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The presence of μ-, δ- and κ-binding sites in homogenates of guinea-pig brain was demonstrated by the use of selective labelling techniques. In saturation experiments, the tritiated ligands [^3H]-[D-Ala^2, MePhe^4, Gly-ol^5]enkephalin, [^3H]-dihydromorphine, [^3H]-morphine and [^3H]-dihydronormorphine labelled only the μ-binding site. The δ-binding site could be labelled selectively with [^3H]-[D-Pen^2, D-Pen^5]enkephalin. However, the less selective δ-ligand, [³H]-[D-Ala², D-Leu⁵] enkephalin, could only be used when its μ-binding was blocked with the unlabelled μ-ligand [D-Ala², MePhe⁴, Gly-ol⁵]enkephalin. Selective labelling of the κ-binding site was more of a problem since the non-selective ligands [^3H]-etorphine, [^3H]-(±)-ethylketazocine and [³H]-(-)-bremazocine bind to the μ-, δ- and κ-sites. Therefore, the κ-binding site could only be labelled selectively when the binding of the tritiated ligands to the μ- and δ-sites was prevented by addition of the unlabelled μ-ligand [D-Ala^2, MePhe^4, Gly-ol^5]enkephalin and the unlabelled δ-ligand [D-Ala², D-Leu⁵]enkephalin. By analysis of the saturation curves obtained using these selective labelling techniques, the proportion of binding sites in homogenates of guinea-pig brain at 25°C was 24% μ-sites; 32% δ-sites and 44% κ-sites. The selective labelling techniques were also used to label the μ, δ- and κ-sites in displacement assays. The compounds with the highest degree of preference for each binding site were: for the μ-site, [D-Ala^2, MePhe^4, Gly-ol^5]enkephalin and Tyr-Pro-MePhe-D-Pro-NH_2; for the δ-site, [D-Pen², L-Pen⁵]enkephalin, [D-Pen², D-Pen⁵]enkephalin and ICI 174864 and for the κ-site, U-50,488H and U-69,593. As far as antagonists were concerned, naloxone displayed the highest preference for the μ-binding site and Mr 2266 had a preference for the κ-binding site but neither compound was highly selective unlike the δ-antagonist ICI 174864. The effect of pre-incubation with β-funaltrexamine on opioid binding was investigated in homogenates of guinea-pig brain and myenteric plexus-longitudinal muscle.

Improved procedures for the glycosylation of serine and threonine utilizing Schiff base activation are reported. The procedures are less expensive and more efficient alternatives to previously published methods. The Schiff bases exhibited ring-chain tautomerism in CDCl₃ as shown by ¹H NMR. Acting as glycosyl acceptors, the Schiff bases reacted at RT with simple sugar peracetate donors with BF₃•OEt₂ promotion to provide the corresponding protected amino acid glycosides in good yields. With microwave irradiation, the reactions were complete in 2-5 minutes. Glycosylation with the dipeptide Schiff base shows the potential of this method in the preparation of peptide building blocks. To investigate this reaction further, direct glycosylation of sugar acetates with FMOC-Ser-OH/OBZl under BF₃•OEt₂ promotion in a microwave provided glycosides in high yield. In addition to the expected glycoside products acetylated side products resulting from acetate migration were isolated, suggesting that activation of the anomeric sugar acetates with a Lewis acid such BF₃•OEt₂ led to an oxocarbenium ion, which rearranged to a 1,2-dioxocarbenium ion because of the acetate participating group at C-2. Solvent participation was also illustrated with acetate migration being more pronounced when CH₃CN was used as a solvent and resulted in less product yield and higher amounts of the acetylated product. The acyl transfer products in these reactions where sugar acetates serve as glycosyl donors is reported for the first time, which also implies that ortho-ester like intermediates are important in the reaction mechanism. Keeping the message segment constant in the sequence H-Tyr-DThr-Gly-Phe-Leu- Ser-CO-NH₂ and modification of the address segment with different carbohydrate moieties had little effect on selectivity for binding at the μ, δ, or κ-opiod receptors. However, substitution of D-threonine with D-serine or the less polar D-alanine in the message segment resulted in a loss of κ-receptor affinity. Further replacement of D-threonine with the more hydrophobic D-valine resulted in complete loss of κ-binding affinity generating pure μ-δ agonists. These data suggests that changes in the message segment of the pharmacophore results in the glycopeptide adopting a conformation that is less favorable for 􀀁-binding receptor activity. Finally, the peripheral administration and i.c.v. tests of the drugs suggest that modifications in the message segment of the pharmacophore influences the potency of these compounds.

