Partial dopamine-agonistic and atypical neuroleptic properties of the amino-ergolines SDZ 208-911 and SDZ 208-912.

The aminoergolines SDZ 208-911 [N-[(8-alpha)-2,6-dimethylergoline-8-yl]-2,2- dimethylpropanamide] and SDZ 208-912 [N-[8-alpha)-2-chloro-6-methylergoline-8-yl]- 2,2-dimethylpropanamide] exhibit nonclassical, neuroleptic-like properties in rodents. Thus, they are equipotent to haloperidol as inhibitors of apomorphine-induced gnawing behavior and conditioned avoidance responding, but are essentially devoid of cataleptogenic activity. In addition, they show high affinity for central D-2 receptors in vitro and elevate striatal homovanillic acid levels. In contrast to haloperidol, however, SDZ 208-911 and 208-912 strongly inhibit prolactin secretion and induce contralateral circling behavior in 6-hydroxydopamine-lesioned animals. These profiles are consistent with the drugs exhibiting varying degrees of partial agonistic activity at dopamine D-2 receptors, with SDZ 208-911 being considerably more agonistic than SDZ 208-912. Support for this contention stems from the ability of SDZ 208-911 to reduce the elevation of striatal L-dopa formation induced by gamma-butyrolactone, and SDZ 208-912's partial reversal of apomorphine's inhibitory action on gamma-butyrolactone activity. SDZ 208-911's effects are reduced after the partial alkylation of D-2 receptors with N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline, confirming its partial agonistic properties. SDZ 208-911 and SDZ 208-912 could be effective against both the positive and negative symptoms of schizophrenia, while exhibiting a reduced incidence of dystonic and parkinsonian side-effects. In addition, their clinical testing might throw more light on the central dopaminergic status of schizophrenic subjects.

Partial brain dopamine D2 receptor agonists in the treatment of schizophrenia.

Partial dopamine agonists showing high affinity but low efficacy at D2 receptors can act as dopaminergic "buffers," reducing dopaminergic activity when it is excessive, and promoting it when reduced. This makes them of interest as potential therapeutic agents for the treatment of both positive and negative symptoms in schizophrenia, where they should also result in fewer or less severe motor disturbances than classical neuroleptics. SDZ 208-911 and SDZ 208-912 are amino-ergolines exhibiting partial agonistic properties in the rat, where they inhibit apomorphine-induced stereotypies, are only weakly cataleptogenic, induce varying degrees of circling behavior after unilateral lesioning of the nigrostriatal pathway, and strongly suppress prolactin secretion. The least agonistically acting agent, SDZ 208-912, should be effective against positive symptoms, whereas SDZ 208-911 could be suitable for the treatment of negative symptoms. In addition to possible therapeutic effects, the clinical testing of this class of agent should help to elucidate the status of central dopaminergic function in schizophrenic psychosis.

Dopamine D2 receptors in the rat brain: autoradiographic visualization using a high-affinity selective agonist ligand.

The non-catechol, selective dopamine D2-agonist compound 3H-205-502 was used to localize dopamine D2 receptors by autoradiography after in vitro labeling of brain sections. The characteristics of the binding of this ligand to tissue sections were those expected from the labeling of dopamine D2 receptors. The binding of 3H-205-502 was inhibited selectively and stereospecifically by dopamine D2 agents but not by dopamine D1 compounds. The autoradiographic localization of 3H-205-502 binding sites showed high densities of dopamine D2 receptors in areas such as the glomerular layer of the olfactory bulb, the nucleus accumbens, caudate-putamen, olfactory tubercle, the lateral septum, and the islands of Calleja. Besides these dopamine-innervated areas the substantia nigra and the ventral tegmental area also showed important receptor densities. Other areas where dopamine D2 receptor binding was found were the stratum lacunosum-moleculare of the hippocampus, bands of labeling in the molecular layer of the 9th and 10th lobules of the cerebellum, and several components of the visual system. This distribution presents similarities and differences with previously reported distributions of dopamine D2 receptors visualized autoradiographically using 3H-labeled agonists and antagonists. In view of the high affinity, guanine nucleotide insensitivity, and dopamine D2 selectivity of this agonist ligand, it is suggested that dopamine D2 receptors exist in different states in different areas. 3H-205-502 appears to be a new and useful tool for the study of dopamine D2 receptors.

Modulation of depolarization stimulated 45Ca2+ uptake in cultured neuronal cells by calcium channel activators and antagonists.

