Chronic treatment with pentazocine or SFK 10047 decrease proenkephalin mRNA levels in the rat striatum and nucleus accumbens.

In order to assess the effect of sigma (sigma) receptor activity on striatal and limbic enkephalinergic cells we measured proenkephalin mRNA levels by in situ hybridization histochemistry after chronic treatment with the sigma-receptor agonist drugs SKF 10047 or pentazocine. Chronic treatment with SKF 10047 decreased proenkephalin mRNA levels in the anterior aspect of the caudate-putamen (CPU) and the nucleus accumbens by 20-22% relative to controls. No significant effect was observed in the medial aspect of the CPU. Treatment with pentazocine decreased proenkephalin mRNA levels by 20-25% in all 3 brain regions. The results demonstrate that sigma-receptor activity can exert tonic effects on proenkephalin mRNA expression in the striatum and the nucleus accumbens of the rat.     

Gender differences in prodynorphin but not proenkephalin mRNA expression in the striatum of adolescent rats exposed to prenatal cocaine

The objective of this study was to determine if prenatal cocaine affects the levels of prodynorphin and proenkephalin mRNA in male and female adolescent rats. Pregnant dams received cocaine or vehicle from gestational days 8–22 and upon delivery, the pups were fostered. At postnatal days 42–44, pups were killed and brains removed and frozen. Sections of striatum and nucleus accumbens were processed for prodynorphin and proenkephalin mRNA expression. Prenatal cocaine did not affect the expression of proenkephalin mRNA, but males showed higher expression than females. However, prodynorphin mRNA was lower in female rats exposed to cocaine compared to controls. Prenatal cocaine appears to have unique effects on neuropeptides during adolescence.     

Different sensitivity of in vivo acetylcholine transmission to D1 receptor stimulation in shell and core of nucleus accumbens.

We investigated whether D1 dopaminergic receptors modulate in vivo acetylcholine output in the shell and core areas of rat nucleus accumbens using the microdialysis technique. Subcutaneous injection (1, 2 and 3 mg/kg) of the D1 agonist SKF 82958 enhanced acetylcholine output in both areas of the nucleus accumbens while the selective D1 antagonist SCH 39166 (0.15 and 0.30 mg/kg, s.c.) lowered it. Both SKF 82958 and SCH 39166 were more effective in the shell than in the core region. The increase in acetylcholine release induced by SKF 82958 in the shell was tetrodotoxin-sensitive. The dopamine release inducer d-amphetamine (1 and 2mg/kg, s.c.) and the dopamine uptake inhibitor cocaine (10 and 20 mg/kg, i.p.) dose-dependently raised acetylcholine release in the shell and core areas. The dopaminergic stimulants, like the direct-acting D1 compounds, were more effective in the shell than in the core compartment of the nucleus accumbens. The acetylcholine increases in the shell induced by d-amphetamine (2 mg/kg), cocaine (20 mg/kg) and SKF 82958 (3 mg/kg) were antagonized by the D1 antagonists SCH 39166 (5 microM) and SCH 23390 (10 microM), applied locally by reverse dialysis. The results suggest that dopamine acting at the D1 receptors exerts a tonic stimulatory control over the cholinergic function of the shell and core compartments of the nucleus accumbens with the shell being more strongly influenced.     

Effect of nicotine on mRNA levels encoding opioid peptides,vasopressin and α3 nicotinic receptor subunit in the rat

