Differential quenching and limits of resolution in autoradiograms of brain tissue labeled with 3H-, 125I- and 14C-compounds

Gi/o-Protein Coupled Receptors in the Aging Brain

Cells translate extracellular signals to regulate processes such as differentiation, metabolism and proliferation, via transmembranar receptors. G protein-coupled receptors (GPCRs) belong to the largest family of transmembrane receptors, with over 800 members in the human species. Given the variety of key physiological functions regulated by GPCRs, these are main targets of existing drugs. During normal aging, alterations in the expression and activity of GPCRs have been observed. The central nervous system (CNS) is particularly affected by these alterations, which results in decreased brain functions, impaired neuroregeneration, and increased vulnerability to neuropathologies, such as Alzheimer's and Parkinson diseases. GPCRs signal via heterotrimeric G proteins, such as G_o, the most abundant heterotrimeric G protein in CNS. We here review age-induced effects of GPCR signaling via the G_i/o subfamily at the CNS. During the aging process, a reduction in protein density is observed for almost half of the G_i/o-coupled GPCRs, particularly in age-vulnerable regions such as the frontal cortex, hippocampus, substantia nigra and striatum. G_i/o levels also tend to decrease with aging, particularly in regions such as the frontal cortex. Alterations in the expression and activity of GPCRs and coupled G proteins result from altered proteostasis, peroxidation of membranar lipids and age-associated neuronal degeneration and death, and have impact on aging hallmarks and age-related neuropathologies. Further, due to oligomerization of GPCRs at the membrane and their cooperative signaling, down-regulation of a specific G_i/o-coupled GPCR may affect signaling and drug targeting of other types/subtypes of GPCRs with which it dimerizes. G_i/o-coupled GPCRs receptorsomes are thus the focus of more effective therapeutic drugs aiming to prevent or revert the decline in brain functions and increased risk of neuropathologies at advanced ages.

Pilot study on biocompatibility of fluorescent nanodiamond-(NV)-Z~800 particles in rats: safety, pharmacokinetics, and bio-distribution (part III)

Introduction

We hereby report on studies aimed to characterize safety, pharmacokinetics, and bio-distribution of fluorescent nanodiamond particles (NV)-Z~800 (FNDP-(NV)) administered to rats by intravenous infusion in a single high dose.

Methods

Broad scale biological variables were monitored following acute (90 minutes) and subacute (5 or 14 days) exposure to FNDP-(NV). Primary endpoints included morbidity and mortality, while secondary endpoints focused on hematology and clinical biochemistry biomarkers. Particle distribution (liver, spleen, lung, heart, and kidney) was assessed by whole organ near infrared imaging using an in vivo imaging system. This was validated by the quantification of particles extracted from the same organs and visualized by fluorescent and scanning electron microscopy. FNDP-(NV)-treated rats showed no change in morbidity or mortality and preserved normal motor and sensory function, as assessed by six different tests.

Results

Blood cell counts and plasma biochemistry remained normal. The particles were principally distributed in the liver and spleen. The liver particle load accounted for 51%, 24%, and 18% at 90 minutes, 5 days, and 14 days, respectively. A pilot study of particle clearance from blood indicated 50% clearance 33 minutes following the end of particle infusion.

Conclusion

We concluded that systemic exposure of rats to a single high dose of FDNP-(NV)-Z~800 (60 mg/kg) appeared to be safe and well tolerated over at least 2 weeks. These data suggest that FNDP-(NV) should proceed to preclinical development in the near future.

Architectonic distribution of the serotonin transporter within the orbitofrontal cortex of the vervet monkey

To elucidate the organization of the serotoninergic innervation within the orbitofrontal cortex (OFC), serotonin transporter (SERT) density was quantified by autoradiography using [(3)H]cyanoimipramine binding. In six adult vervet monkeys, 15 architectonic areas were delineated according to cytoarchitectonic (Nissl), myeloarchitectonic (Gallyas) and chemoarchitectonic (acetylcholinesterase) criteria to assess SERT distribution at two levels of organization: cortical area and cortical type. For cortical type, the 15 areas were evenly divided into three different categories primarily based upon the degree of granularization of layer IV: agranular, dysgranular, and granular. Within agranular and dysgranular, but not granular cortical types, SERT density was area-specific and progressively decreased in a medial to lateral gradient. Across cortical types, SERT density decreased in a caudal to rostral gradient: agranular>dysgranular>granular. A similar caudal to rostral gradient was seen when serotonin content was measured (using high performance liquid chromatography) in areas representative of each cortical type. Collectively, these results suggest that the serotoninergic innervation is organized according to both cortical type and area, and is thus structured to differentially modulate information processing within the OFC.

Quantitative architectural analysis: a new approach to cortical mapping

Recent progress in anatomical and functional MRI has revived the demand for a reliable, topographic map of the human cerebral cortex. Till date, interpretations of specific activations found in functional imaging studies and their topographical analysis in a spatial reference system are, often, still based on classical architectonic maps. The most commonly used reference atlas is that of Brodmann and his successors, despite its severe inherent drawbacks. One obvious weakness in traditional, architectural mapping is the subjective nature of localising borders between cortical areas, by means of a purely visual, microscopical examination of histological specimens. To overcome this limitation, more objective, quantitative mapping procedures have been established in the past years. The quantification of the neocortical, laminar pattern by defining intensity line profiles across the cortical layers, has a long tradition. During the last years, this method has been extended to enable a reliable, reproducible mapping of the cortex based on image analysis and multivariate statistics. Methodological approaches to such algorithm-based, cortical mapping were published for various architectural modalities. In our contribution, principles of algorithm-based mapping are described for cyto- and receptorarchitecture. In a cytoarchitectural parcellation of the human auditory cortex, using a sliding window procedure, the classical areal pattern of the human superior temporal gyrus was modified by a replacing of Brodmann's areas 41, 42, 22 and parts of area 21, with a novel, more detailed map. An extension and optimisation of the sliding window procedure to the specific requirements of receptorarchitectonic mapping, is also described using the macaque central sulcus and adjacent superior parietal lobule as a second, biologically independent example. Algorithm-based mapping procedures, however, are not limited to these two architectural modalities, but can be applied to all images in which a laminar cortical pattern can be detected and quantified, e.g. myeloarchitectonic and in vivo high resolution MR imaging. Defining cortical borders, based on changes in cortical lamination in high resolution, in vivo structural MR images will result in a rapid increase of our knowledge on the structural parcellation of the human cerebral cortex.

