Brain neurotransmitter receptor-binding characteristics in rats after oral administration of haloperidol, risperidone and olanzapine

The present study was conducted to characterize the binding of neurotransmitter receptors (dopamine D(2), serotonin 5-HT(2), histamine H(1), adrenaline alpha(1) and muscarine M(l) receptors) in the rat's brain after the oral administration of haloperidol, risperidone, and olanzapine. Haloperidol at 1 and 3 mg/kg displayed significant activity to bind the D(2) receptor (increase in the Kd value for [(3)H]raclopride binding) in the corpus striatum with little change in the activity toward the 5-HT(2) receptor (binding parameters for [(3)H]ketanserin). In contrast, risperidone (0.1-3 mg/kg) showed roughly 30 times more affinity for the 5-HT(2) receptor than D(2) receptor. Also, olanzapine (1-10 mg/kg) was most active toward the H(1) receptor in the cerebral cortex, corpus striatum, and hippocampus, was less active in binding 5-HT(2) and D(2) receptors, and showed the least affinity for alpha(1) and M(1) receptors. In conclusion, haloperidol and risperidone administered orally selectively bind D(2) and 5-HT(2) receptors, respectively, in the rat brain, while olanzapine binds H(1), 5-HT(2), and D(2) receptors more than alpha(1) and M(1) receptors.     

Distinct alpha-noradrenergic receptors differentiated by binding and physiological relationships.

Adult mice received two 70 μg doses of 6-hydroxydopamine intracisternally 72 hours apart, and the muscarinic binding properties of discrete brain regions were then investigated at various time intervals. Three days after the second injection, ³H-norepinephrine uptake was drastically reduced in all brain regions studied, and a distinct decrease in muscarinic receptor density was observed in the striatum (?18%), medulla-pons (?17%) and cerebellum (?15%) of lesioned animals as compared with controls. No changes were detected in muscarinic receptor density in the cortex or the hippocampus of treated animals, nor were any changes seen in the affinity of the labelled ligand for its receptor or in the displacement properties of the muscarinic binding by agonists in any of the regions studied. These effects still persisted after 60 days, with a further reduction in striatal muscarinic density to 74% of control values. Data are interpreted with respect to the proposed model for cholinergic modulation of central catecholamine release and cholinergic-catecholaminergic interactions in the striatum.     

Effect of intrastriatal injection of soman on acetylcholine, dopamine and serotonin metabolism

Intrastriatal injection of soman (14.85 nmol) inhibits cholinesterase (ChE) activity in the striatum with much smaller decreases in ChE activity in other brain areas of the rat. As would be expected, there is a substantial increase in striatal acetylcholine (ACh) content shortly after soman injection. However, this increase is no longer significant 1 h following intrastriatal injection. There is no change in striatal KACh 20 min, 1 h or 24 h following soman injection. ACh content is not affected in the parietal cortex, hippocampus, or medulla/pons following intrastriatal soman injection. However, KACh and/or ACh turnover are reduced in these brain areas following soman injection. There is no consistent effect on dopamine (DA) metabolism in any of the brain areas studied. However, serotonin (5-HT) metabolism appears to be affected in the cortex, hippocampus and medulla/pons following intrastriatal injection of soman. Possible mechanisms of the actions of local injection of soman on brain Ach and 5-HT metabolism are discussed, as well as the differences observed between the effects of local and peripheral administration of soman on DA metabolism in the striatum.     

Brain dopamine receptors: 20 Years of progress

I present a brief overview of the contribution of Paul Greengard's laboratory to the field of dopamine receptor research. I show that the work on the biochemical pharmacology of dopamine receptors was part of the intellectual foundation for the division of dopamine receptors into two general pharmacological categories.Special issue dedicated to Dr. Paul Greengard.     

