Characterization and autoradiographic distribution of neurotensin binding sites in the human brain

The characteristics and topographical distribution of monoiodo¹²⁵I-Tyr₃-neurotensin (NT) binding sites in normal human brain tissue were studied on brain sections and by quantitative autoradiography. Sections at the level of the substantia nigra show a dissociation constant and maximal binding capacity of4.8 ± 0.8nM and 70 ± 7fmol/mg protein, respectively. High density of¹²⁵I-NT binding sites were mainly found in dopaminergic (DA)-rich areas such as the substantia nigra, the ventral tegmental area, the striatum and the nucleus accumbens, further supporting an interaction between NT and DA neurons in human brain.     

Quantitative autoradiographic localization of prostaglandin E2 binding sites in monkey diencephalon

Quantitative autoradiography was performed to investigate the mapping of prostaglandin E2 binding sites in the Macaca fuscata fuscata diencephalon. Autoradiographs were prepared by incubation of 10-micron-thick serial frozen sections with 3H-prostaglandin E2 and were processed by using a rotating drum-scanner and a computer-assisted image-processing system with 3H-microscales as standards. The localization of prostaglandin E2 binding sites was remarkably discrete in the diencephalon. The highest concentrations were found in the median and medial preoptic areas, supramammilary nucleus of the hypothalamus, and centromedian nucleus of the thalamus. High density was observed in the medial and dorsal hypothalamic areas; paraventricular, anterior, dorsomedial, and infundibular nuclei of the hypothalamus; and in the anteroventral, periventricular, paraventricular, laterodorsal, and habenular nuclei of the thalamus. The distribution correlates well with the known effects of prostaglandin E2 and may also give us useful clues in unveiling the novel role of prostaglandin E2 in a variety of brain functions.     

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.     

Quantitative autoradiographic distribution of multiple neurokinin binding sites in rat spinal cord

As a means of evaluating the role of neurokinins (NKs) in spinal function, the present study examines the quantitative autoradiographic distribution in the rat spinal cord of [125I]Bolton-Hunter-substance P, (2-[125I]iodohistidyl1)-neurokinin A and [125I]Bolton-Hunter-eledoisin as respective radioligands for NK-1, NK-2 and NK-3 receptors. These putative NK receptor sub-types are clearly differentially distributed at the various levels of the spinal cord. NK-1 sites represent the most abundant population of spinal NK receptors. They are most concentrated in the dorsal and ventromedial borders of the dorsal horn, the intermediolateral nucleus of the thoracic cord and the phrenic motor nucleus in the cervical ventral horn. NK-2 and NK-3 sites are also present in the spinal cord, although in much lower quantities than NK-1 sites. NK-2 sites are mostly found along the dorsal and ventromedial borders of the dorsal horn, in a narrow band connecting the two lateral horns of the thoracic cord, around the central canal of the lumbar and sacral segments and lamina IX of the cervical ventral horn. NK-3 sites are most dense in the dorsal border of the dorsal horn, with moderate amounts in the lateral horn of the thoracic cord and around the central canal of lumbar and sacral segments. The differential distribution of these 3 classes of NK sites in the spinal cord suggests that each NK receptor sub-type could mediate specific sensory, autonomic and/or motor functions at the spinal level.     

Quantitative autoradiographic distribution of calcitonin gene-related peptide (hCGRP alpha) binding sites in the rat and monkey spinal cord.