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.

Cocaine-induced alterations in the density of monoaminergic receptors in the embryonic guinea pig cerebral wall

Quantitative receptor autoradiography was used to examine the effect of chronic cocaine exposure on the density of alpha1-, alpha2- and beta-adrenergic, 5-HT1A- and 5-HT2-serotonergic, and D1- and D2-dopaminergic receptors in the fetal guinea pig cerebral wall which contained forming motor area of the cerebral cortex. The pregnant guinea pig received two daily subcutaneous injections of 20 mg/kg cocaine beginning on the 20th day of pregnancy (E20). The control animals received injections of equivalent volume of saline. The receptor densities were examined between days 5-30 of the treatment, which corresponds to E25-E50. By the fifth day of treatment (E25), cocaine produced downregulation of all receptors studied throughout the entire depth of the fetal cerebral wall. More extended treatment, however, resulted in recovery of receptor levels. Finally, from days 20-30 of treatment (E40-E50) there was a significant upregulation of noradrenergic and dopaminergic receptor sites. These findings demonstrate that exposure to cocaine in utero can influence adrenergic, serotonergic, and dopaminergic receptors in the embryonic cerebral wall, which may lead to alteration in corticogenesis. Furthermore, the present study reveals that, in the course of chronic treatment, cocaine may completely reverse its receptor regulatory activity in the fetal brain.

Receptor autoradiographic mapping of the mesial motor and premotor cortex of the macaque monkey

This study analyzes regional and laminar distribution patterns of neurotransmitter binding sites in the motor areas of the macaque mesial frontal cortex. Differences in distribution patterns are compared with the cytoarchitectonic parcellation. Binding sites were analyzed with quantitative in vitro receptor autoradiography in unfixed brains of five macaque monkeys. Alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic acid (AMPA), kainate, and N-methyl-D-aspartate (NMDA) binding sites were labeled with [3H]AMPA, [3H]kainate, and [3H]MK-801, respectively, muscarinic binding sites with [3H]pirenzepine or [3H]oxotremorine-M, noradrenergic binding sites with [3H]prazosin or [3H]UK-14304, gamma-aminobutyric acid (GABA)A binding sites with [3H]muscimol, and serotoninergic binding sites with [3H]ketanserine. Adjacent sections were stained with a modified Nissl method for cytoarchitectonic analysis. In the motor areas F1, F3, and F6, [3H]AMPA, [3H]pirenzepine, and [3H]oxotremorine-M binding was maximal in layers II, III, and V, and [3H]kainate binding was maximal in layers V and VI. Clear-cut changes in laminar distribution patterns of [3H]AMPA, [3H]kainate, and [3H]oxotremorine-M binding sites very closely matched corresponding cytoarchitectonic borders. Mean areal binding densities of all ligands to F1, F3, and F6 were plotted as polar plots for each area. A polygon was obtained for each area ("neurochemical fingerprint") when all the density values belonging to one area were connected with each other. The "neurochemical fingerprints" of F1, F3, and F6 were virtually identical in shape but increased in size from F1 to F6. This result reflects the functional similarity of these motor-related areas and possibly correlates with their differential involvement in motor control. Areas F1, F3, and F6 can thus be grouped into one "neurochemical family" of areas.

Autoradiographic localization of neurotransmitter binding sites in the hypoglossal and motor trigeminal nuclei of the rat

The hypoglossal and motor trigeminal nuclei contain somatic motoneurons innervating the tongue, jaw, and palate. These two cranial motor nuclei are myotopically organized and contain neurotransmitter binding sites for thyrotropin-releasing hormone, substance P, and serotonin. Quantitative autoradiography was used to localize thyrotropin-releasing hormone, substance P, and serotonin-1A and serotonin-1B binding sites in the hypoglossal and motor trigeminal nuclei and to relate the relative distributions of these binding sites to the myotopic organizations of the two nuclei. In the hypoglossal nucleus, high-to-moderate concentrations of all four binding sites were present in the dorsal and ventromedial subnuclei, whereas low concentrations were noted in the ventrolateral subnucleus. In the motor trigeminal nucleus, high concentrations of serotonin-1B, moderate densities of thyrotropin-releasing hormone, and low levels of substance P and serotonin-1A binding sites were present in both the ventromedial and dorsolateral subnuclei. These observations demonstrate that neurotransmitter binding sites in the hypoglossal and motor trigeminal nuclei are heterogeneously localized and that their distributions correspond to the previously described myotopic organizations of each nucleus.

High-resolution scatchard analysis shows D1 receptor binding on pyramidal and nonpyramidal neurons

In order to better understand the mechanism of action of atypical antipsychotic drugs (APDs), it is important to clarify how the dopamine system is integrated within local corticolimbic circuits. Toward this end, a high-resolution (HR) Scatchard technique has been used to measure the relative density (Bmax) and affinity (Kd) of D1 receptors on large neurons (> 100 microm2), on small neurons (< 100 microm2), and in neuropil (NPL) of rat medial prefrontal cortex (mPFC) and to determine the laminar distribution of these receptors for each neuronal compartment. Using [3H] SCH23390 as a ligand, all Kd and Bmax values were found to be similar indicating that D1 receptor activity is not preferentially localized to either large or small neuronal subtypes in mPFC. The density of D1 receptor binding in all three compartments was found to be almost twice as great in layers V and VI, as compared to superficial layers II and III. These results suggest that the blockade of D1 receptors associated with some atypical APDs may involve both pyramidal and nonpyramidal neurons in the PFC.

