Substituted phenoxyalkylpiperazines as dopamine D3 receptor ligands.

A novel series of potential antipsychotic agents were prepared by combination of condensed heterocycles containing bridgehead nitrogen with (2-methoxyphenyl)piperazine using phenoxyalkyl spacer of variable length. The affinity of the compounds was determined at rat cloned D3 and rat D2, 5-HT1A receptors by an vitro receptor binding assay. The D3 selectivity of the compounds was calculated from the Ki values.

Double activity imaging reveals distinct cellular targets of haloperidol, clozapine and dopamine D(3) receptor selective RGH-1756.

Acute administration of typical (haloperidol) and atypical (clozapine) antipsychotics results in distinct and overlapping regions of immediate-early gene expression in the rat brain. RGH-1756 is a recently developed atypical antipsychotic with high affinity to dopamine D(3) receptors that results in a unique pattern of c-Fos induction. A single injection of either antipsychotic results in c-fos mRNA expression that peaks around 30 min after drug administration, while the maximum of c-Fos protein induction is seen 2 h after challenge. The transient and distinct temporal inducibility of c-fos mRNA and c-Fos protein was exploited to reveal and compare cellular targets of different antipsychotic drugs by concomitant localization of c-fos mRNA and c-Fos immunoreactivity in brain sections of rats that were timely challenged with two different antipsychotics. Double activity imaging revealed that haloperidol, clozapine and RGH-1756 share cellular targets in the nucleus accumbens, where 40% of all labeled neurons displayed both c-fos mRNA and c-Fos protein. Haloperidol activates cells in the caudate putamen, while clozapine-responsive, single labeled neurons were dominant in the prefrontal cortex and major island of Calleja. RGH-1756 targets haloperidol-sensitive cells in the caudate putamen, but cells that are activated by clozapine and RGH-1756 in the major island of Calleja are different.

Analysis of the mesotelencephalic dopamine system by quantitative-trait locus introgression.

One of the significant factors that affect brain dopamine function is the activity of tyrosine hydroxylase (TH), the first and rate-limiting enzyme in catecholamine biosynthesis. For the analysis of the genetically determined role of dopamine function and TH in behavior and in the regulatory mechanisms of the mesotelencephalic dopamine system we devised a novel genetic strategy (Vadasz; Mouse Genome 88:16-18; 1990). We hypothesized that phenotypic introgression and recombinant fixation could ensure the transfer of Quantitative Trait Loci (QTL) from one strain onto the genetic background of another strain, and new, genetically very similar quasi-congenic strains could be created that would carry individual QTLs, or QTLs in various combinations. Here we summarize the construction of the first set of QTL Introgression strains, and present evidence that QTLs that are responsible for the continuous variation of mesencephalic tyrosine hydroxylase activity (TH/MES), have been transferred onto the C57BL/6By (B6) strain background from BALB/cJ (C) and CXBI (I) donor strains with high and low TH/MES, respectively. The QTL transfer was carried out in two directions by repeated backcross-intercross cycles with concomitant selection for the extreme high and low expressions of TH/MES in replicates, resulting in four QTL Introgression lines. Analysis of regional brain TH activities in the course of the QTL introgression indicated that (a) TH activity in B6.I lines showed quite limited heritability, (b) TH/MES was not highly correlated with striatal TH, and (c) the control of hypothalamic and olfactory tubercle TH activities was largely independent from that of TH/MES. Examination of the open-field (OF) behavior data demonstrated that TH activity did not correlate significantly with OF behavior. After 5 backcross-intercross cycles, TH/MES in each replicate line was still significantly different from that of the B6 background strain. A genomewide scanning of microsatellite markers in the QTL introgression lines demonstrated that about 96% of the markers were of background (B6) type. These results indicate the successful transfer of TH/MES QTLs. After the QTL transfer phase of the experiment altogether more than 100 new RQI strains were initiated in the QTL Introgression lines by strict brother x sister mating. After fixing the introgressed QTLs, ten of the inbred RQI strains were tested for TH/MES. The results showed that in one of the new RQI strains TH/MES was restored to a level that is characteristic to the C donor strain, while TH/MES values in some other strains were between those of the background and donor strains, confirming our hypothesis that phenotypic introgression and recombinant fixation can ensure a virtually complete transfer of QTLs. We conclude from this study that complex, continuously distributed neural traits can successfully be subjected to QTL introgression, and the results raise the possibility that the RQI method can be efficiently applied for gene mapping of complex neural and behavioral traits even if their phenotypic expression is sensitive to confounding developmental and environmental variations, genetic interactions, and genotype-environment interactions.