Calcitonin gene-related peptide (CGRP) has been implicated in various spinal functions on the basis of its presence in the substantia gelatinosa and motoneurons and the biological effects induced by intrathecal CGRP injections. We investigated here the comparative distribution of [125I]hCGRP alpha binding sites in various segments of the rat and monkey spinal cord. The immunocytochemical localization of CGRP-like material in rat spinal cord was also evaluated for comparison. In the rat spinal cord, high densities of [125I]hCGRP alpha binding sites were observed in lamina I, in a U-shaped band that included lamina X and the medial parts of laminae III-IV and in the intermediolateral and intermediomedial nuclei. The substantia gelatinosa (lamina II) contained relatively lower, but still significant, densities of [125I]hCGRP alpha binding sites, while the ventral horn showed low amounts of specific labeling. CGRP-like immunoreactive fibers, on the other hand, were heavily concentrated in laminae I-II and in the reticulated portion of lamina V of the dorsal horn. Immunoreactivity to CGRP antiserum was also noted in fibers around the central canal and in a number of motoneurons of the ventral horn. In the monkey spinal cord, [125I]hCGRP alpha binding sites were present in lamina I in a U-shaped band that included lamina X and the medial portions of laminae V-VI. Relatively low levels of [125I]hCGRP alpha binding were detected in laminae II to IV of the dorsal horn, while the ventral horn was more enriched with specific [125I]hCGRP alpha binding sites. Thus, it appears that the autoradiographic distribution of [125I]hCGRP alpha sites is species dependent in the spinal cord. Additionally, some differences are observed between the localization of [125I]hCGRP alpha binding sites and immunoreactive material in the rat spinal cord. These differences may be relevant to the purported roles of CGRP-like peptides in spinal functions such as nociception, control of sympathetic output, and motor control.     

On the distribution of cholecystokinin receptor binding sites in the human brain: an autoradiographic study

Cholecystokinin (CCK) binding sites were localized by in vitro autoradiography in human postmortem brain materials from 12 patients without reported neurological diseases using [125I]Bolton-Hunter CCK octapeptide (BHCCK-8) as a ligand. The pharmacological characteristics of BHCCK-8 binding to mounted tissue sections were comparable to those previously reported in the rat. CCK-8 being the most potent displacer, followed by caerulein, CCK-4, and gastrin I. The distribution of BHCCK-8 binding sites was heterogeneous. These sites were highly concentrated in a limited number of gray matter areas and nuclei. The highest binding densities were seen in the glomerular and external plexiform layers of the olfactory bulb. BHCCK-8 binding sites were also enriched in the neocortex, where they presented a laminar distribution with low levels in lamina I, moderate concentration in laminae II to IV, high density in lamina V, and low levels in lamina VI. A different laminar distribution was seen in the visual cortex, where a low receptor density was observed in lamina IV but higher density in laminae II and VI. In the basal ganglia the nucleus accumbens, caudatus, and the putamen presented moderate to high densities of binding sites, while the globus pallidus lacked sites of BHCCK-8 binding. In the limbic system the only area presenting moderate to high density was the amygdaloid complex, particularly in the granular nucleus, while most of the thalamic nuclei were extremely poor or lacked BHCCK-8 binding. The hippocampal formation showed low (CA1-3) to moderate (subiculum) densities. Midbrain areas generally disclosed very low levels of BHCCK-8 binding sites. The pontine gray and the nucleus reticularis tegmenti pontis showed a relatively high density of CCK-8 receptor specific binding. Moderate to very high densities were found in few nuclei of the lower brainstem and spinal cord as the inferior olives and their accessory nuclei, the arcuate nuclei, the striae medullares, the efferent (motor) nucleus of the vagus, and the substantia gelatinosa of the cervical and thoracic spinal cord. These results are discussed in relation to the distribution of endogenous peptide and to the known physiological and pharmacological effects of substances acting on these receptors.     

Quantitative autoradiographic distribution of [3H]AF-DX 116 muscarinic-M2 receptor binding sites in rat brain

The distribution of muscarinic-M2 receptors in rat brain was investigated by in vitro autoradiography using [3H]AF-DX 116, a putative probe for the muscarinic-M2 receptor subtype. Incubation of rat brain coronal sections with 10 nM [3H]AF-DX 116 showed highest binding site densities in discrete areas such as the superior colliculus and certain thalamic and brainstem nuclei, similar to the distribution reported for [2H]acetylcholine/M2 sites. [3H]AF-DX 116 site densities were markedly lower in forebrain areas such as cortex, striatum, and hippocampus, in contrast to the distribution seen for [3H]pirenzepine-M1 binding sites, which were concentrated in these forebrain areas; however, differential patterns of labeling were observed for the two muscarinic-M2 probes, [3H]AF-DX 116 and [3H]acetylcholine, in the hippocampal formation. Although [3H]AF-DX 116 binding was broadly distributed in multiple subfields of the hippocampus, [3H]acetylcholine binding was discretely distributed in a manner resembling that of acetylcholinesterase staining. This suggests the existence of muscarinic-M2 subtypes in the CNS, especially in the hippocampal formation.     