1 ABSTRACT In this Thesis, we studied properties of μ-, δ-, and κ-opioid receptors in lymphocytes isolated from rat spleen. This splenocytes were exposed to mitogen concanavalin A or opiate morphine and cultivated for 48 hours. Under physiological conditions, level of opioid receptors in immune cells is very low. Due to various factors such as presence of opioids, mitogens, long-term exposition to stress, expression of these receptors can be amplified. In this study we demonstrated, that concanavalin A causes up-regulation of μ-, δ- and κ-opioid receptors in lymphocytes isolated from rat spleen. In control cells no significant signal of μ- or δ-receptors was observed. In contrast, κ-opioid receptors were detected already in control cells. Concanavalin A stimulation caused a 2.4 - fold increase of these receptors. In lymphocytes treated with morphine only μ-opioid receptors were up-regulated, whereas in control cells, there was no signal for these receptor type. δ-opioid receptors were not detected in control or morphine treated cells. κ-opioid receptors were determined in control and also in morphine affected lymphocytes but the amount of these receptors wasn't changed by morphine. Detection of μ-, δ- and κ-opioid receptors using Western blot technique in lymphocytes isolated from rat spleen, that were...

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1. Whole-cell patch recordings were made from substantia gelatinosa (SG) neurons in transverse lumbar spinal cord slices of 15- to 30-day-old rats. 2. Endomorphin 1 (EM-1) or EM-2 (≤ 10 μM) hyperpolarized or induced an outward current in 26 of the 66 SG neurons. The I-V relationship showed that the peptide activates an inwardly rectifying K + current. 3. EM-1 or EM-2 (0.3-10 μM) suppressed short-latency excitatory postsynaptic currents (EPSCs) and long-latency inhibitory postsynaptic currents (IPSCs) in nearly all SG neurons tested or short-latency IPSCs in six of the 10 SG neurons. [Met 5] enkephalin or [D-Ala 2, N-Me-Phe 4, Gly 5-ol]-enkephalin (DAMGO) (1-10 μM) depressed EPSCs and IPSCs. EM-1 or EM-2 depressed synaptic responses without causing a significant change in holding currents or inward currents induced by glutamate. 4. Glutamate also evoked a short-latency outward current in five SG neurons or a biphasic current in two neurons; the outward current was blocked by tetrodotoxin (TTX, 0.3 μM) or bicuculline (10 μM). EM-1 or DAMGO (1 or 5 μM) attenuated the glutamate-evoked outward or biphasic currents in four of the seven SG neurons. 5. EM-1 (1 μM) reduced the frequency, but not the amplitude of miniature EPSCs or miniature IPSCs. 6. Naloxone (1 μM) or the selective μ-opioid receptor antagonist β-funaltrexamine (β-FNA, 25 μM) antagonized the action of EM; EM-induced hyperpolarizations persisted in the presence of the κ-opioid receptor antagonist (nor-binaltorphimine dihydrochloride, 1 μM) and/or σ-opioid receptor antagonist (naltrindole hydrochloride, 1 μM). 7. It may be concluded that EM acting on μ-opioid receptors hyperpolarizes a population of SG neurons by activating an inwardly rectifying K + current, and attenuates excitatory and inhibitory synaptic currents evoked in a population of SG neurons, probably by a presynaptic site of action.

Beta-arrestins have been suggested to regulate μ-, δ-, and κ-opioid receptor-mediated responses. In the present study, we examined the effects of pretreatment with β-arrestin-2 antibody on tail-flick inhibition induced by opioid receptor agonists in the mouse spinal cord. Intrathecal (i.t.) pretreatment with β-arrestin-2 antibody potentiated the antinociception induced by i.t.-administered μ-opioid receptor agonists [D-Ala2,NMePhe4,Gly-ol5]enkephalin (DAMGO) and endomorphin-1, but not endomorphin-2, the δ-opioid receptor agonist [D-Ala2]deltorphin II or the κ-opioid receptor agonist U50,488H. The present result suggests that β-arrestin-2 may tonically down-regulate a selected population of μ-opioid receptors activated by endomorphin-1 or DAMGO in the mouse spinal cord.

