Structure and functional expression of the cloned rat neurotensin receptor

The structure of neuropeptide receptors

Recently, the primary structures of 17 different receptors for neuropeptides and small peptide hormones have been elucidated by molecular cloning. All but one belong to the superfamily of G-protein coupled receptors which share a topography consisting of seven transmembrane domains. Comparison of primary structures shows that two classes of peptide receptors exist. One referred to as the 'neurokinin-type receptors', possesses many of the typical, conserved amino acid sequence motifs of the aminergic transmitter receptors (e.g. beta-adrenoceptor). The other, referred to the 'secretin-type receptors', displays unrelated and distinctly different sequence motifs which are conserved between the three presently known members of this class. These are the secretin, calcitonin and parathyroid hormone/parathyroid hormone-like polypeptide receptors. One may speculate that many other peptides with a core of biological activity in the N-terminal or middle region may have receptors of the secretin-type.

Ontogenesis and binding properties of high-affinity neurotensin receptors in human brain

The ontogenesis of neurotensin binding sites was studied in human brain of subjects deceased from Sudden Infant Death Syndrome. Monoiodo-Tyr3 neurotensin specifically recognized 2 distinct classes of binding sites in human brain homogenate. The high affinity sites were already present at birth and increased to a maximal level of 240 fmol/mg protein 1 month after birth. Thereafter, the density of these sites decreased to reach a value of 8 fmol/mg protein in 15-month-old brain, a value similar to that found in adult brain. The dissociation constant of the high-affinity sites (about 0.3 nM) did not vary from birth to adulthood. The high-affinity binding sites were sensitive to GTP which decreased their affinity for neurotensin by a factor of 3, indicating that these sites are functional receptors coupled to GTP-binding proteins. By contrast, the low-affinity sites were insensitive to GTP and could be partly blocked by the antihistaminic drug levocabastine. These sites were absent in human brain during the first post-natal year and could be detected only in brain homogenate of 15-month-old infants. The transient increase in high-affinity neurotensin binding sites after birth suggests that neurotensin could act as a regulatory peptide during brain development.

Neurotensin stimulates growth of colonic mucosa in young and aged rats

Neurotensin, a tridecapeptide widely distributed in the gut, stimulates growth of small bowel mucosa in young and aged rats. In the present study, the effect of long-term neurotensin administration on the growth of colonic mucosa was examined in young (2-month-old) and aged (24-month-old) rats. Subcutaneous injections of saline (control) or neurotensin (300 micrograms/kg) in gelatin were given to the groups of rats every 8 hours for 10 days. During treatment, all rats were maintained on a regular chow diet. Rats were killed on day 11; the entire colon was removed, mucosa was scraped and weighed, and DNA, RNA, and protein contents were determined. Neurotensin induced growth of colonic mucosa in both age groups. In young rats, neurotensin increased weight and DNA, RNA, and protein contents of colonic mucosa. The ratio of DNA content, an index of cellular hyperplasia, was increased significantly in the neurotensin-treated young rats compared with age-matched controls, indicating an overall increase in mucosal cellularity. In the aged rats, growth was characterized by an increase in weight and RNA and protein contents, but not DNA content, thus suggesting cellular hypertrophy. These results suggest that neurotensin has an important regulatory function in the growth of colonic mucosa; however, the mode of action, at the cellular level, appears to be different depending on age.

Different postnatal development of cells expressing mRNA encoding neurotensin receptor

In situ hybridization histochemistry revealed three different ontogenetic patterns of localized expression of the high-affinity type of neurotensin receptor mRNA in the developing rat brain: one comprises sites which showed transient expression of neurotensin receptor mRNA during the first postnatal week, the expression greatly decreasing thereafter (type I); another comprises sites at which there is a gradual increase in neurotensin receptor mRNA after birth, as there is in cell number and intensity, with advancing age, followed by a plateau (type II); the third comprises sites at which there is much expression of neurotensin receptor mRNA already at birth, and a slight decrease thereafter (type III). The cerebral cortex, except retrosplenial and entorhinal cortices, and the anterior dorsal thalamic nucleus exhibit the type I pattern, while the horizontal and vertical limbs of the diagonal band of Broca, magnocellular preoptic nucleus, substantia innominata, ventral part of the suprachiasmatic nucleus, medial habenular nucleus, ventral tegmental area and substantia nigra pars compacta exhibit the type II pattern. The tenia tecta, retrosplenial and entorhinal cortices exhibit the type III pattern. One of the most striking findings in this study was that the entire neocortex and most of the limbic cortex exhibit the type I pattern, i.e. neurotensin receptor mRNA is expressed transiently long before a neuronal network is established there. This suggests that neurotensin plays an important role in cortical development, other than its reported transmitter-like role in the adult.