Fluorescent-labeled lipophilic analogues of serotonin, dopamine, and acetylcholine: synthesis, mass spectrometry, and biological activity

4,4-Difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-dodecanoyl derivatives of serotonin, dopamine, choline, and N,N-dimethylaminoethanol, with the fluorescence maximum at 512 nm (lambda(exc) 470 nm), and 4,4-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene-3-dodecanoyl derivatives of choline and N,N-dimethylaminoethanol, with the fluorescence maximum at 554 nm (lambda(exc) 470 nm), were synthesized. These compounds yield protonated molecular ions of 100% intensity upon mass spectrometry with electrospray ionization at atmospheric pressure. The fragmentation of molecular ions under the conditions of secondary mass spectrometry mainly proceeds through the elimination of hydrogen fluoride from the fluorescent core of the molecules. Experiments on sea urchin Lytechinus variegatus embryos and larvae showed that these compounds easily penetrate into the cells and are accumulated in the cytoplasm. They do not differ in their biological activity from similar derivatives of arachidonic acid described previously and are agonists of serotonin or acetylcholine or antagonists of nicotinic acetylcholine receptors. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 5; see also http: // www.maik.ru.     

Schistosoma mansoni: differences in acetylcholine, dopamine, and serotonin control of circular and longitudinal parasite muscles

The physiological and pharmacological properties of circular and longitudinal somatic musculature in adult male Schistosoma mansoni were compared using cut muscle sections. Carbachol reduced tone in both circular and longitudinal muscle, but was without effect on circular muscle bathed in high Mg2+, indicating that cholinergic receptors were not associated with circular muscle membrane. 5-Hydroxytryptamine (5-HT) induced rhythmic contractile activity in both sets of muscle. It decreased muscle tone in circular muscle but increased the tone of longitudinal muscle. Metergoline blocked 5-HT effects on both sets of muscle. 5-HT continued to be effective on both sets of muscle bathed in high-Mg2+ medium, indicating that serotonergic receptors were present on both circular and longitudinal muscle membranes. Dopamine decreased both circular and longitudinal muscle tone. Its effects on circular muscle were still present after exposure to high Mg2+, but its effects on the longitudinal muscle were significantly reduced, leading to the conclusion that dopaminergic sites were probably associated with circular muscle membrane but not that of longitudinal muscle. Also, spiroperidol blocked stimulus responsiveness of the circular muscle but not that of the longitudinal muscle. From these studies it appears that there are significant physiological and pharmacological differences between circular and longitudinal muscles in the adult male schistosome.     

Lobeline esters as novel ligands for neuronal nicotinic acetylcholine receptors and neurotransmitter transporters

Vesicular monoamine transporter-2 (VMAT2) is a viable target for development of pharmacotherapies for psychostimulant abuse. Lobeline (1) is a potent antagonist at α4β21 nicotinic acetylcholine receptors, has moderate affinity (K_i = 5.46 μM) for VMAT2, and is being investigated currently as a clinical candidate for treatment of psychostimulant abuse. A series of carboxylic acid and sulfonic acid ester analogs 2–20 of lobeline were synthesized and evaluated for interaction with α4β21 and α71 neuronal nicotinic acetylcholine receptors (nAChRs), the dopamine transporter (DAT), serotonin transporter (SERT) and VMAT2. Both carboxylic acid and sulfonic acid esters had low affinity at α71 nAChRs. Similar to lobeline (K_i = 4 nM), sulfonic acid esters had high affinity at α4β21 (K_i = 5–17 nM). Aromatic carboxylic acid ester analogs of lobeline (2–4) were 100–1000-fold less potent than lobeline at α4β21 nAChRs, whereas aliphatic carboxylic acid ester analogs were 10–100-fold less potent than lobeline at α4β21. Two representative lobeline esters, the 10-O-benzoate (2) and the 10-O-benzenesulfonate (10) were evaluated in the ³⁶Rb⁺ efflux assay using rat thalamic synaptosomes, and were shown to be antagonists with IC₅₀ values of 0.85 μM and 1.60 μM, respectively. Both carboxylic and sulfonic acid esters exhibited a range of potencies (equipotent to 13–45-fold greater potency compared to lobeline) for inhibiting DAT and SERT, respectively, and like lobeline, had moderate affinity (K_i = 1.98–10.8 μM) for VMAT2. One of the more interesting analogs, p-methoxybenzoic acid ester 4, had low affinity at α4β21 nAChRs (K_i = 19.3 μM) and was equipotent with lobeline, at VMAT2 (K_i = 2.98 μM), exhibiting a 6.5-fold selectivity for VMAT2 over α4β2 nAChRs. Thus, esterification of the lobeline molecule may be a useful structural modification for the development of lobeline analogs with improved selectivity at VMAT2.     

