Autoradiographic localization of [3H]neurotensin-binding sites in the hippocampal region of the rat and primate brain

Neurotensinergic Excitation of Dentate Gyrus Granule Cells via Gαq-Coupled Inhibition of TASK-3 Channels

Neurotensin (NT) is a 13-amino acid peptide and serves as a neuromodulator in the brain. Whereas NT has been implicated in learning and memory, the underlying cellular and molecular mechanisms are ill-defined. Because the dentate gyrus receives profound innervation of fibers containing NT and expresses high density of NT receptors, we examined the effects of NT on the excitability of dentate gyrus granule cells (GCs). Our results showed that NT concentration dependently increased action potential (AP) firing frequency of the GCs by the activation of NTS1 receptors resulting in the depolarization of the GCs. NT-induced enhancement of AP firing frequency was not caused indirectly by releasing glutamate, GABA, acetylcholine, or dopamine, but due to the inhibition of TASK-3 K(+) channels. NT-mediated excitation of the GCs was G protein dependent, but independent of phospholipase C, intracellular Ca(2+) release, and protein kinase C. Immunoprecipitation experiment demonstrates that the activation of NTS1 receptors induced the association of Gαq/11 and TASK-3 channels suggesting a direct coupling of Gαq/11 to TASK-3 channels. Endogenously released NT facilitated the excitability of the GCs contributing to the induction of long-term potentiation at the perforant path-GC synapses. Our results provide a cellular mechanism that helps to explain the roles of NT in learning and memory.

Retrosplenial/presubicular continuum in primates: a developmental approach in fetal macaques using neurotensin and parvalbumin as markers

In spite of numerous hodological and neuropsychological studies emphasizing the multimodal connections and integrative functions of the retrosplenial cortex in primates, the precise fate of its caudoventral extent and the composition of the merging area with the hippocampal formation remain a matter of debate. We reported previously how the anlage of the retrosplenial cortex merges with the immature presubicular zone in the fetal rhesus monkey at the end of the first trimester of gestation. In the present study, this caudal area was further defined on a chemoarchitectonic basis, particularly during the late prenatal and perinatal stages, which correspond to the development of the cingulate sulcus and temporal gyri, and the differentiation of the retrosplenial/subicular complex. Neurotensin (NT), a pyramidal cell marker in the limbic cortex, and parvalbumin (PV), a marker of a subset of inhibitory local circuit neurons in the hippocampal formation, were used as immunocytochemical markers. According to distinct chemoarchitectural patterns, (1) areas 29 l and 29 m of the retrosplenial cortex formed a triangle-shaped ventral expansion which merged with a similar but dorsal expansion of the pre/parasubicular fields. A temporal extension of area 29 m down to area TH could not be detected. The pre/parasubiculum contributed with area 29 m to the lateral bank of the calcarine sulcus as far as the most caudal extent of the hippocampal formation. (2) The lamina principalis interna of the presubiculum was well individualized and did not appear as a simple horizontal shift of adjoining fields. (3) NT and PV displayed a distinct temporal profile of development. NT was already expressed in the pyramidal cells of the prospective retrosplenial cortex and ventral hippocampal formation at E47 (term 165 days). Major pathways of the hippocampal formation and retrosplenial cortex (fimbria, fornix, angular and cingulum bundles) were progressively labeled indicating early developing projections. A large set of NT-positive afferents reached the retrosplenial cortex between E114 and E120. Their laminar distribution was compatible with a thalamic or a subicular origin. (4) The development of PV expression was delayed until the last quarter of gestation, supporting its proposal as a signal of functional onset. The developmental fate and the particular connections of the presubiculum suggest that its functional importance should be further investigated during infancy and adulthood.

Species differences in the localization of neuropeptide FF receptors in rodent and lagomorph brain and spinal cord

Quantitative in vitro receptor autoradiography of [125I][D-Tyr1,(NMe)Phe3]NPFF was used to study the regional distribution of neuropeptide FF receptors in rodent and lagomorph brain. In rat, mouse, rabbit, and Afghan pika [125I][D-Tyr1,(NMe)Phe3]NPFF binding sites were enriched in the superficial layers of dorsal horn of the spinal cord and in parabrachial nucleus, central gray matter, hypothalamus, and reunions thalamic nucleus. In other neuroanatomical regions, important species differences in NPFF receptor patterns are observed. In marked contrast, the brain and the spinal cord of the Octodon degus are devoid of NPFF receptors. The present study shows that in different species regional variations in brain NPFF receptor binding occur.