Region-specific tritium enrichment, and not differential beta-absorption, is the major cause of 'quenching' in film autoradiography

Tritium quenching refers to the situation in which estimates of tritium content generated by film autoradiography depend on the chemical composition of the tissue as well as on the concentration of the radioisotope. When analysing thin brain sections, for example, regions rich in lipid content generate reduced optical densities on x-ray film compared with lipid-poor regions even when the total tissue concentration of tritium in those regions is identical. We hypothesize that the dried thickness of regions within sections depends upon the relative concentrations and types of lipid within the regions. Areas low in white matter dry thinner than areas high in white matter, leading to a relative enrichment of tritium in the thinner regions. To test this model, a series of brain pastes were made with different concentrations of grey and white matter and impregnated with equal amounts of tritium. The thickness of dried sections was compared with percentage of white matter and apparent radioactive content as determined by autoradiogram analysis. The results demonstrated that thickness increased, and apparent radioactivity decreased, with higher percentages of white matter. In the second experiment, thickness measurements from dried sections were successfully used to correct the apparent radioisotope content of autoradiograms created from tritium containing white- and grey-matter tissue slices. We conclude that within-section thickness variation is the major physical cause for 'tritium quenching'.

NMDA receptors in mouse barrel cortex during normal development and following vibrissectomy

The development of N-methyl-D-aspartate (NMDA) receptors and the effects of vibrissectomy upon [3H]MK-801 binding were examined in the barrel cortex of mice. Autoradiographic studies showed that initially very low binding of [3H]MK-801 sharply increased during the second postnatal week reaching the adult level by the end of the third week. Scatchard analysis performed on cortical membrane preparations indicated that this rise of [3H]MK-801 labelling was due to an increase in the number of binding sites and a decrease of Kd at postnatal day 15 and 28. The interlaminar differences of labelling were registered from postnatal day 8. Changes of interlaminar distribution were found during the second and third postnatal weeks. In adult barrel cortex the highest binding was found in supragranular layers. In layer IV of the cortex, the pattern of binding resembled the pattern of barrels. Unilateral denervation of vibrissae performed in neonatal and adult mice did not alter the intensity of [3H]MK-801 labelling or the laminar distribution of binding sites. These results suggest that NMDA receptor binding does not reflect the plastic changes occurring in the barrel cortex.

Neurotransmitter receptors in the proliferative zones of the developing primate occipital lobe

Film autoradiography was used to investigate the expression of several neurotransmitter receptor subtypes in the transient ventricular and subventricular proliferative zones of the developing occipital lobe in two groups of macaque monkey fetuses. The first group of fetuses were between 60 and 93 days after conception (E60-E93), when the ventricular and subventricular zones of the monkey occipital lobe produce neurons destined for the visual cortex. In the second group, fetuses were between E107 and E128, after generation of cortical neurons has ceased. In the E60-E93 group of fetuses, ventricular and subventricular zones displayed high densities of 5-HT1-serotonergic, D1-dopaminergic, alpha 1- and alpha 2-adrenergic and high affinity kainate receptors. The activation of these receptors has previously been shown to stimulate cell proliferation in other cell systems. The possible involvement of these receptors in regulation of neuronal production is also supported by their absence in the deep laminae of the embryonic cerebral wall after E107, after cortical neurogenesis has been completed. The only exception is a high density of alpha 2-adrenergic receptors maintained near the ventricular surface long after all cortical neurons have been generated. We also found that during neurogenesis, proliferative zones in E66-E90 fetuses displayed virtually no 5-HT2-serotonergic, D2-dopaminergic, beta-adrenergic, M1-muscarinic cholinergic, gamma aminobutyric acid (GABA)A, N-methyl-D-aspartate (NMDA), or alpha-amino-3-hydroxy-5-menthy-4-isoxazole proprionate (AMPA) sites; most of these receptor subtypes have been reported to mediate the suppression of cell proliferation. The present findings suggest that dividing and/or newly generated cortical neurons are capable of receiving specific signals from multiple neurotransmitters present in their environment.

D1- and D2 dopaminergic receptors in the developing cerebral cortex of macaque monkey: a film autoradiographic study

Film autoradiography was used to study the distribution of D1- and D2-dopaminergic receptors in the prefrontal association, somatosensory, primary motor and visual regions in the developing cerebral cortex of macaque monkeys. D1 receptors were labeled with [125I]SCH23982, while D2 sites were visualized with [125I]epidepride. D1- and D2-dopaminergic sites are already present in all cortical areas at embryonic day 73, the earliest age observed in this study. In contrast to the adult cortex, where D1 and D2 receptors have different distributions, during development there are substantial similarities in the laminar patterns of these sites. In particular, both D1 and D2 receptors tend to concentrate in the marginal zone and layer V of the developing cortical plate. The autoradiograms also show a high density of D1-dopaminergic sites in the transient ventricular and subventricular zones, where cortical neurons are generated. Although there is a significant rearrangement of the early laminar patterns, the adult distribution of both dopaminergic receptors in most cortical areas is achieved prenatally, soon after all cortical neurons assume their final positions. An early presence in the cerebral wall, a high density in the proliferative zones and fast maturation of the laminar distribution suggests that dopaminergic receptors may be involved in the regulation of cortical development.