Summary The effect of acute and chronic nicotine treatment of rats on the mRNA levels coding for the three opioid peptide precursors, for provasopressin and for the a3 subunit of nicotinic receptors in brain, pituitary and/or adrenal medulla of rats was investigated. Nicotine was found to increase the levels of proenkephalin mRNA in the adrenal medulla, but did not affect the levels of PENK mRNA in striatum, hypothalamus and hippocampus. The mRNA levels of prodynorphin were increased together with that of provasopressin in the hypothalamus after nicotine, whereas the prodynorphin mRNA levels in the hippocampus and the striatum remained unchanged. Nicotine treatment resulted in an increase in the pro-opiomelanocortin mRNA levels in the anterior pituitary and in a decrease in the intermediate pituitary, but did not change the levels of pro-opiomelanocortin mRNA in the hypothalamus. The levels of mRNA coding for the ₃ subunit of nicotinic receptors in the hypothalamus and the adrenal medulla remained unchanged. The increase in the prodynorphin and provasopressin mRNA levels in the hypothalamus was most pronounced 1 day after s.c. application of two doses of 0.4 mg/kg nicotine (about 100% above control). A smaller increase in mRNA concentrations (about 30%) was found after tonic infusion of the drug for 4 days (4 mg/kg per day), whereas no change was observed after tonic infusion of nicotine for 7 and 14 days indicating the development of complete tolerance. The increase in proenkephalin mRNA levels in the adrenal medulla was highest after the short-term application of nicotine (about 150% above control). Less, but still significant increases in the mRNA levels (about 40%) were also seen after 7 and 14 days of tonic nicotine administration suggesting that no complete desensitization is developing to the effect of nicotine. This desensitization appeared to be less pronounced when the drug was applied in a pulsatile manner using minipumps, since a high increase in the PENK mRNA levels (100% above control levels) was observed after intermittent infusion of nicotine (six boli per day of 1 mg/kg for 7 days). These findings demonstrate that nicotine can alter gene expression of opioid peptides and vasopressin in certain rat tissues, and that the mode of drug administration plays an important role in this effect of nicotine. The possibility that the pulsatile administration of nicotine by cigarette smokers may also result in an altered expression of opioid peptide genes in humans is discussed.Abbreviations PENK proenkephalin - POMC pro-opiomelanocortin - MSH melanocyte stimulating hormone - PDYN prodynorphin - CRF corticotropin releasing factor     

Blockade of cannabinoid receptors by SR141716 selectively increases Fos expression in rat mesocorticolimbic areas via reduced dopamine D2 function.

The present study investigated, in rats, whether blockade of cannabinoid CB1 receptors may alter Fos protein expression in a manner comparable to that observed with antipsychotic drugs. Intraperitoneal administration of the selective CB1 receptor antagonist, SR141716, dose-dependently (1.0, 3.0 and 10 mg/kg) increased Fos-like immunoreactivity in mesocorticolimbic areas (prefrontal cortex, ventrolateral septum, shell of the nucleus accumbens and dorsomedial caudate-putamen), while motor-related structures such as the core of the nucleus accumbens and the dorsolateral caudate-putamen were unaffected. In the ventrolateral septum, taken as a representative structure, the Fos-inducing effect of SR141716 (10 mg/kg) was maximal 2 h after injection and returned to near control levels by 4 h. Within the prefrontal cortex, SR141716 increased the number of Fos-positive cells predominantly in the infralimbic and prelimbic cortices, presumptive pyramidal cells being the major cell types in which Fos was induced. The D1-like receptor antagonist, SCH23390 (0.1 mg/kg), did not prevent the Fos-inducing effect of SR141716 in any brain region examined (prefrontal cortex, nucleus accumbens, ventrolateral septum and dorsomedial caudate-putamen), although SCH23390 significantly reduced Fos expression induced by cocaine (20 mg/kg) in all these regions. By contrast, the dopamine D2-like agonist, quinpirole (0.25 mg/ kg), counteracted SR141716-induced Fos-like immunoreactivity in the ventrolateral septum, the nucleus accumbens and the dorsomedial caudate-putamen, while no antagonism was observed in the prefrontal cortex. Microdialysis experiments in awake rats indicated that SR141716, at doses which increased Fos expression (3 and 10 mg/kg), did not alter dopamine release in the shell of the nucleus accumbens. Finally, SR141716 increased the levels of neurotensin-like immunoreactivity in the nucleus accumbens, but not in the caudate-putamen. Collectively, the present results show that blockade of cannabinoid receptors increases Fos- and neurotensin-like immunoreactivity with characteristics comparable to those reported for atypical neuroleptic drugs.     