Quantitative autoradiographic study of L-glutamate binding sites in normal and atrophic human cerebellum.

In the present work the distribution of L-glutamate binding sites in the different layers of human cerebellum of normal individuals and of seven patients who died with olivopontocerebellar atrophy (OPCA) was examined with the technique of quantitative autoradiography. Specific L-[3H]glutamate binding was higher in the molecular than in the granule cell layer of normal cerebellar tissue. A significant decrease of L-[3H]glutamate specific binding was observed in the molecular layer of all OPCA tissues. In the granule cell layer L-[3H]glutamate binding was decreased only in two patients who suffered from late-onset sporadic OPCA and in one patient who suffered from a form of OPCA inherited in a dominant manner. Quisqualate-sensitive binding sites were the most abundant binding sites in the molecular layer of normal cerebella, whereas N-methyl-D-aspartic acid (NMDA)-sensitive binding sites were the most abundant type in the granule cell layer. A significant decrease of quisqualate-sensitive and an increase in NMDA-sensitive binding sites were observed in the molecular layer of OPCA cerebellar tissues. No significant changes were observed in the granule cell layer of these tissues.     

Quantitative autoradiographic localization of [125I]alpha-bungarotoxin binding sites in the honeybee brain

Binding sites for the nicotinic acetylcholine receptor antagonist, [125I]alpha-bungarotoxin, were localized in the honeybee brain by in vitro autoradiography. Highest binding site densities were localized in the suboesophageal ganglion, the optic tubercles, optic lobes medulla and lobula, antennal lobes, dorsal lobes and the alpha-lobes of the mushroom bodies. The distribution pattern of these putative nicotinic acetylcholine receptors suggests that acetylcholine is involved in several sensory pathways and in central information processing in the honeybee brain.     

Quantitative autoradiography of cocaine binding sites in human brain postmortem.

Quantitative autoradiography was used to study cocaine binding sites in the human brain postmortem. Tritiated cocaine was applied to brain sections from three drug- and disease-free subjects at a low (10 nM) concentration and at a high (1 microM) concentration, the latter being in the range of brain concentrations of cocaine found in users of the drug. Nonspecific binding was assessed in the presence of 100 microM unlabeled cocaine. At low (10 nM) concentrations of labeled cocaine, the basal ganglia exhibit the highest density of binding sites, with considerably lower densities in thalamus, cortex, and hippocampus. Cocaine binding at high (1 microM) concentrations displayed a different distribution pattern, more homogeneous with some cortical regions exhibiting binding site densities close to those seen in the basal ganglia. Preliminary competition experiments with several drugs indicate that dopamine uptake inhibitors completely block cocaine binding to the basal ganglia, while serotonin uptake inhibitors were more effective in the hippocampus. These findings suggest that cocaine binds to dopamine uptake sites in the human basal ganglia postmortem but that it also interacts with other classes of binding sites, depending on the concentration and brain region examined.     

Iodinated-NPY binding sites: autoradiographic study in the rat brain

Several authors have described the presence of iodinated neuropeptide-Y binding sites on membranes of the mammalian CNS. In the present study we show a mapping of iodinated-NPY binding sites in the rat brain using receptor autoradiography. The sections were incubated with 125I-Bolton-Hunter coupled NPY (0.5-03 nM), in the absence or presence of 1 microM cold NPY. Some autoradiograms are studied by means of an image analyzer (VDC 501 Tesak) equipped with the host computer PDP 11 Digital, in order to enhance the contrast of the labeling. A very high density of NPY receptors is present in the limbic regions (hippocampus, amygdaloid complex, septal nuclei), in the cortex, and in some thalamic nuclei, while in some hypothalamic regions (paraventricular nucleus and median eminence) we detected a lower amount of NPY receptors. At the mesencephalic level, the substantia nigra presents a very high density of NPY receptors.     