The effect of dihydropyridine calcium agonists and antagonists on 45Ca2+ uptake into primary neuronal cell cultures was investigated. K+ stimulated neuronal 45Ca2+ accumulation in a concentration dependent manner. This effect was further enhanced by the calcium agonists Bay K 8644 and (+)-(S)-202-791 with EC50 values of 21 nM and 67 nM respectively. The calcium antagonists PN 200-110 and (-)-(R)-202-791 inhibited Bay K 8644 (1 microM) stimulated uptake with IC50 values of 20 nM and 130 nM respectively. 45Ca2+ efflux from neuronal cells was measured in the presence and absence of Na+. Efflux occurred at a much greater rate from cells incubated in the presence of Na+, indicating the existence of an active Na+/Ca2+ exchanger in these neurons. The data suggests that voltage sensitive calcium channels of these neurons are sensitive to dihydropyridines and thus that dihydropyridine binding sites have a functional role in these neuronal cultures.

The effect of dihydropyridine calcium agonists and antagonists on neuronal voltage sensitive calcium channels.

The effect of dihydropyridine agonists and antagonists on neuronal voltage sensitive calcium channels was investigated. The resting intracellular calcium concentration of synaptosomes prepared from whole brain was 110 +/- 9 nM, as assayed by the indicator quin 2. Depolarisation of the synaptosomes with K+ produced an immediate increase in [Ca2+]i. The calcium agonist Bay K 8644 and antagonist nifedipine did not affect [Ca2+]i under resting or depolarising conditions. In addition, K+ stimulated 45Ca2+ uptake into synaptosomes prepared from the hippocampus was insensitive to Bay K 8644 and PY 108-068 in normal or Na+ free conditions. In neuronally derived NG108-15 cells the enantiomers of the dihydropyridine derivative 202-791 showed opposite effects in modulating K+ stimulated 45Ca2+ uptake. (-)-R-202-791 inhibited K+ induced 45Ca2+ uptake with an IC50 of 100 nM and (+)-S-202-791 enhanced K+ stimulated uptake with an EC50 of 80 nM. These results suggest that synaptosomal voltage sensitive calcium channels either are of a different type to those found in peripheral tissues and cells of neural origin or that expression of functional effects of dihydropyridines requires different experimental conditions to those used here.

[Pathophysiology of senile dementia]. / Pathophysiologie der senilen Demenz.

In recent years considerable progress has been made in our understanding of the pathophysiology of Alzheimer's dementia and dementia of Alzheimer's type. The disorder selectively affects cortical and subcortical neuronal systems. Especially affected are neurons which utilize acetylcholine or somatostatin as transmitter substance. Cortical somatostatin-positive neurons are reduced in number and many of those persisting exhibit morphological changes consistent with neuronal degeneration. Many neurons displaying tangles and plaques contain somatostatin after immunostaining. Thus, degeneration of somatostatin containing neurons appears to be an early and even critical event in the development of Alzheimer's dementia.

Interaction of benzodiazepine receptor agonists and inverse agonists with the GABA benzodiazepine receptor complex.

The effects of the benzodiazepine receptor agonists, antagonists and inverse agonists on the in vitro binding of several ligands which label different recognition sites of the GABA benzodiazepine receptor complex are summarized. Also, results with a novel biochemical in vitro functional model of the GABA benzodiazepine receptor complex are presented. They are compatible with the concept that drugs which act on benzodiazepine receptors can lead to a bidirectional modulation of the gain of GABAergic neurotransmission.

Modulation of acetylcholine release from rat striatal slices by the GABA/benzodiazepine receptor complex.

GABA, THIP and muscimol enhance spontaneous and inhibit electrically induced release of tritium labelled compounds from rat striatal slices which have been pre-labelled with 3H-choline. Baclofen is inactive in this model. Muscimol can inhibit electrically induced release of tritiated material by approximately 75% with half maximal effects at 2 microM. The response to muscimol can be blocked by the GABA antagonists bicuculline methobromide, picrotoxin, anisatin, R 5135 and CPTBO (cyclopentylbicyclophosphate). Drugs which act on the benzodiazepine receptor (BR) require the presence of muscimol to be effective and they modulate the effects of muscimol in a bidirectional manner. Thus BR agonists enhance and inverse BR agonists attenuate the inhibitory effects of muscimol on electrically induced release. Ro15-1788, a BR antagonist, does not modulate the inhibitory effects of muscimol but antagonizes the actions of clonazepam, a BR agonist, and of DMCM, an inverse BR agonist. These results demonstrate that a GABA/benzodiazepine receptor complex can modulate acetylcholine release from rat striatal slices in vitro.

