Effects of the 5-HT1A partial agonists gepirone, ipsapirone and buspirone on local cerebral glucose utilization in the conscious rat

New expression of 5-HT1A receptor in astrocytes in the gerbil hippocampal CA1 region following transient global cerebral ischemia

5-Hydroxytryptamine (5-HT, serotonin) plays protective or detrimental roles in the development of ischemic damage. In the present study, we investigated the time-course changes in 5-HT1A receptor protein expression in the gerbil hippocampal CA1 region after transient global cerebral ischemia. 5-HT1A receptor immunoreactivity in the stratum pyramidale (SP) of the CA1 region was decreased from 6 h and hardly observed 1 and 2 days after ischemic insult. Five and 10 days after ischemia/reperfusion, 5-HT1A receptor immunoreactivity was increased and detected in astrocyte of the ischemic CA1 region. Furthermore, the pattern of changes in 5-HT1A receptor protein levels in the CA1 region after ischemia-reperfusion was similar to that observed in the immunohistochemical data. These results indicate that 5-HT1A receptor protein expressions may be related with the ischemia-induced neuronal death and the function of astrocytes in the ischemic hippocampal CA1 region.

WITHDRAWN: Is acute tryptophan depletion a valid method to assess central serotonergic function?

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Pharmacological, neurochemical, and behavioral profile of JB-788, a new 5-HT1A agonist

A novel pyridine derivative, 8-{4-[(6-methoxy-2,3-dihydro-[1,4]dioxino[2,3-b]pyridine-3-ylmethyl)-amino]-butyl}-8-aza-spiro[4.5]decane-7,9-dione hydrochloride, termed JB-788, was designed to selectively target 5-HT(1A) receptors. In the present study, the pharmacological profile of JB-788 was characterized in vitro using radioligands binding tests and in vivo using neurochemical and behavioural experiments. JB-788 bound tightly to human 5-HT(1A) receptor expressed in human embryonic kidney 293 (HEK-293) cells with a K(i) value of 0.8 nM. Its binding affinity is in the same range as that observed for the (+/-)8-OH-DPAT, a reference 5HT(1A) agonist compound. Notably, JB-788 only bound weakly to 5-HT(1B) or 5-HT(2A) receptors and moreover the drug displayed only weak or indetectable binding to muscarinic, alpha(2), beta(1) and beta(2) adrenergic receptors, or dopaminergic D(1) receptors. JB-788 was found to display substantial binding affinity for dopaminergic D(2) receptors and, to a lesser extend to alpha(1) adrenoreceptors. JB-788 dose-dependently decreased forskolin-induced cAMP accumulation in HEK cells expressing human 5-HT(1A), thus acting as a potent 5-HT(1A) receptor agonist (E(max.) 75%, EC(50) 3.5 nM). JB-788 did not exhibit any D(2) receptor agonism but progressively inhibited the effects of quinpirole, a D(2) receptor agonist, in the cAMP accumulation test with a K(i) value of 250 nM. JB-788 induced a weak change in cAMP levels in mouse brain but, like some antipsychotics, transiently increased glycogen contents in various brain regions. Behavioral effects were investigated in mice using the elevated plus-maze. JB-788 was found to increase the time duration spent by animals in anxiogenic situations. Locomotor hyperactivity induced by methamphetamine in mouse, a model of antipsychotic activity, was dose-dependently inhibited by JB-788. Altogether, these results suggest that JB-788 displays pharmacological properties, which could be of interest in the area of anxiolytic and antipsychotic drugs.