Functional reconstitution of a receptor-activated signal transduction pathway in Xenopus laevis oocytes using the cloned human C5a receptor

We have used the polymerase chain reaction to isolate and clone the cDNA encoding the human C5a receptor, and have injected the cDNA-derived receptor cRNA into Xenopus laevis oocytes for functional characterization of the receptor protein. Receptor activity was determined either electrophysiologically by measuring the agonist-dependent opening of [Ca2+]i-dependent Cl- channels, or by analysing the agonist-dependent efflux of 45Ca2+ from the oocytes. Using both methodologies, injection of pure C5a receptor cRNA failed to confer C5a sensitivity on the oocytes. In contrast, marked responses to C5a were observed when the receptor cRNA was supplemented with poly(A)+ RNA isolated from undifferentiated HL-60 cells, which is devoid of C5a receptor mRNA. Binding studies using radioiodinated C5a revealed that the C5a receptor polypeptide was in fact synthesized and targeted to the oocyte plasma membrane in oocytes injected with receptor cRNA alone, and that the level of receptor expression was not influenced by coinjection of poly(A)+ RNA from undifferentiated HL-60 cells. These results strongly suggest that the human C5a receptor requires a specific cofactor(s) lacking in Xenopus oocytes but present in undifferentiated HL-60 cells, to generate intracellular signals in oocytes. Identification and characterization of this factor will provide important information about the molecular mechanisms by which G-protein-coupled receptors activate phospholipase C.

Expression of functional bradykinin receptors in Xenopus oocytes

mRNA prepared from various tissues and cultured cells was injected into Xenopus laevis oocytes. Three to five days after injection, the response of the oocytes to the peptide bradykinin was monitored. The oocytes were voltage clamped and the membrane currents generated on application of agonist were recorded. mRNA from NG108-15, rat uterus, and human fibroblast cell line WI38 gave similar responses to bradykinin (1 microM), with an initial inward current (10-20 nA) followed by a prolonged period of membrane current oscillations. The same pattern of response was given by total RNA from rat dorsal root ganglia. No response to bradykinin (10 microM) was recorded from oocytes injected with rat brain mRNA, although these oocytes gave peak inward currents of about 75 nA in response to serotonin (10 microM). mRNA from both NG108-15 cells and rat uterus was fractionated on sucrose gradients. This resulted in an approximately five-fold increase in the size of the response compared to that given by unfractionated mRNA. The largest responses were given by mRNA fractions with a size of approximately 4.5 kb. Data were obtained consistent with the expression of both B1 and B2 receptors by WI38 human fibroblasts and with the expression of only the B2 type of receptor by NG108-15 cells.

A family of metabotropic glutamate receptors

Three cDNA clones, mGluR2, mGluR3, and mGluR4, were isolated from a rat brain cDNA library by cross-hybridization with the cDNA for a metabotropic glutamate receptor (mGluR1). The cloned receptors show considerable sequence similarity with mGluR1 and possess a large extracellular domain preceding the seven putative membrane-spanning segments. mGluR2 is expressed in some particular neuronal cells different from those expressing mGluR1 and mediates an efficient inhibition of forskolin-stimulated cAMP formation in cDNA-transfected cells. The mGluRs thus form a novel family of G protein-coupled receptors that differ in their signal transduction and expression patterns.

Sequence alignment of the G-protein coupled receptor superfamily

The multitude of G-protein coupled receptor (GPR) superfamily cDNAs recently isolated has exceeded the number of receptor subtypes anticipated by pharmacological studies. Analysis of the sequence similarities and unique features of the members of this family is valuable for designing strategies to isolate related cDNAs, for developing hypotheses concerning substrate-ligand and receptor-effector interactions, and for understanding the evolution of these genes. We have compiled and aligned the 74 unique amino acid sequences published to date and review the present understanding of the structural motifs contributing to ligand binding and G-protein coupling.

