The periaqueductal gray matter mediates opiate-induced immunosuppression.

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.

Long-term treatment with lithium prevents the development of dopamine receptor supersensitivity.

Long-term treatment of rats with haloperidol produced an increased sensitivity to the locomotor and stereotypic effect of apomorphine. This behavioral dopaminergic supersensitivity was accompanied by increased binding of [3H] spiroperidol in the striatum. Rats treated concurrently with lithium and haloperidol failed to develop both behavioral sensitivity to apomorphine and increased striatal dopamine receptor binding. The ability of lighium to prevent recurrent manicdepressive episodes may be related, in part, to its ability to stabilize dopaminergic receptor sensitivity.

(D-Ala2)-Met-enkephalinamide: a potent, long-lasting synthetic pentapeptide analgesic.

[D-Ala2]-Met-enkephalinamide (DALA), a synthetic enkephalin analog designed by in vitro analysis, binds to opiate receptors almost as tightly as methionine-enkephalin. Since it is not susceptible to degradation by brain enzymes, low doses (5 to 10 micrograms) cause profound, long-lasting, morphine-like analgesia when microinjected into rat brain.

Metabolic mapping of the brain during rewarding self-stimulation.

Local rates of cerebral glucose utilization were measured in rats by the quantitative 2-deoxy-D-[14C]glucose autoradiographic method during electrical stimulation of the ventral tegmental area. Rats trained in intracranial self-stimulation showed a pattern of changes in forebrain metabolic activity distinctly different from the pattern seen in rats stimulated by the experimenter. These findings provide information about the distribution of local cerebral activity specific to reinforced instrumental behavior.

Opiate receptor gradients in monkey cerebral cortex: correspondence with sensory processing hierarchies.

In order to obtain information on the possible functions of endogenous opiates in the primate cerebral cortex, we assessed the distribution of mu-like opiate receptors (which selectively bind 3H-labeled naloxone) and delta-like opiate receptors (which selectively bind 3H-labeled D-Ala2, D-Leu5-enkephalin) throughout the cerebral cortex of the rhesus monkey. Stereospecific [3H]naloxone binding sites increased in a gradient along hierarchically organized cortical systems that sequentially process modality-specific sensory information of a progressively more complex nature. Specific [3H]enkephalin binding sites, in contrast, were relatively evenly distributed throughout the cerebral cortex. These results, in combination with electrophysiological studies of monkeys and humans, suggest that mu-like opiate receptors may play a role in the affective filtering of sensory stimuli at the cortical level, that is, in emotion-induced selective attention.

Tight binding dopamine reuptake inhibitors as cocaine antagonists. A strategy for drug development.

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.

Synthesis of an affinity ligand ('UPHIT') for in vivo acylation of the kappa-opioid receptor.

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.

3H-nicotine and 125I-alpha-bungarotoxin-labeled nicotinic receptors in the interpeduncular nucleus of rats. I. Subnuclear distribution.

The distribution of nicotinic receptors within the interpeduncular nucleus (IPN) was determined in male rats following in vitro labeling with the cholinergic ligands 3H-nicotine and 125I-alpha-bungarotoxin (BTX). Autoradiographic images of two rostrocaudal levels of IPN were analyzed by computer-assisted densitometry and the optical density contributed by displaceable labeling was determined in the rostral, central, intermediate, and lateral subnuclei. 3H-nicotine labeling density within the four subnuclei differs significantly at both levels of IPN. The greatest density of labeling is localized in the rostral subnucleus, followed in order of diminishing density by the central, intermediate, and lateral subnuclei. Labeling within the rostral subnucleus is prominently localized within its central zone. In the central subnucleus, a dense concentration of binding sites is apparent in the middle region, adjacent to less dense vertically oriented columns; 3H-nicotine binding sites in the lateral subnuclei appear to be most concentrated medially, adjacent to the intermediate subnuclei. 125I-BTX labeling density within the four subnuclei also differs significantly at both levels of IPN. The greatest density of labeling is found in the rostral subnucleus, followed in order of decreasing density by the lateral, central, and intermediate subnuclei. The ovoid regions of the rostral subnucleus contain dense 125I-BTX labeling. In the lateral subnuclei, 125I-BTX binding appears to be predominantly along the lateral margins of the subnucleus. The present data indicate that the IPN contains two distinct populations of putative cholinergic nicotinic receptors identified, respectively, by 3H-nicotine and 125I-BTX labeling. Each population of labeled receptors is uniquely localized in patterns that suggest differences in density within and across subnuclei.

