Biomedical subjects
Publications and source records attributed to A Pert.
The effect of a 5-HT3 antagonist, ICS 205-930, on ethanol-induced changes in extracellular dopamine, was investigated with in vivo microdialysis. Pretreatment of rats with ICS 205-930 effectively attenuated the subsequent increases in dopamine, in both the nucleus accumbens and corpus striatum. This suggests that 5-HT may be involved in the effects of ethanol on dopaminergic systems.
Regional neurotransmitter changes after acute and chronic electroconvulsive shock (ECS) were studied using the technique of repeated microdialysis. Microdialysis was carried out on alternate sides of the brains of anaesthetised rats before and during the first and the eighth ECS or sham (control) treatments. Extracellular fluid release of monoamines and their metabolites was measured in the frontal cortex, striatum and nucleus accumbens using HPLC with electrochemical detection. The first ECS produced selective regional responses, shown by increased concentrations of noradrenaline (NA) and dopamine (DA) in frontal cortex, by unchanged DA content in striatum, and by a small rise in NA and a fall in DA concentrations in nucleus accumbens. Concentrations of metabolites increased after ECS in all regions studied, and for homovanillic acid and dihydroxyphenylacetic acid, the temporal pattern of these changes did not resemble that of DA. Comparison of neurotransmitter responses as per cent of baseline release after the first and eighth ECS treatments showed they were identical. Basal release of monoamines and metabolites before the first ECS or sham treatment was similar in all regions studied. Prior to the eighth treatment, basal release of NA in the frontal cortex and DA in the striatum was elevated in the ECS-treated animals, while basal release of NA in the nucleus accumbens was reduced in both ECS- and sham-treated animals. These data suggest that acute and chronic ECS have different and region-specific effects on neurotransmitter release, although the overall pattern of these responses is not changed by chronic treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
A series of U50,488 related isothiocyanates was synthesized from enantiomerically pure (S,S)-(+)-trans-2-pyrrolidinyl-N-methylcyclohexylamine [(+)-7] and (R,R)-(-)-trans-2-pyrrolidinyl-N-methylcyclohexylamine [(-)-7]. DCC coupling of (+)- and (-)-7 with nitrophenylacetic acids followed by catalytic hydrogenation and treatment with thiophosgene afforded a series of six isomeric aryl isothiocyanate analogues of U50,488. Similarly, DCC coupling of (+)- and (-)-7 with (+)- and (-)-N-t-Boc-protected phenylglycines afforded four isomeric alkyl isothiocyanates. Evaluation of the isothiocyanates for their capacity to produce wash-resistant inhibition of mu, delta, and kappa sites in vitro was performed using rat and guinea pig brain membranes. None of the compounds was able to irreversibly inhibit binding of [3H]bremazocine to guinea pig and rat brain membranes (depleted of functional mu and delta receptors by pretreatment with acylating agents BIT and FIT). However, (1S,2S)-trans-2-isothiocyanato-N-methyl-N-[2- (1-pyrrolidinyl)cyclohexyl]benzeneacetamide [(-)-1] was able to specifically and irreversibly inhibit kappa receptors labeled by [3H]-U69,593: Incubation of rat brain membranes for 60 min at 25 degrees C with 1 microM of (-)-1 resulted in a wash-resistant reduction of the binding to 11.2 +/- 2.5% of the control. Binding analysis revealed the wash-resistant reduction in [3H]-U69,593 binding by (-)-1 to be through an increase in the Kd without effect on the Bmax. (-)-1 failed to effect mu or delta binding in rat or guinea pig brain under the same conditions. The enantiomer of (-)-1, (1R,2R)-trans-2-isothiocyanato-N-methyl-N-[2- (1-pyrrolidinyl)cyclohexyl]benzeneacetamide [(+)-1], failed to affect kappa receptors labeled by [3H]-U69,593 under the same conditions as for (-)-1. (1S,2S)-trans-3-Isothiocyanato-N-methyl-N-[2- (1-pyrrolidinyl)cyclohexyl]benzeneacetamide [(-)-2] inhibited to 49.6 +/- 5.1% of the control, in a wash-resistant manner, kappa receptors labeled by [3H]-U69,593. However, (-)-2 was not as selective as (-)-1 since it also reduced [3H]DADLE (delta) binding to 82.4 +/- 8.0% of the control value. (1S,2S)-trans-4-Isothiocyanato-N-methyl-N-[2-(1-pyrrolidinyl)- cyclohexyl]benzeneacetamide [(-)-3] exhibited selective wash-resistant inhibition of delta receptors labeled by [3H]DADLE resulting in a reduction in binding to 42.9 +/- 4.2% of control.(ABSTRACT TRUNCATED AT 400 WORDS)