In vivo autoradiography of [H]SCH 39166 in rat brain: selective displacement by D1/D5 antagonists

The purpose of this study was to examine the receptor occupancy of D1/D5 antagonists for D1-like dopamine receptors in rat brain using [³H]SCH 39166, a highly selective D1/D5 antagonist with low affinity for 5HT2 receptors. A single concentration of triated SCH 39166 was administered to rats, with or without competing doses of the D1/D5 antagonist SCH 23390 and unlabeled SCH 39166, the D2-like antagonists haloperidol or the 5-HT₂ antagonist ketanserin. The bound radioactivity in the cortex, striatum, nucleus accumbens and olfactory tubercle was then quantified using an in vivo autoradiographic procedure. The results indicated that [³H]SCH 39166 was dose dependently displaced by the D1/D5 antagonists in regions associated with both the nigro-striatal pathway and the mesolimbic dopamine pathway, particularly the nucleus accumbens. Neither haloperidol nor ketanserin displaced [³H]SCH 39166 in any of the regions examined. The data were compared with previously published data examining the in vivo binding of [³H]SCH 39166 in rat brain homogenates. The relative values obtained were comparable to values detected in rat brain homogenates after in vivo binding of [³H]SCH 39166.     

In vivo autoradiography of [3H]SCH 39166 in rat brain: selective displacement by D1/D5 antagonists

The purpose of this study was to examine the receptor occupancy of D1/D5 antagonists for D1-like dopamine receptors in rat brain using [3H]SCH 39166, a highly selective D1/D5 antagonist with low affinity for 5HT2 receptors. A single concentration of triated SCH 39166 was administered to rats, with or without competing doses of the Dl/D5 antagonist SCH 23390 and unlabeled SCH 39166. the D2-like antagonists haloperidol or the 5-HT, antagonist ketanserin. The bound radioactivity in the cortex, striatum, nucleus accumbens and olfactory tubercle was then quantified using an in vivo autoradiographic procedure. The results indicated that [3H]SCH 39166 was dose dependently displaced by the Dl/D5 antagonists in regions associated with both the nigro-striatal pathway and the mesolimbic dopamine pathway, particularly the nucleus accumbens. Neither haloperidol nor ketanserin displaced [3H]SCH 39166 in any of the regions examined. The data were compared with previously published data examining the in vivo binding of [3H]SCH 39166 in rat brain homogenates. The relative values obtained were comparable to values detected in rat brain homogenates after in vivo binding of [3H]SCH 39166.     

Effects of cortical and striatal dopamine D1 receptor blockade on cued versus noncued behavioral responses

Various lines of evidence suggest that disruptions in brain dopamine (DA) transmission produce behavioral impairments that can be overcome by salient response-eliciting environmental stimuli. We examined here whether D1 receptor blockade within striatal or frontal cortical DA target regions would differentially affect head entry responses elicited by an auditory cue compared with those occurring during noncued intertrial intervals. Rats received 2 drug-free 28-trial daily sessions in which an auditory cue was immediately followed by food delivery. On the following day, separate groups of rats received bilateral infusions of D1 antagonist SCH23390 to the dorsomedial striatum (DMS), nucleus accumbens (NAcc) core, or the medial prefrontal cortex (mPFC). SCH23390 infused into the DMS and NAcc core suppressed noncued head entries but had no effect on head entries in response to the auditory cue. SCH23390 infused to the mPFC did not reduce either cued or noncued approach responses. Systemic administration of the drug, in contrast, reduced the frequency of both cued and noncued approaches. The results are consistent with the notion that has emerged from the Parkinson's literature that reduced DA transmission produces behavioral suppression that can be overcome by salient environmental response elicitors, and extends this notion by showing that D1 receptor transmission within the striatum strongly suppresses noncued responses while leaving the identical behavior intact when cued by an environmental stimulus.     