Cholinergic binding sites in rat brain: analysis by age and cognitive status

Age-related alterations in the density of cholinergic receptor binding and reuptake sites were examined in discrete forebrain regions of behaviorally tested rats using quantitative autoradiography. Neurochemical changes associated with chronological age alone were distinguished from memory-dependent alterations by correlating density of binding sites with performance in the Morris water maze task. An initial analysis of tritium quenching indicated no reliable differential quenching in the study population. Modest age-related reductions in selected subtypes of cholinergic binding sites in basal forebrain, basal ganglia, and thalamus were observed. However, these reductions were not correlated with a spatial memory deficit. In contrast, no significant changes in the analysis by chronological age were detected for the density of [3H]hemicholinium binding to high affinity choline uptake sites or [3H]pirenzepine binding to M1 receptors in any brain region but strong correlations were found between behavioral performance of aged rats and density of these sites in dorsal hippocampal subfield CA3 and dentate gyrus. These findings indicate the value of combined neurobiological/behavioral assessment.

Adrenergic and serotonergic receptors in aged monkey neocortex

Autoradiography was employed to compare the distribution and density of adrenergic (alpha 1, alpha 2, and beta) and serotonergic (5-HT1 and 5-HT2) receptors in the neocortex of young adult (3 to 10 years of age) and aged (> 20 years of age) rhesus monkeys. The age-related changes in the density of adrenergic and serotonergic sites were area and layer specific. A decrease in the density of alpha 1 receptors occurred only in the superficial layers of the somatosensory cortex, whereas the density of alpha 2 receptors declined in layer I of the prefrontal cortex and in most layers of the motor and somatosensory regions. The increase in beta receptors was largely confined to the deep layers of the motor and somatosensory areas. The density of 5-HT1 sites decreased in most layers of the somatosensory cortex, while 5-HT2 receptors declined in the deep layers of the motor cortex and middle strata of the visual cortex. Overall, adrenergic and serotonergic receptors were least affected in the prefrontal cortex and most compromised in the motor and somatosensory cortex of aged primates.

Dopamine D2 receptor expression in hippocampus and parahippocampal cortex of rat, cat, and human in relation to tyrosine hydroxylase-immunoreactive fibers

A detailed study comparing the distribution of D2 receptors and tyrosine hydroxylase-immunoreactive fibers in the hippocampus and parahippocampal cortices of the rat, cat, and human was conducted. The distribution of [125I]epidepride binding to D2 receptors along the transverse and longitudinal axes of the hippocampus and parahippocampus differed among the species. In rat hippocampus, the number of sites was highest in septal portions of lacunosum-moleculare of CA1 and stratum moleculare of the subiculum. Virtually no binding to D2 receptors existed in the temporal hippocampus. For the cat hippocampus, the highest binding existed in the inner one-third of the molecular layer of the dentate gyrus (DG). There were also significant numbers of D2 receptors in strata radiatum and oriens of the CA subfields, with almost undetectable levels in lacunosum moleculare and subiculum. The number of sites was higher in the septal than temporal hippocampus. In the human hippocampus, highest binding was observed in the molecular layer of DG and the subiculum, with lower levels in strata oriens and lacunosum-moleculare of CA3, and very low binding in CA1. The histochemical demonstration of the pattern of mossy fibers revealed an organization complementary to that of D2 receptors in cat and human. In none of the species was there significant expression of D2 receptors in the entorhinal cortex, except in the caudal extreme of this region in the rat. In that region a trilaminar pattern was exhibited that continued into the perirhinal cortex. A trilaminar pattern of D2 receptor expression was observed in the perirhinal cortex of all species, with the highest values in the external and deep laminae and low expression in the middle laminae. The organization of dopamine fibers was assessed by comparing the distribution of tyrosine hydroxylase-positive and dopamine beta-hydroxylase-immunoreactive fibers in these same regions. It revealed consistent mismatches between the pattern of D2 receptor expression and dopaminergic innervation in all three species. The implications for this mismatch are discussed. It is hypothesized that the distribution of D2 receptors, and not of dopamine fibers, determines what neural systems dopamine influences in the hippocampal complex.

Laminar distribution of NMDA receptors in cat and monkey visual cortex visualized by [3H]-MK-801 binding

Glutamate is the major excitatory neurotransmitter of the mammalian central nervous system. Two major classes of glutamate receptors have been reported. The actions of glutamate on its N-methyl-D-aspartate (NMDA)-type receptor may underlie developmental and adult plasticity as well as neurotoxicity. The NMDA-type of glutamate receptor in cat and monkey visual cortex was visualized by means of in vitro receptor autoradiography with the noncompetitive NMDA-receptor antagonist [3H]-MK-801. The kinetics, performed on tissue sections, revealed an apparently single, saturable site with an approximate dissociation constant (KD) of 18.5 nM in cat and 15.9 nM in monkey visual cortex. Autoradiography, performed on frontal sections of cat and monkey visual cortex, revealed a heterogeneous laminar distribution of NMDA receptors. Cat areas 17, 18, 19, and the lateral suprasylvian areas exhibited a similar NMDA-receptor distribution. In these areas, NMDA receptors were most prominent in layer II and the upper part of layer III. In monkey striate cortex, NMDA receptors were primarily concentrated in layers II, upper III, IVc, V, and VI. In monkey secondary visual cortex, [3H]-MK-801 labeling was most prominent in layers II, V, and VI; whereas in the temporal visual areas included in this study layer II displayed the heaviest receptor labeling. In neither cat nor monkey could we observe significant differences in NMDA-receptor distribution between different retinotopic subdivisions within a single visual area. Neither did we detect any periodic changes in NMDA-receptor distribution that would correspond to the compartments defined by cytochrome-oxidase in monkey V1 and V2.

