Lamina I neurons constitute a major output pathway from the dorsal horn of the spinal cord, relaying sensory information to the brain. Investigating how the excitability of these neurons is controlled is important for the understanding of nociceptive processing. The extensive co-localization of the major inhibitory neurotransmitters GABA (gamma-aminobutyric acid) and glycine in the marginal zone of the rat spinal cord, raises the issue of their respective role in this spinal area. Therefore, I developed a spinal cord slice preparation that allowed us to clearly delineate lamina I neurons for in vitro studies. I used whole cell patch clamp recording in identified lamina I neurons to study spontaneously occurring inhibitory postsynaptic currents (IPSCs), and stimulus evoked IPSCs. In particular, spontaneous miniature (action potential independent) IPSCs (mIPSCs) were studied as they are thought to reflect transmitter release from single vesicles. An important initial finding was that lamina I neurons were almost exclusively bombarded by glycine receptor (GlyR)-mediated mIPSCs. However, all cells appeared to express both GABA A receptors (GABAARs) and GlyRs. Moreover, recording of mIPSCs in the presence of a benzodiazepine revealed GABAAR-mediated mIPSCs with kinetic properties consistent with the interpretation that GABA ARs are likely located at extrasynaptic sites in lamina I neurons. Thus, GABA and glycine appeared to be co-released from the same synaptic vesicles. Together with IPSCs evoked from low- and high-intensity electrical stimulations, the results indicated that glycine is responsible for most tonic inhibitory control in lamina I, while GABAAR-mediated inhibition may be more relevant for the control of evoked input. Paired-pulse stimulations indicated that tonically released GABA appeared to first serve to activate presynaptic GABAB autoreceptors. To test the plasticity of GABAergic and glycinergic systems in lamina I, I have investigated their possible

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The metabolism of several anabolic 17$ alpha$-methyl steroids, namely formebolone, mestanolone, methandienone, methyltestosterone, oxandrolone, oxymetholone and stanozolol, were investigated. The identification of metabolites was based on GC/MS analysis of different derivatives, and chemical synthesis of corresponding reference steroids. Common metabolic reactions have been studied and structure-metabolism relationships were discussed. New biotransformation routes, such as oxidative pathways of 2-formyl and 2-hydroxymethylene steroids, have been unveiled. The mechanism of 17-epimerization of these 17$ beta$-hydroxy-17$ alpha$-methyl steroids in vivo has also been clarified. / A simple and convenient method for the preparation of 17$ beta$-tertiary sulfate derivatives of these steroids has been developed. A stereoselective approach was used for the partial synthesis of reference steroids in order to confirm the stereochemical features of an acidic metabolite of oxymetholone.

Stress activates dopamine (DA) transmission in the basolateral amygdala (BLA), medial prefrontal cortex (mPFC) and nucleus accumbens (NAc), and DA transmission in these regions mediates different aspects of the behavioural response to stress. Evidence indicates that a functional interdependence exists between the DA projections to these areas. mPFC DA exerts an inhibitory influence on stress-induced NAc DA release. Similarly, BLA DA modulates mPFC and NAc DA function, although it is unknown if this is also the case in response to stress. Thus, we examined whether BLA DA modulates NAc and mPFC DA release in response to stress. We first determined the effects of BLA DA depletion on stress-induced NAc and mPFC DA release. BLA DA depletion potentiated the NAc and attenuated the mPFC DA responses to stress. We then examined the effects of intra-BLA D1 and D2/D3 receptor antagonists on the NAc and mPFC DA responses to stress. BLA D1, but not D2/D3, receptor antagonism potentiated and attenuated stress-induced NAc and mPFC DA release, respectively. Co-administration of D1 antagonist into BLA and DA agonists into mPFC abolished the potentiation of stress-induced NAc DA release, indicating that BLA D1 receptor modulation of the NAc DA stress response occurs indirectly by modulating stress-induced mPFC DA release. We then turned to examining the influence of BLA DA on behavioural measures of information processing which are themselves modulated by NAc and mPFC DA function. The effects of BLA D1 and D2/D3 receptor blockade on prepulse inhibition (PPI) and latent inhibition (LI) were examined. BLA D1 receptor antagonist enhanced and D2/D3 receptor antagonist reduced PPI. Conversely, neither BLA DA receptor antagonist had an effect on LI. Finally, we determined the effects of BLA D1 and D2/D3 receptor antagonists on acoustic startle habituation. Although BLA DA receptor antagonism had no effect on this measure, both D1 and D2/D3 receptor blockade reduc