A comparison of D1 receptor binding and mRNA in rat brain using receptor autoradiographic and in situ hybridization techniques.

D1, a subtype of the dopamine receptors, is widely distributed in the nervous system and has been shown to be positively coupled to adenylate cyclase. Using a combination of in vitro receptor autoradiographic and in situ hybridization techniques, the present study examines the co-distribution of D1 receptor binding sites and D1 receptor mRNA in adjacent rat brain sections. D1 receptor binding sites were labeled using the selective antagonist [3H](R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzaz epin- 7-ol (SCH23390) (4.6 nM), in the presence of 1 microM ketanserin, while the D1 receptor mRNA was visualized with a 35S-labeled riboprobe corresponding to a region between transmembrane domains III and VI of the rat D1 receptor (base pairs 383-843). Analysis of serial sections suggested a good agreement between D1 receptor binding and mRNA in several brain regions, including the paleocortex, caudate-putamen, nucleus accumbens, amygdala, and suprachiasmatic nucleus. Marked discrepancies between D1 receptor binding and mRNA were observed in other brain regions including the entopeduncular and subthalamic nuclei, substantia nigra (pars reticulata), hippocampus, and cerebellum. While technical considerations may contribute to these results, much of the discordance between the distributions is probably due to the differential localization of D1 receptor mRNA in cell bodies and receptor binding sites on fibers and may provide insights into receptor synthesis, transport, and membrane insertion. In the basal ganglia, for instance, D1 receptors are synthesized in the striatum and are either transported to efferent projections in areas such as the substantia nigra, or remain localized in striatal cells bodies. Ibotenic acid lesions in the striatum are consistent with these conclusions and demonstrate a coordinate loss of D1 receptor binding and mRNA in the caudate-putamen that is accompanied by a degeneration of fibers projecting to substantia nigra and a loss of D1 binding in the pars reticulata. Neurons in the dentate gyrus and in the granular layer of the cerebellum, on the other hand, synthesize D1 receptors and transport them entirely to either their dendritic or axonal fields, respectively, in the molecular layer. This analysis provides a better understanding of dopaminergic receptor systems in the CNS and their anatomical organization.     

Effect of apomorphine on striatal synaptotagmin 7 mRNA levels in reserpinized rats

Synaptotagmin 7 (Syt 7) is a Ca2+ sensor implicated in the regulation of membrane fusion in vesicular transport, but its precise role in neurons is still a matter of controversy. Dopaminergic drugs have been shown to modulate its expression in the striatum. Here we investigate whether dopamine receptor agonist-up-regulation of Syt 7 mRNA is specifically involved in the pathophysiological adaptations of hypersensitive striatum by analyzing other dopaminergic neurons containing brain regions. We treated rats with systemic reserpine injections that rapidly depletes dopamine throughout the brain, but leaves dopaminergic neurons spared from destruction. We analyzed the effects of apomorphine, a D1 and D2 receptor agonist on Syt 7 mRNA expression in caudate putamen, nucleus accumbens, cingulate cortex, substantia nigra compacta, ventral tegmental area and hippocampus. The treatment with reserpine resulted in akinesia, catalepsy and rigidity and up-regulation of proenkephalin and down-regulation of preprotachykinin mRNA in caudate putamen, indicating a severe depletion. By acute treatment with apomorphine proenkephalin mRNA was down-regulated and preprotachykinin mRNA up-regulated in the caudate putamen of reserpinized rats. Apomorphine increased Syt 7 mRNA levels only in striatum (caudate putamen and nucleus accumbens) of reserpinized rats, while in other brain regions it did not have such effect. The reserpinization and/or apomorphine treatment had no effect on Syt 1 mRNA expression in caudate putamen. It may be concluded, that in the striatum depleted of biogene amines, such as occurs after reserpine treatment, the up-regulation of Syt 7 could play a specific role as part of hypersensitive response to dopaminergic agonists.     

Neuroleptics increase c-fos expression in the forebrain: contrasting effects of haloperidol and clozapine.