Serotonin-1A receptor imaging in recurrent depression: replication and literature review

INTRODUCTION

Serotonin-1A receptor (5-HT1AR) function appears to be decreased in major depressive disorder (MDD) based on physiological responses to 5-HT1AR agonists in vivo and to 5-HT1AR binding in brain tissues postmortem or antemortem. We have previously assessed 5-HT1AR binding potential (BP) in depression using positron emission tomography (PET) and [carbonyl-(11)C]WAY-100635, and we have demonstrated reduced 5-HT1AR BP in the mesiotemporal cortex (MTC) and raphe in depressives with primary recurrent familial mood disorders (n=12) versus controls (n=8) [Drevets WC, Frank E, Price JC, Kupfer DJ, Holt D, Greer PJ, Huang Y, Gautier C, Mathis C. PET imaging of serotonin 1A receptor binding in depression. Biol Psychiatry 1999;46(10):1375-87]. These findings were replicated by some, but not other, studies performed in depressed samples that were more generally selected using criteria for MDD. In the current study, we attempted to replicate our previous findings in an independent sample of subjects selected according to the criteria for primary recurrent depression applied in our prior study.

METHODS

Using PET and [carbonyl-(11)C]WAY-100635, 5-HT1AR BP was assessed in 16 depressed subjects and 8 healthy controls.

RESULTS

Mean 5-HT1AR BP was reduced by 26% in the MTC (P<.005) and by 43% in the raphe (P<.001) in depressives versus controls.

CONCLUSIONS

These data replicate our original findings, which showed that BP was reduced by 27% in the MTC (P<.025) and by 42% in the raphe (P<.02) in depression. The magnitudes of these reductions in 5-HT1AR binding were similar to those found postmortem in 5-HT1AR mRNA concentrations in the hippocampus in MDD [López JF, Chalmers DT, Little KY, Watson SJ. Regulation of serotonin 1A, glucocorticoid, and mineralocorticoid receptor in rat and human hippocampus: implications for neurobiology of depression. Biol Psychiatry 1998;43:547-73] and in 5-HT1AR-binding capacity in the raphe in depressed suicide victims [Arango V, Underwood MD, Boldrini M, Tamir H, Kassir SA, Hsiung S, Chen JJ, Mann JJ. Serotonin 1A receptors, serotonin transporter binding and serotonin transporter mRNA expression in the brainstem of depressed suicide victims. Neuropsychopharmacology 2001;25(6):892-903]. There exists disagreement within the literature, however, regarding the presence and direction of 5-HT1AR-binding abnormalities in depression, which may be explained in some cases by differences in anatomical location (e.g., [Stockmeier CA, Shapiro LA, Dilley GE, Kolli TN, Friedman L, Rajkowska G. Increase in serotonin-1A autoreceptors in the midbrain of suicide victims with major depression--postmortem evidence for decreased serotonin activity. J Neurosci 1998;18(18):7394-401]) and in other cases by pathophysiological heterogeneity within MDD (e.g., some depressives hypersecrete cortisol, which would be expected to down-regulate 5-HT1AR expression [López JF, Chalmers DT, Little KY, Watson SJ. Regulation of serotonin 1A, glucocorticoid, and mineralocorticoid receptor in rat and human hippocampus: implications for neurobiology of depression. Biol Psychiatry 1998;43:547-73]). Antidepressant drug treatment does not alter these abnormalities in 5-HT1AR binding [Sargent PA, Kjaer KH, Bench CJ, Rabiner EA, Messa C, Meyer J, Gunn RN, Grasby PM, Cowen PJ. Brain serotonin1A receptor binding measured by positron emission tomography with [11C]WAY-100635: effects of depression and antidepressant treatment. Arch Gen Psychiatry 2000;57(2):174-80; Moses-Kolko EL, Price JC, Thase ME, Meltzer CC, Kupfer DJ, Mathis CA, Bogers WD, Berman SR, Houck PR, Schneider TN, Drevets WC. Measurement of 5-HT1A receptor binding in depressed adults before and after antidepressant drug treatment using positron emission tomography and [11C]WAY-100635. Synapse 2007;61(7):523-30] but may compensate for blunted 5-HT1AR function by increasing post-synaptic 5-HT1AR transmission [Chaput Y, de Montigny C, Blier P. Presynaptic and postsynaptic modifications of the serotonin system by long-term administration of antidepressant treatments. An in vivo electrophysiologic study in the rat. Neuropsychopharmacology 1991;5(4):219-29].