Postnatal development of central nervous alpha 2-adrenergic binding sites: an in vitro autoradiography study in the tree shrew

The postnatal development of the alpha 2-adrenoceptor pattern was investigated by in vitro receptor autoradiography with the antagonist [3H]rauwolscine in the brains of tree shrews (Tupaia belangeri). At birth, high numbers of [3H]rauwolscine binding sites are diffusely distributed in the whole brain with exception of the neocortex which is very weakly labeled at this time. While the number of [3H]rauwolscine binding sites in the cerebellum decreases to low levels during the first three postnatal weeks, several brain regions show a significant increase in binding sites which are progressively concentrated in distinct nuclei. In the medulla oblongata, the diffuse labeling pattern changes so that binding sites become centralized in the dorsomedial nuclei. In the pons, similar changes can be observed with a moderate labeling of the locus coeruleus on postnatal day 10 and a strong labeling in the adult. In the thalamus, a transient appearance of high numbers of [3H]rauwolscine binding sites can be observed during the second and third postnatal week in specific nuclei. In the preoptic area and hypothalamus, there are only minor postnatal changes but the numbers of [3H]rauwolscine binding sites decrease between postnatal day 5 and adulthood. The high number of binding sites in the limbic system does not significantly change after birth. In the neocortex and the superior colliculus, the [3H]rauwolscine labeling pattern which is characteristic for the adult is achieved not before the third postnatal week. Competition experiments demonstrate that [3H]RAUW binds with high affinity to alpha 2-adrenoceptors in the postnatal as well as in the adult brain. Therefore, this study demonstrates region specific developmental profiles of the pattern of alpha 2-adrenoceptors in the postnatal tree shrew brain.

A rapid and efficient method for the radiosynthesis and purification of [125I]SCH23982

The radiosynthesis of (1R)-(+)-1-phenyl-3-methyl-7-[125I]iodo-8-hydroxy- 2,3,4,5-tetrahydro-1H-3-benzazepine (commonly referred to as SCH23982) and its use as a high affinity D1 dopamine antagonist ligand have been reported previously. We now provide a simple and inexpensive protocol for the rapid and efficient synthesis of this radioligand based on the Cloramine-T-catalyzed reaction between the commercially available precursor (R)-(+)-1-phenyl-3-methyl- 8-hydroxy-2,3,4,5-tetrahydro-1H-3-benzazepine and carrier-free sodium [125I]iodide. [125I]SCH23982 is separated rapidly (within 20 min) from the precursor and reaction byproducts (e.g., chlorinated precursor, SCH23390) by reverse-phase HPLC on a C-8 column. The major iodinated product has been identified as SCH23982 based on co-chromatography with authentic SCH23982, UV spectral characteristics, and biological activity. The chromatographic effluent containing the active product is adsorbed on a C-18 Sep-Pak cartridge to remove mobile-phase constituents and permit it to be eluted and diluted to the desired concentration; this technique is used also for periodic repurification. Our synthesis protocol results in final purified product that incorporates ca. 50% of the initial 125I (tested using starting quantities of 1-10 mCi Na125I); the final product has a specific activity of ca. 2500 +/- 350 Ci/mmol. Data from in vitro receptor autoradiographic and homogenate studies with this radioligand are consistent with previously reported values in terms of expected receptor distribution, affinity, and density (KD of 1.0 nM, Bmax of 1400 fmol/mg protein in rat striatal membranes).

N-methyl-D-aspartate receptors are transiently expressed in the developing spinal cord ventral horn

Quantitative receptor autoradiography was used to map the distribution of N-methyl-D-aspartate (NMDA) receptors in the developing rat spinal cord. Three different specific ligands, which label partially overlapping subpopulations of NMDA receptors, were used: an agonist (L-[3H]glutamate), a noncompetitive antagonist ([3H]MK-801), and a competitive antagonist ([3H]CGP-39653). In the adult, NMDA receptors labeled with all three ligands are restricted to the substantia gelatinosa in the spinal dorsal horn. In marked distinction, at postnatal day 7 NMDA receptors labeled with L-[3H]glutamate and [3H]MK-801 are present throughout the spinal gray matter. NMDA receptors in the neonatal spinal ventral horn have a higher affinity for L-[3H]glutamate than those in the adult substantia gelatinosa. Over the second and third postnatal weeks, NMDA receptors are lost from all areas of the spinal gray matter except for the substantia gelatinosa. Neonatal NMDA receptors identified with [3H]CGP-39653 are restricted to the substantia gelatinosa. These results show that the immature ventral horn contains a subpopulation of NMDA receptors and raise the possibility that motor neurons transiently express NMDA receptors in early postnatal life. Ventral horn NMDA receptors may be a component of the mechanisms by which the mature phenotype of motor neurons is acquired through activity-dependent processes. The loss of NMDA receptors over the course of development may play a role in limiting the period of motor neuron plasticity.

The distribution of cholinergic muscarinic receptors in the dog frontal lobe

The topographical distribution of cholinergic muscarinic receptor (MChR) sites was studied by means of quantitative receptor autoradiography using [3H]quinuclidinyl benzilate ([3H]QNB) in the frontal (prefrontal, premotor and motor) cortex of the dog. The mean binding value in the frontal cortex was 408 +/- 5.0 fmol/mg tissue and the only area that differed significantly from the mean was the primary motor cortex, where the binding value was significantly lower. In the dorsal part of the prefrontal and premotor cortical subregions studied, a tri-laminar pattern of [3H]QNB labelling was observed, with a superficial dense band of label corresponding to cortical layers I, II and III. The deep high density band overlaid layer V and the upper part of the layer VI. In the ventral part of the prefrontal cortex this pattern gradually disappeared and in the most ventral part no laminar differences were seen. In contrast, in primary motor areas, the deep band of labelling corresponding to layer V was much less pronounced than in the frontal association cortex. Variations in the distribution of MChR sites seem to reflect to some extent the greater cytoarchitectonic differentiation of the dorsal zone and also the similarity between the ventral zone and the limbic cortex described by us previously.

