uptake implying a non-physiological transporter. The failure of potassium to evoke the release of preloaded [3H]harmane from rat brain cortex indicates that the properties of this putative endogenous ligand for imidazoline binding sites do not resemble that of a conventional neurotransmitter.

Borne Identity: Leading Endogenous Suspects at Imidazoline Binding Sites

Over the past few years, a vast amount of research has shed light on the pharmacology of imidazoline binding sites (I-BS). To date, at least three classes of imidazoline binding sites have been characterised in accordance to their localisation, drug selectivity, proposed signalling pathways and functional roles. The existence of these sites raises the question as to whether an endogenous modulator exists. The identification of an endogenous extract denoted as clonidine displacing substance prompted the search for the active ingredient capable of mimicking the action of selective ligands at these sites. A number of candidates have been isolated and their functional activities have been assessed at these sites. Such endogenous ligands include agmatine, imidazoleacetic acid ribotide and the β-carboline harmane. As of yet, no consensus has been made to confirm the identity of the endogenous ligand at I-BS. The current review collates and reports what is known about these substances and their functional significance at I-BS.

Fluorinated analogues of marsanidine, a highly α2-AR/imidazoline I1 binding site-selective hypotensive agent. Synthesis and biological activities

The aim of these studies was to establish the influence of fluorination of the indazole ring on the pharmacological properties of two selective α2-adrenoceptor (α2-AR) agonists: 1-[(imidazolidin-2-yl)imino]-1H-indazole (marsanidine, A) and its methylene analogue 1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indazole (B). Introduction of fluorine into the indazole ring of A and B reduced both binding affinity and α2-AR/I1 imidazoline binding site selectivity. The most α2-AR-selective ligands were 6-fluoro-1-[(imidazolidin-2-yl)imino]-1H-indazole (6c) and 7-fluoro-1-[(imidazolidin-2-yl)imino]-1H-indazole (6d). The in vivo cardiovascular properties of fluorinated derivatives of A and B revealed that in both cases the C-7 fluorination leads to compounds with the highest hypotensive and bradycardic activities. The α2-AR partial agonist 6c was prepared as a potential lead compound for development of a radiotracer for PET imaging of brain α2-ARs.

Imidazoline binding sites mediates anticompulsive-like effect of agmatine in marble-burying behavior in mice

Agmatine is a cationic amine formed by decarboxylation of l-arginine by the mitochondrial enzyme arginine decarboxylase and widely distributed in mammalian brain. Although the precise function of endogenous agmatine has been largely remained unclear, its exogenous administration demonstrated beneficial effects in several neurological and psychiatric disorders. This study was planned to examine the role of imidazoline binding sites in the anticompulsive-like effect of agmatine on marble-burying behavior. Agmatine (20 and 40mg/kg, ip), mixed imidazoline I1/α2 agonists clonidine (60µg/kg, ip) and moxonidine (0.25mg/kg, ip), and imidazoline I2 agonist 2- BFI (10mg/kg, ip) showed significant inhibition of marble burying behavior in mice. In combination studies, the anticompulsive-like effect of agmatine (10mg/kg, ip) was significantly potentiated by prior administration of moxonidine (0.25mg/kg, ip) or clonidine (30µg/kg,) or 2-BFI (5mg/kg, ip). Conversely, efaroxan (1mg/kg, ip), an I1 antagonist and idazoxan (0.25mg/kg, ip), an I2 antagonist completely blocked the anticompulsive-like effect of agmatine (10mg/kg, ip). These drugs at doses used here did not influence the basal locomotor activity in experimental animals. These results clearly indicated the involvement of imidazoline binding sites in anti-compulsive-like effect of agmatine. Thus, imidazoline binding sites can be explored further as novel therapeutic target for treatment of anxiety and obsessive compulsive disorders.

