Characterisation of imidazoline I2 binding sites in pig brain

The domestic piglet: an important model for investigating the neurodevelopmental consequences of early life insults

Insults in the prenatal and early postnatal period increase the risk for behavioral problems later in life. One hypothesis is that pre- and postnatal stressors influence structural and functional brain plasticity. Understanding the mechanisms is important, but progress has lagged because certain studies in human infants are impossible, while others are extremely difficult. Furthermore, results from popular rodent models are difficult to translate to human infants owing to the substantial differences in brain development and morphology. Because it overcomes some of these obstacles, the domestic piglet has emerged as an important model. Piglets have a gyrencephalic brain that develops similar to the human brain and that can be assessed in vivo by using clinical-grade neuroimaging instruments. Furthermore, owing to their precocial nature, piglets can be weaned at birth and used in behavioral testing paradigms to assess cognitive behavior at an early age. Thus, the domestic piglet represents an important translational model for investigating the neurodevelopmental consequences of early life insults.

Decrease of Obesity by Allantoin via Imidazoline I 1 -Receptor Activation in High Fat Diet-Fed Mice

The activation of the imidazoline I₁-receptor (I₁R) is known to regulate appetite. Allantoin, an active ingredient in the yam, has been reported to improve lipid metabolism in high fat diet- (HFD-)fed mice. However, the effect of allantoin on obesity remains unclear. In the present study, we investigated the effects of allantoin on HFD-induced obesity. The chronic administration of allantoin to HFD-fed mice for 8 weeks significantly decreased their body weight, and this effect was reversed by efaroxan at a dose sufficient to block I₁R. The epididymal white adipose tissue (eWAT) cell size and weight in HFD-fed mice were also decreased by allantoin via the activation of I₁R. In addition, allantoin significantly decreased the energy intake of HFD-fed mice, and this reduction was associated with a decrease in the NPY levels in the brain. However, no inhibitory effect of allantoin on energy intake was observed in db/db mice. Moreover, allantoin lowered HFD-induced hyperleptinemia, and this activity was abolished by I₁R blockade with efaroxan. Taken together, these data suggest that allantoin can ameliorate energy intake and eWAT accumulation by activating I₁R to improve HFD-induced obesity.

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.

Chronic treatment with selective I2-imidazoline receptor ligands decreases the content of pro-apoptotic markers in rat brain

Selective I(2)-imidazoline receptor ligands induce neuroprotection through various molecular mechanisms including blockade of N-methyl-D-aspartate (NMDA) receptors. To investigate new neuroprotective mechanisms associated with I(2)-imidazoline receptors, the effects of selective (2-styryl-2-imidazoline (LSL 61122), 2-(2-benzofuranyl)-2-imidazoline (2-BFI), 2-(4,5-dihydroimidazol-2-yl) quinoline hydrochloride (BU-224)) and non-selective (idazoxan) I(2)-drugs on canonical apoptotic pathways were assessed in rat brain cortex. The acute treatment with LSL 61122 (10 mg/kg) reduced the content of mitochondrial (pro-apoptotic) Bax (-33%) and cytochrome c (-31%), which was prevented by idazoxan, an I(2)-receptor antagonist. The sustained stimulation of I(2)-imidazoline receptors with selective drugs (10 mg/kg, every 12 h for seven days) was associated with down-regulation of key components of the extrinsic (Fas receptor: -20%; Fas associated protein with death domain (FADD) adaptor: -47-54%) and/or intrinsic (Bax: -20-23%; cytochrome c: -22-28%) apoptotic signalling and/or up-regulation of survival anti-apoptotic factors (p-Ser194 FADD/FADD ratio: +1.6-2.5-fold; and/or Bcl-2/Bax ratio: +1.5-fold), which in the long-term could dampen cell death in the brain. Similar chronic treatments with LSL 60101 (the imidazole analogue of 2-BFI) and idazoxan (a mixed I(2)/α(2)-ligand) did not induce significant alterations of pro- or anti-apoptotic proteins. The disclosed anti-apoptotic mechanisms of selective I(2)-imidazoline drugs may work in concert with other molecular mechanisms of neuroprotection (e.g. blockade of NMDA receptors) that are engaged by I(2)-ligands.

The endogenous alkaloid harmane: acidifying and activity-reducing effects on hippocampal neurons in vitro

RATIONALE

The endogenous alkaloid harmane is enriched in plasma of patients with neurodegenerative or addictive disorders. As harmane affects neuronal activity and viability and because both parameters are strongly influenced by intracellular pH (pH(i)), we tested whether effects of harmane are correlated with altered pH(i) regulation.