Opiate receptor localization in rat cerebral cortex.

The differential distributions of [3H]naloxone-labeled and [3H]D-Ala-D-Leu-enkephalin-labeled opiate receptors in rat cerebral cortex were localized autoradiographically and quantified by grain counting and computerized densitometry. In addition, receptor distributions were compared to terminal patterns of thalamocortical projections labeled by axoplasmic transport of [3H]amino acids. Opiate receptors labeled with [3H]naloxone in a mu ligand selectivity pattern show striking laminar heterogeneity and are densest in limbic cortical areas, intermediate in the motor cortex, and fewest in the primary sensory areas. By contrast, opiate receptors labeled with [3H]D-Ala2-D-Leu5-enkephalin in a delta ligand selectivity pattern are much more homogeneously distributed across both regions and laminae within regions. Mu receptors in most cortical areas have density peaks in layers I and VI and each peak shows a density gradient that is sloped within the layer so that the highest densities are at the most superficial and the deepest portions of cortex. In addition, there is an intermediate peak whose laminar position varies depending on the area in which it is found. In rostral agranular cortex, including limbic and motor areas, the [3H]naloxone binding peaks are in layers I, III, and VI. In primary somatosensory cortex, the intermediate peak is in layer Va and in most of remaining homotypical cortex it is in layer IV. Some areas have only bilaminar labeling, in superficial and deep layers; these include portions of the sulcal and retrosplenial cortices. Piriform and entorhinal cortices have dense [3H]naloxone binding only in the deepest layer and show a descending gradient of density toward the superficial layer. The positions of the mu receptor peaks were compared with termination patterns of projections originating in the thalamus. Close correspondence was found between receptor binding in the prelimbic, primary somatosensory, and entorhinal areas and projection terminations arising from the thalamic mediodorsal, posterior, and central medial nuclei, respectively. Although regional variations in [3H]D-Ala2-D-Leu5-enkephalin-labeled receptor density are uncommon, a gradual decrease in the number of sites along the dorsomedial wall of the cortex from anterior cingulate to caudal retrosplenial limbic cortex can be observed. Laminar variations in binding density are small as well; higher concentrations of the peptide binding sites are usually found in the deep cortical layers. These findings emphasize aspects of opiate receptor architecture which may be relevant to identifying cortical "opiatergic" neurocircuitry and raise the possibility of opiate modulation of thalamocortical transmission.

3H-nicotine- and 125I-alpha-bungarotoxin-labeled nicotinic receptors in the interpeduncular nucleus of rats. II. Effects of habenular deafferentation.

The cholinergic innervation of the interpeduncular nucleus (IPN) is wholly extrinsic and is greatly attenuated by bilateral habenular destruction. We describe changes in the labeling of putative nicotinic receptors within this nucleus at 3, 5, or 11 days after bilateral habenular lesions. Adjacent tissue sections of the rat IPN were utilized for 3H-nicotine and 125I-alpha-bungarotoxin (125I-BTX) receptor autoradiography. Compared to sham-operated controls, habenular destruction significantly reduced autoradiographic 3H-nicotine labeling in rostral (-25%), intermediate (-13%), and lateral subnuclei (-36%). Labeling in the central subnucleus was unchanged. Loss of labeling was maximal at the shortest survival time (3 days) and did not change thereafter. In order to establish whether this loss was due to a reduction in the number or the affinity of 3H-nicotine-binding sites, a membrane assay was performed on microdissected IPN tissue from rats that had received surgery 3 days previously. Bilateral habenular lesions produced a 35% reduction of high-affinity 3H-nicotine-binding sites, with no change in binding affinity. Bilateral habenular lesions reduced 125I-BTX labeling in the intermediate subnuclei, and a slight increase occurred in the rostral subnucleus. In the lateral subnuclei, 125I-BTX labeling was significantly reduced (27%) at 3 days but not at later survival times. In view of the known synaptic morphology of the habenulointerpeduncular tract, it is concluded that a subpopulation of 3H-nicotine binding sites within the IPN is located on afferent axons and/or terminals. This subpopulation, located within rostral, intermediate, and lateral subnuclei, may correspond to presynaptic nicotinic cholinergic receptors. Sites that bind 125I-BTX may include a presynaptic subpopulation located in the lateral and possibly the intermediate subnuclei.