Participation of central imidazoline binding sites in antinociceptive effect of ethanol and nicotine in rats

Despite synergistic morbidity and mortality, concomitant consumption of alcohol and tobacco is increasing, and their antinociceptive effect has been linked with co-abuse. Present study was designed to investigate the role of imidazoline binding sites in the antinociceptive effect of nicotine, ethanol, and their combination. Separate group of male Sprague-Dawley rats (200-250 g) were treated with different doses of alcohol (0.50-2 g/kg, i.p.) or nicotine (0.25-1 mg/kg, i.p.), and their combination evaluated in tail flick test. Influence of endogenous imidazoline binding site ligands, agonist, and antagonists were determined by their prior treatment with effective or subeffective doses of either ethanol or nicotine. Ethanol, nicotine, or their subeffective dose combination exhibited significant antinociceptive effects in dose-dependent manner. Antinociceptive effect of ethanol and nicotine was significantly augmented by intracerebroventricular (i.c.v.) administration of endogenous imidazoline receptor ligands, harmane (25 μg/rat, i.c.v.) and agmatine (10 μg/rat, i.c.v.), as well as imidazoline I1 /α2 adrenergic receptor agonist, clonidine (2 μg/rat, i.c.v.), I1 agonist moxonidine (25 μg/rat, i.c.v.), and imidazoline I2 agonist, 2-BFI (10 μg/rat, i.c.v.). Conversely, antinociception elicited by ethanol or nicotine or their subeffective dose combination was antagonized by pretreatment with imidazoline I1 antagonist, efaroxan (10 μg/rat, i.c.v.), and I2 antagonist, idazoxan (4 μg/rat, i.c.v.), at their per se ineffective doses. These findings project imidazoline binding ligands as important therapeutic molecules for central antinociceptive activity as well as may reduce the co-abuse potential of alcohol and nicotine.

Monoamine Oxidases: The Biochemistry of the Proteins As Targets in Medicinal Chemistry and Drug Discovery

Monoamine oxidase (MAO, EC.1.4.3.4) has been a drug target for 60 years, with the primary rationale of developing drugs to treat neuropsychiatric disorders. The biological importance of MAO is to regulate amine levels is the brain and to metabolize amines and drugs in the periphery. This review of the biochemistry of MAO A and MAO B describes the functional properties of the two enzymes integrated with knowledge of the structures of the many MAOinhibitor complexes published in the last 10 years. The analysis of activity, and the chemical and kinetic mechanisms are discussed. Inhibition studies on human MAO in vitro are now facilitated by assays using readily available materials but the kinetics of MAO involving alternative oxidative pathways and sensitivity to the oxygen concentration mean that careful analysis of the data is required as well as the good practice of determining mechanism of inhibition and kinetic constants. Kinetic constants can then be compared with thermodynamic calculations. Inhibitors bind to both the oxidized and reduced forms of MAO present during turnover so both forms should be considered when using molecular dynamics to facilitate drug design. Interaction of inhibitors with the active site can be detected as changes in the visible spectrum and these changes can provide clues about the flavin adduct formed for irreversible inhibitors or about the proximity to the flavin for reversible inhibitors. Developing areas (knock-out mice for behavior, the imidazoline binding site, and imaging to monitor the activity and the inhibition of MAO in the patient) are mentioned.

Guinea-pig ileum as ex vivo model useful to characterize ligands displaying Imidazoline I2 and Adrenergic alpha2 mixed activity: a preliminary study

