RESUMO
The present study was designed to examine the effects of intraperitoneal (i.p.) administration of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on the efflux of cyclic adenosine monophosphate (cAMP) in the extracellular fluid of the dorsal hippocampus, using in vivo microdialysis. One week after implantation of the guide, probes were inserted in conscious rats and perfused with Ringer solution. Steady basal levels of cAMP (2.9 +/- 0.1 pmol/ml, n = 74 rats) were obtained after at least three hours of stabilisation. The 8-OH-DPAT dose-dependently increased the basal efflux of cAMP, which was most apparent between 20-40 min after the injection. The largest dose of 8-OH-DPAT (1 mg/kg) tested, induced a maximum response of approximately 50%, whereas injections of saline did not alter the efflux of cAMP. Treatment with (+/-)pindolol (10 mg/kg) did not significantly affect the basal efflux of cAMP, whereas it markedly inhibited the increase in levels of cAMP, induced by 0.5 mg/kg 8-OH-DPAT (injected 40 min later). Simultaneous behavioural observations demonstrated that (+/-)pindolol also attenuated various components of the 8-OH-DPAT-induced behavioural syndrome. Addition of 3-isobutyl-1-methylxanthine (IBMX), forskolin or noradrenaline, to the perfusion fluid, strongly enhanced the levels of cAMP in the extracellular fluid from the hippocampus. Injection of 8-OH-DPAT (1 mg/kg) during perfusion with IBMX induced a similar increase in levels of cAMP, as under normal perfusion conditions. However, 8-OH-DPAT did not significantly alter the efflux of cAMP, when probes were perfused with either forskolin or forskolin and IBMX.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Adenilil Ciclases/metabolismo , Hipocampo/efeitos dos fármacos , Tetra-Hidronaftalenos/farmacologia , 1-Metil-3-Isobutilxantina/farmacologia , 8-Hidroxi-2-(di-n-propilamino)tetralina , Animais , Comportamento Animal/efeitos dos fármacos , Colforsina/farmacologia , AMP Cíclico/análise , Diálise , Hipocampo/enzimologia , Masculino , Norepinefrina/farmacologia , Radioimunoensaio , Ratos , Ratos Endogâmicos , Tetra-Hidronaftalenos/administração & dosagemRESUMO
In this study, we compared the localization of central 5-HT1 binding sites of rat and guinea pig. The 5-HT1B sites were absent in the guinea pig brain. Good correlations were found between species in the regional distribution of 5-HT1 sites labelled with [3H]5-HT (r = 0.73), 5-HT1A sites labelled with [3H]8-OH-DPAT (r = 0.87), and 5-HT1B versus 5-HT1D sites labelled with [3H]5-HT in the presence of ipsapirone and DOI (r = 0.76). Despite the overall similarities, species differences were observed in many brain regions. The CA1/CA2 fields of the hippocampus and the dorsal subiculum displayed significantly more 5-HT1A receptor binding in guinea pig than in rat. Conversely, the 5-HT1A binding in dorsolateral septum, cingulate cortex and laminae IV-V of the neocortex, was more pronounced in rat. Areas almost exclusively containing 5-HT1B or 5-HT1D sites, such as the ventral pallidum, globus pallidus and substantia nigra, expressed markedly more [3H]5-HT binding in rat as compared to guinea pig, while the opposite occurred in claustrum, dorsal endopiriform nucleus, lateral geniculate nucleus, and superficial grey layer of the superior colliculus. The implications of the species differences are illustrated by the binding of [3H]eltoprazine. The distribution of [3H]eltoprazine binding sites showed a good correlation with that of the 5-HT1B sites in rat (r = 0.89), and with that of the 5-HT1A sites in guinea pig (r = 0.97). The data give rise to the possibility that differences in the presence and distribution of 5-HT1 receptor sites are related to species differences in behavioural, neurochemical and physiological responses to drugs with 5-HT1 receptor affinity.