The mechanisms by which the atypical neuroleptic clozapine produces its therapeutic effects in the treatment of schizophrenia without causing the extrapyramidal side effects that are characteristic of most antipsychotic drugs remain unclear. Recently, a single injection of the typical antipsychotic haloperidol has been shown to increase c-fos expression in the striatum [Dragunow et al. (1990) Neuroscience 37, 287-294]. C-fos is a proto-oncogene that encodes a 55,000 mol. wt phosphoprotein, Fos, which is thought to assist in the regulation of "target genes" containing an AP-1 binding site. Because a wide variety of physiological and pharmacological stimuli increase c-fos expression, it has been proposed that Fos immunohistochemistry might be useful in mapping functional pathways in the central nervous system. The present experiments examined some potential neuroanatomical differences in the actions of clozapine and haloperidol by comparing their effects on c-fos expression in the medial prefrontal cortex, nucleus accumbens, striatum and lateral septum. The effects of the selective dopamine receptor antagonists SCH 23390 (D1) and raclopride (D2) were also examined. Haloperidol (0.5, 1 mg/kg) and raclopride (1, 2 mg/kg) produced large increases in the number of Fos-containing neurons in the striatum and nucleus accumbens. SCH 23390 (0.5, 1 mg/kg) reduced the number of Fos-positive neurons in the nucleus accumbens and striatum, and had no effect in the other regions. Neither haloperidol nor raclopride increased the number of Fos-positive neurons in the medial prefrontal cortex. Haloperidol, but not raclopride, produced a modest increase in c-fos expression in the lateral septal nucleus. Clozapine (10, 20 mg/kg) was without effect in the striatum; however, it significantly increased the number of Fos-positive neurons in the nucleus accumbens, medial prefrontal cortex and lateral septal nucleus. Destruction of mesotelencephalic dopaminergic neurons with 6-hydroxydopamine abolished the increase in Fos expression in the nucleus accumbens and striatum produced by haloperidol and raclopride, and also blocked the clozapine-induced increase in the nucleus accumbens. However, the inductive effects of clozapine and haloperidol on c-fos expression in the lateral septal nucleus and of clozapine in the medial prefrontal cortex were not affected by the 6-hydroxydopamine lesions. These results suggest that clozapine's unique therapeutic profile may be related to its failure to induce Fos in the striatum as well as its idiosyncratic actions in the lateral septum and medial prefrontal cortex. The effects of clozapine in these latter regions do not appear to be mediated by dopaminergic mechanisms.     

Opioid gene expression in rat striatum is modulated via opioid receptors: evidence from localized receptor inactivation

The irreversible opiate antagonists beta-funaltrexamine (beta-FNA) and beta-chlornaltrexamine (beta-CNA) were injected into rat striatum. One day later, mu-opioid receptor binding, as assessed by receptor autoradiography, was abolished in the injected striatum, while [3H]spiperone binding remained largely unaffected. In situ hybridization was used to examine possible effects on striatal proenkephalin mRNA and prodynorphin mRNA content. The levels of proenkephalin mRNA were increased ipsilaterally following beta-CNA injection, but were slightly decreased following beta-FNA injection. Prodynorphin mRNA content was also increased by beta-CNA administration. The results provide evidence for a differential modulation of striatal opioid peptide gene expression via distinct opioid receptors.     

Autoradiographic identification of D1 dopamine receptors labelled with [3H]dopamine: distribution, regulation and relationship to coupling.