Effects of anesthesia upon 18F-FDG uptake in rhesus monkey brains

The kinetics of 18F-fluorodeoxyglucose (18F-FDG) in the monkey brain were monitored, and comparisons were made between the conscious state and when under ketamine and pentobarbital anesthesia. Rhesus monkeys were intravenously injected with 18F-FDG and followed by 60 min of PET scanning. In the conscious state, the 18F-FDG concentration reached a plateau 5 min after intravenous injection. Under ketamine anesthesia, the 18F-FDG concentration gradually increased with time in all monitored regions. At 60 min after injection, the concentration in the striatum was about 3.2 times greater than that in the conscious state, and about 4.5 times greater in the cerebral cortex. Under pentobarbital anesthesia, the 18F-FDG concentration in the occipital cortex was slightly lower. These findings demonstrate that 18F-FDG concentration in the monkey brain is significantly affected by anesthesia. The results also imply the existence of a short-term regulation mechanism for hexokinase activity in intact monkey brain.

A simplified autoradiographic method with alpha-[14C]methyl-tryptophan to measure serotonin synthesis rate in the rat brain

BACKGROUND

To minimize blood sampling necessary for the autoradiographic (ARG) method using alpha-[(14)C]methyl-tryptophan (alpha-MTrp), a simplified method using a standard exposure time (theta(S)) was proposed and the accuracy of the method was evaluated.

METHODS

A total of 168 rats from three sets of experiments with different serotonergic drugs to evaluate changes in cerebral serotonin (5-hydroxytryptamine; 5-HT) synthesis rate were used. In the acute treatment study, rats received a drug injection 30 min before the tracer experiment. In the repeated treatment study, the same dose of drug was injected for 7 days. The two-time point method provided a parameter of brain trapping constant (K*) from the slope of linear regression of the Patlak plot, from which 5-HT synthesis rate is calculated. The measured exposure time (theta(M)) for 60 and 150 min after the tracer injection obtained from individual blood sampling in the original method and the theta(S) calculated from theta(M) were used for evaluation of differences in K* values.

RESULTS

No significant difference in theta(M) was noted among different experiments, although plasma radioactivity at the end of experiment was significantly different between the acute and the repeated treatments for one of the three drugs. No difference in K* for each treatment was observed between the original method and the simplified single blood sampling method because there was no difference in theta(M) among three experiments and between theta(M) and theta(S).

CONCLUSION

The simplified alpha-MTrp ARG method, which uses theta(S) and a single arterial blood sample at the end of each experiment, can be used for the measurement of 5-HT synthesis rate in the rat brain.

The effect of apomorphine and buspirone on regional cerebral blood flow during the performance of a cognitive task-measuring neuromodulatory effects of psychotropic drugs in man

Psychopharmacological activation, in conjunction with positron emission tomographic measurements of regional cerebral blood flow (rCBF), was used to investigate the neurotransmitter basis of a specific cognitive function in man. Monoaminergic neurotransmission was pharmacologically manipulated during performance of auditory - verbal memory tasks. Statistical parametric mapping was used to identify the brain sites of interaction between memory-induced increases in rCBF and active drugs. Memory task-induced increases in rCBF in the left prefrontal cortex were attenuated by apomorphine, a non-selective dopamine agonist, whilst buspirone, a serotonin1A partial agonist, augmented rCBF increases in this area. In addition, apomorphine and buspirone augmented memory-induced increases in rCBF centred in the posterior cingulate cortex, whilst buspirone alone attenuated rCBF increases in the retrosplenial cortex and posterior parahippocampal gyrus. These regionally selective interactions may represent neuromodulatory effects of monoaminergic neurotransmission on a specific cognitive function in man.