Assuntos
Encéfalo/metabolismo , Receptores de Serotonina/metabolismo , 8-Hidroxi-2-(di-n-propilamino)tetralina , Anfetaminas/farmacologia , Animais , Autorradiografia , Encéfalo/anatomia & histologia , Cobaias , Ligantes , Masculino , Piperazinas/metabolismo , Piperazinas/farmacocinética , Pirimidinas/farmacologia , Ratos , Ratos Endogâmicos , Receptores de Serotonina/efeitos dos fármacos , Antagonistas da Serotonina/farmacologia , Especificidade da Espécie , Tetra-Hidronaftalenos/metabolismoRESUMO
The present study was designed to assess whether the antiaggressive effects of eltoprazine are mediated via presynaptic and/or postsynaptic 5-HT1 receptors. We describe the effects of central 5-HT depletion 1) on the behaviour of resident TMD-S3 rats in a territorial situation, 2) on the efficacy of eltoprazine to inhibit offensive aggression, and 3) on the 5-HT1A, 5-HT1B and 5-HT1C receptor binding in brains of rats previously used in behavioural studies. Male resident rats were given combined 5,7-dihydroxytryptamine (5,7-DHT) injections into the dorsal and median raphe nuclei. Two to four weeks after the lesions, rats were confronted with an intruder Wiser rat in their home cage for a 10-min period. The 5,7-DHT treatment resulted in a modest reduction of offensive behaviour, while having no effects on other social and nonsocial behaviours. Oral administration of eltoprazine (1 mg/kg) specifically reduced offensive aggression in both sham- and 5,7-DHT-lesioned animals, leaving social interest and exploration intact or even increasing it. A low dose (0.3 mg/kg) of eltoprazine did not affect the behavioural repertoire of sham-operated rats, whereas this dose significantly reduced offense behaviours in the 5,7-DHT-lesioned residents. Quantitative autoradiographic studies 5 weeks after 5,7-DHT treatment revealed a significant increase in radioligand binding to 5-HT1A, 5-HT1B and 5-HT1C sites in many brain regions studied, except for the raphe nuclei where [3H]8-OH-DPAT binding to 5-HT1A sites was markedly reduced. The concentrations of 5-HT and 5-HIAA in frontal cortex were reduced to approximately 10% of controls. The results indicate that serotonin has a stimulatory rather than an inhibitory influence on offensive aggressive behaviour. Central 5-HT depletion does not prevent the antiaggressive effects of eltoprazine, indicating a role for postsynaptic 5-HT1 receptors in the modulation of offensive aggression. The 5,7-DHT-induced overall upregulation of 5-HT1A, 5-HT1B and 5-HT1C binding sites suggests that these three receptor subtypes receive a tonic serotonergic influence. It is conceivable that this postsynaptic 5-HT1 receptor supersensitivity is reflected by the increased efficacy of eltoprazine to inhibit offensive aggression.
Assuntos
Agressão/efeitos dos fármacos , Piperazinas/farmacologia , Receptores de Serotonina/fisiologia , Sinapses/fisiologia , 5,7-Di-Hidroxitriptamina/farmacologia , 8-Hidroxi-2-(di-n-propilamino)tetralina , Animais , Autorradiografia , Monoaminas Biogênicas/metabolismo , Encéfalo/anatomia & histologia , Masculino , Ratos , Ratos Endogâmicos , Receptores de Serotonina/efeitos dos fármacos , Serotonina/fisiologia , Antagonistas da Serotonina/farmacologia , Sinapses/efeitos dos fármacos , Tetra-Hidronaftalenos/farmacologiaRESUMO
Eltoprazine (DU 28853) inhibits offensive aggressive behaviour in several animal species. We characterized the binding of radiolabelled eltoprazine in rat brain by autoradiography. [3H]Eltoprazine displayed saturable and high-affinity binding to several brain areas, including the basal ganglia, hippocampal formation and cerebral cortex (Kd values ranging from 4.2 to 9.5 nM). The maximal binding capacities (Bmax) for [3H]eltoprazine were similar to those for [3H]5-HT and were highest in the substantia nigra and subiculum. Competition with eltoprazine for [3H]ligand binding to the various 5-HT1 receptor subtypes revealed preferential binding to 5-HT1A (IC50 values ranging from 42 to 50 nM) and 5-HT1B (IC50 values ranging from 25 to 38 nM) recognition sites. The drug had moderate affinity for 5-HT1C sites (IC50 = 282 nM). Addition of GTP or its stable analogue Gpp(NH)p to the radioligand assay caused a marked reduction (50-90%) in both [3H]eltoprazine and [3H]5-HT binding. These effects were substantially less in the choroid plexus. The binding of the antagonist (-)[125I]Iodocyanopindolol ([125I]ICYP) to 5-HT1B recognition sites, as quantified in the subiculum and substantia nigra, was either unaltered or slightly enhanced by the addition of 10(-3) M GTP. Furthermore, GTP did not affect the competition for [125I]ICYP binding by the 5-HT1-antagonist methiothepin, whereas it did significantly reduce the displacement by eltoprazine, resulting in an almost twofold increase in IC50 values. The data indicate that the anti-aggressive drug eltoprazine preferentially binds to 5-HT1A and 5-HT1B receptor sites and that this interaction is modulated by guanine nucleotides.