Autoradiographic characterization of 125I-neurotensin binding sites in human entorhinal cortex

The laminar and rostro-caudal distribution of 125I-neurotensin binding sites is described in human entorhinal cortex using quantitative autoradiography. Specific binding was most prominent over the cell clusters of layer II of the entorhinal cortex throughout its rostro-caudal extent. Dense binding was also observed in the adjacent presubiculum and cortical amygdaloid transition area, whereas minimal binding was detected in the hippocampus and dentate gyrus. 125I-Neurotensin may serve as a selective probe for neurotensin receptor alterations and layer II-specific cytoarchitectural disturbances in the entorhinal cortex in neuropsychiatric diseases associated with abnormalities of the mesial temporal lobe.

Chronic ethanol administration downregulates neurotensin receptors in long- and short-sleep mice

Neurotensin (NT) has been shown to differentially alter many of the physiologic responses to ethanol administration in long-sleep (LS) and short-sleep (SS) mice, which were selectively bred for differences in hypnotic sensitivity to ethanol. These mice have been shown to differ in NT receptor densities in cortical and mesolimbic brain regions and it has been suggested that ethanol actions may be mediated, in part, by neurotensinergic processes. The present study was conducted to further examine this hypothesis by determining the effects of acute and chronic ethanol administration on NT receptor systems in these mice. Scatchard analysis of [3H]NT binding in brain membranes from mice chronically treated with ethanol yielded a one-site model, whereas binding in membranes from control mice were best described by a two-site model. Values for binding capacity (Bmax) were significantly reduced in several brain regions, and binding site density for total, levocabastine-sensitive, and levocabastine-insensitive binding sites were also reduced. The maximum effect was seen after 2 weeks of chronic ethanol consumption. Three weeks after withdrawal from ethanol, Kd and Bmax had returned to control values. Similarly, binding density in all regions for total, levocabastine-sensitive, and levocabastine-insensitive sites had returned to control values within 2 weeks. NT receptor characteristics measured 2 h post-3.0 g/kg ethanol revealed that ethanol caused a rapid downregulation of both subtypes of NT receptors. The finding that both acute and chronic ethanol significantly downregulate the neurotensin receptor systems further supports the hypothesis that ethanol's actions may be mediated in part by neurotensinergic systems.

Beta-adrenergic receptor distribution in human and rat hippocampal formation: marked species differences

The topography of beta-adrenergic receptors in the rat and human hippocampal formation was assessed by in vitro binding of 125I-pindolol to tissue sections. Marked differences were found in the distribution of beta-adrenergic receptors and in the relative amounts of beta 1 and beta 2 receptor subtypes in the two species. In the human, the highest receptor densities were present in the pyramidal cell layer and in the stratum lacunosum-moleculare. In the rat hippocampus, those regions contained the lowest densities of 125I-pindolol binding sites. The highest densities of beta-adrenergic receptors in the rat hippocampal formation were found in the ventral subiculum and in the entorhinal cortex. In contrast, in the human hippocampus, the subiculum and entorhinal cortex contained relatively low densities of the receptors. Competition studies with beta 1- and beta 2-selective antagonists revealed that beta 2-adrenergic receptors predominate in the human hippocampus and beta 1-adrenergic receptors predominate in the rat hippocampus. The marked species differences observed suggest that the pharmacological responsivity of the hippocampus to adrenergic agents and the role of noradrenaline in regulation of hippocampal function could be very different in rats compared to humans.