Serotonin in the regulation of brain microcirculation

Manipulation of brainstem serotonin (5-HT) raphe neurons induces significant alterations in local cerebral metabolism and perfusion. The vascular consequences of intracerebrally released 5-HT point to a major vasoconstrictor role, resulting in cerebral blood flow (CBF) decreases in several brain regions such as the neocortex. However, vasodilatations, as well as changes in blood-brain barrier (BBB) permeability, which are blocked by 5-HT receptor antagonists also can be observed. A lack of relationship between the changes in flow and metabolism indicates uncoupling between the two variables and is suggestive of a direct neurogenic control by brain intrinsic 5-HT neurons on the microvascular bed. In line with these functional data are the close associations that exist between 5-HT neurons and the microarterioles, capillaries and perivascular astrocytes of various regions but more intimately and/or more frequently so in those where CBF is altered significantly following manipulation of 5-HT neurons. The ability of the microvascular bed to respond directly to intracerebrally released 5-HT is underscored by the expression of distinct 5-HT receptors in the various cellular compartments of the microvascular bed. Thus, it appears that while some 5-HT-mediated microvascular functions involve directly the blood vessel wall, others would be relayed through the perivascular astrocyte. The strategic localization of perivascular astrocytes and the different 5-HT receptors that they harbor strongly emphasize their putative pivotal role in transmitting information between 5-HT neurons and microvessels. It is concluded that the cerebral circulation has full capacity to adequately and locally adapt brain perfusion to changes in central 5-HT neurotransmission either directly or indirectly via the neuronal-astrocytic-vascular tripartite functional unit. Dysfunctions in these neurovascular interactions might result in perfusion deficits and might be involved in specific pathological conditions.

Cerebral metabolic effects of serotonin drugs and neurotoxins

The functional effects of serotonin (5-HT) drugs and toxins on regional cerebral metabolic rates for glucose (rCMRglc) have been determined in rats with the in vivo, quantitative, autoradiographic [14C]2-deoxyglucose technique. Serotonin agents produced rCMRglc patterns different and more specific that one would predict from binding studies. At low doses 5-HT1 agonists reduced rCMRglc in limbic areas and at high doses increased rCMRglc in brain motor regions. The 5-HT2 agonists dose-dependently decreased rCMRglc in proencephalic areas and increased it in thalamic nuclei. 5-HT3 receptor antagonism resulted in rCMRglc decreases in limbic, auditory and visual areas and agents with 5-HT3 receptor activity increased rCMRglc in brain regions with high 5-HT3 receptor densities. Serotonin anxiolytics (e.g. azapirones) and antidepressants (e.g. tryciclic and non-tryciclic 5-HT reuptake inhibitors) reduced rCMRglc selectively in limbic areas and in brainstem monoaminergic nuclei. Dose, time from administration, receptor affinity, behavioral and neurochemical correlates, 5-HT system lesion and circulating glucocorticoid were all relevant factors in determining the rCMRglc effects of 5-HT drugs. Acutely neurotoxic amphetamines markedly increased rCMRglc in brain regions such as the nucleus accumbens that are thought to mediate amphetamine reinforcing properties; on the long term, toxic or electrolytic lesions or chronic treatment with 5-HT agonists produced minimal rCMRglc alterations in spite of marked and persistent changes in 5-HT function. In lesioned or chronically treated rats, acute challanges with 5-HT and non 5-HT agonists demonstrated specific deficits that were not detected in a resting state. Serotonin neuromodulation has been studied in humans by using positron emission tomography with 15O-water. Sequential measurements of regional cerebral blood flow (rCBF) were obtained during combined pharmacological challange with the 5-HT1A agonist buspirone and cognitive activation. Buspirone increased a memory related rCBF activation in task specific regions. This technique can provide a strong theoretical basis for the understanding of 5-HT drug mode of action in normal human brain and in neuropsychiatric diseases. Brain metabolism studies in animals will still be needed to elucidate the factors (e.g. pharmacokinetic and pharmacodynamic) relevant to the cerebral response to 5-HT drugs in humans.