Comparative autoradiographic distribution of calcium channel antagonist binding sites for 1,4-dihydropyridine and phenylalkylamine in rat, guinea pig and human brain

1. The autoradiographic distribution of calcium channel antagonist binding sites for 1,4-dihydropyridine and phenylalkylamine has been investigated in rat, guinea pig and human brain.

2. 1,4-dihydropyridine([³H] (+) PN200-110) and phenylalkylamine ([³H] (−) D-888) binding sites are identically distributed in the brain of the three mammalian species studied.

3. High densities of calcium antagonist binding sites are present in brain areas enriched in synaptic contacts such as the hippocampus, cortex and striatum. Low to moderate densities of sites are found in other regions such as the thalamus, hypothalamus and brain stem.

4. These data demonstrate the existence of specific calcium antagonist binding sites in mammalian brain including man. These sites are discretely distributed with highest concentrations present in the hippocampus and cortex. Moreover, the similar distribution of binding sites for [³H](+)PN200-110 and [³H](−) D-188 suggests that 1,4-dihydropyridine and phenylalkylamine bind to the same receptor site complex in mammalian brain.     

Localization of high-affinity binding sites for oxytocin and vasopressin in the human brain. An autoradiographic study

Sites which bind oxytocin and vasopressin with high affinity were detected in the brain and upper spinal cord of 12 human subjects, using in vitro light microscopic autoradiography. Tissue sections were incubated with tritiated vasopressin, tritiated oxytocin or an iodinated oxytocin antagonist. The ligand specificity of binding was assessed with unlabelled vasopressin or oxytocin in excess, as well as in competition experiments using synthetic structural analogues. The distribution of vasopressin binding sites differed markedly from that of oxytocin binding sites in the forebrain, while there was overlap in the brainstem. Vasopressin binding sites were detected in the dorsal part of the lateral septal nucleus, in midline nuclei and adjacent intralaminar nuclei of the thalamus, in the hilus of the dentate gyrus, the dorsolateral part of the basal amygdaloid nucleus and the brainstem. The distribution of oxytocin binding sites in the brainstem has been recently reported (Loup et al., 1989). Oxytocin binding sites were also observed in the basal nucleus of Meynert, the nucleus of the vertical limb of the diagonal band of Broca, the ventral part of the lateral septal nucleus, the preoptic/anterior hypothalamic area, the posterior hypothalamic area, and variably in the globus pallidus and ventral pallidum. The presence of oxytocin and vasopressin binding sites in limbic and autonomic areas suggests a neurotransmitter or neuromodulator role for these peptides in the human central nervous system. They may also affect cholinergic transmission in the basal forebrain and consequently play a role in Alzheimer's disease.     

Quantitative autoradiographic analysis of somatostatin binding sites in discrete areas of rat forebrain

Somatostatin has been localized in several hypothalamic and extrahypothalamic brain regions where it may function as a classical neurotransmitter or as a modulator of neural activity. In the present study, somatostatin binding sites were studied by incubation of coronal sections of rat forebrain with 125I-Tyr1-somatostatin, Ultrofilm autoradiography, computerized microdensitometry and comparison with 125I standards. Highest concentrations of somatostatin binding sites (fmol/mg protein) were found in the claustrum (151), basolateral nucleus of the amygdala (90), deep layers of the cerebral cortex (61), lateral olfactory nuclei (58), CA1 and CA2 areas of hippocampus (57), medial and lateral septal nuclei (54), and the medial habenula (44). Scatchard analysis of individual forebrain areas with high densities of somatostatin binding sites was also performed. Regulation of brain somatostatin binding sites may be studied as one approach to examining the involvement of central somatostatin pathways in various physiological and behavioral states.     

