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Biomedical subjects

Richard Young

Publications and source records attributed to Richard Young.

32 records · Page 2Linked to original sources
PubMed2004

Cecal volvulus in two African green monkeys (Cercopithecus athiops sabeus).

Following short-term signs of weakness, depression, and/or anorexia of less than 24 h, two adult male African green monkeys (Cercopithecus aethiops sabeus) of St. Kitts origin died from complications of cecal volvulus. Gaseous distention was radiologically apparent in one animal. Necropsy of both monkeys revealed cecal volvulus, one at the ileocecal junction and one involving a segment of the distal portion of the ileum and cecum. Congestion and hemorrhage were evident microscopically in the lamina propria of the affected intestine, with variable necrosis.

Animals↗
PubMed2003

In vitro characterization of ephedrine-related stereoisomers at biogenic amine transporters and the receptorome reveals selective actions as norepinephrine transporter substrates.

Ephedrine is a long-studied stimulant available both as a prescription and over-the-counter medication, as well as an ingredient in widely marketed herbal preparations, and is also used as a precursor for the illicit synthesis of methamphetamine. Ephedrine is related to phenylpropanolamine, a decongestant removed from the market place due to concerns that its use increased the risk of hemorrhagic stroke. Standard pharmacology texts emphasize that ephedrine is both a direct and indirect adrenergic agonist, activating adrenergic receptors both by direct agonist activity as well as by releasing norepinephrine via a carrier-mediated exchange mechanism. Chemically, ephedrine possesses two chiral centers. In the present study, we characterized the stereoisomers of ephedrine and the closely related compounds pseudoephedrine, norephedrine, pseudonorephedrine (cathine), methcathinone, and cathinone at biogenic amine transporters and a large battery of cloned human receptors (e.g., "receptorome"). The most potent actions of ephedrine-type compounds were as substrates of the norepinephrine transporter (EC50 values of about 50 nM) followed by substrate activity at the dopamine transporter. Screening the receptorome demonstrated weak affinity at alpha2-adrenergic and 5-hydroxytryptamine7 receptors (Ki values 1-10 microM) and no significant activity at beta-adrenergic or alpha1-adrenergic receptors. Viewed collectively, these data indicate that the pharmacological effects of ephedrine-like phenylpropanolamines are likely mediated by norepinephrine release, and although sharing mechanistic similarities with, they differ in important respects from those of the phenylpropanonamines methcathinone and cathinone and the phenyisopropylamines methamphetamine and amphetamine.

Adrenergic Agents↗
PubMed2003

Behavioral and biochemical investigations of bupropion metabolites.

The stimulus effects of bupropion metabolites were examined in a drug discrimination procedure using (-)nicotine- and (+)amphetamine-trained rats. (+)- and (-)threohydrobupropion partially substituted in each group. R,R-hydroxybupropion produced vehicle-appropriate responding in (-)nicotine animals but, when given in combination with the training dose of (-)nicotine, resulted in an attenuated effect. S,S-Hydroxybupropion partially (66%) substituted for (-)nicotine. In (+)amphetamine-trained animals, S,S-hydroxybupropion (ED50=4.4 mg/kg) generalized completely and was similar in potency to bupropion (ED50=5.4 mg/kg). Bupropion and its metabolites lacked affinity for nicotinic acetylcholinergic receptors, but all antagonized (-)nicotine-induced 86Rb+ efflux in cells expressing alpha3beta4 nicotinic cholinergic receptors. S,S-Hydroxybupropion possessed affinity at the dopamine transporter comparable to bupropion, and was also found to bind at the norepinephrine transporter. Although it is unlikely that any metabolite isomer is chiefly responsible for the stimulus actions of bupropion, some probably play a role in the complex actions of this agent.

Amphetamine↗
PubMed2002

(-)6-n-Propylnicotine antagonizes the antinociceptive effects of (-)nicotine.