Different laminar distributions of dopamine D1 and D2 receptors in the rat hippocampal region

The distribution of dopamine (DA) D1 and D2 receptors in the hippocampal region was studied using in vitro receptor autoradiography with 125I-SCH 23982 and 125I-NCQ 298, respectively. The specific binding of both ligands indicated the existence of D1 as well as D2 receptors in the rat hippocampal region. A closer analysis revealed, however, a different laminar distribution of the two receptor subtypes: layers with a high density of one DA receptor subtype had low density of the other. Thus, in the entorhinal cortex, which contained the highest densities of both subtypes, the following pattern was seen. Layers 2, 4, 5 and 6 had high densities of D1 receptors and low densities of D2 receptors while layers 1 and 3 had high densities of D2 receptors and low densities of D1 receptors. The parasubiculum contained D1 receptors but not D2 receptors and the presubiculum had D2 receptors in layer 2 but few D1 receptors. Similar patterns were recorded in Ammon's horn: the part of stratum lacunosum-moleculare which was rich in D1 was poor in D2 receptors. The interdigitating laminar distribution of D1 and D2 receptors suggests that the effects of DA are mediated via D1 and D2 receptors located at different levels along the intrinsic hippocampal circuit.

Dopamine D2 receptors in the rat, monkey and the post-mortem human hippocampus. An autoradiographic study using the novel D2-selective ligand 125I-NCQ 298

The distribution of dopamine D2 receptors in the hippocampal region of the rat, monkey and the postmortem human brain was studied with in vitro receptor autoradiography using the selective salicylamide ligand 125I-NCQ 298. Specific binding was defined in the presence of the D2-selective compound raclopride. In all 3 species, higher densities of specifically bound 125I-NCQ 298 was found in the retrohippocampal structures than in the hippocampus proper. In the rat, layers 1 and 3 of the entorhinal cortex and layer 2 of the presubiculum were found to be rich in specific binding sites. In the monkey, the highest densities were detected in the deep layers (4 through 6) of the entorhinal cortex (EC) and in layer 2 of the presubiculum. Relatively high density of binding was found in the granule cell layer of area dentata. In the human brain, less specific binding was seen as compared to the other two species; the highest densities occurred in the outer layers of the presubiculum and in the hilus of area dentata. These findings show that D2 receptors are present in the hippocampal region and that the retrohippocampal region, including the entorhinal cortex, is enriched in dopamine D2 receptors.

Distribution of 125I-neurotensin binding sites in human forebrain: comparison with the localization of acetylcholinesterase

The distribution of 125I-neurotensin binding sites was compared with that of acetylcholinesterase reactivity in the human basal forebrain by using combined light microscopic radioautography/histochemistry. High 125I-neurotensin binding densities were observed in the bed nucleus of the stria terminalis, islands of Calleja, claustrum, olfactory tubercle, and central nucleus of the amygdala; lower levels were seen in the caudate, putamen, medial septum, diagonal band nucleus, and nucleus basalis of Meynert. Adjacent sections processed for cholinesterase histochemistry demonstrated a regional overlap between the distribution of labeled neurotensin binding sites and that of intense acetylcholinesterase staining in all of the above regions, except in the bed nucleus of the stria terminalis, claustrum, and central amygdaloid nucleus, where dense 125I-neurotensin labeling was detected over areas containing only weak to moderate cholinesterase staining. At higher magnification, 125I-neurotensin-labeled binding sites in the islands of Calleja, supraoptic nucleus of the hypothalamus, medial septum, diagonal band nucleus, and nucleus basalis of Meynert were selectively associated with neuronal perikarya found to be cholinesterase-positive in adjacent sections. Moderate 125I-neurotensin binding was also apparent over the cholinesterase-reactive neuropil of these latter three regions. These data suggest that neurotensin (NT) may directly influence the activity of magnocellular cholinergic neurons in the human basal forebrain, and may be involved in the physiopathology of dementing disorders such as Alzheimer's disease, in which these neurons have been shown to be affected.

Neurotensin receptors in the human spinal cord: a quantitative autoradiographic study