On the basis of experiments made on striatal membranes, Leff and Creese [Molec. Pharmac. (1985) 27, 184-192] have proposed that tritiated dopamine binds to a high-affinity agonist state of D1 dopamine receptors (D1h) which adopt this conformation when they are associated with the GTP-binding protein involved in the transduction process. Quantitative autoradiography was thus used to look for the distribution of these D1h sites in the rat brain and to compare it with that of D1 receptors labelled with [3H]7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benz aze pine [( 3H]SCH23390), a D1 antagonist. The effects of unilateral 6-hydroxydopamine lesion of the ascending dopamine pathways on the density of [3H]dopamine D1h and [3H]SCH23390 binding sites in the striatum and the nucleus accumbens were also analysed. In the striatum, when D2 receptors were blocked by spiroperidol (20 nM), [3H]dopamine was found to bind specifically to dopamine receptors of the D1 type. Complementary experiments made with dopamine uptake blockers indicated that high-affinity dopamine uptake sites were not labelled by [3H]dopamine under our experimental conditions. The anatomical distribution of [3H]dopamine D1h binding sites was found to be markedly different from that of [3H]SCH23390 binding sites. This was particularly the case in the substantia nigra, some amygdaloid nuclei and the prefrontal cortex--structures in which the ratios between [3H]SCH23390 and [3H]dopamine binding sites were more than seven-fold higher than that observed in the striatum. [3H]SCH23390 binding was not significantly affected in either the striatum or the nucleus accumbens six weeks after a complete unilateral destruction of ascending dopamine pathways. In contrast, a marked decrease in [3H]dopamine D1h binding sites was found in both structures, but this effect was lower in the medioventral (-60%) than in the laterodorsal (-81%) part of the striatum, even though dopamine denervation was uniform throughout the structure. Preincubation of the sections with dopamine (0.5 microM) led to a partial recovery (+126%) in the lesioned striatum and an increase of [3H]dopamine labelling in the control striatum (+68%). This suggest that the presence of dopamine stabilizes the D1h state of D1 receptors. The absence or low amount of dopamine, either due to dopamine denervation or naturally occurring (prefrontal cortex), would then impair the [3H]dopamine D1h binding. In addition, a lower coupling of D1 receptors with adenylate cyclase was observed in the substantia nigra when compared to that in the striatum: this may explain the relatively weak [3H]dopamine binding in the substantia nigra.(ABSTRACT TRUNCATED AT 400 WORDS)     

Chronic and acute effects of 3,4-methylenedioxy-N-methylamphetamine ('Ecstasy') administration on the dynorphinergic system in the rat brain

The prodynorphin system is implicated in the neurochemical mechanism of psychostimulants. Exposure to different drugs of abuse can induce neuroadaptations in the brain and affect opioid gene expression. The present study aims to examine the possibility of a common neurobiological substrate in drug addiction processes. We studied the effects of single and repeated 3,4-methylenedioxy-N-methylamphetamine ('Ecstasy') on the gene expression of the opioid precursor prodynorphin, and on the levels of peptide dynorphin A in the rat brain. Acute (8 mg/kg, intraperitoneally) 3,4-methylenedioxy-N-methylamphetamine markedly raised, two hours later, prodynorphin mRNA levels in the prefrontal cortex, and in the caudate putamen, whereas it decreased gene expression in the ventral tegmental area. Chronic (8 mg/kg, intraperitoneally, twice a day for 7 days) 3,4-methylenedioxy-N-methylamphetamine increased prodynorphin mRNA in the nucleus accumbens, hypothalamus and caudate putamen and decreased it in the ventral tegmental area. Dynorphin A levels increased after chronic treatment in the ventral tegmental area and decreased after acute treatment in the nucleus accumbens, prefrontal cortex and hypothalamus. These findings confirm the role of the dynorphinergic system in mediating the effects of drugs of abuse, such as 3,4-methylenedioxy-N-methylamphetamine, in various regions of the rat brain, which may be important sites for the opioidergic mechanisms activated by addictive drugs.     