Quantitative autoradiographic localization of binding sites to excitatory and inhibitory receptors in epileptic-damaged hippocampus

Abnormalities within different transmitter systems may contribute to the brain damage seen in epilepsy and to the epileptogenesis. In order to elucidate the distribution of excitatory and inhibitory transmitter receptors, quantitative receptor autoradiography was performed in human hippocampi (n = 9) resected at surgery for temporal lobe epilepsy (TLE) and in nonepileptic autopsy controls (n = 6). Tissue pathology was studied in parallel to evaluate the relationship between receptor densities and neuronal loss. The binding to the excitatory N-methyl-d-aspartate (NMDA) receptor/channel site and to the muscarinic cholinergic receptor was measured. Inhibitory receptors chosen for study were the γ-aminobutyric acid type A (GABA_A) and benzodiazepine (BZ). There was a strong correlation between reduced receptor binding and neuronal loss. A general reduction in binding to all receptors was seen in epileptic patients compared to controls, most pronounced in the cornu ammonis (CA) 1, the area with most severe sclerosis. There was a greater relative reduction in binding to excitatory receptors than to inhibitory receptors. NMDA/channel receptor binding was reduced between 68% and 98% and muscarinic receptor binding between 32% and 75% in different hippocampal regions. The corresponding reduction to GABA_A receptors was 3%–65% and to BZ receptors 0%–81%. These data may support the theory that brain damage seen in TLE is caused by excessive excitatory activation.     

Hemicholinium-3 binding sites in rat brain: a quantitative autoradiographic study

Quantitative in vitro autoradiography was used to study the distribution of [3H]hemicholinium-3 ([3H]HC-3) binding sites in the rat brain. Regional concentrations of HC-3 binding sites were corrected for regional tissue quenching of tritium in a number of brain structures. Specific binding of 10 nM [3H]HC-3 was highest in the interpeduncular nucleus, followed by the caudate-putamen, olfactory tubercle, amygdala, and the medial and lateral habenulae. There was a high positive correlation between regional HC-3 binding and choline acetyltransferase activity in rat brain; however, a novel pattern of the distribution of cholinergic terminals in the subnuclei of the interpeduncular nucleus was discovered. The apparent Kd in the 1-5 nM range and the pharmacological specificity of the HC-3 binding site agreed with data for choline uptake and for the HC-3 binding site as determined in membrane preparations. HC-3 autoradiography appears to be a useful anatomical marker for cholinergic terminals.     

Galanin receptors in the brain of a teleost: autoradiographic distribution of binding sites in the Atlantic salmon.

The distribution of galanin (GAL) binding sites in the brain of the Atlantic salmon (Salmo salar) was investigated by means of radioligand binding in conjunction with autoradiography by using high-performance liquid chromatography (HPLC) characterized radio-iodinated porcine galanin ([125I]GAL). On slide-mounted sections of frozen salmon brain homogenate, [125I]GAL (4 nM) bound rapidly and reversibly to a single population of sites with a Kd of 1.0 +/- 0.08 nM (n = 3) and Bmax of 2.38 +/- 0.19 fmol/mg wet tissue. Specific [125I]GAL binding was found in cellular regions, in fiber tracts, and in neuropil areas throughout the brain, except for in the olfactory bulb, pineal organ, and cerebellum. Autoradiographic microdensitometric measurements revealed high total [125I]GAL binding in the ventral hypothalamus (inferior lobes; around 7-12 fmol/mg tissue), the dorsal spinal cord (between 6 and 12 fmol/mg tissue), sublayers of the optic tectum (around 8 fmol/mg), torus semicircularis (around 7 fmol/mg), and glomerular complex (around 6 fmol/mg). Intermediate densities of [125I]GAL binding (3-5 fmol/mg tissue) were found in the pituitary, telencephalon, dorsolateral thalamic nucleus, and raphe nuclei and in association with the forebrain bundles. Except for in the optic tectum, there is a good concordance of [125I]GAL binding sites and GAL-immunoreactive fiber projections in most brain areas of the salmon. The wide distribution of GAL binding sites provides further evidence that a GAL-like substance might be involved in a diversity of brain functions of teleosts. The topographic distribution of target sites in the hypothalamo-hypophyseal axis indicates that GAL-like substances may have both direct and indirect effect on pituitary functions while in extrahypothalamic areas, functional implications by GAL may include involvement in somatosensory, central gustatory, olfactory, and visual functions. This study provides evidence for the presence of a specific GAL receptor in the brain of the Atlantic salmon. Together the distribution of GAL binding and GAL-like molecules provide a covering delineation of the GAL neuronal system in the brain of the Atlantic salmon. Comparisons with mammals suggest that the GAL receptor molecule has been well preserved during evolution and that GAL-like substances may be present, and even possess similar functional properties, throughout the vertebrate phylogeny.     