Developmental changes in tritium autoabsorption

Developmental changes in autoabsorption of tritium emissions were examined in 30 brain regions in the rat at Postnatal Days 0, 4, 7, 10, 14, 21, and 28 and adulthood. Rats received tritiated 2-deoxyglucose in vivo. Alternate brain sections were extracted in chloroform, and autoradiographs were developed from extracted and nonextracted sections. The ratio of optical density values in extracted vs nonextracted sections was used to determine autoabsorption for each structure. Three principal temporal patterns in the development of adult levels of autoabsorption, determined by the optical density ratios, were identified: (1) a minimal increase pattern in which autoabsorption rose only slightly between birth and adulthood; (2) a plateau pattern in which a rapid early increase was followed by stable values; and (3) a late increase pattern in which autoabsorption remained relatively constant until Postnatal Day 28, with a large increase between Day 28 and adulthood. In addition, optical density ratios fluctuated during the second postnatal week in close to one-third of the structures. The data suggest that developmental events affecting the ratio of gray to white matter produce substantial local variations in the development of adult levels of autoabsorption that are distinct for each structure. To correct for autoabsorption effects in ontogenetic studies using tritium autoradiography, it is necessary to determine directly the degree of autoabsorption at a particular time point for the structure of interest. Our results indicate that the technique of in vivo administration of tritiated 2-deoxyglucose followed by chloroform extraction appears to be a sensitive and reproducible method for assessing autoabsorption at all ages.

Voltage-dependent L-type calcium channels in the development and plasticity of mouse barrel cortex

Entry of calcium ions into the neuron is a triggering signal for initiation of several processes which may lead to modification of synaptic connectivity. The developmental changes of voltage-dependent L-type calcium channel (VDLCC) were studied using [3H]PN 200 110 nifedipine displaceable binding in the barrel cortex of mice, a model structure for studying cortical plasticity. In vitro binding autoradiography was used to examine quantitatively the pattern of [3H]PN 200 110 binding to brains of animals aged from 3 to 70 days. The binding values in the somatosensory cortex rose two-fold in the period examined, reaching a plateau in the 4th postnatal week. The laminar pattern of binding changed during development, with the locus of heaviest labeling shifting from layer IV to II/III in the third postnatal week and thin bands of labeling developing in layers IV and VI. A very faint barrel-like pattern of labeling in the barrel field was observed. Neither this pattern nor the binding values were altered by unilateral neonatal removal of all vibrissal follicles. Saturation studies of binding to crude synaptosomal fractions of cerebral cortex of mice aged 3, 15, 28 and 70 days revealed the presence of a single binding site, with Bmax increasing from 48.7 +/- 5.1 fmol/mg protein at postnatal day 3 to 191.7 +/- 9.6 fmol/mg protein at day 70. No developmental changes in KD values were found. No correlation was found between the critical period for cytoarchitectonic plasticity of the barrels and the time when high values of VDLCC binding were observed.

Comparison of serotonin 5-HT1 receptors and innervation in the visual cortex of normal and dark-reared cats

The visual cortical serotoninergic system was compared in normal and dark-reared cats to determine whether visual experience is necessary for its normal development. In vitro receptor binding of [3H]5-HT indicated an increase in 5-HT1 receptor number in dark-reared cats with no change in affinity. This elevation was specific to the visual cortex and no changes were found in the frontal cortex as a result of dark rearing. Autoradiographic histology revealed that in the normal cat visual cortex, 5-HT1 receptors were present in all cortical layers and were slightly more dense in supragranular and infragranular layers. In dark-reared cats, there was a marked elevation in receptor density in supragranular and infragranular layers and little change within layer IV. Immunohistochemical techniques (anti-5-HT) were used to compare serotoninergic innervation in the visual cortex of normal and dark-reared cats. In normal cat visual cortex, serotonin fibers were most dense in the superficial layers (I-III), least dense in layers IV and VI, and intermediate in layer V. No differences were found between normal and dark-reared cats in the laminar distribution or density of serotoninergic innervation. These results indicate that visual experience is necessary for the normal development of the visual cortical serotonin system. The findings that the effects of dark rearing were specific to the visual cortex and that within the visual cortex these effects were specific to supra- and infragranular layers are consistent with a possible role for serotonin in the prolonged physiological plasticity that occurs in the visual cortex of dark-reared cats.

Sodium channel density in hypomyelinated brain increased by myelin basic protein gene deletion

Trophic control over the expression and membrane distribution of voltage-dependent ion channels is one of the principal organizing events underlying the maturation of excitable cells. The myelin sheath is a major structural determinant of regional ion channel topography in central axons, but the exact molecular signals that mediate local interactions between the oligodendrocyte and axolemma are not known. We have found that large caliber fibre pathways in the brain of the mutant mouse shiverer (shi, gene on chromosome 18), whose developmental fate of myelination is averted by deletion of five exons in the myelin basic protein gene, have a striking excess of sodium channels. As cytoplasmic membranes of shiverer oligodendroglia still adhere to axons, the evidence indicates that myelin basic protein or a myelin basic protein-dependent glial transmembrane signal associated with compact myelin formation, rather than a simple glial-axon contact inhibition or an intrinsic genetic program of neuronal differentiation, could be critical in downregulating sodium channel density in axons. Here we use the shiverer mutant to show that mature central nervous system projection neurons with large caliber unmyelinated fibres sustain functional excitability by increasing sodium channel density. This axon plasticity, triggered by the absence of a single glial protein, contributes to the unexpectedly mild degree of neurological impairment in the mutant brain without myelin, and may be a potentially inducible mechanism determining the recovery of function from dysmyelinating disease.