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It is apparent that stimuli associated with psychomotor stimulants as well as opiates acquire the ability to elicit motor behaviors that probably reflect the acquisition and operation of incentive motivational processes. Such conditioning also appears to be a critical determinant of behavioral sensitization seen with repetitive administration of these agents. The conditioning of motor excitation to stimuli associated with psychomotor stimulants follows the principles of classical conditioning and is relatively long lasting. Dopaminergic mechanisms appear to be involved in the acquisition of such conditioned behaviors, since neuroleptics are effective blockers of the process. Dopaminergic blockade probably disrupts conditioning through several different mechanisms including attenuation of the conditioned and unconditioned excitatory properties of the CS and blockade of the US. DA blockade prevents stimuli associated with psychomotor stimulants from acquiring and subsequently generating positive affective motivational states that are reflected by increases in motoric output. While dopamine appears to be necessary for the formation of conditioned motor excitation, it is not critically involved in the expression of the conditioned effects. This seems to suggest that DA may serve only to modulate the formation of motivationally significant associations but is not involved in the expression of conditioned drug effects that may be mediated through DA-independent pathways. The amygdala and nucleus accumbens are two structures in the CNS involved in the acquisition of conditioned motor excitation. Interestingly, both of these brain regions are the recipients of mesolimbic DA input. Dopamine probably plays different roles in each region during the conditioning process. In the amygdala, mesolimbic DA may serve to modulate processes that attach emotional significance to environmental stimuli; further, DA may play a role in determining which stimuli gain access to structures afferent to the amygdala, including the nucleus accumbens. Dopamine in the nucleus accumbens, on the other hand, serves to determine which limbic inputs gain access to the motor pathways. In this way, DA in the nucleus accumbens may translate the motivational determinants of behavior that are mediated by limbic structures into biologically relevant actions. Understanding the mechanisms that determine the conditioning of drug effects to associated stimuli also has possible relevance for elucidating processes underlying addictive behaviors. For example, it has been proposed (Stewart et al. 1984) that the acquisition of incentive motivational properties by stimuli associated with drugs determines the craving in addicts.(ABSTRACT TRUNCATED AT 400 WORDS)
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The experiments reported in this study tested the hypothesis that tight binding dopamine (DA) reuptake inhibitors might act as cocaine antagonists. Binding studies demonstrated that the high affinity dopamine reuptake inhibitor, 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3-phenylpropyl]piperazine (GBR12909) produced a wash-resistant inhibition of the DA transporter in rat striatal membranes as labeled by [3H]cocaine or [3H]1-[2-(diphenyl- methoxy)ethyl]-4-(3-phenylpropyl)piperazine [( 3H]GBR12935), indicative of tight binding. In vivo microdialysis experiments showed that administration of 25 mg/kg GBR12909 to rats produced a modest, but not statistically significant, increase in the extracellular levels of striatal DA, while this same dose of GBR12909 inhibited the ability of cocaine to elevate extracellular DA levels by 64%. These data suggest that tight binding DA reuptake blockers may provide a fruitful approach for developing a cocaine antagonist.
The periaqueductal gray matter of the mesencephalon (PAG) subserves a variety of diverse autonomic functions and also appears to be a site for opiate action in the induction of immunosuppression. Microinjections of morphine into the PAG, but not into other opiate receptor-containing neuroanatomical sites, result in a rapid suppression of natural killer (NK) cell activity. The NK cell suppression can be blocked by prior peripheral administration of the opiate antagonist naltrexone. These findings demonstrate that certain central actions of opiates that produce changes in NK cell function are mediated through opiate receptors in the PAG and identify a brain region involved in opiate regulation of immune function.