It has now been accepted for several years, that a receptors exist as at least two distinct entities denoted sigma1 and sigma 2. We have previously shown in our laboratory that several seIective sigma 1 ligands potentiate the neuronal response to NMDA in the dorsal hippocampus of rat. The non selective beta/sigma2 ligand, DTG, also potentiates the neuronal response. However, when it is administered at doses between 3 and 40 mug/kg, the increase of NMDA-induced activation turns in to an epileptoid activity. Data presented in this thesis suggest that similarly to sigma 1 ligands, selective sigma2 ligands such as Lu 28-179, Lu 29-252 and BD 1008 dose-dependently potentiate the NMDA response. Interestingly, the effects of these drugs are not reversed by the non selective sigma 1/sigma2 antagonist haloperidol, by the neurosteroid progesterone nor by the selective a sigma1 antagonist NE-100. The sigma 2 ligand CB-64D also potentiates, dose-dependently, the NMDA response, its effect, however is reversed by haloperidol and by the neurosteroid progesterone. All sigma2 ligands failed to generate any epileptoid activity on their own but, with the subsequent administration of a sigma1 agonist (JO-1784), an epileptoid activity was induced. This epileptoid activity was not observed following the subsequent administration of the sigma 1 agonist (+)-pentazocine. / The sigma receptor is believed to be a non opioid receptor insensitive to naloxone. However, recently, a protein has been identified that resembles the sigma opioid receptor originally proposed by Martin and colleagues in 1976. Therefore to answer this discrepancy, we verified the spectrum of sigma ligands for which the potentiation of the NMDA response is mediated by the naloxone-sensitive sigma receptor. The potentiation of the NMDA response induced by (+)-pentazocine, but not JO-1784, BD-737 and L, 687-384, was suppressed by naloxone. / The data presented in this thesis suggest that: (1) similarly to sigma1 ligands, sigma2 agonists potentiate the NMDA response; (2) the coactivation of one type of sigma1 and sigma2 receptors appears to be necessary to induce epileptoid activity; (3) haloperidol may not act as a sigma2 antagonist; (4) and (+)-pent azocine might act on two types of sigma1 receptor: one which is haloperidol sensitive and an other, which is naloxone sensitive but different than the opiate receptors.

The effects of the selective 5-HT$ sb{ rm 1A}$ receptor agonist flesinoxan on neuroendocrine function, temperature, and behavior were assessed in healthy male volunteers using a double-blind, placebo-controlled cross over design. Flesinoxan (7 and 14 $ mu$g/kg) administered intravenously in 11 healthy volunteers, elicited a dose-related decrease in body temperature and an increase in growth hormone, ACTH, cortisol and prolactin plasma levels. In a second independent study, 12 healthy volunteers were pretreated with either the 5-HT$ sb{ rm 1A}$ antagonist pindolol (30 mg, p.o.), the non-selective 5-HT$ sb1$-5-HT$ sb2$ antagonist, methysergide (4 mg, p.o.), or placebo prior to being administered of flesinoxan (1 mg, i.v.). The growth hormone response to flesinoxan was blocked by pindolol but not by methysergide whereas the prolactin response was blocked by methysergide but not by pindolol. The ACTH and cortisol response to flesinoxan were potentiated by methysergide. The flesinoxan-induced hypothermia was attenuated by both methysergide and pindolol, although the latter effect did not reach statistical significance. The present results suggest that the growth hormone response, and to a lesser extent the hypothermic response to intravenous infusion of flesinoxan may serve as a valid index of 5-HT$ sb{ rm 1A}$ receptor function in human.

In this study, light and electron microscopic quantitative analyses were used to examine whether exogenous nerve growth factor (NGF) and/or monosialoganglioside GM1 treatment could affect non-cholinergic systems in the neocortex of the adult rat brain after a devascularising lesion. The two neuronal systems I looked at were the extrinsic noradrenergic and intrinsic somatostatinergic systems. Immediately after unilateral vascular decortication, adult rats received for seven days, via minipump, vehicle, NGF (12 $ mu$g/day) and/or GM1 (1.5 mg/day) into the cerebroventricular space. Thirty days after the lesion, the animals were perfused with histological fixatives, the brains removed and relevant sections processed for dopamine $ beta$-hydroxylase (DBH) and somatostatin immunocytochemist at the light and electron microscopic levels. The lesion caused a reduction in the total length of the DBH immunoreactive (IR) fiber segments, which was not attenuated by either NGF or GM1 treatment or both combined. The somatostatin-IR network, on the other hand, was unaffected by the lesion and there was no sprouting of the somatostatin fibers with trophic factor therapy. I observed, however, a marginally significant decrease in the somatostatin fiber network when NGF and GM1 were administered simultaneously. I also found no significant differences in the size and number of synapses of both the DBH-IR and somatostatin-IR boutons, following lesion and drug treatments. These results suggest that NGF and/or GM1 therapy does not cause regrowth in the noradrenergic and somatostatinergic cortical fiber networks and presynaptic elements following a devascularizing lesion.