Transient increase in [3H]Ro 15-4513 specific binding in the superficial gray layer of the rat superior colliculus induced by visual deafferentation

The imidazodiazepine compound [3H]Ro 15-4513, a partial inverse agonist of benzodiazepine receptors of the central type, binds with high affinity (order of 10(-8) M) to a single population of benzodiazepine binding sites in the mammalian central nervous system. A quantitative autoradiographic study was carried out to determine the effects of one eye removal on [3H]Ro 15-4513 specific binding to rat brain sections in the superficial gray layer or stratum griseum superficiale (SGS) of the superior colliculus. Retinal afferent degeneration due to right eye removal, performed 3 and 7 days before sacrifice, led to a significant and symmetrical increase in the [3H]Ro 15-4513 specific binding in both right and left SGS by enhancing the binding affinity of the radioligand. This transient phenomenon disappeared when a longer survival period of 45 days was allowed to elapse. Conversely, unilateral lesion of the primary visual areas had no apparent effects on the specific binding of the radioligand. The absence of any loss of binding sites after either type of lesion suggests that the benzodiazepine receptors are probably not situated on the optic nerve axon terminals, nor on the cortical axon terminals originating from primary visual areas. In the SGS, as in other rat brain structures, benzodiazepine receptors of the central type are functionally coupled with GABAA receptors and form 'GABAA receptors/benzodiazepine receptors/chloride channel' complexes. The involvement of the local GABAergic system in the postlesion plasticity of benzodiazepine receptors was studied by testing the effects of exogenously applied GABA on [3H]Ro 15-4513 specific binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of dopaminergic receptors in the primate cerebral cortex: quantitative autoradiographic analysis using [3H]raclopride, [3H]spiperone and [3H]SCH23390

A widespread distribution of dopamine D1 receptors in the neocortex is well recognized. However, the presence of dopamine D2 receptors in this structure has only recently been established [Martres et al. (1985) Eur. J. Pharmac. 118, 211-219; Lidow et al. (1989) Proc. natn. Acad. Sci. U.S.A. 86, 6412-6416]. In the present paper, a highly specific antagonist, [3H]raclopride, was used for autoradiographic determination of the distribution of D2 receptors in 12 cytoarchitectonic areas of the frontal, parietal, and occipital lobes of the rhesus monkey. A low density of D2-specific [3H]raclopride binding (1.5-4.0 fmol/mg tissue) was detected in all layers of all cortical areas studied. Throughout the entire cortex, the highest density of binding was consistently found in layer V. This is a unique distribution not observed so far for any other neurotransmitter receptor subtype in monkey cerebral cortex, including D1 receptor. In addition, a comparison was made of the distribution of [3H]raclopride and [3H]spiperone, which has been commonly used in previous attempts to label cortical D2 receptors. We found marked differences in the distribution of these two radioligands. In the prefrontal cortex, the pattern of [3H]spiperone binding in the presence of ketanserin resembled the combined distribution of 5-HT1C serotoninergic and alpha 2-adrenergic sites as well as D2 receptors. Thus, [3H]raclopride provides a better estimation of the D2 receptor distribution than does [3H]spiperone. The distribution of D2-specific binding of [3H]raclopride was also compared with the D1-specific binding of [3H]SCH23390 in the presence of mianserin to block labeling to 5-HT2 and 5-HT1C sites. The density of D1-specific [3H]SCH23390 binding was 10-20 times higher than that of D2-specific [3H]raclopride binding throughout the cortex. The densities of both [3H]raclopride and [3H]SCH23390 binding sites display a rostral-caudal gradient with the highest concentrations in prefrontal and the lowest concentrations in the occipital cortex. However, the binding sites of these two ligands had different laminar distributions in all areas examined. In contrast to preferential [3H]raclopride binding in layer V, a bilaminar pattern of [3H]SCH23390 labeling was observed in most cytoarchitectonic areas, with the highest concentrations in supragranular layers I, II and IIIa and infragranular layers V and VI. Whereas [3H]raclopride binding was similar in all cytoarchitectonic areas, [3H]SCH23390 exhibited some region-specific variations in the primary visual and motor cortex. The different regional and laminar distributions of D1 and D2 dopaminergic receptors indicates that they may subserve different aspects of dopamine function in the cerebral cortex.

Organization of serotonin 1A and 1B receptors in the nucleus of the solitary tract

We utilized 3H-8-hydroxy-N,N-dipropyl-2-aminotetralin (3H-DPAT) and 125I-iodocyanopindolol (125I-CYP) to label serotonin (5HT) 1A and 5HT1B receptors, respectively, in sections of the rat brain after characterizing the pharmacologic specificity of these agents. We then used quantitative autoradiography to measure the concentrations of 5HT1A and 5HT1B receptors in individual subnuclei of the nucleus of the solitary tract (NTS) and adjacent structures of the dorsal vagal complex. The highest 5HT1A receptor concentrations were observed within the central and intermediate subnuclei of the NTS, with low quantities of 3H-DPAT binding sites observed in the hypoglossal nucleus and dorsal motor nucleus of the vagus. In contrast, the density of 5HT1B receptors was relatively homogeneous through all NTS subnuclei, with the highest concentrations localized within the ventrolateral subnucleus. The hypoglossal and dorsal motor nuclei had slightly higher 5HT1B receptor densities than the NTS subnuclei, whereas the area postrema had a very low density. These data suggest that 5HT1A receptors are organized in a manner consistent with the cytoarchitectural and hodological parcellation of the NTS into individual subnuclei. The high concentrations of 5HT1A receptors in the central and intermediate subnuclei suggest a role for these receptors in medullary reflex pathways subserving deglutition. The relatively high density of 5HT1B receptors in the ventrolateral subnucleus suggests that these receptors modulate respiratory neurons, whereas the diffuse organization of 5HT1B receptors in the remaining subnuclei suggests that they are associated with central 5HT afferent pathways to the NTS. Further studies will be required to understand the physiologic role of 5HT1 receptors within the NTS.