The isothiocyanate analog (1S,2S-trans-2-isothiocyanato-4,5-dichloro-N- methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide, 3a) of the highly selective kappa-opioid receptor agonist, U50,488, was prepared as a potential site-directed affinity ligand for acylation of kappa-opioid receptors in vivo. The isothiocyanate (3a) which we have designated UPHIT and its enantiomer (3b) were synthesized in 3 steps starting from optically pure (1S,2S)-(+)-trans-2-pyrrolidinyl-N-methyl-cyclohexylamine (4a) and its enantiomer (4b), respectively, thus defining their absolute stereochemistry. Binding in vitro of the 1S,2S enantiomer 3a to kappa receptors labelled by [3H]U69,593 was shown to occur with an IC50 value of 25.92 +/- 0.36 nM, whereas 827.42 +/- 5.88 and 115.10 +/- 1.23 nM were obtained for the IC50 value of the 1R,2R enantiomer (3b) and (+/-)-3 respectively. Intracerebroventricular (ICV) injection of 100 micrograms of (+/-)-3 into guinea-pig brain followed by analysis of remaining kappa-binding sites 24 h later revealed that (+/-)-3 depleted 98% of the kappa receptors that bind [3H]U69,593 and 40% of those that bind [3H]bremazocine. These preliminary data suggest exciting uses for these compounds in furthering our knowledge of the kappa-opioid receptor.
Repeated, intermittent administration of psychomotor stimulants has been shown to produce increasing effects (behavioral sensitization) in many species of animals. In a novel two-day sensitization paradigm, rats that received a single high dose of cocaine (40 mg/kg) compared with saline on day 1 showed an increased locomotor response to a challenge dose (10 mg/kg) on day 2. This effect is conditioned or context-dependent; i.e., it is only observed if the rats received cocaine in an environment similar to the test environment. If the cocaine-induced hyperactivity on day 1 is prevented with pharmacological agents such as haloperidol and diazepam, sensitization on day 2 does not occur. Furthermore, although moderate (0.2 mg/kg) and high doses (0.5 mg/kg) of haloperidol (day 1) prevented the development of sensitization to cocaine, they were ineffective when given prior to the day 2 challenge dose in preventing the expression of sensitization. Thus, this type of cocaine sensitization appears to involve conditioning, show stimulus generalization, and offer a possible model for clinical neuroleptic nonresponsiveness once stimulant-induced pathological behavior has been induced.
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Slide-mounted brain sections were used to visualize the distribution of opiate receptors in the hypothalamus of male and female hamsters using the vitro film autoradiography. Sex differences were found in the binding density and patterns of [3H]naloxone-labeled receptors. The distribution and density of [3H][D-Ala2,D-Leu5]enkephalin-labeled delta-receptors in adjacent brain sections were similar in males and females. Male hamsters showed a U-shaped pattern of [3H]naloxone binding in the sexually dimorphic nuclear complex with 28% and 34% greater labeling of the sexually dimorphic nucleus (SDN) and bed nucleus/stria terminalis (BNST), respectively, than periovulatory estrous females. Estrous and diestrous females showed a V-shaped pattern of [3H]naloxone binding in the same region, but binding density was higher at diestrus. Greater specific [3H]naloxone binding in diestrous females was also evident following extensive prewashing of slide-mounted tissue sections indicating that residual endogenous opioids were not occupying receptors, and thus, reducing the labeling of receptors in tissue from estrous females. An estrous-linked change in the affinity of hypothalamic opiate receptors was suggested by findings that [3H]naloxone binding density was greater in tissue from diestrous females when incubations were conducted in the presence of a 1-nM, but not a 10-nM, concentration of the labeled antagonist. Finally, a dense are of [3H]naloxone binding was discovered in the dorso-suprachiasmatic region of the hypothalamus. These data provide evidence for a sexual dimorphism in the distribution and density of opiate receptors in hamsters. The data suggest that mu- or kappa-receptors are more likely than delta-receptors to be involved in mediating hypothalamic effects of endogenous and exogenous opioids on reproductive functions in this species.