Several 6-alkyl analogues of nicotine were examined in radioligand binding and in vivo functional assays. Although (-)6-ethylnicotine (3) binds with high affinity at nACh receptors (Ki=5.6 nM) and produces nicotine-like actions, its n-propyl homologue (-)4 (Ki=22 nM) failed to produce such effects. In fact, (-)4 antagonized the antinociceptive effects of (-)nicotine in the tail-flick assay in mice, but not the spontaneous activity or discriminative stimulus effects of (-)nicotine. Compound (-)4 appears to selectively antagonize only one of the three effects examined and is an interesting cholinergic agent for subsequent investigation.

Analgesics↗
PubMed2002

Nicotine and bupropion share a similar discriminative stimulus effect.

Bupropion is a weakly potent central nervous system (CNS) stimulant that is marketed both as an antidepressant and as an anti-smoking aid. The mechanism(s) by which it produces its effects is not well understood. In the present study, the effect of bupropion was examined in rats trained to discriminate the stimulus effect of 0.60 mg/kg of (-)-nicotine from saline in a two-lever drug discrimination task. In tests of stimulus generalization (substitution), the nicotine (ED(50)=0.17 mg/kg) stimulus completely generalized to bupropion (ED(50)=5.50 mg/kg). In addition, interaction studies were conducted that evaluated the effect of 3.0 mg/kg of bupropion, a dose that when given alone produced saline-appropriate responding, in combination with various doses of nicotine. This application resulted in an enhancement of the potency of nicotine (ED(50)=0.05 mg/kg), as indicated by a leftward shift of the nicotine dose-effect function. In tests of stimulus antagonism, various doses of bupropion were administered prior to the training dose of nicotine and were found to be ineffective as antagonists of the nicotine stimulus. In contrast, the nicotinic acetylcholine receptor (nicotine receptor) antagonist mecamylamine (AD(50)=0.40 mg/kg) completely blocked the stimulus effect of nicotine. Mecamylamine did not attenuate the stimulus generalization of bupropion. The results demonstrated that bupropion can produce a nicotine-like response in nicotine-trained animals, but it does so via a mechanism of action that is unlike that of nicotine. It is speculated that bupropion may be somewhat effective as an anti-smoking treatment in people who are motivated to quit smoking because low doses of bupropion produce a nicotine-like effect(s) that serve as a suitable substitute for nicotine.

Animals↗
PubMed2002

Functional diversity among 5-substituted nicotine analogs; in vitro and in vivo investigations.

Two 5-substituted derivatives of nicotine (nicotinic acetylcholine receptor: K(i)=2.4 nM) were synthesized and evaluated: 5-bromonicotine (K(i)=6.9 nM) and 5-methoxynicotine (K(i)=14.3 nM). Despite their high affinity, neither 5-bromonicotine nor 5-methoxynicotine mimicked nicotine in producing antinociceptive (tail-flick, hotplate), hypolocomotor, or hypothermic effects in mice. Neither agent antagonized the hypolocomotor actions of nicotine, whereas 5-methoxynicotine, but not 5-bromonicotine, antagonized the antinociceptive (tail-flick) activity of nicotine in a dose-related manner. In tests of stimulus generalization using rats trained to discriminate 0.6 mg/kg of (-)-nicotine from vehicle, 5-bromonicotine substituted for nicotine. Further evaluation of 5-bromonicotine indicated that it might be a partial agonist at alpha4beta2 receptors (stimulation of Rb(+) efflux; alpha4beta2 receptors expressed in oocytes) and at alpha3-containing nicotinic acetylcholine receptors (synaptosomal dopamine release). Thus, 5-bromonicotine might be acting as a partial agonist at alpha4beta2 receptors and/or some of its effects might be related to interactions with non-alpha4beta2 receptors. Clearly, the effects of 5-bromonicotine and 5-methoxynicotine are different from those of nicotine, and from one another. These actions demonstrate that substitution at the 5-position of nicotine exerts a profound influence on the pharmacological profile as well as agonist/antagonist properties of nicotine.

Analgesics↗
PubMed2002

Further characterization of the stimulus properties of 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline.

