By using a strategy based on nucleotide sequence homology, we have cloned a cDNA encoding a functional serotonin (5-HI) receptor. The deduced amino acid sequence of the 5--HT7 receptor displays limited homology with that of other 5-HT receptors. In addition to the seven stretches of hydrophobic amino acids that characterize the superfamily of receptors interacting with guanine nudeotide-binding proteins, the 448-aa sequence of the 5-HT7 receptor contains a hydrophobic domain located at its N-terminal end. Genomic analysis indicated the presence of introns interrupting the coding sequence. The 5-HT7 receptor, stably expressed in transfected CHO ceils, bound [3H]5-HT with hh affnity (Kd = 1 nM), like receptors of the 5-HT1 subfamily from which, however, it was dearly distuished by its phaacology.5-HT in nanomolar concentrations stimulated cAMP accumulation in these CHO celis by =40-fold, whereas lysergic acid diethylamide displayed low intrinsic agonist actiity. These various properties differentiate the 5-HT7 receptor from the four other subfamilies of mammalian 5-HT receptors (i.e., the 5-HTi-, 5-HT2-, 5-HT3-, and 5-HT4-like subfamllies) and, therefore, appear to define another receptor subfamily. Northern blot and in situ hybridization analyses showed the 5-HT7 transcripts to be expressed in discrete areas of the limbic brain (e.g., pyramidal hippocampus cells, tenia tecta, amygdaloid, or nmammiary nudei), suggesting that the receptor mediates serotoninergic controls in functions like mood, learning, or neuroendocrine and vegetative behaviors.Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter that exerts its effects mainly in the central nervous and gastrointestinal systems by interacting with a large variety of receptors. These were initially distinguished through the use of traditional pharmacological approaches with isolated organs (1) and, then, in binding studies (2). More recently, with the introduction of molecular biology approaches in the field (3), a wealth of additional 5-HT receptor subtypes could be characterized.Now, it appears that, whereas the 5-HT3 receptor is a ligand-gated ion channel (4), mammalian 5-HT receptors with seven putative transmembrane domains (TMs) and coupled to guanine nucleotide-binding (G) proteins can be divided into three subfamilies, depending on molecular, ligand binding, and effector-coupling properties. Members of the 5-HT1 subfamily [except, perhaps, the preliminarily characterized 5-HT5 receptor (5)-i.e., 5-HT1A (3, 6), 5-HT1B (7-9), 5-HTlD (10-12), 5-HT1E (13), and 5-HT1F (14) receptors-are encoded by intronless genes, display nanomolar affinity for 5-HT, and are negatively coupled to adenylyl cyclase. The 5-HT2 subfamily contains the homologous 5-HT,c (15) andThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. (16) There is evidence, however, for the existence of additional 5-HT receptors. For...

Brain-derived neurotrophic factor (BDNF), like other neurotrophins, is a polypeptidic factor initially regarded to be responsible for neuron proliferation, differentiation and survival, through its uptake at nerve terminals and retrograde transport to the cell body. A more diverse role for BDNF has emerged progressively from observations showing that it is also transported anterogradely, is released on neuron depolarization, and triggers rapid intracellular signals and action potentials in central neurons. Here we report that BDNF elicits long-term neuronal adaptations by controlling the responsiveness of its target neurons to the important neurotransmitter, dopamine. Using lesions and gene-targeted mice lacking BDNF, we show that BDNF from dopamine neurons is responsible for inducing normal expression of the dopamine D3 receptor in nucleus accumbens both during development and in adulthood. BDNF from corticostriatal neurons also induces behavioural sensitization, by triggering overexpression of the D3 receptor in striatum of hemiparkinsonian rats. Our results suggest that BDNF may be an important determinant of pathophysiological conditions such as drug addiction, schizophrenia or Parkinson's disease, in which D3 receptor expression is abnormal.

We have identified ([3H]7-OH-DPAT) as a selective probe for the recently cloned dopamine D3 receptor and used it to assess the presence of this receptor and establish its distribution and properties in brain. In transfected Chinese hamster ovary (CHO) cells, it binds to D3 receptors with subnanomolar affinity, whereas its affinity is approximately 100-, 1000-, and 10,000-fold lower at D2, D4, and D, receptors, respectively. Specific [3H]7-OH-DPAT binding sites, with a Kd of0.8 nM and a pharmacology similar to those at reference D3 receptors of CHO cells, were identified in rat brain. D3 receptors differ from D2 receptors in brain by their lower abundance (2 orders of magnitude) and distribution, restricted to a few mainly phylogenetically ancient areas-e.g., paleostriatum and archicerebellum-as evidenced by membrane binding and autoradiography studies. Native D3 receptors in brain are characterized by an unusually high nanomolar affinity for dopamine and a low modulatory influence of guanyl nucleotides on agonist binding. These various features suggest that D3 receptors are involved in a peculiar mode of neurotransmission in a restricted subpopulation of dopamine neurons.Dopamine is an important neurotransmitter in brain, being involved physiologically in the control of cognitive, motor, and endocrine processes and pathologically in Parkinson and possibly mental diseases.Until recently, it was largely believed that its various actions were mediated by two receptor subtypes, termed D1 and D2 (1, 2). Molecular biology approaches have led, however, to the identification and cloning of the genes corresponding not only to these two receptor subtypes (3-7) but also to additional and less expected ones, termed D3 (8), D4 (9), and D5 (10, 11). For the latter receptors, the information so far available derives from molecular biology approaches; their pharmacology and signaling system have only been studied in transfected cells, generally fibroblasts, and their distribution has been indirectly approached by studies of mRNA localization. Nevertheless, these otherwise valuable approaches suffer from some limitations. When expressed in fibroblasts, receptors might find a membrane environment, which could modify their pharmacological specificity, and a repertoire of cellular components, particularly GTP-binding proteins (G proteins), which may differ from that found in neurons. Regarding distribution, mRNA detection reveals the sites of receptor synthesis rather than receptor localization, which may be different. Therefore, there is an obvious interest in studying the native receptor protein in brain, particularly in the case ofthe D3 receptor, whose pharmacology in Chinese hamster ovary (CHO) cells and cerebral localization of its mRNA suggest that it may represent an important target for antipsychotics (8,12,13).Starting with the idea that designing a selective radioactive probe for the D3 receptor would help to settle these issues, we have screened a series of dopamine agonists and thereby identified 7-hydroxy-N,...