Probes for narcotic receptor mediated phenomena. 17. Synthesis and evaluation of a series of trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacet amide (U50,488) related isothiocyanate derivatives as opioid receptor affinity ligands.

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)

Heteroaromatic analogs of 1-[2-(diphenylmethoxy)ethyl]- and 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazines (GBR 12935 and GBR 12909) as high-affinity dopamine reuptake inhibitors.

A new series of heteroaromatic GBR 12935 [1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)-piperazine] (I) and GBR 12909 [1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine] (2) analogs was synthesized and evaluated as dopamine transporter (DAT) ligands. Analogs 5-16, in which the benzene ring in the phenylpropyl side chain of the GBR molecule had been replaced with a thiophene, furan, or pyridine ring, exhibited high affinity and selectivity for the DAT vs serotonin transporter (SERT) and stimulated locomotor activity in rats in a manner similar to the parent compound 2. In cocaine and food self-administration studies in rhesus monkeys, both thiophene-containing (6 and 8) and pyridine-containing (14 and 16) derivatives displayed potency comparable to 2 in decreasing the cocaine-maintained responding at the doses tested (0.8, 1.7, and 3 mg/kg). However, these compounds did not produce the degree of separation between food- and cocaine-maintained responding that was seen with 2. Among the bicyclic fused-ring congeners 17-38, the indole-containing analog of 2, 22, showed the greatest affinity for binding to the DAT, with IC50 = 0.7 nM, whereas the corresponding indole-containing derivative of 1, 21, displayed the highest selectivity (over 600-fold) at this site vs the SERT site.

Development of novel, potent, and selective dopamine reuptake inhibitors through alteration of the piperazine ring of 1-[2-(diphenylmethoxy)ethyl]-and 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazines (GBR 12935 and GBR 12909).

The design, synthesis, and biological evaluation of compounds related to the dopamine (DA) uptake inhibitors: 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (1) and 1-[2-[bis-(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (2) (GBR 12395 and GBR 12909, respectively), directed toward the development and identification of new ligands interacting with high potency and selectivity at the dopamine transporter (DAT) is reported. The substitution of the piperazine ring in the GBR structure with other diamine moieties resulted in the retention of the high affinity of new ligands for the DAT. Some of the modified GBR analogs (e.g. 8, 10, (-)-49, or (-)-50) displayed substantially higher selectivity (4736- to 693-fold) for the dopamine (DA) versus the serotonin (5HT) reuptake site than the parent compounds. The bis(p-fluoro) substitution in the (diphenylmethoxy)ethyl fragment slightly increased the affinity of the ligands at the DA reuptake site but reduced their selectivity at this site (e.g. 9 and 8, 11 and 10, or 17 and 16, respectively). Congeners, such as the series of monosubstituted and symmetrically disubstituted piperazines and trans-2,5-dimethylpiperazines, which lack the (diphenylmethoxy)ethyl substituent lost the affinity for the DAT yet exhibited very high potency for binding to the sigma receptors (e.g.28). The chiral pyrrolidine derivatives of 1, (-)-49, and (+)-49, exhibited an enantioselectivity ratio of 181 and 146 for the inhibition of DA reuptake and binding to the DAT, respectively.

Different neural mechanisms underlie dizocilpine maleate- and dopamine agonist-induced locomotor activity.

This study evaluated and compared the role of mesoaccumbens dopamine and the ventral pallidal region in the locomotor stimulatory action of the non-competitive N-methyl-D-aspartate antagonist dizocilpine maleate and dopamine agonists. Intra-accumbens injections of both amphetamine (1, 5 and 25 nmol) and dizocilpine maleate (1, 5, 25 and 50 nmol) induced a dose-dependent increase in locomotor activity. The N-methyl-D-aspartate antagonist was somewhat less effective than amphetamine. 6-Hydroxydopamine dopamine-depleting lesions of the nucleus accumbens completely blocked locomotor stimulation induced by focal administrations of amphetamine (5 nmol), but were ineffective in altering the actions of dizocilpine maleate (50 nmol). Ibotenic acid lesions of the ventral pallidal region and muscimol injections into this area also prevented the stimulatory effects of systemic amphetamine (1 mg/kg), while having no effect on the locomotor-activating actions of systemic dizocilpine maleate (0.3 mg/kg). Microdialysis studies revealed that systemically administered apomorphine (2 mg/kg) significantly decreased extracellular GABA in the pallidum, which was accompanied by substantial increases in locomotor output. Systemically administered dizocilpine maleate (0.3 mg/kg), on the other hand, also increased locomotor activity without having any effect on pallidal GABA. These data, taken together, indicate that while the locomotor effects of dopamine agonists are dependent upon intact mesoaccumbens dopamine and involve GABAergic efferents from the nucleus accumbens to the ventral pallidum, dizocilpine maleate's stimulatory actions are independent of such mechanisms.