METHODS AND RESULTS

Pyramidal neurons in the CA3 field of hippocampal slices were investigated under bicarbonate-buffered conditions. Harmane (50 and 100 microM) reversibly decreased spontaneous firing of action potentials and caffeine-induced bursting of CA3 neurons. In parallel experiments, 50 and 100 microM harmane evoked a neuronal acidification of 0.12+/-0.08 and 0.18+/-0.07 pH units, respectively. Recovery from intracellular acidification subsequent to an ammonium prepulse was also impaired, suggesting an inhibition of transmembrane acid extrusion by harmane.

CONCLUSION

Harmane may modulate neuronal functions via altered pH(i)-regulation. Implications of these findings for neuronal survival are discussed.

The use of pigs in neuroscience: Modeling brain disorders

The use of pigs in neuroscience research has increased in the past decade, which has seen broader recognition of the potential of pigs as an animal for experimental modeling of human brain disorders. The volume of available background data concerning pig brain anatomy and neurochemistry has increased considerably in recent years. The pig brain, which is gyrencephalic, resembles the human brain more in anatomy, growth and development than do the brains of commonly used small laboratory animals. The size of the pig brain permits the identification of cortical and subcortical structures by imaging techniques. Furthermore, the pig is an increasingly popular laboratory animal for transgenic manipulations of neural genes. The present paper focuses on evaluating the potential for modeling symptoms, phenomena or constructs of human brain diseases in pigs, the neuropsychiatric disorders in particular. Important practical and ethical aspects of the use of pigs as an experimental animal as pertaining to relevant in vivo experimental brain techniques are reviewed. Finally, current knowledge of aspects of behavioral processes including learning and memory are reviewed so as to complete the summary of the status of pigs as a species suitable for experimental models of diverse human brain disorders.

3-[5-(4,5-dihydro-1H-imidazol-2-yl)-furan-2-yl]phenylamine (Amifuraline), a promising reversible and selective peripheral MAO-A inhibitor

On the basis of the observation that the central side effects of MAO inhibitors may represent a major limit for their use in pathological processes involving peripheral MAOs, we investigated the possibility of generating novel inhibitors able to target specifically peripheral MAOs. To address this issue, we designed compounds 7-28. From biological results, the 2-(5-phenyl-furan-2-yl)-4,5-dihydro-1H-imidazole (Furaline, 17) proved to be a suitable lead. In fact, in enzyme assays on homogenate preparation from rat liver and HEK cells expressing MAO-A or MAO-B, compounds possessing the frame of 17 behaved as selective and reversible MAO-A inhibitors. Interestingly, in in vivo studies the amino derivative 21 (Amifuraline), endowed with good hydrophilic character, was able to significantly inhibit liver but not brain MAO-A.

The imidazoline I2-site ligands BU 224 and 2-BFI inhibit MAO-A and MAO-B activities, hydrogen peroxide production, and lipolysis in rodent and human adipocytes

Numerous imidazolinic agents exhibit antihyperglycaemic properties and have been described to promote insulin secretion, however their effects on adipose tissue development have been poorly investigated. Since white adipose tissue (WAT) plays an important role in glucose homeostasis and expresses imidazoline (I(2)) binding sites abundantly, this work aimed at studying extrapancreatic actions of two I(2)-site ligands, BU 224 and 2-BFI in adipocytes. Interaction with monoamine oxidase (MAO) was investigated by measuring the ability to modulate [(14)C]tyramine oxidation and hydrogen peroxide production. Direct influence on glucose uptake or on lipolytic activity was tested on mouse, rat, rabbit and human adipocytes. BU 224 and 2-BFI behaved as reversible inhibitors of both MAO-A and -B, as demonstrated by total inhibition of tyramine oxidation in human adipocytes and platelets or in liver from rats previously treated with selective MAO-inhibitors. Moreover, they weakly inhibited semicarbazide-sensitive amine oxidase. Like classical MAO-inhibitors, they were unable to produce hydrogen peroxide and to activate glucose uptake but prevented tyramine to do so in rodent or human adipocytes. BU 224 and 2-BFI also differed from MAO-inhibitors since they inhibited lipolysis at millimolar concentrations via a still undefined pathway independent of alpha(2)-adrenoceptor stimulation, beta-adrenergic antagonism and MAO activation. However, chronic treatment of obese Zucker rats with 2-BFI did not modify the maximal lipolytic capacity or the mild insulin resistance status of their adipocytes. Taken together, our observations demonstrate on WAT novel effects of BU 224 and 2-BFI different from their already reported actions on brain or endocrine pancreas.