Rapid agonist-induced decrease of neurotensin receptors from the cell surface in rat cultured neurons

The regulation of neurotensin receptors was studied in vitro in primary cultures of neuronal cells. High affinity receptors for [3H]neurotensin were found in homogenates and at the cell surface of intact neurons cultured from the brain of rat embryos. When intact cells were incubated with 3 nM neurotensin (1-13), a rapid decrease in [3H]neurotensin binding was observed; about 60% of neurotensin receptors disappeared from the cell surface in less than 15 min. This corresponded to a reduction of the Bmax value without a change in the binding affinity. The decrease in neurotensin receptor number was also induced by the active fragment (8-13) of neurotensin but not by its inactive fragment (1-8). It was partially inhibited by bacitracin, at concentrations which are known to interact with receptor internalization, and was not detected when intact cells were incubated at 0-4 degrees with the unlabeled peptide. When intact neurons were incubated with [3H]neurotensin, there was a rapid ligand uptake and the kinetics of endocytosis were similar to those of the cell surface receptor disappearance. Once endocytosed, [3H]neurotensin could not be released (or displaced) from either intact neurons or homogenates, suggesting the sequestration of the labeled peptide in vesicles or other subcellular structures. Therefore, the present results suggest that the rapid agonist-induced decrease in the number of neurotensin receptors from the cell surface corresponds to an internalization process which involves a simultaneous receptor-mediated peptide endocytosis.

Binding and internalization of iodinated neurotensin in neuronal cultures from embryonic mouse brain

The binding and internalization of labeled neurotensin were studied by means of biochemical and light microscopic radioautography techniques in primary cultures of neurons from whole cerebral hemispheres of mouse embryos. Saturable, high affinity neurotensin binding was detected 5-7 days postplating in cells incubated with 0.1 nM 125I-Tyr3-neurotensin at 37 degrees C or 10 degrees C. The binding capacity at equilibrium was 3 times higher at 37 degrees C than at 10 degrees C. Moreover, whereas virtually all the radioactivity bound at 10 degrees C was membrane-bound (i.e. was readily washable by a hypertonic, high pH, NaCl solution), more than 70% of the radioactivity bound at 37 degrees C was intracellular (i.e. resisted the same treatment). Light microscopic radioautograms of whole cells revealed that approximately 16% of neurons were labeled with 125I-Tyr3-neurotensin at either 37 degrees C or 10 degrees C. The labeling was observed over cell bodies and processes, and the density of silver grains associated with perikarya, as compared to processes, was proportionally higher at 37 degrees C than at 10 degrees C. Semi-thin (1 micron thick) sections through cells incubated at 37 degrees C confirmed that a major fraction of the radioactivity was intracellular and showed that it was mainly confined to the cytoplasm. These results indicate that 125I-Tyr3-neurotensin binds to a distinct subset of primary cultured neurons and that a large proportion of the bound radioactivity undergoes rapid internalization in a temperature-dependent manner. It is proposed that this internalization is ligand-induced and that it may play a role in the modulation of central neurotensin receptor levels.

The neurobiology of neurotensin: focus on neurotensin-dopamine interactions

Neurotensin (NT) is a tridecapeptide which fulfills many of the requisite criteria for a role as a central nervous system (CNS) neurotransmitter. It is closely associated with CNS dopamine neurons and has been shown to interact with dopamine at physiological, anatomical and behavioral levels. Neurotensin is colocalized with dopaminergic neurons in the hypothalamus and midbrain. In addition, it blocks behaviors associated with activation of the dopaminergic pathways. Centrally administered NT has been shown to mimic many of the actions of antipsychotic drugs. In addition, the concentration of NT in cerebrospinal fluid is decreased in patients with schizophrenia. Administration of clinically effective antipsychotic drugs increases concentrations of NT in the caudate nucleus and nucleus accumbens. NT has been shown to play a role in signal transduction by mostly mobilizing calcium stores following inositol phosphate formation. This has been linked to subsequent events in protein phosphorylation. Lipophilic NT receptor agonists may represent a novel approach to the development of a new class of antipsychotic drugs.