Assuntos
Agressão/efeitos dos fármacos , Química Encefálica/efeitos dos fármacos , Nucleotídeos de Guanina/farmacologia , Piperazinas/metabolismo , Receptores de Serotonina/metabolismo , Animais , Autorradiografia , Encéfalo/anatomia & histologia , Encéfalo/efeitos dos fármacos , Guanosina Trifosfato/farmacologia , Guanilil Imidodifosfato/farmacologia , Técnicas In Vitro , Radioisótopos do Iodo , Iodocianopindolol , Cinética , Pindolol/análogos & derivados , Piperazinas/farmacologia , Ensaio Radioligante , Ratos , Receptores de Serotonina/efeitos dos fármacos , Serotonina/farmacologiaRESUMO
In this study we report the effects of eltoprazine, a phenylpiperazine derivative with high affinity for 5-hydroxytryptamine1 (5HT1) binding sites, on membrane properties of hippocampal neurons. Intracellular recordings were made from cornus ammoni-1 pyramidal neurons in rat hippocampal slices. Responses to eltoprazine were compared with 5HT-induced responses. Superfusion with 5HT induced a dose-dependent hyperpolarization of the membrane accompanied by a resistance decrease. Eltoprazine evoked membrane changes that were similar to but much weaker than those induced by 5HT. Both the 5HT- and eltoprazine-evoked membrane hyperpolarizations were largely suppressed in the presence of spiperone. The eltoprazine-induced effects persisted in the presence of tetrodotoxin and tetraethylammonium and also when haloperidol and phentolamine were added to the medium, indicating that the small agonistic effects of eltoprazine are not due to an indirect activation of dopamine or alpha adrenergic receptors. Superfusion with eltoprazine furthermore resulted in a marked reduction of the response to concomitantly applied 5HT. Dose-response curves for 5HT were shifted to the right in the presence of eltoprazine, while the maximal response was diminished. Hyperpolarizations induced by baclofen, which presumably activates the same K+ conductance as 5HT, were not significantly reduced by eltoprazine. Our data, added to the previously demonstrated high affinity of eltoprazine for 5HT1 sites, suggest that in the hippocampal cornus ammoni-1 area eltoprazine acts as a partial 5HT1 agonist with a relatively low intrinsic activity but a considerable potency to suppress hyperpolarizing responses to 5HT.
Assuntos
Agressão/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Piperazinas/farmacologia , Serotonina/farmacologia , Animais , Hipocampo/fisiologia , Técnicas In Vitro , Masculino , Potenciais da Membrana/efeitos dos fármacos , Ratos , Ratos Endogâmicos , Receptores de Serotonina/efeitos dos fármacosRESUMO
Eltoprazine, a phenylpiperazine derivative, selectively reduces offensive aggression in animal models. The present study was designed to localize and characterize the binding sites of [3H]eltoprazine in the rat brain and to compare the distribution of these sites with the distribution of [3H]5-HT binding sites. The binding of [3H]eltoprazine to whole tissue sections was saturable and revealed an apparent dissociation constant (Kd) of 11 nM. Autoradiographic studies demonstrated a widespread distribution of [3H]eltoprazine binding sites throughout the brain. Specific [3H]eltoprazine binding was completely displaced by 5-HT; conversely, unlabelled eltoprazine reduced [3H]5-HT binding to the levels of non-specific binding. The overall distribution of [3H]eltoprazine binding sites showed a strong resemblance to the location of 5-HT1 binding sites labelled with [3H]5-HT. Yet, regions enriched in 5-HT1A and 5-HT1C sites (e.g. dentate gyrus and choroid plexus, respectively) revealed relatively more [3H]5-HT binding as compared to [3H]eltoprazine binding, whereas [3H]eltoprazine binding was more pronounced in 5-HT1B receptor dense areas such as the dorsal subiculum, substantia nigra, ventral pallidum and globus pallidus. Displacement of [3H]eltoprazine with various selective serotonergic drugs demonstrated binding of [3H]eltoprazine to 5-HT1 receptor subtypes. The pharmacological and anatomical data indicate that eltoprazine binds to 5-HT1A, 5-HT1B and to a lesser extent to 5-HT1C binding sites in the rat brain. These results emphasize the important role of serotonin in the regulation of offensive aggression and suggest that eltoprazine may serve as a new tool to study the involvement of central 5-HT1 receptors in the expression of this behaviour.