[35S]-t-butylbicyclophosphorothionate binding sites are constituents of the gamma-aminobutyric acid benzodiazepine receptor complex.

t- Butylbicyclophosphorothionate ( TBPS ), a derivative of potent GABA antagonistic cage convulsants, has recently been introduced ( Squires , R. F., J.E. Casida , M. Richardson, and E. Saederup (1983) Mol. Pharmacol. 13:326-336) as ligand for a GABA-A receptor-linked drug receptor. Using conventionally prepared washed membrane fractions from rat cerebral cortex, we have confirmed that in the presence of 200 mM NaBr [35S] TBPS binds to a high affinity population of binding sites (Kd 26 +/- 5 nM) and that muscimol inhibits [35S] TBPS binding (IC50 0.32 microM) allosterically. In 200 mM NaCl the apparent affinity of [35S] TBPS binding sites is lower (Kd 60 +/- 5 nM), and muscimol has biphasic effects with stimulation at low concentrations of muscimol (EC50 0.023 microM) followed by inhibition at high concentrations (IC50 0.72 microM). Both base line [35S] TBPS binding (in 200 mM NaCl) and muscimol inhibition of [35S] TBPS binding (in 200 mM NaBr) are bidirectionally modulated by the occupancy of benzodiazepine receptors with its ligands. Benzodiazepine receptor agonists, regardless of their structure, enhance and inverse benzodiazepine receptor agonists inhibit base line [35S] TBPS binding and muscimol inhibition of [35S] TBPS binding. Fourteen ligands for benzodiazepine receptors display a similar in vitro profile as benzodiazepine receptor agonists or inverse benzodiazepine receptor agonists on [35S] TBPS binding as their anti- or proconvulsive effects in vivo suggest (Jensen, L. H., E. N. Petersen, and C. Braestrup (1983) Life Sci. 33: 393-399). That [35S] TBPS binding sites are constituents of a GABA benzodiazepine receptor complex is also suggested by a number of membrane pretreatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium antagonist binding sites in the rat brain: quantitative autoradiographic mapping using the 1,4-dihydropyridines [3H]PN 200-110 and [3H]PY 108-068.

An in vitro autoradiographic technique has been used for the quantitative mapping of calcium antagonist binding sites (CABS) in the rat brain, using the 1,4-dihydropyridines [3H]PN 200-110 and [3H]PY 108-068 as ligands. CABS were distributed throughout the brain in a highly heterogeneous fashion. The highest densities of CABS were observed in the olfactory bulb, hippocampus and parts of the amygdala. The neocortex was also rich in CABS. The basal ganglia, thalamus and hypothalamus presented intermediate levels of CABS while low densities of sites were seen in areas such as the cerebellum, pons and white matter tracts. The distributions of CABS in brain does not correlate with indexes of brain blood flow, regional glucose utilization or the distributions of receptor binding sites for drugs and neurotransmitters analyzed until now. No correlation exists between CABS distribution and that of any neurotransmitter or brain enzyme described so far. The heterogeneous distributions of CABS is suggestive of a neuronal localization, an idea supported by lesion experiments.

The interaction of [3H]PY 108-068 and of [3H]PN 200-110 with calcium channel binding sites in rat brain.

The binding properties of the tritiated calcium channel antagonists PY 108-068 and PN 200-110 were investigated in membrane fractions from rat brain in vitro. Both ligands reversibly interact with one apparent population of stereoselective binding sites which have pharmacological properties described for calcium channel binding sites. In a calcium buffer enhancement of [3H]PY 108-068 binding is observed with an EC50 at pCa 6.28 [3H]PN 200-110 binding is less sensitive to allosteric stimulation by diltiazem and to allosteric inhibition by verapamil and D 600 than [3H]PY 108-068 binding, suggesting that the former ligand may stabilize a high affinity configuration of the binding sites. After i.v. administration of [3H]PY 108-068 in vivo binding to membranes is observed in brain and heart, which, in contrast to total tissue radioactivity is sensitive to inhibition by unlabelled (+)PN 200-110. These observations suggest that PY 108-068 can interact with its binding sites also in vivo. The results of ex vivo binding studies in brain and heart with [3H]PY 108-068 confirm and extend these observations. It could be shown that all investigated 1,4-dihydropyridines (PY 108-068, PN 200-110, nifedipine, Bay K 8644) after i.p. administration can readily enter brain and heart tissue.

The effects of lesions in the rat hippocampus suggest the association of calcium channel blocker binding sites with specific neuronal population.