Expression cloning of a rat B2 bradykinin receptor

A cDNA encoding a functional bradykinin receptor was isolated from a rat uterus library by a clonal selection strategy using Xenopus laevis oocytes to assay for expression of bradykinin responses. The predicted protein is homologous to the seven transmembrane G protein-coupled superfamily of receptors. Bradykinin and its analogs stimulate a Cl- current oocytes expressing the receptor with the rank order of potency: bradykinin approximately Lys-bradykinin greater than [Tyr8]-bradykinin much greater than [Phe6]bradykinin. This is the rank order of potency observed for these compounds in competitive binding assays on soluble receptor from rat uterus. Des-Arg9-bradykinin (10 microM) elicits no response when applied to oocytes expressing the receptor; thus, the cDNA encodes a B2 type bradykinin receptor. [Thi5,8,DPhe7]bradykinin, where Thi is beta-(2-thienyl)-alanine, is a very weak partial agonist and inhibits the bradykinin-mediated ion flux, suggesting the cDNA encodes a smooth muscle, rather than a neuronal, B2 receptor subtype. Receptor message has a distribution consistent with previous reports of bradykinin function and/or binding in several tissues and is found in rat uterus, vas deferens, kidney, lung, heart, ileum, testis, and brain. Receptor subtypes are a possibility because several tissues contain two or three message species (4.0, 5.7, and 6.5 kilobases). Southern blot high-stringency analysis demonstrated that the rat, guinea pig, and human genomes contain a single gene. As bradykinin is a key mediator of pain, knowledge of the primary structure of this receptor will allow a molecular understanding of the receptor and aid the design of antagonists for pain relief.

Purification and characterization of neurotensin receptor from rat brain with special reference to comparison between newborn and adult age rats

Scatchard analysis of saturation curves was performed to compared newborn and adult rat neurotensin receptor using [3H] neurotensin as a tracer. The membrane fraction of newborn rat cerebral cortex has a single population of neurotensin receptor (Kd = 0.13 nM, Bmax = 710 fmol/mg protein), whereas adults have two distinct neurotensin binding sites (high affinity site, Kd1 = 0.13 nM; low affinity site, Kd2 = 20 nM). High affinity neurotensin receptor, solubilized with digitonin, was purified from newborn rat cortex by affinity chromatography. An overall purification of 14,000-fold was achieved. The binding of [3H] neurotensin to the purified receptor is saturable and specific, with a Kd of 0.45 nM. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in the presence of 2-mercaptoethanol revealed purified material of a single major band of Mr = 55,000.

Structure-antinociceptive activity of neurotensin and some novel analogues in the periaqueductal gray region of the brainstem

Neurotensin, an endogenous tridecapeptide, produces a potent, naloxone-insensitive antinociceptive response when it is microinjected into the periaqueductal gray region of the rat brainstem. In the present study, the ED50 for neurotensin in inducing antinociception was 1.5 nmol, two times more potent than morphine. We sought to find whether neurotensin's antinociceptive effects were mediated by the same receptor that mediates its other functions. We found that the structure-activity relationship of neurotensin-induced antinociception was different from that required for the stimulation of intracellular cyclic GMP production in neuroblastoma clone N1E-115 and the binding to N1E-115 cells, human brain tissue, or rat periaqueductal gray. These data suggest there exists a subtype of neurotensin receptors in neural tissue that mediates its antinociceptive actions.

Characterization of neurotensin binding sites on rat mesencephalic cells in primary culture

Many studies have reported the presence of high amounts of neurotensin (NT) binding sites in the mesencephalon of adult rat, and their possible role in mediating the effects of the peptide on the activity of mesencephalic dopaminergic neurons. In the present study, we demonstrate the presence of NT sites in primary cultures of embryonic rat mesencephalic cells. On these cells, a single class of high affinity 125I-NT binding sites was observed. The value of the apparent affinity constant (0.3 nM) did not show any significant change throughout time, from 3 to 14 days in culture. The number of sites, however, increased until day 11 and decreased thereafter. Acetylneurotensin (8-13), NT and neuromedin N were potent competitors of 125I-NT binding, while NT (1-10), NT (1-11) and levocabastine were uneffective. These results indicate that the sites detected in the mesencephalic cultures share common binding properties with the high-affinity NT sites already described in adult rat brain. The neuronal localization of the NT sites was suggested by their presence in neuron-enriched serum-free cultures and their absence in glial cultures. Autoradiographic studies confirmed the cellular localization of NT sites and indicated that, under our experimental conditions, cells labeled by 125I-NT represented 0.14% of the initially plated cell number. Taken together, these results show that the development of mesencephalic neurons in primary culture is associated with an increased expression of NT binding sites. Since such cultures have been shown previously to contain functional dopaminergic neurons, we suggest that they could provide a good model to investigate the modulation of the activity of these neurons by NT.