D1-like and D2 dopamine receptor antagonists administered into the shell subregion of the rat nucleus accumbens decrease cocaine, but not food, reinforcement

Cocaine self-administration experiments were designed to assess the respective roles of D1-like and D2-like dopamine receptors in the ventral forebrain in cocaine reinforcement. D1-like or D2-like dopamine receptor antagonists were microinjected into the nucleus accumbens core, nucleus accumbens shell, neostriatum or lateral septum prior to sessions in which cocaine was self-administered under a progressive ratio schedule by rats. The results indicated that administration of a D1/5 (SCH-23390) or a D2/D3/D4 (eticlopride), but not a D3 (U99194A) or D4 (L-750,667), dopamine receptor antagonist into the core and shell of the nucleus accumbens decreased the reinforcing efficacy of cocaine. However, in control experiments intra-accumbal core administration of SCH-23390 or eticlopride decreased food self-administration, whereas administration of these drugs into the accumbens shell had no effect on food reinforcement. Neither SCH-23390 nor eticlopride influenced cocaine reinforcement when administered into the neostriatum or lateral septum. Collectively, these results indicate that D1-like and D2 dopamine receptors in the nucleus accumbens shell selectively modulate the reinforcing efficacy of cocaine, whereas D1-like and D2 dopamine receptors in the accumbens core have a more general influence on reinforced behaviors.     

Dopaminergic D1 and D2 receptor antagonists decrease prosomatostatin mRNA expression in rat striatum.

The effect of acute dopamine receptor antagonist treatment on cellular prosomatostatin mRNA expression was investigated in the adult rat striatum using the technique of non-radioactive in situ hybridization. Adult female Wistar rats were given a single intraperitoneal injection of either raclopride (D2 antagonist), SCH 23390 (D1 antagonist) or the D1 (S) enantiomer SCH 23388. Animals were killed either 1, 3 or 9 h following the single i.p. injection and their brains rapidly removed. Striatal sections were then processed for in situ hybridization using an alkaline phosphatase-labelled oligonucleotide probe complementary to a portion of the rat somatostatin cDNA. Blockade of dopamine D1 and D2 receptors resulted in a significant decrease in the cellular content of prosomatostatin mRNA. However, no change in the number of prosomatostatin mRNA containing striatal cells was observed following any of the treatments at any time point. These findings demonstrate that the cellular content of prosomatostatin mRNA in the adult rat striatum is influenced by selective dopamine D1 and D2 receptor antagonists. Further, these findings are consistent with a functional interaction between dopamine and somatostatin in the rat striatum.     

Quantitative autoradiographical analysis of the age-related modulation of central dopamine D1 and D2 receptors

Quantitative autoradiography of [3H]SCH 23390 and [3H](-)-sulpiride binding was performed in the brain of rats of various ages (3, 11 and 24 months) in order to study the changes in D1 and D2 receptor density with age. Binding of [3H]SCH 23390 in the caudate-putamen decreased progressively and markedly at rostral levels in 11- and 24- compared with 3-month-old rats (max. decrease -63%) while at caudal levels significant decrease was observed only in 24-month-old rats. [3H](-)-Sulpiride binding progressively decreased during aging in the caudate-putamen at rostral levels and the decrease was more pronounced laterally (-70% at 24 months), while at caudal levels no significant decrease was observed. D1 and D2 binding sites also decreased in the nucleus accumbens and olfactory tubercle of aged rats, while in the substantia nigra only the D1 receptors appeared to be modified with aging. No change was found in the entopeduncular nucleus, amygdala, frontoparietal, suprarinal-prefrontal and anterior cingulate cortex. The results indicate that the age-associated decrease of D1 and D2 receptors is not widespread, being confined to dopaminergic areas with high density of dopamine receptors.     

Autoradiographic localization of D1 and D2 dopamine receptors in the human brain

The distribution of dopamine D1 and D2 receptors in several human brain regions was investigated using autoradiography with the radioligands [3H]SCH 23390 and [3H]spiroperidol. The highest densities of both dopamine receptor types are seen in the nucleus caudatus, putamen and nucleus accumbens. Whereas the density of the D2 receptors is similar in the two segments of the globus pallidus, the pars medialis of the globus pallidus contains a three-fold higher concentration of D1 receptors than the pars lateralis. D1 and D2 receptors are present in the amygdala and substantia nigra. Both receptor types are absent in the cerebellum. The thalamus contains low densities of D1 receptors but no D2 receptors. Only D2 receptors are seen in the anterior lobe of the pituitary gland. The whole cerebral cortex is rich in D1 receptors, while D2 receptors, in low concentrations, are confined to the entorhinal area and cingulate cortex.     