Innervation of substantia nigra neurons by cholinergic afferents from pedunculopontine nucleus in the rat: neuroanatomical and electrophysiological evidence.

Dopaminergic neurons of the substantia nigra pars compacta are excited by nicotine and acetylcholine, and possess both high-affinity nicotine binding sites and intense acetylcholinesterase activity, consistent with a cholinoceptive role. A probable source of cholinergic afferents is the pedunculopontine nucleus, which forms part of a prominent group of cholinergic perikarya located caudal to the substantia nigra in the tegmentum. Although pedunculopontine efferents, many of them cholinergic, project to the substantia nigra pars compacta, it has not been established whether they terminate in this structure. In the first experiment, which combined retrograde tracing with immunohistochemical visualization of cholinergic neurons, cholinergic cells in and around the pedunculopontine nucleus were found to send projections to the substantia nigra. This projection was almost completely ipsilateral. Subsequent experiments employed anaesthetized rats; kainate was microinfused into tegmental sites in order to stimulate local cholinergic perikarya, and concurrently, extracellular recordings were made of single dopaminergic neurons in the substantia nigra. Consistent with our anatomical findings, unilateral microinfusion of kainic acid in or near the pedunculopontine nucleus increased the firing rate of dopaminergic neurons situated remotely in the ipsilateral substantia nigra. The kainate-induced excitation of nigral dopaminergic neurons was dose-related and was prevented by intravenous administration of the centrally-acting nicotinic cholinergic antagonist mecamylamine. These results suggest that cholinergic perikarya in the vicinity of the pedunculopontine tegmental nucleus innervate dopaminergic neurons in the substantia nigra pars compacta via nicotinic receptors.

Locomotor activity induced by the non-competitive N-methyl-D-aspartate antagonist, MK-801: role of nucleus accumbens efferent pathways.

We have recently shown that focal administration of dizocilpine hydrogen maleate (MK-801, a non-competitive N-methyl-D-aspartate antagonist) within the nucleus accumbens increases locomotor activity in a dopamine-independent manner. The purpose of this study was to investigate the neural network underlying locomotor stimulation induced by N-methyl-D-aspartate receptor blockade in the accumbens. In the first experiment, we examined the effect of different doses (1, 5 and 25 nmol) of the active and inactive enantiomers of the N-methyl-D-aspartate antagonist, (+)- and (-)-MK-801, respectively, focally administered in the nucleus accumbens. Only the active enantiomer induced a significant increase in locomotor activity; furthermore, the effect induced by the two highest doses of (+)-MK-801 was significantly different from that induced by (-)-MK-801. In the second part of the study, we performed ibotenic acid lesions to the major output nuclei of the accumbens, the ventral pallidum, mediodorsal thalamus, ventrolateral/ventromedial thalamus and pedunculopontine tegmental nucleus, to observe their effect on locomotor activity induced by focal (+)-MK-801 (25 nmol) administration into the accumbens. None of the lesions had any effect on spontaneous locomotor activity. Hyperactivity induced by accumbens MK-801 administrations was unaffected by ibotenic acid lesions of the pedunculopontine tegmental nucleus, while lesions of the mediodorsal thalamus induced only a partial inhibition. In contrast, ibotenic acid lesions of the ventral pallidum and ventrolateral/ventromedial thalamus completely blocked the motor response induced by accumbens MK-801. These data indicate that the intact mediodorsal thalamus, which has been proposed as a part of the loop that relays accumbens information to the prefrontal cortex, does not seem to be a structure of primary importance in MK-801 locomotor activity. On the contrary, the motor nuclei of the thalamus appear to play a more relevant role, suggesting that different neural substrates may mediate dopamine and glutamate functional output from the nucleus accumbens.

Distinct pattern of c-fos mRNA expression after systemic and intra-accumbens amphetamine and MK-801.