Molecular cloning of a novel putative G-protein coupled receptor expressed during rat spermiogenesis

A cDNA clone encoding a novel putative G-protein coupled receptor has been isolated from a rat testis cDNA library using a PCR-amplified cDNA fragment as a hybridization probe. Northern blot analysis reveals that a corresponding 1.5 kb mRNA is exclusively expressed in testis. By in situ hybridization experiments this mRNA has been localized in spermatocytes and spermatids but not in spermatogonia, Leydig or sertoli cells. Ontogenic studies show that expression of the receptor-encoding mRNA and sexual maturation are correlated reaching highest levels during the second and third months. Although the ligand for this receptor has not yet been identified, this receptor may play a role during reproduction.

G proteins and G-protein-coupled receptors: structure, function and interactions

The G protein family continues to grow and at least 15 heterotrimeric G proteins have now been identified. This review deals with the nature of the functional domains of the members of the G-protein-coupled receptor family as well as the associated G proteins.

Receptors for neurotensin in canine small intestine

We have previously characterized the neurotensin receptors on the circular smooth muscle (CM) of the canine small intestine (1). In the present studies, using radioligand binding technique, neurotensin receptors were localized on the membranes from deep muscular (DMP) and the submucous plexus while no binding was observed on either the longitudinal smooth muscle or myenteric plexus membranes. The high affinity binding sites (Kd 0.1-0.2 nM) on DMP membranes were similar to those on CM; the low affinity component was of much lower affinity (Kd approximately 40 nM). DMP had 4-6 times higher density of binding sites than the CM. The recognition properties of DMP receptors were similar to those on the CM and reduced sulfhydryl groups were required for the binding activity. The action of neurotensin on the contractility of the canine small intestine, therefore, appears to be through a direct action on the circular smooth muscle and through the prejunctional action on the DMP neurons through distinct receptors. Thiol groups in the neurotensin receptors may be important for the receptor function.

Current developments in G-protein-coupled receptors

The rate at which receptors have been cloned has recently increased dramatically--existing families have been extended and new families created. The rapid cloning by homology of 'orphan receptors' has also stimulated the development of a new reverse pharmacology.

Endothelin receptor: a profoundly desensitizing receptor expressed in Xenopus oocytes

Xenopus oocyte expression studies can help to define the physiological properties of a receptor and can aid in receptor cloning. Expression of an endothelin receptor in oocytes injected with brain mRNA is inferred from depolarizations induced by several endothelin-related peptides. The response is abolished by intracellular EGTA injection but not in the absence of extracellular Ca2+. It is not present in non-injected oocytes, and reverses at a potential indicating that it is mediated by an increased Cl-1 conductance. Responses display striking, long-lasting desensitization. The expressed endothelin receptor thus displays properties characteristic of several receptors coupled to changes in phosphoinositide turnover, several of which have been successfully cloned using this response as a reporter.

The electrophysiological actions of neurotensin in the central nervous system

The endogenous neuropeptide, neurotensin (NT) alters the firing frequencies of certain neurons in the central nervous system (CNS). This is one of the findings that support the hypothesis that NT is a neurotransmitter substance. The direct application of NT on CNS neurons causes predominantly excitatory effects. These effects occur in a dose-related fashion via a calcium-dependent postsynaptic mechanism. The C-terminal hexapeptide fragment, NT 8-13 exerts similar electrophysiological effects to NT, while the N-terminal octapeptide fragment, NT 1-8 is devoid of such activity. NT produces a significant increase in the firing rates of individual neurons in the substantia nigra (SN), ventral tegmental area (VTA), medial prefrontal cortex (MPF), hypothalamus, and periaqueductal grey (PAG). This excitation occurs with a rapid onset and is readily reversible after cessation of NT application. In contrast, NT has no effect or weak inhibitory effects on the firing rates of neurons in the locus coeruleus (LC) and cerebellum. These electrophysiological actions of NT appear to be unique and not shared by other neurotransmitter and neuropeptide receptor antagonists and agonists that have been studied via direct co-application. NT attenuates dopamine (DA)-induced inhibition associated with direct application onto neurons in the SN and VTA both in vivo and in vitro. Intracellular recordings suggest that direct application of higher concentrations of NT appears to produce 'depolarization block' on individual neurons in the SN, VTA, MPF, and hypothalamus. The electrophysiological consequences of NT application not only show similarities to clinically efficacious antipsychotic medications, but also demonstrate the ability of NT to modulate the activity of dopamine (DA) neurons at the cellular level via specific NT binding sites. These findings further underscore the possibility that NT may play a pre-eminent role in the pathogenesis of, and psychopharmacological management of neurological and psychiatric disorders purportedly related to perturbation of CNS DA systems including schizophrenia.