The anatomical localization of neurotensin receptors in the human spinal cord was examined in 12 cases aged 4-68 years using quantitative autoradiographic methods following the incubation of fresh, unfixed cryostat sections with 4 nM [3H]neurotensin. Characterization of the pharmacological specificity of the [3H]neurotensin binding sites in the human spinal cord from displacement studies with neurotensin and various neurotensin fragments indicated that, whereas 1.0 microM neurotensin and the carboxy-terminal fragment neurotensin almost completely displaced [3H]neurotensin binding (4 nM), the amino-terminal fragments neurotensin and neurotensin1-11 were weak inhibitors. This requirement for the carboxy-terminal fragment neurotensin is consistent with [3H]neurotensin binding to specific neurotensin receptors in the human spinal cord. In all cases the autoradiograms demonstrated that neurotensin receptors were distributed in a similar fashion in the gray matter of the cervical, thoracic, lumbar, sacral and coccygeal regions of the human spinal cord. At all 21 spinal levels examined, the highest density of neurotensin receptors was localized in lamina II of the dorsal horn. Within lamina II the receptors were especially concentrated in the deeper inner segment (IIi) where they formed a dense band lying immediately dorsal to lamina III. The density of receptors in this inner region of lamina II (23.5 fmol/mg) was almost double that in the outer segment of lamina II (12.2 fmol/mg), which showed the next highest density of receptors, and more than three times that in the adjacent lamina I (6.9 fmol/mg) and lamina III (7.1 fmol/mg). A moderate density of receptors was present in the intermediomedial (8.0 fmol/mg) and intermediolateral (8.0 fmol/mg) nuclei of lamina VII, and in lamina IX (4.4 fmol/mg). The density of labelling in the remaining laminae of the spinal cord was very low. These results indicate that neurotensin receptors are mainly localized in somatic and visceral sensory and motor regions of the human spinal cord and suggest that neurotensin may play a role in modulating sensory-motor functions in the human spinal cord.

Cholecystokinin-octapeptide (CCK-8) receptors in the hippocampal region: a comparative in vitro autoradiographic study in the rat, monkey and the postmortem human brain

Quantitative in vitro receptor autoradiography of 125I-CCK-8 was used to study the regional distribution of CCK-8 receptors in the primate hippocampal region. In the monkey, specific 125I-CCK-8 binding sites were enriched in layer 2 of the presubiculum, layers 1, 2, and 4 of the entorhinal area and in the inner two-thirds of the molecular layer of the area dentata. Moderate to low densities were detected in layer 3 of the entorhinal area, the deep layers of the presubiculum, all layers of subiculum and subfields CA1 and CA3 of Ammon's horn. In the human brain, the highest densities of 125I-CCK-8 binding sites were detected in layer 2 of the presubiculum and layer 2 of the lateral entorhinal area. Moderate to low levels were detected in the Ammon's horn and area dentata. This pattern of receptor distribution overlaps only partly with that found in the rat and indicates phylogenetic differences in the localization of CCK-8 receptors within the hippocampal region.

Neurotensin in the human brain

The localization of neurotensin-immunoreactive sites in the adult human brain was investigated by the indirect immunoperoxidase method of Sternberger [Sternberger (1979) Immunocytochemistry. Wiley, New York]. Our results demonstrate a widespread, albeit uneven occurrence of neurotensin-immunoreactive cells and processes throughout the central nervous system. Immunoreactive cells are prominent in the medial hypothalamus and in various regions of the limbic system, including the amygdaloid body, septal area, bed nucleus of the stria terminalis and piriform cortex. A few cells were also found in the dorsal synencephalon, superior colliculus, periaqueductal grey and spinal trigeminal nucleus. The distribution of immunoreactive fibres corresponds well with that reported for rodents. Areas with the highest concentration of neurotensin-immunoreactive processes included all the areas where immunoreactive neurons were found and, in addition, periventricular thalamic nuclei, the sublenticular region, lateral parts of the brainstem reticular formation and the vagus-solitarius complex. Comparison mapping studies of melanin-containing neurons on sections treated with neurotensin antiserum revealed an anatomical relation between almost all the catecholaminergic cell clusters with peptide-containing fibres.