Cyclo (Leu-Gly) + haloperidol: effects on dopamine receptors and conditioned avoidance responding

Behavioral effects of cyclo (Leu-Gly) (cLG), administered either acutely or chronically, were assessed in combination with haloperidol in the rat. cLG administered chronically, produced a significant reduction in the increase in apomorphine-induced stereotypy produced by chronic haloperidol infusion. On the other hand, the same dose of cLG which reduced this induction of dopamine receptor supersensitivity due to chronic haloperidol treatment, failed to produce a change in the potency of haloperidol in blocking conditioned avoidance responding in the rat. Furthermore, degeneration-induced supersensitivity of dopamine neurons, produced by unilateral destruction of the nigrostriatal pathway, was not reduced by acute or chronic treatment with cLG as measured by apomorphine-induced rotation. These data suggest that cLG may decrease motor system side effects thought to be caused by chronic antipsychotic administration without affecting the therapeutic efficacy of the antipsychotic agent.     

Brain serotonin and norepinephrine after convulsions and reserpine

Decreased brain norepinephrine (Schildkraut , 1969) and decreased brain serotonin (Shaw , Camp and Eccleston , 1967; Bourne et al., 1968) have been implicated in current hypotheses about the psychiatric syndrome, depression. Reserpine, which causes depression in some people, depletes brain norepinephrine and serotonin and, possibly, replicates in laboratory animals some of the biochemical changes in brains of depressed patients. Electrically-induced convulsions are an effective treatment of depression. There have been numerous studies of the effects of convulsive electrical stimulation on norepinephrine and serotonin in brains of laboratory animals. They have employed different schedules of administration of convulsions, short (minutes) or long (hours to days) periods after convulsion before killing the animals, and various methods of extraction and assay of the amines. Results have varied. For example, Kato , Gozsy , Roy and Groh (1967) found that a series of convulsions, administered daily for 11 days elevated whole brain serotonin but not norepinephrine. On the other hand, Hinesley , Norton and Aprison (1968) observed that a series of seven convulsions, one every other day, elevated norepinephrine only in cerebral hemispheres, whereas serotonin was elevated only in midbrain and pons-medulla. Our present report is the first to deal with both norepinephrine and serotonin in animals given both serial injections of reserpine and a series of electrically-induced convulsions.     

In vivo binding of 3H-N-methylspiperone to dopamine and serotonin receptors

3H-N-methylspiperone (3H-NMSP) was used to label dopamine-2 and serotonin-2 in vivo in the mouse. The striatum/cerebellum binding ratio reached a maximum of 80 eight hours after intravenous administration of 3H-NMSP. The frontal cortex/cerebellum ratio was 5 one hour after injection. The binding of 3H-NMSP was saturable in the frontal cortex and cerebellum between doses of 10 and 1,000 micrograms/kg. Between 0.01 and 10 micrograms/kg the ratio total/nonspecific binding increased from 14 to 21. Inhibition of 3H-NMSP binding in the frontal cortex and striatum by ketanserin, a selective serotonin-2 antagonist, demonstrated that 20% of the total binding in the striatum was to serotonin-2 receptors and 91% of the total binding in the frontal cortex was to serotonin-2 receptors. Compared to 3H-spiperone, 3H-NMSP results in a much higher specific/nonspecific binding ratio in the striatum and frontal cortex and displays more than a two-fold higher brain uptake.     