Chlorisondamine (CHL) is a nicotinic antagonist that blocks for several weeks most of the centrally-mediated behavioural effects of nicotine. However, the mechanism for the long-lasting action of CHL in vivo and the brain regions it targets are largely unknown. We hypothesized that the persistent blockade produced by CHL may result from uptake by neuronal terminals, followed by retrograde transport and accumulation of CHL (or metabolite) in the perikarya. The hypothesis was tested in rats, using locomotor tests to measure nicotinic antagonism within mesolimbic dopaminergic neurons. Results did not entirely support the hypothesis. Our hypothesis also predicted that CHL would block the stimulatory effect of nicotine on cerebral glucose utilization only in regions where CHL accumulates in appreciable amounts. To determine which brain regions are targeted by CHL, we used the 2-deoxy-D- (1-$ sp{14}$C) glucose method (Sokoloff et al., 1977). Again, the hypothesis was not supported.

The overall objective of this project was to study the ontogeny and receptor signaling of myocardial alpha1adrenoceptor (alpha1AR) subtypes. It was found that alpha1AR-mediated inotropic effects and phosphatidylinositide (PI) turnover in neonatal and adult rat myocardium are mediated by different receptor subtypes. In neonatal rats, alpha 1AAR play a predominant role, although both alpha1AAR and alpha 1BAR are present in approximately equal amount as assayed by ligand binding; however, both alpha1AAR and alpha1BAR contribute to the positive inotropic response of adult rat myocardium. alpha1D AR are not functionally expressed in neonatal rat hearts but may play a minor role in adult myocardium. On the other hand, alpha1DAR are the predominant subtypes mediating the contractile response of the rat aorta to alpha1AR agonists. / alpha1AR-mediated positive inotropic effect seems to be mediated by Ca2+-independent PKC isoforms (nPKC); the activation of Ca2+-dependent isoforms (cPKC) may inhibit the myocardial contraction. This inference is suggested by the following data: (1) phenylephrine-induced positive inotropic response was potentiated by DAG kinase inhibitor R59949, and inhibited by PKC inhibitor BIM but not by selective cPKC inhibitor G0 6976; (2) phenylephrine caused a translocation of nPKC (delta and epsilon) but not of cPKC(alpha); (3) simultaneous activation of both cPKC and nPKC by PDBu and selective activation of cPKC by thymeleatoxin resulted in negative inotropy, which was blocked by BIM as well as Go 6976. / In neonatal hearts, inactivation of alpha1BAR by CEC potentiated alpha 1AAR-mediated effects on PKC activation, Ca2+ signaling and hypertrophy. Based on these data, I present a model describing a possible mechanism by which alpha1BAR antagonize alpha1AAR-mediated effects via negative coupling to Ca2+ channels. This antagonistic relationship between alpha1AAR and alpha1BAR may be required physiologically for normal alpha1AR-mediated myocardial responses.* / *Please refer to dissertation for diagram.

Neuropeptide Y (NPY) and NPY receptors are concentrated in the hippocampal formation where they modulate cognitive functions and seizures. The cellular mechanisms underlying the physiological roles of NPY in the hippocampus are still rather elusive. Cultured hippocampal cells offer a simple model to study the expression of hippocampal NPY receptor subtypes and their respective cellular distribution. / The present thesis examines the presence of NPY receptors in primary dissociated hippocampal cells in culture using a combination of molecular, pharmacological and immunocytochemical approaches. Receptor binding experiments revealed the preferential expression of Y1-like receptors over the Y2, Y4 and Y5 subtypes in rat hippocampal cultures. Cultured hippocampal cells expressed high level of Y1 receptors and very low amounts (below detection) of the Y2, Y 4 and Y5 receptor binding sites. The genuine nature of the Y1-like receptor expressed in these cells was confirmed using amplification (RT-PCR) of Y1 receptor mRNAs. The cellular phenotype expressing Y1 receptor was investigated using double labeling methods. Specific autoradiographic and immunolabeling signals of Y1-like receptors were observed on neurons (70% of the total population of neurons) and astrocytes (20% of the total population of glia cells) as revealed respectively by neuron specific enolase (NSE) and glial fibrillary acidic protein (GFAP) immunostaining. The Y1 receptor labeling is distributed uniformly over neuronal cell bodies and processes compared to a non-uniform and clustered distribution on type I astrocytes. Neurons labeled by the various Y1 receptor markers were mostly glutamate-positive as revealed by double labeling. Interestingly, a small proportion (2--5%) of NPY-positive hippocampal neurons (NPY-positive cells represent around 10% of the total population of neurons) were also enriched with Y1 receptor labeling. These results suggest the possible autoregulatory role for the Y1 receptor on NPY release. / Taken together, these anatomical and pharmacological results suggest that Y1 receptor may play an important role in the hippocampus via the regulation of astrocytic and/or neuronal functions and the modulation of the release of glutamate and/or NPY.