Pharmacological manipulation of both dopamine and glutamate systems affects motor responses in laboratory animals. The two systems, however, seem to act in opposite ways, since direct or indirect activation of dopamine receptors induces similar stimulatory effects to those seen following blockade of N-methyl-D-aspartate receptors. In the present study we compared the pattern of c-fos activation induced by systemic and intra-accumbens administration of the non-competitive N-methyl-D-aspartate antagonist MK-801 and the indirect dopamine agonist amphetamine. Systemic MK-801 induced c-fos mRNA expression in the motor cortex and preferentially in the motor thalamus, i.e. ventrolateral nucleus. Systemic amphetamine, on the other hand, enhanced c-fos mRNA expression in the shell of the accumbens and in limbic thalamic nuclei such as the anteroventral and anterodorsal nuclei. The main effect observed after intra-accumbens administrations of either drug was enhanced c-fos expression in the thalamus, somewhat similar to what seen following systemic administration. In fact also in this case there was a preferential activation of the limbic thalamus by amphetamine and the motor thalamus by MK-801. The present results confirm that different neural substrates underlie behavioral effects induced by systemic administrations of N-methyl-D-aspartate receptor antagonists and dopamine agonists. Further they suggest that intra-accumbens manipulation of the two neural systems could affect different efferent pathways from this structure activating different thalamic targets.

Electrophysiological actions of nicotine on substantia nigra single units.

Extracellular recordings of single unit activity were made in the substantia nigra (SN) of chloral hydrate-anaesthetized rats. Dopaminergic neurones of the pars compacta (SNC) were stimulated by (-)-nicotine bitartrate (1.0 mg kg-1) given subcutaneously (s.c.). This action was prevented by the secondary amine mecamylamine HCl (2.0 mg kg-1 i.v.) but not by a ganglion-blocking dose of the bisquaternary compound chlorisondamine Cl (0.1 mg kg-1 i.v.). Mecamylamine reduced the spontaneous activity of dopaminergic neurones. Nicotine, when administered intravenously (2-128 micrograms kg-1 cumulative dose), also stimulated dopamine cells and this action was dose-related. Nicotine, administered intravenously, (2-128 micrograms kg-1 cumulative dose) markedly excited non-dopamine cells in the pars reticulata (SNR) in a dose-related manner. In rats pretreated with chlorisondamine (0.1 mg kg-1 i.v.), nicotine induced a small excitatory or depressant action, but the marked excitation was not seen. Mecamylamine (2 mg kg-1 i.v.) completely prevented the actions of nicotine. The results are consistent with a direct excitatory action of nicotine on dopaminergic neurones of the substantia nigra pars compacta. The pronounced excitatory action of systemically administered nicotine on non-dopamine cells of the pars reticulata appears to be of peripheral origin.

Alterations in striatal acetylcholine overflow by cocaine, morphine, and MK-801: relationship to locomotor output.

The activity of cholinergic interneurons in the striatum appears to be modulated by a variety of different systems including dopamine, opiate, and glutamate. The purpose of this study was to characterize the effects of drugs known to act on these three systems (i.e., cocaine, morphine, and MK-801) on striatal ACh overflow with microdialysis procedures, and to determine if alterations in ACh function induced by these agents are related to changes in locomotor activity. Cocaine was found to increase striatal ACh following intraperitoneal injections of 20 and 40 mg/kg, but not 10 mg/kg. The increases in locomotor activity induced by cocaine appeared to be dose dependent, while the effects on striatal ACh were not. Injections of 0.1 mg/kg MK-801 (a non-competitive NMDA receptor antagonist) produced dramatic increases in locomotor activity while decreasing striatal ACh overflow. A lower dose (0.03 mg/kg) of MK-801 failed to alter locomotor activity or striatal ACh. Morphine produced an apparent dose-dependent elevation in striatal ACh while only the lowest dose (5 mg/kg) increased locomotor activity. There appears to be no relationship between alterations in striatal ACh and locomotor output following systemic administration of these psychoactive agents.

Assessing pharmacologically induced dopamine receptor sensitivity changes with the Ungerstedt turning model.

Rats were lesioned unilaterally in the substantia nigra with 6-hydroxydopamine. Turning in response to apomorphine and amphetamine was assessed before and 5 days after 3-week treatment with haloperidol. After haloperidol withdrawal, contralateral turning, measured at 5 min following IP injection of 1 mg/kg apomorphine, was significantly less than before haloperidol treatment and ipsilateral turning, measured at 30 min following IP injection of 2 mg/kg amphetamine, was significantly greater than before the haloperidol treatment. These results suggest that dopamine receptor sensitivity increased on the unlesioned side compared to the lesioned side.