D1-receptor antagonists: comparison of [3H]SCH39166 to [3H]SCH23390.

A radiolabeled form of the benzonaphthazephine, SCH39166 was used to characterize the binding of this D1 antagonist in cortex, and an autoradiographic comparison of the localization of [3H]SCH39166 to [3H]SCH23390 (D1 antagonist and forerunner of SCH39166) binding was performed. The Kd for [3H]SCH39166, calculated from dissociation and association rate constants (1.09 nM), was comparable to the Kd value derived from Scatchard analyses of saturation data (1.74 nM). [3H]SCH39166 binds to brain tissue in a saturable manner with high affinity and low non-specific binding. Inhibition of [3H]SCH39166 binding by dopaminergic and serotonergic agents supports the hypothesis that this is indeed a D1-specific compound with little overlap onto serotonin (5-HT) receptors. The affinity of [3H]SCH39166 for 5-HT2 and 5-HT1c receptors is at least an order of magnitude lower than the affinity of [3H]SCH23390 for these same receptor sites. Quantitative autoradiographic analysis of [3H]SCH39166 and [3H]SCH23390 binding indicates high D1-receptor density in the caudate-putamen, nucleus accumbens, olfactory tubercle, substantia nigra and entopeduncular nucleus. Low levels of binding (not significantly above background) were detected with [3H]SCH39166 in lamina IV of the cortex and in choroid plexus; areas which had significant [3H]SCH23390 binding and are known to have a high density of 5-HT (5-HT2 and 5-HT1c respectively) receptors.     

A comparison of D1 receptor binding and mRNA in rat brain using receptor autoradiographic and in situ hybridization techniques.

D1, a subtype of the dopamine receptors, is widely distributed in the nervous system and has been shown to be positively coupled to adenylate cyclase. Using a combination of in vitro receptor autoradiographic and in situ hybridization techniques, the present study examines the co-distribution of D1 receptor binding sites and D1 receptor messenger RNA in adjacent rat brain sections. D1 receptor binding sites were labeled using the selective antagonist [3H]SCH23390 (4.6 nM) in the presence of 1 microM ketanserin, while the D1 receptor messenger RNA was visualized with a 35S-labeled riboprobe corresponding to a region between transmembrane domains III and VI of the rat D1 receptor (bp 383-843). Analysis of serial sections suggested a good agreement between D1 receptor binding and messenger RNA in several brain regions, including the paleocortex, caudate-putamen, nucleus accumbens, amygdala and suprachiasmatic nucleus. Marked discrepancies between D1 receptor binding and messenger RNA were observed in other brain regions including the entopeduncular and subthalamic nuclei, substantia nigra (pars reticulata), hippocampus and cerebellum. While technical considerations may contribute to these results, much of the discordance between the distributions is likely due to the differential localization D1 receptor messenger RNA in cell bodies and receptor binding sites on fibers and may provide insights into receptor synthesis, transport and membrane insertion. In the basal ganglia, for instance, D1 receptors are synthesized in the striatum and are either transported to efferent projections in areas such as the substantia nigra, or remain localized in striatal cells bodies. Ibotenic acid lesions in the striatum are consistent with these conclusions and demonstrate a coordinate loss of D1 receptor binding and messenger RNA in the caudate-putamen that is accompanied by a degeneration of fibers projecting to substantia nigra and a loss of D1 binding in the pars reticulata. Neurons in the dentate gyrus and in the granular layer of the cerebellum, on the other hand, synthesize D1 receptors and transport them entirely to either their dendritic or axonal fields, respectively, in the molecular layer. This analysis provides a better understanding of dopaminergic receptor systems in the CNS and their anatomical organization.