Spike-and-wave neocortical patterns in rats: genetic and aminergic control.

Spontaneously occurring and drug-induced high voltage spike-and-wave electroencephalogram patterns were examined in inbred rats of the Fischer 344 and Buffalo strains and of the random-bred Sprague-Dawley strain at different ages. In addition, tyrosine hydroxylase activity and dopamine D2 receptor density were determined in the substantia nigra, corpus striatum, olfactory tubercle and ponsmedulla areas of Fisher 344 and Buffalo animals. High voltage spike-and-wave episodes were present in 87.5% of the 3-month-old and in 100% of the older Fischer 344 rats. High voltage spike-and-wave episodes were completely absent in 3-month-old Buffalo and Sprague-Dawley animals but could be induced by systemic injection of pentylenetetrazol and at an older age they appeared in 58.3% (12-month) and 71.4% (greater than 26-month) of the subjects of these strains. The incidence and duration of high voltage spike-and-wave episodes were significantly higher/longer in Fischer 344 rats than in the age-matched Buffalo and Sprague-Dawley animals. The dopamine blocker acepromazine induced a several-fold increase of the incidence and duration of high voltage spike-and-wave episodes in 3-month-old Fischer 344 rats, but failed to induce high voltage spike-and-wave episodes in Buffalo animals at this age. However, acepromazine also triggered high voltage spike-and-wave episodes in Buffalo rats when they were pretreated with subthreshold doses of pentylenetetrazol. Tyrosine hydroxylase activity was significantly higher in the substantia nigra, corpus striatum and olfactory tubercle of the Fischer 344 strain than in Buffalo rats. The higher tyrosine hydroxylase activity was paralleled with significantly higher D2 binding values in the corpus striatum and olfactory tubercle of Fischer 344 rats. These findings suggest that the neocortical high voltage spike-and-wave phenotype is genetically mediated and that the inbred Fischer 344 and Buffalo rats with defined bilineal origin will facilitate future works aimed at the identification of genetic elements involved in the generation of neocortical high voltage spike-and-wave episodes. The significant genotype x age interaction supports the suggestion, however, that high voltage spike-and-wave episodes are likely to be influenced by more than one gene; some of them are probably related to the regulation of brain aminergic systems.

Substituted ergolines: potential antipsychotics with unique profile. II. Neurochemical characterization.

A series of lumilysergol and lysergol derivatives were studied with a number of neurochemical methods. The compounds investigated showed heterogenous profiles on receptor binding tests. They were mostly active on D-2 receptors, but some alpha-1, alpha-2 and 5-HT-2 affinity could also be demonstrated. None of the drugs showed remarkable D-1 activities tested on basal and DA-stimulated adenylate cyclase (AC) enzyme in vitro. On the basis of the effects of the drugs on the mouse whole brain monoamine neurotransmitter and metabolite levels and neurotransmitter biosynthesis rates along with the receptor binding data we conclude that their actions are mainly related to the central dopaminergic system(s). The 2-halo-lumilysergole derivatives were less potent than the 2-halo-lysergoles with respect to their dopaminergic actions. We found the substitution at position 8 to be substantial to achieve agonistic or antagonistic properties, and, interestingly, 2,8-dihalo-lysergoles have proven to be DA agonists. The neurochemical findings are in good agreement with the behavioral results presented in the accompanying paper. We confirmed the behavioral data in that there are two subgroups among 2-halo-lysergoles possessing antipsychotic activity with opposite effects on DA receptors.

Characterization of beta-adrenergic receptors in rat ovary.

Specific beta-adrenergic receptors were characterized in rat ovary, using an in vitro receptor binding assay with [3H]dihydroalprenolol. The ligand was bound to a single class of saturable and high affinity receptors (dissociation constant = 3.5 nM and maximum capacity = 3.4 pmol/g tissue). In competition studies, the binding was stereoselective for the (-)-isomer of isoproterenol. Known beta-adrenergic agonists displaced the ligand from ovarian receptors with the following order of potency: isoproterenol greater than epinephrine much greater than norepinephrine, which is typical for a beta 2-adrenergic receptor.