Structure and function of G protein coupled receptors

Application of a molecular genetic techniques has allowed the isolation and identification of more than 50 members of the G protein-coupled receptor family. Their specificities range from sensory receptors such as the opsins and odorant receptors through those for the amines, peptides and other small molecules to those for glycoprotein hormones. These studies make it clear that traditional pharmacological methods, often underestimate receptor diversity. G protein-coupled receptors share a common structure consisting of 7 transmembrane alpha helical segments. Receptor structure-function relationships are discussed in the light of results obtained by site-directed mutagenesis and the construction of chimeric receptors. Studies which have allowed the identification of ligand-binding domains, and of sequences defining G protein specificity as well as those involved in receptor desensitization and downregulation are also discussed.

Synaptic receptors and intracellular signal transduction in the cerebellum

Glutamate receptor subtypes mediating excitatory synaptic neurotransmission in the cerebellar cortex are briefly reviewed from molecular biological, electrophysiological and pharmacological points of view. In particular, molecular biological findings of a novel family of AMPA-selective glutamate receptors are introduced, and the pharmacological and electrophysiological properties and the identity of cerebellar N-methyl-D-aspartate-sensitive receptors probably existing on Purkinje cells are discussed in comparison with well-established cerebral NMDA receptors. As possible intracellular mechanisms of the long-term depression of parallel fiber-Purkinje cell neurotransmission, the perspective of the roles of novel messengers, nitric oxide and arachidonic acid, is particularly commented based on recent information about cerebral long-term events. The specificity and possible independence of cerebellar excitatory amino acid receptors and linked intracellular second messengers are also suggested, taking the highly active guanylate cyclase system in Purkinje cells and other cerebellum-specific proteins into consideration.

Cloning and expression of a cDNA encoding an endothelin receptor

Endothelins are a newly described peptide family consisting of three peptides (ET-1, ET-2 and ET-3) which are the most potent vasoconstrictive peptides known. They are crucial in the regulation of vascular smooth muscle tone. The diverse functions of endothelins are thought to be mediated by interaction with many different receptors coupled to the inositol phosphate/calcium ion messenger pathway. However, because of the structural resemblance of the three peptides, the presence and nature of multiple endothelin receptors remain to be elucidated. We report here the cloning of a complementary DNA encoding a bovine endothelin receptor, which has a transmembrane topology similar to that of other G protein-coupled receptors and shows specific binding, with the highest selectivity to ET-1 in animal cells transfected with the cloned cDNA. This receptor messenger RNA is widely distributed in the central nervous system and peripheral tissues, particularly in the heart and lung. Our results support the view that there are other receptor subtypes.

Replica filter assay of human beta-adrenergic receptors expressed in E.coli

We have developed a replica filter assay that permits the direct identification of bacterial colonies expressing membrane receptors. E.coli transformed with appropriate phage or plasmid vectors containing human beta-adrenergic receptor cDNAs were grown on LB/agar plates. Bacterial colonies transferred onto nitrocellulose filters showed specific [125I]-iodocyanopindolol binding. beta-adrenergic receptors expressed in bacteria retained their pharmacological properties when transferred onto filters. This strategy, which is considerably simplified and more rapid compared to similar methods based upon expression of receptor genes in eukaryotic cells, may be a useful tool for cloning membrane receptors.

Localization of neuropeptide receptor mRNA in rat brain: initial observations using probes for neurotensin and substance P receptors

The expression of receptors for neurotensin and substance P was examined in rat brain and spinal cord using in situ hybridization with synthetic oligonucleotide probes. Strong hybridization signals for neurotensin receptor mRNA were observed over neurons i.a. in the diagonal band, medial septal nucleus, nucleus basalis magnocellularis, suprachiasmatic nucleus, supramammillary area, substantia nigra and ventral tegmental area. Strong hybridization signals for substance P receptor mRNA were observed over scattered, large neurons in the striatum, and in the spinal cord over neurons in the dorsal horn, the area around the central canal and preganglionic autonomic neurons. Thus, discrete neurons in several brain regions express a G-protein-coupled receptor with which endogenous neurotensin and substance P may interact.