Photophysics of a neurotransmitter: ionization and spectroscopic properties of serotonin.

The neurotransmitter serotonin plays a modulatory role in the regulation of various cognitive and behavioral functions such as sleep, mood, pain, depression, anxiety, and learning by binding to a number of serotonin receptors present upon the cell surface. The spectroscopic properties of serotonin and their modulation with ionization state have been studied. Results show that serotonin fluorescence, as measured by its intensity, emission maximum, and lifetime, is pH dependent. These results are further supported by absorbance changes that show very similar pH dependence. Changes in fluorescence intensity and absorbance as a function of pH are consistent with a pK(a) of 10.4 +/- 0.2. The ligand-binding site for serotonin receptors is believed to be located in one of the transmembrane domains of the receptors. To develop a basis for monitoring the binding of serotonin to its receptors, its fluorescence in nonpolar media has been studied. No significant binding or partitioning of serotonin to membranes under physiological conditions was observed. Serotonin fluorescence in solvents of lower polarity is characterized by an enhancement in intensity and a blue shift in emission maximum, although the solvatochromism is much less pronounced than in tryptophan. In view of the multiple roles played by the serotonergic systems in the central and peripheral nervous systems, these results are relevant to future studies of serotonin and its binding to its receptors.     

Increased striatal acetylcholine after 14 months cis-flupenthixol treatment in rats suggests functional supersensitivity of dopamine receptors

Rats received continuous administration of cis-flupenthixol (0.8-1.2 mg/kg/day) or trans-flupenthixol (0.9-1.2 mg/kg/day) in drinking water for 14 months. The administration of cis-flupenthixol, but not trans-flupenthixol, caused apparent cerebral dopamine receptor supersensitivity. Thus, animals receiving cis-flupenthixol, but not trans-flupenthixol, showed enhanced apo-morphine-induced stereotyped behaviour. Dopamine concentration in striatum was not altered by drug treatment but striatal HVA and DOPAC concentrations were reduced in animals receiving cis-flupenthixol, but not trans-flupenthixol. No consistent change in Bmax of KD for specific striatal 3H-spiperone binding was observed after 14 months drug intake. However, in cis-flupenthixol treated animals a 40% increase in Bmax was observed following 2 weeks drug withdrawal. Continuous cis-flupenthixol intake increased striatal acetylcholine concentrations; trans-flupenthixol was without effect. This suggests the apparent increase in cerebral dopamine receptor supersensitivity caused by continuous long-term cis-flupenthixol administration is of functional importance in the intact animal.     

Brain acetylcholine, adenine nucleotides and their degradation products after intraperitoneal and intracerebral adenosine administration.

The paper describes adenosine effects on the acetylcholine synthesis and the profiles of adenine nucleotides, adenosine, inosine, and hypoxanthine in the rat brain in vivo after intracerebral (intraventricular) and intraperitoneal administration of adenosine. Intracerebral as well as extracerebral adenosine injection caused a dose- and time-dependent increase of the cerebral acetylcholine level, which was not accompanied by an equal development of the contents of adenine compounds and their degradation products. However, a considerable turnover of adenosine was observed in the brain after both routes of administration concerning the nucleotide as well as the degradation pathway. The kinetics of the purified enzymes of choline acetyltransferase and acetylcholinesterase were not influenced by adenosine. By this, the adenosine-caused increase of the cerebral acetylcholine cannot be explained by a direct molecular attack of adenosine on the enzymes of the synthesis or degradation of acetylcholine. An indirect mechanism which includes cAMP was discussed as a possible interpretation at present.     