The lack of an effective analgesic treatment makes pain a clinical challenge and the need of a novel approach to identify new agents is urgent. In this scenario I2-ligands can be considered an alternative strategy in pain therapy. The development of an &lt;em&gt;ex vivo&lt;/em&gt; model useful for the evaluation of functional activities at both a2 and I2-IBs (imidazoline binding sites) is an important task in pharmacological sciences since several I2 ligands display activity also towards a receptors. The present study aims to develop an &lt;em&gt;ex vivo&lt;/em&gt; model for estimating the activity of I2-IBs ligands in a biological sample where a1 and a2 adrenergic receptors are present. For this purpose the imidalzoline endogenous ligand, harmane, reference compounds, 2BFI and BU224, and imidazoline derivatives 1-3 have been selected taking into account their in vitro activity towards IBs and adrenergic receptors. All compounds have been tested &lt;em&gt;ex vivo&lt;/em&gt; in guinea pig-ileum where a2A-ARs are prejunctionally and I2-IBS postjunctionally localized. Adrenergic component has been identified by the studying the interference of compounds on the electrically-evoked contraction while I2-IBs activity by testing the ability of compounds to inhibit the carbachol-evoked contractions in the presence of prazosin to mask the a1 adrenoceptors. Compounds 1 and 2 were found I2-IBs antago nists (pIC50=4.2 and 4.0, respectively) whereas compound 3 was I2-IBs agonist (EC50=0.38 mM); All ligands were a2 adrenergic agonists. This paper suggests guinea-pig ileum as the first &lt;em&gt;ex vivo&lt;/em&gt; approach for establishing both the intrinsic activity of I2-IBs ligands and the physiological correlation between IBs and adrenergic system.

Monoamine Oxidases: The Biochemistry of the Proteins As Targets in Medicinal Chemistry and Drug Discovery

Monoamine oxidase (MAO, EC.1.4.3.4) has been a drug target for 60 years, with the primary rationale of developing drugs to treat neuropsychiatric disorders. The biological importance of MAO is to regulate amine levels is the brain and to metabolize amines and drugs in the periphery. This review of the biochemistry of MAO A and MAO B describes the functional properties of the two enzymes integrated with knowledge of the structures of the many MAOinhibitor complexes published in the last 10 years. The analysis of activity, and the chemical and kinetic mechanisms are discussed. Inhibition studies on human MAO in vitro are now facilitated by assays using readily available materials but the kinetics of MAO involving alternative oxidative pathways and sensitivity to the oxygen concentration mean that careful analysis of the data is required as well as the good practice of determining mechanism of inhibition and kinetic constants. Kinetic constants can then be compared with thermodynamic calculations. Inhibitors bind to both the oxidized and reduced forms of MAO present during turnover so both forms should be considered when using molecular dynamics to facilitate drug design. Interaction of inhibitors with the active site can be detected as changes in the visible spectrum and these changes can provide clues about the flavin adduct formed for irreversible inhibitors or about the proximity to the flavin for reversible inhibitors. Developing areas (knock-out mice for behavior, the imidazoline binding site, and imaging to monitor the activity and the inhibition of MAO in the patient) are mentioned.

Behavioural, neurochemical and neuroendocrine effects of the endogenous β-carboline harmane in fear-conditioned rats

The putative endogenous imidazoline binding site ligand harmane enhances neuronal activation in response to psychological stress and alters behaviour in animal models of anxiety and antidepressant efficacy. However, the neurobiological mechanisms underlying harmane's psychotropic effects are poorly understood. We investigated the effects of intraperitoneal injection of harmane (2.5 and 10 mg/kg) on fear-conditioned behaviour, hypothalamo-pituitary-adrenal axis activity, and monoaminergic activity within specific fear-associated areas of the rat brain. Harmane had no significant effect on the duration of contextually induced freezing or 22 kHz ultrasonic vocalisations and did not alter the contextually induced suppression of motor activity, including rearing. Harmane reduced the duration of rearing and tended to increase freezing in non-fear-conditioned controls, suggesting potential sedative effects. Harmane increased plasma ACTH and corticosterone concentrations, and serotonin (in hypothalamus, amygdaloid cortex, prefrontal cortex and hippocampus) and noradrenaline (prefrontal cortex) content, irrespective of fear-conditioning. Furthermore, harmane reduced dopamine and serotonin turnover in the PFC and hypothalamus, and serotonin turnover in the amygdaloid cortex in both fear-conditioned and non-fear-conditioned rats. In contrast, harmane increased dopamine and noradrenaline content and reduced dopamine turnover in the amygdala of fear-conditioned rats only, suggesting differential effects on catecholaminergic transmission in the presence and absence of fear. The precise mechanism(s) mediating these effects of harmane remain to be determined but may involve its inhibitory action on monoamine oxidases. These findings support a role for harmane as a neuromodulator, altering behaviour, brain neurochemistry and neuroendocrine function.