Regional distribution of benzodiazepine binding sites in the human newborn and infant hypothalamus. A quantitative autoradiographic study

Using in vitro quantitative autoradiography and [3H]flunitrazepam we examined the rostrocaudal distribution of benzodiazepine binding sites in the human neonate/infant hypothalamus. The autoradiographic analysis shows the presence of a heterogeneous distribution throughout the rostrocaudal extent of this brain structure. High [3H]flunitrazepam binding corresponds primarily to the diagonal band of Broca and the preoptic region. The labelling in the preoptic region showed a rostrocaudal increase, contrasting in that with the other hypothalamic structures. Intermediate densities were present in the septohypothalamic, suprachiasmatic, periventricular and paraventricular nuclei as well as in the mammillary complex. Low binding was observed in the other hypothalamic structures. The benzodiazepine binding sites analyzed belong mostly to type II receptors. In an attempt to unravel possible differences related to age, we compared the autoradiographic distribution in three postnatal age ranges. The topographical distribution of these binding sites was almost identical in each period analyzed. We found, however, that benzodiazepine binding is generally low in the neonatal period and a tendency in increasing densities is observed during development. Taken together, these results provide evidence for a large distribution of benzodiazepine binding sites in neonate/infant hypothalamus, suggesting their implication in the development of this brain structure and the maintenance of its various functions.     

Quantitative autoradiographic analysis of mu and delta opioid binding sites in the rat hippocampal formation

The distributions of mu and delta opioid binding sites were studied in rat hippocampal formation by using quantitative in vitro autoradiography. Mu binding sites, labeled with 125I-FK-33824, showed a highly organized laminar distribution. Binding was greatest at the foot of the obliterated hippocampal fissure in stratum lacunosum-moleculare of CA3. Stratum pyramidale and stratum lacunosum-moleculare of CA2 and stratum pyramidale of CA3 were next highest in mu binding, followed by stratum oriens and stratum radiatum of CA2, stratum oriens of CA3, and stratum pyramidale of CA1. The distribution of delta binding sites, labeled with 125I-D-ala2-D-leu5-enkephalin in the presence of the unlabeled mu receptor ligand PL-032, was similar to the distribution of mu binding in that binding within each region was greatest in a band centered over stratum pyramidale and in stratum lacunosum-moleculare. Over all, delta binding was greatest in CA2 followed by CA3 and then CA1. Compared to mu binding, delta binding was relatively enriched in stratum moleculare of the dentate gyrus. These laminar distributions correlate reasonably well with the distribution of enkephalin immuno-reactivity in hippocampal formation, although binding was surprisingly low in stratum lucidum, an area rich in dynorphin and enkephalin immunoreactivity.     

In vitro autoradiographic localization of calcitonin binding sites in human medulla oblongata

In this study we examined the distribution of calcitonin (CT) binding sites in the human medulla oblongata by in vitro autoradiography. In competition studies, the rank order of potency for calcitonins competing for ¹²⁵I-salmon CT binding was salmon CT > porcine CT > human CT, which is consistent with physiologically relevant CT receptors in other systems. For the determination of CT binding in the human medulla, 20-μm cryostat sections were incubated with ¹²⁵I-salmon CT in the presence or absence of 10^?6 M unlabelled salmon CT to map specific CT binding sites. Punctate binding was observed over discrete nuclei of the medulla. High binding densities were seen over subnuclei of the dorsal motor nucleus of the vagus, the nucleus of the solitary tract, the intermediate reticular zone, the gigantocellular and dorsal paragigantocellular nuclei, and the raphe obscurus nucleus. Moderate levels of binding were observed over the lateral paragigantocellular nucleus and the rostral extent of the epiolivary nucleus. The cuneate and gracile nuclei and the fiber tracts did not contain detectable binding, while the inferior olivary nucleus had moderate levels of nonspecific binding. The localization of calcitonin binding sites in the human presents similarities but also important differences to the distribution in rat and cat. The most notable difference is the extreme binding densities in the intermediate reticular zone of the human. The location of binding sites suggests involvement of calcitonin in regulation of autonomic function.