This investigation is based on the premise that conformational restriction of abused phenylalkylamines in a tetrahydroisoquinoline conformation alters their pharmacology in such a manner that their original action is lost and that a new action emerges. TDIQ or 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline, is a conformationally constrained phenylalkylamine that serves as a discriminative stimulus in animals. Although TDIQ bears structural resemblance to phenylalkylamine stimulants (e.g., amphetamine), hallucinogens (e.g., 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane [DOM]), and designer drugs (e.g., N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane [MDMA], N-methyl-1-(4-methoxyphenyl)-2-aminopropane [PMMA]), the TDIQ stimulus failed to generalize to (+)amphetamine or MDMA. In the present investigation, further evaluations were made of the stimulus nature of TDIQ. Specifically, the stimulus similarities of TDIQ, PMMA, and DOM were examined. In no case was stimulus generalization (substitution) observed. The results confirm that TDIQ produces stimulus effects distinct from those of the abovementioned phenylalkylamines. We also examined the structure-activity relationships of a series of TDIQ analogs, including several that might be viewed as conformationally restricted (CR) analogs of phenylalkylamine hallucinogens, stimulants, and designer drugs. These agents were examined in rats trained to discriminate either DOM (1.0 mg/kg), (+)amphetamine (1.0 mg/kg), MDMA (1.5 mg/kg), or TDIQ (5.0 mg/kg) from saline vehicle. Whereas we have demonstrated that none of these agents retains their respective phenylalkylamine stimulus actions, several of these agents were found to substitute for TDIQ. N-Methylation abolished TDIQ-stimulus action. These results, coupled with previous findings, imply that TDIQ derivatives represent a novel class of phenylalkylamines analogs with unique stimulus properties. Preliminary radioligand binding studies suggest that an alpha2-adrenergic mechanism might underlie the stimulus effects produced by TDIQ.

Animals↗
PubMed2002

Effect of 1-(3,4-methylenedioxyphenyl)-2-aminopropane and its optical isomers in PMMA-trained rats.

1-(3,4-Methylenedioxyphenyl)-2-aminopropane (MDA) is a drug of abuse that is known to produce stimulus effects similar to those of the stimulant phenylalkylamine (+)amphetamine and the hallucinogenic phenylalkylamine 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). Earlier, a working model was described to account for the stimulus effects produced by phenylalkylamines. Such agents can produce one or more of three distinct effects: an amphetamine effect, a DOM effect and a third effect that is typified by the agent N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA). Because MDA is known to produce two of the three effects, in the present investigation, we sought to determine if racemic MDA or either of its optical isomers could produce a PMMA-like effect in animals. Administration of S(+)MDA, R(-)MDA and (+/-)MDA to rats trained to discriminate 1.25 mg/kg of PMMA from saline vehicle under a VI 15-s schedule of reinforcement resulted in substitution in each case. (+/-)MDA and S(+)MDA were nearly equipotent and several fold more potent than R(-)MDA. The results are not only consistent with the proposed model but also identify (+/-)MDA as the first phenylalkylamine shown to produce all three types of stimulus effects (i.e., amphetamine-like, DOM-like and PMMA-like) in rats.

3,4-Methylenedioxyamphetamine↗
PubMed2002

Effect of PMA optical isomers and 4-MTA in PMMA-trained rats.

1-(4-Methoxyphenyl)-2-aminopropane (PMA) and its sulfur analog, 1-(4-methylthiophenyl)-2-aminopropane (4-MTA), have been misrepresented as the controlled substance analog, N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA; "Ecstasy"). Because MDMA has been shown to produce both amphetamine-like and N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA)-like stimulus effects in rats, we examined S(+)PMA, R(-)PMA and 4-MTA in rats trained to discriminate either PMMA (1.25 mg/kg) or (+)amphetamine (1.0 mg/kg) from saline vehicle. The sulfur analog of PMMA (i.e., 4-MTMA) was also examined. The PMMA stimulus generalized to R(-)PMA (ED50=0.4 mg/kg), whereas S(+)PMA produced a maximum of 72% PMMA-appropriate responding. 4-MTA (ED50=0.3 mg/kg) also substituted for PMMA, but 4-MTMA produced a maximum of only 36% PMMA-appropriate responding. None of the four agents substituted for (+)amphetamine. Hence, like MDMA, R(-)PMA and 4-MTA are capable of producing PMMA stimulus effects in rats, but unlike MDMA, neither agent substituted for (+)amphetamine.