Sensitivity of neuronal nicotinic acetylcholine receptors to the opiate antagonists naltrexone and naloxone: receptor blockade and up-regulation

In HEK293 cells stably expressing alpha4beta2 nAChRs, naltrexone, but not naloxone, blocked alpha4beta2 nAChRs via an open-channel blocking mechanism. In primary hippocampal cultures, naltrexone inhibited alpha7 nAChRs up-regulated by nicotine, and in organotypic hippocampal cultures naltrexone caused a time-dependent up-regulation of functional alpha7 nAChRs that was detected after removal of the drug. These results indicate that naltrexone could be used as a smoking cessation aid.     

Increased uptake sites for serotonin and dopamine with decreased S2 serotonin receptors in microencephalic rat brain

Methylazoxymethanol (MAM)-induced cerebral hypoplasia resulted in a significant increase in densities of both serotonin uptake sites in frontal cortex and dopamine uptake sites in striatum, suggesting serotonergic and dopaminergic axon terminals were compressed in the smaller brain volumes. The density of S2 serotonin receptors in MAM-lesioned frontal cortex was decreased probably due to down-regulation, while densities of D1 and D2 dopamine receptors in striatum were identical between MAM-lesioned rats and control rats.     

Narcotic dependence, narcotic action and dopamine receptors.

Acute systematic administration of narcotic analgesics increases the firing rate of nerve cells in the zona compacta of the substantia nigra, causes an increase in the rate of dopamine turnover in striatal and mesolimbic areas of the brain, stimulates prolactin release, inhibits brain self-stimulation and discriminated shock-avoidance, blocks cardiovascular effects of systemically injected dopamine, blocks aggression as well as compulsive jumping in mice treated with DOPA and amphetamine, antagonizes stereotypy induced by apomorphine or amphetamine, and blocks apomorphine-induced vomiting in dogs. Chronic administration of narcotic analgesics results in withdrawal signs upon the cessation of the drug administration. These signs include, tolerance to the increase in striatal dopamine turnover caused by narcotic analgesics or haloperidol, aggressive behaviors which are further stimulated by directly or indirectly acting dopamine-receptor agonists and are blocked by dopamine-receptor blockers, facilitation of recovery from the “lateral hypothalamic syndrome”, an increase in basal levels of striatal adenylate cyclase which shows greater sensitivity to dopamine, and, an enhanced sensitivity to apomorphine-induced reduction of dopamine turnover. It is therefore, concluded that acute administration of narcotic drugs results in an inhibition of dopamine-receptor activity while chronic administration of these drugs results in an increased response of these dopamine receptors to dopamine agonists. Recent experiments on the interaction of other drugs with narcotic analgesics suggest that, unlike the direct action of neuroleptics on the dopamine receptors, the narcotic action on dopamine receptors is indirect.     

Structural analogues of 5-OMe-BPAT: synthesis and interactions with dopamine D2, D3, and serotonin 5-HT1A receptors.

Several structural analogues of 5-methoxy-2-[N-(2-benzamidoethyl)-N-n-propylamino]tetralin (5-OMe-BPAT, 1), a representative of a series of 2-aminotetralin-derived benzamides with potential atypical antipsychotic properties, were synthesized and evaluated for their ability to bind to dopamine D2A, D3, and serotonin 5-HT1A receptors in vitro. The structure affinity relationships revealed that the aromatic ring of the benzamide moiety of 1 contributes to the high affinities for all three receptor subtypes. Furthermore, 1 may interact with the dopamine D2 and D3 receptors through hydrogen bond formation with its carbonyl group. Investigation of the role of the amide hydrogen atom by amide N-alkylation was not conclusive, since conformational aspects may be responsible for the decreased dopaminergic affinities of the N'-alkylated analogues of 1. The effects of the amide modifications on the serotonin 5-HT1A receptor affinity were less pronounced, suggesting that the benzamidoethyl side-chain of 1 as a whole enhances the affinity for this receptor subtype probably through hydrophobic interactions with an accessory binding site. The structural requirements for the substituents at the basic nitrogen atom supported the hypothesis that the 2-aminotetralin moieties of the 2-aminotetralin-derived substituted benzamides may share the same binding sites as the 2-(N,N-di-n-propylamino)tetralins.