Distribution of [3H]cholecystokinin octapeptide binding sites in the hippocampal region of the rat brain as shown by in vitro receptor autoradiography

The distribution of binding sites for the neuropeptide cholecystokinin octapeptide in the rat hippocampal region was studied by using quantitative in vitro receptor autoradiography. Biochemical analysis of [3H]cholecystokinin octapeptide binding to tissue sections of the hippocampal region showed it to be of high affinity, to be saturable and approximately 50% specific at saturating concentrations. The binding of [3H]cholecystokinin octapeptide to hippocampal sections was dose-dependently blocked by cholecystokinin octapeptide, cholecystokinin and by pentagastrin. The autoradiographic analysis showed high densities of [3H]cholecystokinin octapeptide binding sites in the hilus of the area dentata, the outer three layers of the retrosplenial area and the presubiculum, layer 3 of the medial, but not the lateral, entorhinal area and the deep and superficial parts of layer 1 and 2, respectively of both the medial and the lateral entorhinal area. Medium binding densities were found in the parasubiculum and remaining layers of the entorhinal area and low densities occurred in the subiculum and in all subfields of Ammon's horn. The angular bundle and fornix-fimbria lacked specific [3H] cholecystokinin octapeptide binding sites. A very similar pattern of binding densities was found for [3H]pentagastrin. Comparisons of the cholecystokinin octapeptide receptor distribution with the cholecystokinin octapeptide innervation of the hippocampal region suggest that there exists a relatively good concordance in some hippocampal subfields such as the presubiculum and the entorhinal area between binding sites for [3H]cholecystokinin octapeptide and cholecystokinin-immunoreactive afferent input.

Distribution of neurotensin receptors in the primate hippocampal region: a quantitative autoradiographic study in the monkey and the postmortem human brain

The distribution of [3H]neurotensin ([3H]NT) binding sites in the monkey and the postmortem human brain was studied by using quantitative in vitro receptor autoradiography. Biochemical experiments carried out on tissue sections of the monkey hippocampus showed that the binding of [3H]NT was saturable, reversible and of high specificity. The hippocampal [3H]NT binding was displaced by fragment NT 8-13 but not fragment NT 1-8 of the peptide. The anatomical analysis showed a highly heterogeneous distribution of [3H]NT binding sites within both the monkey and the human hippocampal region. In both species the highest density of [3H]NT binding sites was found in the presubiculum (rank order of binding density: layer 2 greater than 6 greater than 1 greater than 3, 4, 5 in both monkey and man) and the entorhinal area (monkey: layer 4 greater than 6 greater than 5 greater than 1 greater than 2 greater than 3; human: layer 1 = 2 greater than 5 greater than 3). The subiculum and Ammon's horn were relatively poor in [3H]NT binding sites in both species. In the area dentata the highest density of [3H]NT binding sites was found in the hilar region.

Ontogeny of [3H]neurotensin binding sites in the rat cerebral cortex: autoradiographic study

The ontogeny of the neurotensin binding sites in the rat caudal cortex such as the retrosplenial cortex, the visual area containing area 17 and 18, the caudal somatosensory area and temporal area was examined by autoradiography. During the early postnatal period (from birth to day 10), very-high-density [3H]neurotensin binding sites were observed in the caudal cortical area, but the number of binding sites decreased markedly with age. On the other hand, the ventral tegmental area and substantia nigra pars compacta had a low density of binding sites at birth, but the density increased until about day 15 and remained even in the adult rat. These findings were confirmed by the biochemical binding analysis.

Neurotensin receptor binding sites in monkey and human brain: autoradiographic distribution and effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment

Neurotensin (NT) receptor binding sites were characterized and localized by using membrane binding assay and in vitro receptor autoradiography in monkey and human brain. Additionally, the effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment on NT binding sites were investigated in monkey. [125I]Tyr3-NT ([125I]NT) apparently binds to a single class of high-affinity sites (Kd in nanomolar range) in both species. Ligand selectivity patterns strongly suggest that the structural requirements of both monkey and human brain NT receptors are very similar to those previously reported in other tissues, such as those of the rat brain and rat stomach. In monkey brain, [125I]NT binding sites are discretely distributed with high densities of sites found in the cingulate cortex, amygdala, hippocampus, ventral tegmental area, substantia nigra, and periaqueductal gray matter. A similar pattern is observed in the human brain. However, the laminar distribution of [125]NT binding sites in cortex varies between monkey and human brain. In monkey brain, [125I]NT binding sites are mostly concentrated in deep cortical layers while the laminar distribution of NT sites changes with cortical areas in human brain. The densities of [125I]NT binding sites are markedly decreased in the caudate, putamen, and substantia nigra in MPTP-treated monkeys. These results suggest strong interactions between NT and dopaminergic systems in both monkey and human brain tissues.