Animals↗
PubMed2002

Central stimulants as discriminative stimuli. Asymmetric generalization between (-)ephedrine and S(+)methamphetamine.

Central stimulants readily serve as training stimuli in drug discrimination studies and typically substitute for one another in tests of stimulus generalization regardless of which is used as training drug. We have previously found that, although substitution occurs between (+)amphetamine and (-)ephedrine, substitution did not occur upon administration of S(+)methamphetamine to (-)ephedrine-trained animals. In the present investigation, rats were trained to discriminate S(+)methamphetamine (1 mg/kg) from saline vehicle and tests of stimulus generalization were performed with several stimulants, including (-)ephedrine. The S(+)methamphetamine stimulus (ED(50)=0.06 mg/kg) generalized to R(-)methamphetamine (ED(50)=1.61 mg/kg), S(+)amphetamine (ED(50)=0.28 mg/kg), S(-)methcathinone (ED(50)=0.21 mg/kg), methylphenidate (ED(50)=0.28 mg/kg), cocaine (ED(50)=3.68 mg/kg) and (-)ephedrine (ED(50)=13.1 mg/kg). Hence, stimulus generalization between S(+)methamphetamine and (-)ephedrine is apparently asymmetrical. In a companion study, R(-)methamphetamine was administered to rats trained to discriminate (-)ephedrine (4 mg/kg); substitution occurred and R(-)methamphetamine (ED(50)=0.92 mg/kg) was found to be nearly equipotent with (-)ephedrine (ED(50)=0.8 mg/kg). Although the exact basis for the observed results are unclear, they are discussed in terms of the different effects of (-)ephedrine and the methamphetamine optical isomers on neurotransmitter release and reuptake.

Animals↗
PubMedDate not supplied

The stimulus effect of 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline is similar to that of cocaine but different from that of amphetamine.

5,6,7,8-Tetrahydro-1,3-dioxolo[4,5-g]isoquinoline (TDIQ) is a conformationally restricted phenylalkylamine related in structure to amphetamine and N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA) that does not act as a locomotor stimulant. To further evaluate this agent, a group of six rats was trained to discriminate 5.0 mg/kg of TDIQ from vehicle and tests of stimulus generalization were conducted to define the stimulus. The TDIQ stimulus (ED(50)=0.9 mg/kg) failed to generalize to the central stimulants (+)amphetamine, methylphenidate or (-)ephedrine but, curiously, generalized to cocaine (ED(50)=1.5 mg/kg). When administered to rats (n=5) trained to discriminate 1.0 mg/kg of (+)amphetamine from vehicle, TDIQ produced a maximum of 7% (+)amphetamine-appropriate responding, whereas when administered to rats (n=7) trained to discriminate 4.0 mg/kg of (-)ephedrine from vehicle, TDIQ produced a maximum of 57% drug-appropriate responding. Administration of MDMA to TDIQ-trained animals resulted in 76% TDIQ-appropriate responding. Tests of stimulus generalization were also conducted with fenfluramine, nisoxetine, clenbuterol, imipramine and buspirone, and tests of antagonism were conducted with haloperidol and R(+)SCH-23390 using the TDIQ-trained animals. Results were inconclusive in that these agents either failed to completely substitute for or failed to completely antagonize the TDIQ stimulus. Nevertheless, the generalization seen with cocaine, the partial generalization seen with (-)ephedrine, MDMA, nisoxetine, clenbuterol and buspirone and the partial antagonism seen with haloperidol suggest that TDIQ might be acting through a mixed mechanism that involves adrenergic, dopaminergic and/or serotonergic systems. Given that TDIQ is an agent that seems to differentiate among the stimuli produced by amphetamine, methylphenidate, ephedrine and cocaine, it is proposed that further tests be undertaken, using animal models of cocaine abuse, to evaluate the potential usefulness of TDIQ as pharmacotherapy in cocaine dependence.

Amphetamine↗