Assuntos
Agressão/efeitos dos fármacos , Encéfalo/metabolismo , Piperazinas/metabolismo , Receptores de Serotonina/metabolismo , Animais , Autorradiografia , Técnicas In Vitro , Masculino , Ratos , Ratos EndogâmicosRESUMO
In this paper we present the neurochemical profile of eltoprazine, a drug that specifically inhibits offensive aggression. Eltoprazine interacts selectively with serotonin (5-HT) receptor subtypes (Ki-values for 5-HT1A, 5-HT1B and 5-HT1C receptors are 40, 52 and 81 nM respectively). Affinity for other neurotransmitter receptors is much lower (Ki-values greater than 400 nM) than for 5-HT1 receptors. The selective interaction with 5-HT1 receptor subtypes is confirmed by in vitro autoradiographic studies using radiolabelled eltoprazine. The overall distribution of [3H]eltoprazine bears a strong resemblance to the localization of 5-HT1 binding sites labelled by [3H]5-HT, although some differences are observed. Eltoprazine (1 microM) inhibits the forskolin stimulated c-AMP production in hippocampus slices of the rat, indicating an agonistic action on the 5-HT1A receptor. The K+ stimulated release of 5-HT from rat cortex slices is inhibited by eltoprazine (pD2 = 7.8). The maximal response, however, was clearly less than that of the full agonist 5-HT, indicating partial agonistic activity on the 5-HT1B receptor (alpha = 0.5). Eltoprazine has a weak antagonistic action (IC50 = 7 microM) on the 5-HT1C receptor as revealed by inhibition of the 5-HT-induced accumulation of inositol phosphates in the choroid plexus of the pig. In vivo, eltoprazine reduces 5-HIAA levels in the striatum, without affecting the 5-HT levels. Eltoprazine also reduces the 5-HT synthesis rate as shown by 5-HTP accumulation after decarboxylase inhibition. These data indicate that eltoprazine acts as a 5-HT agonist in vivo in a dose range that affects aggressive behaviour (0.3-3 mg/kg p.o.). Taken together from a variety of neurochemical studies there is strong evidence both in vitro and in vivo that the pharmacological actions of eltoprazine can be attributed to an interaction with the 5-HT system, most probably via a (partial) agonistic action on 5-HT1A and 5-HT1B receptors.
Assuntos
Encéfalo/metabolismo , Piperazinas/farmacologia , Psicotrópicos/farmacologia , Animais , Sítios de Ligação , Monoaminas Biogênicas/metabolismo , Encéfalo/efeitos dos fármacos , Encéfalo/ultraestrutura , Corpo Estriado/metabolismo , Masculino , Neurônios/química , Neurotransmissores/fisiologia , Fosfatidilinositóis/metabolismo , Piperazinas/metabolismo , Piperazinas/farmacocinética , Ratos , Ratos Endogâmicos , Receptores de Serotonina/metabolismo , Receptores de Serotonina/fisiologia , Sistemas do Segundo Mensageiro , Serotonina/metabolismo , Serotonina/farmacocinética , Serotonina/fisiologia , Antagonistas da Serotonina , Suínos , Distribuição Tecidual , TrítioRESUMO
When the lateral olfactory tract (LOT) of the golden hamster, Mesocricetus auratus, is transected in the first week of postnatal life, axons can grow back past the lesion and achieve functional reinnervation of caudal projection regions. In contrast, when the tract is sectioned after postnatal day 7 (P7), axons do not reinnervate regions caudal to the cut. The experiments reported here investigated whether regenerative failure after tract section in pups older than P7 is accompanied by developmental changes in the astrocytic response. LOT transections were performed at P3 and P9 and the glial reaction was observed at survival times ranging from 12 hr to 2 weeks. Immunocytochemistry with glial fibrillary acidic protein (GFAP) was employed for histological visualization of astrocytic reactivity. Staining for GFAP immunoreactivity showed an appreciable glial reaction after tract section at both P3 and P9, but the extent of astrocytic hypertrophy and proliferation of glial processes was considerably greater and more extensive after tract section at P9. Radial glial cells were observed 2 weeks after LOT transection at P3 but were absent after lesions made at P9. The results from this study suggest that the developmental loss of regenerative capacity after LOT transection may be related to maturational changes in the glial response. In particular, the presence of radial glial elements after P3 lesions could serve to establish a more favorable microenvironment for axonal elongation.