Dose-dependent effects of buspirone on behavior and cerebral glucose metabolism in rats

In this study we compared the effects of the anxiolytic buspirone on behavior and regional cerebral metabolic rates for glucose (rCMRglc) with those of the reference serotonin (5-HT)1A agonist 8-hydroxy-2(di-N-propylamino)tetralin (DPAT). Behavioral effects were assessed by scoring the 5-HT syndrome. rCMRglc was measured in 56 brain regions by using the quantitative autoradiographic [14C]2-deoxyglucose technique, at 10 min after i.p. injection of DPAT (1 mg/kg) or buspirone (0.4, 4 and 40 mg/kg) in awake male Fischer-344 rats. Whereas DPAT produced an intense 5-HT syndrome, buspirone had no behavioral effect. A low dose (0.4 mg/kg) of buspirone reduced rCMRglc in 18 brain areas (32%), more markedly in limbic areas and raphe nuclei. These were the only rCMRglc effects buspirone had in common with the potent 5-HT1A agonist DPAT and suggest that low dose buspirone activates preferentially 5-HT1A receptors. Hence, this receptor subtype may mediate buspirone functional effects on the limbic system and, given the role of these brain areas in mood control, possibly buspirone therapeutic actions. High doses (4 and 40 mg/kg) of buspirone produced widespread rCMRglc decreases in 46 (82%) and 44 (79%) of the areas studied and increased rCMRglc in one brain area, the lateral habenula, that was not affected by DPAT or a low dose of buspirone. The topographic distribution and direction of rCMRglc changes by high doses of buspirone differ from those produced by the 5-HT1A agonist DPAT. Instead these changes resemble the rCMRglc effects of dopaminergic D2 antagonists like haloperidol and are consistent with some pharmacological and binding properties of buspirone.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of the 5-HT1A receptor agonist ipsapirone on voluntary alcohol intake in rats

The effect of the azapirone derivative ipsapirone on anxiety and the free-choice consumption of alcohol was studied in male rats. Animals were housed three in a cage with a different composition each day to increase anxiety. The animals were offered a two-bottle free choice consumption of tap water or a 5% ethanol solution. Ipsapirone was given in the drinking fluid daily at about 10 mg/kg per day. As expected, social unstable groups exhibited a higher level of anxiety as compared to social stable groups. Ipsapirone reduced significantly the anxiety in the unstable group. Pretreatment with ipsapirone before alcohol exposure resulted in a marked decrease of subsequent ethanol intake by about 45% as compared to drug free control animals. Administration of the drug to rats already drinking alcohol showed a similar decrease of ethanol intake by about 50%. These results indicate that the relatively specific 5-HT1A receptor agonist ipsapirone, given orally, reduces anxiety as well as alcohol initiation or maintenance in rats.

Comparison of the effect of buspirone and 1-(2-pyrimidinyl)-piperazine on cerebral glucose utilization in the rat

The novel anxiolytic and antidepressant, buspirone, and its main metabolite 1-(2-pyrimidinyl)-piperazine (1-PP), which is pharmacologically active, were examined for their effect on regional cerebral glucose utilization in awake rats using quantitative 2-deoxyglucose autoradiography. At a dose of 1 mg/kg, buspirone reduced glucose utilization in the hippocampus by approximately 15%, whilst 1-PP at the same dose had no effect. In comparison, at a higher dose, 10 mg/kg of both buspirone and 1-PP decreased glucose utilization in the hippocampus by 20% and 27%, respectively. In addition, widespread reductions in local cerebral glucose utilization were noted with this higher dose of 1-PP; such generalized effects are compatible with those reported for alpha 2 adrenoceptor antagonists. Buspirone at 1 and 10 mg/kg increased glucose utilization by 40% and 65%, respectively, in the lateral habenular nucleus, whilst 1-PP at 1 and 10 mg/kg had no effect. The findings suggest that buspirone's effects on glucose utilization cannot be attributed to 1-PP, unless high doses of buspirone are administered.