The binding of calcium antagonists in the rat hippocampal formation was studied using autoradiography. Hippocampal slices were labeled in vitro with [3H]PN 200-110. High densities of binding sites for calcium antagonists were found in the molecular layer of the dentate gyrus and in the CA3 subfield of the hippocampus. After ablation of the granule cells by local injection of colchicine a marked decrease in the number of [3H]PN 200-110 binding sites density was observed on these areas, while binding to other parts of the hippocampal formation and brain was spared. These results strongly suggest the localization of high densities of calcium channels to the granule cells of the dentate gyrus.

Differential modulation of etazolate or pentobarbital enhanced [3H] muscimol binding by benzodiazepine agonists and inverse agonists.

Flunitrazepam, a benzodiazepine agonist increases, and DMCM, an inverse agonist decreases the stimulation by etazolate or pentobarbital of [3H] muscimol binding to membranes of rat cerebral cortex. Ro 15-1788 has no marked effects but antagonizes the action of both flunitrazepam and DMCM. The investigation of several drugs acting on benzodiazepine receptors on etazolate enhancement of [3H] muscimol binding suggests that their receptor interaction reflects a spectrum from agonists to inverse agonists.

Clinical symptomatology and computer analyzed EEG before, during and after anxiolytic therapy of alcohol withdrawal patients.

In a double-blind study the clinical symptomatology and quantitatively analyzed EEG of 42 hospitalized chronic alcoholics (ICD 303) undergoing alcohol withdrawal were investigated before, during and after 3 weeks' treatment with 2 pharmacokinetically different benzodiazepines: the short-acting lopirazepam (a new pyridodiazepine) and the long-acting prazepam. At the end of weeks 1 and 3 the titrated optimal daily doses were 24 and 23 mg lopirazepam and 35 and 32 prazepam, respectively, thus confirming our earlier pharmaco-EEG predictions that on a mg to mg basis the former drug is slightly more CNS potent than the latter. Thereafter, the patient population was divided into 6 subgroups: 2 groups continuing on active medication, 2 groups receiving placebo, and 2 groups with no pharmacotherapy for 1 week. Clinical assessments included the CGI, the Hamilton Anxiety Score, the Zung Self-Rating Scale for Anxiety and Depression, the Zerssen Befindlichkeitsskala and the questionnaire for somatic findings and side effect and were carried out on days 0, 7, 21 and 28 as was a radioreceptor assay for benzodiazepines in plasma. Quantitative EEG investigations were carried out on days 0, 21 and 28 and included recordings before and 2 h after one single dose of 10 mg. Statistical analysis demonstrated a marked and highly significant decrease in psychopathology as well as good drug tolerance at the end of the first week of therapy and thereafter a slight continuation in improvement until the end of the 3rd week. There were, however, no statistically significant differences between the 2 active compounds, nor were there any statistically significant differences between the 6 subgroups in the 4th week. On the other hand, blood level investigations demonstrated that even after a 3-week treatment period, blood levels dropped down to a morning minimum 12 h after the last evening medication of the short-acting lopirazepam, while plasma levels of the long-acting prazepam remained high. This was also reflected in the spectral analyzed EEG, which showed, after one single dosage of both drugs, a typical anxiolytic profile which was more pronounced after lopirazepam than prazepam, while after the chronic administration (12 h after the evening medication) only prazepam showed an anxiolytic profile. The lopirazepam-treated patients exhibited on the one hand a lack of benzodiazepine-specific alterations, but showed on the other hand EEG changes possibly reflecting clinical improvement. The relevance of the findings will be discussed.

Anion-dependent modulation of [3H]muscimol binding and of GABA-stimulated [3H]flunitrazepam binding by picrotoxin and related CNS convulsants.

Picrotoxin, isopropylbicyclophosphate (IPTBO) and related CNS-convulsants have allosteric effects on the binding of ligands to the GABA/benzodiazepine receptor complex. When binding experiments were performed at 23 degrees C and at 35 degrees C, these drugs inhibited [3H]muscimol binding and muscimol- or GABA-stimulated [3H]flunitrazepam binding, respectively. Both effects required the presence of C1-, Br-, I- but not of F- or SO4(2-). Picrotoxin and IPTBO could only partially inhibit [3H]muscimol binding. In contrast other GABA antagonists and convulsants like bicuculline, 3 alpha-hydroxy-16-imino-5 beta-17-aza-androstan-11-one (R 5135), strychnine and d-tubocurarine interferred completely with [3H]muscimol binding, also in the absence of those ions mentioned above which were essential for the effects of picrotoxin. Our results support the notion that drugs like picrotoxin and IPTBO which interfere with the GABA receptor effector system, may lead to an allosteric perturbation of GABA-recognition sites.