Methylation of imidazoline related compounds leads to loss of α2-adrenoceptor affinity. Synthesis and biological evaluation of selective I1 imidazoline receptor ligands

Methylated analogues of imidazoline related compounds (IRC) were prepared; their abilities to bind I1 imidazoline receptors (I1Rs), I2 imidazoline binding sites (I2BS) and α2-adrenoceptor subtypes (α2ARs) were assessed. Methylation of the heterocyclic moiety of IRC resulted in a significant loss of α2AR affinity. Amongst the selective ligands obtained, LNP 630 (4) constitutes the first highly selective I1R agent showing hypotensive activity after intravenous administration.

Targeting imidazoline site on monoamine oxidase B through molecular docking simulations

Monoamine oxidase (MAO) is an enzyme of major importance in neurochemistry, because it catalyzes the inactivation pathway for the catecholamine neurotransmitters, noradrenaline, adrenaline and dopamine. In the last decade it was demonstrated that imidazoline derivatives were able to inhibit MAO activity. Furthermore, crystallographic studies identified the imidazoline-binding domain on monoamine oxidase B (MAO-B), which opens the possibility of molecular docking studies focused on this binding site. The goal of the present study is to identify new potential inhibitors for MAO-B. In addition, we are also interested in establishing a fast and reliable computation methodology to pave the way for future molecular docking simulations focused on the imidazoline-binding site of this enzyme. We used the program 'molegro virtual docker' (MVD) in all simulations described here. All results indicate that simplex evolution algorithm is able to succesfully simulate the protein-ligand interactions for MAO-B. In addition, a scoring function implemented in the program MVD presents high correlation coefficient with experimental activity of MAO-B inhibitors. Taken together, our results identified a new family of potential MAO-B inhibitors and mapped important residues for intermolecular interactions between this enzyme and ligands.

Imidazoleacetic acid-ribotide in the rodent striatum: A putative neurochemical link between motor and autonomic deficits in parkinson’s disease

We have previously demonstrated that imidazole-4-acetic acid-ribotide (IAA-RP) is present in the mammalian brain and is an endogenous ligand at imidazoline binding sites. In the present study, we used a polyclonal antiserum to visualize IAA-RP-containing neurons in the rat caudoputamen. We observe IAA-RP-immunostained neurons scattered throughout the dorsal and ventral striatum. Most of these cells co-localize GABA, but none are parvalbumin-immunoreactive. In contrast, approximately 50% of the calbindin D28k-immunopositive striatal neurons co-localize IAA-RP. Electrophysiological studies using corticostriatal slices demonstrated that bath application of IAA-RP reversibly depresses the synaptically mediated component of field potentials recorded in the striatum by stimulation of cortical axons. Addition of competitive glutamate receptor antagonists completely blocks the response, confirming its association with glutamatergic transmission. Using paired-pulse stimuli, IAA-RP was shown to exert, at least in part, a presynaptic effect, but blockade of GABAA receptor-mediated transmission did not alter the response. Lastly, we show that this effect is attributable to imidazoline-1 receptors, and not to α2 adrenergic receptors. Since IAA-RP is an endogenous central regulator of blood pressure, and cardiovascular dysfunction is a common symptom associated with Parkinson's disease (PD), we speculate that IAA-RP-related abnormalities may underlie some of the autonomic dysfunction that occurs in PD.