The therapeutic benefits attributed to activation of peripheral mechanoreceptors are poorly understood. There is growing evidence that mechanical stimulation modulates substrates in the supraspinal central nervous system (CNS) that are outside the canonical somatosensory circuits. This work demonstrates that activation of peripheral mechnoreceptors via mechanical stimulation (MStim) is sufficient to increase dopamine release in the nucleus accumbens (NAc), alter neuron firing rate in the ventral tegmental area (VTA) and increase membrane translocation of delta opioid receptors (DORs) in the NAc. Further, we demonstrate that these effects are dependent on DORs and acetylcholine receptors. Additionally, MStim can block neuronal markers of chronic ethanol dependence including ethanol-induced changes to VTA GABA neuron firing during withdrawal, and DA release profiles after reinstatement ethanol during withdrawal. These are presented in tandem with evidence that MStim also ameliorates behavioral indices of ethanol withdrawal. Finally, exercise, a modality that includes a mechanosensory component, is shown to alter expression of kappa opioid receptors (KORs) in the NAc. This change substantively depresses KORs influence over evoked DA release in direct contraversion to the effects of chronic ethanol. These changes translate into reduced drinking behavior.

The goal of this dissertation was to investigate the role of μ-opioid receptors in the mechanism of ethanol-stimulated dopamine release in the nucleus accumbens shell (NAcS) of rats. The underlying hypothesis is that blockade of the μ-opioid receptors leads to an attenuation of ethanol-stimulated mesolimbic dopamine release. We prepared ethanol-naïve male Long Evans rats (n = 95) for intravenous (i.v.) drug administration and in vivo microdialysis (in awake, freely moving animals), and analyzed our samples using HPLC and GC for dopamine and ethanol detection, respectively. In one set of experiments, we looked at the effects of naltrexone, a non-selective opioid antagonist, on ethanol-stimulated mesolimbic dopamine release. First of all, we checked to see if naltrexone affected basal dopamine levels in the NAcS. Thereafter, we looked for a dose of naltrexone (i.v.) that was effective in suppressing the release of dopamine in the NAcS evoked by morphine (1 mg/kg, i.v.). Subsequently, we checked to see if doses of naltrexone that inhibited morphine-evoked dopamine were also effective in attenuating dopamine release due to ethanol (1g/kg, 10% w/v, i.v.). To do this, we pretreated rats with naltrexone doses, followed 20 min later by morphine, ethanol or saline (all drugs were administered i.v.). In another set of experiments, we looked at the effect of β-funaltrexamine, a selective μ-opioid antagonist, on ethanol-stimulated dopamine release in the NAcS. Similarly to the previous set of experiments, we looked for a dose of β-funaltrexamine (s.c.) that was effective in suppressing the release of dopamine the NAcS evoked by morphine (1 mg/kg, i.v.), and checked to see if this dose of β-funaltrexamine was also effective in attenuating ethanol-stimulated dopamine release in the NAcS. For the β- funaltrexamine experiments, rats were pretreated with β-funaltrexamine (s.c.) 20- 25 h before i.v. infusions of saline, morphine and ethanol. Morphine increased dopamine release in the NAcS. Naltrexone and β- funaltrexamine significantly attenuated morphine-evoked dopamine release. Also, ethanol increased dopamine release in the NAcS. Naltrexone and β- funaltrexamine, at doses effective in attenuating morphine-evoked dopamine release, suppressed the prolongation, but not the initiation of dopamine release in the NAcS due to ethanol. Naltrexone and β-funaltrexamine did not affect the peak concentration and clearance of ethanol in the brain. The conclusion of this study is that the μ-opioid receptors are involved in a delayed component of ethanol-stimulated dopamine release in the NAcS in ethanol-naïve rats. This is the first study to show that the ethanol-stimulated dopamine response consists of a delayed μ-opioid mechanism. / text