1-Methyl-4-phenylpyridine (MPP+) is an oxidative metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydroxypyridine (MPTP). MPP+ produced local cell death when injected directly into substantia nigra compacta, locus coeruleus, or dorsal and median raphe nuclei of rats. Corresponding significant decreases in dopamine, serotonin and norepinephrine levels were observed in the terminal areas. These observations indicate that MPP+ is a non-selective neurotoxin which causes lesions not only in dopaminergic neurons but also in noradrenergic and serotonergic systems following intracranial administration. Selective lesioning of these monoaminergic systems could only be achieved by a stereotaxic injection of MPP+ into specific brain regions containing monoamine neurons.
Cyclofoxy, a fluorinated analog of naltrexone, has been designed specifically to permit in vivo labeling of opiate receptors in experimental animals and ultimately, humans. Recently, using positron emission tomography (PET), 3-[18F]acetylcyclofoxy was shown to accumulate in opiate receptor-rich brain regions of a live baboon and to be stereospecifically displaced by injections of (-)-naloxone but not (+)-naloxone. Autoradiographic evidence is presented here that the unacetylated compound, [3H]cyclofoxy, labels a population of opiate receptors in brain after in vivo injections that is virtually identical to that labeled by [3H]naloxone. The in vivo binding patterns of [3H]cyclofoxy in brain were similar to those obtained following incubation of slide-mounted brain sections in vitro. Intravenous injections of [3H]cyclofoxy to rats yielded high (greater than 4:1) striatal and thalamic to cerebellar binding ratios in brain homogenates, supernatants and in 24 micron-thick brain sections 60 min after 30 mu Ci per animal (spec. act. = 16.4 Ci/mmol). Autoradiographs revealed the typical opiate antagonist binding profile with marked retention of [3H]cyclofoxy in the striatal patches, subcallosal streak, medial habenula and central thalamus with little retention of label in cerebellum. [3H]Cyclofoxy binding was reversible since the radiolabeled drug disappeared from brain tissue within 2 h after injections to rats, or could be removed from brain slices in vitro by washing slide-mounted tissue sections for 45 min. In addition, after in vitro washing the same brain sections again bound [3H]cyclofoxy or [3H]naloxone in the same pattern. When pre-washed brain sections were incubated with [3H]cyclofoxy in the presence of unlabeled naloxone, [3H]cyclofoxy binding was reduced to background levels. These data show that [3H]cyclofoxy labels-sensitive opiate receptors in vivo and in vitro. The present results combined with evidence that cyclofoxy demonstrates a low level of toxicity in animals suggest that cyclofoxy is an excellent tool with which to study the physiological role of opiate receptors in living animals using in vivo autoradiography, and in humans using PET.
Alpha 2-adrenergic receptors mediate adrenergic stimulation of growth hormone (GH) secretion in the rat. The GH response to the alpha 2-adrenergic agonist clonidine has thus been used as an index of alpha 2-adrenergic receptor responsiveness. Pharmacologic manipulations known to upregulate alpha 2-adrenergic receptor sensitivity would then be expected to result in an enhancement of the GH response to clonidine. To test this hypothesis, rats were injected in the lateral ventricle with either 6-hydroxydopamine or sterile saline. One month following the lesion, urethane-anesthetized rats from each group were administered clonidine or saline. Venous samples for plasma GH were drawn prior to or following the clonidine or saline administration. Rats administered clonidine had greater GH responses than those administered saline within either the lesioned or nonlesioned groups. The GH response to clonidine was significantly greater in the lesioned group than in the nonlesioned group. As 6-hydroxydopamine pretreatment upregulates alpha 2-adrenergic receptors, these results support the validity of the use of the GH response to clinidine as an index of alpha 2-adrenergic receptor responsiveness.