A new method for quenching correction leads to revisions of data in receptor autoradiography

Differential quenching of beta-emission affects strongly the analysis of receptor distribution patterns in quantitative receptor autoradiography with tritiated ligands. Different methods for the quenching correction have been described in the past, but some of these are of limited value, if a detailed anatomical parcellation is necessary. Other methods correct exclusively local variations in lipid concentration, which is an important, but only one of several factors causing quenching. A new method for the measurement of quenching (or autoradiographic efficiency) is presented, which permits an anatomically detailed and direct determination of the total quenching without lipid extraction procedures. This method is based on the measurement of autoradiographic efficiency in cryostat sections homogeneously labeled with tritiated formaldehyde by an underlying gelatine section containing this labeled compound. Regional and layer specific measurements of autoradiographic efficiency in cortical and subcortical regions of the human and rat brain are reported. A significant correlation was found between the density of myelin and autoradiographic efficiency but other factors were also shown to influence differential quenching. The use of the here presented correction procedure leads to revisions of the laminar distribution patterns reported for different receptors in human and rat cortical areas. Our results show, that a complete quenching correction is necessary for the mapping of receptor distributions with tritiated ligands.

Elevations of local cerebral glucose utilization by the beta-carboline ZK 93426

The effects of the benzodiazepine receptor antagonist ZR 93,426, a beta-carboline, on local cerebral glucose utilization (LCGU) was examined by using quantitative in-vivo autoradiography with [3H]2-deoxyglucose. ZK 93,426 was found to increase local cerebral glucose utilization primarily in prefrontal, cingulate, olfactory and visual cortical regions, as well as the claustrum, nucleus accumbens, anteroventral thalamus, substantia nigra, and dorsal raphe nucleus. This pattern of changes of LCGU produced by ZK 93,426 seems to represent neither a mirror image of the metabolic effects of benzodiazepine receptor agonists nor the pattern of effects on LCGU induced by the partial inverse agonist beta-carboline FG 7142. The unique pattern of regional changes of glucose utilization induced by ZK 93,426 are discussed with respect to recent findings on its promnestic and antiamnestic properties in animals and humans. It is concluded that ZK 93,426 does not seem to fit into the conventional classification scheme of benzodiazepine receptor ligands; thus, the term 'selective inverse agonist' is proposed.

Autoradiographic localization of thyrotropin-releasing hormone and substance P receptors in the rat dorsal vagal complex

We utilized quantitative autoradiography to localize receptors for thyrotropin-releasing hormone (TRH) and substance P in individual subnuclei of the rat nucleus tractus solitarii (NTS) and the dorsal vagal complex. Within the NTS, TRH receptor concentrations were highest within the gelatinosus and centralis subnuclei and the medial subnucleus rostral to the area postrema, moderate within the intermediate subnucleus and the medial subnucleus adjacent to the area postrema, and low within the ventrolateral and commissural subnuclei and the medial subnucleus caudal to the area postrema. In contrast, substance P receptor concentrations were high throughout the medial subnucleus, moderate in all other subnuclei medial to the tractus solitarius, and relatively low in subnuclei lateral to the tractus solitarius. The dorsal motor nucleus of the vagus contained high concentrations of both TRH and substance P receptors, whereas we observed low TRH and moderate substance P receptors in the area postrema. High TRH and moderate substance P receptors were observed in the adjacent hypoglossal nucleus. In addition, we compared the concentrations of TRH receptors between chloroform-defatted and nondefatted tissue sections, and noted little effect of white matter tritium quench upon the observed TRH receptor concentrations. These results suggest that neurotransmitter receptors within the rat dorsal vagal complex are organized in a manner consistent with previous cytoarchitectural and hodological partitioning of the NTS and that the distribution of an individual neurotransmitter receptor in the NTS may correspond to the role of that transmitter in modulating autonomic function.

Regional differences in the distribution of muscarinic cholinergic receptors in the macaque cerebral cortex

The in vitro autoradiographic technique was used to characterize the density and laminar distribution of muscarinic cholinergic receptors in 12 cytoarchitectonic areas in the frontal, parietal, and occipital lobes of the rhesus monkey. The entire population of muscarinic receptors was labeled with [3H]quinuclidinyl-benzilate; the M1 receptor subtype was labeled with [3H]pirenzepine; and the density of the M2 receptor subtype was estimated by subtracting the density of M1 receptors from the total population. The overall density of M1 and M2 receptor subtypes was similar throughout the cerebral cortex. However, their laminar distribution varied regionally. In cortical regions of the parietal and occipital lobes and in the primary motor cortex of the frontal lobe, both M1 and M2 receptor subtypes were concentrated in the supragranular layers. By contrast, in prefrontal cortical areas, the combined population of M1 and M2 receptors was evenly distributed across the cortical layers, though M1 receptors were most dense and M2 receptors least dense in layer IV. The difference in the distribution of cholinergic receptors in the prefrontal cortex compared to other neocortical areas reveals a degree of chemoarchitectural specificity of this region with respect to cholinergic markers that has escaped immunohistochemical and other anatomical and functional techniques.

Quantitative autoradiographic mapping of serotonin 5-HT1 and 5-HT2 receptors and uptake sites in the neocortex of the rhesus monkey

The in vitro autoradiographic technique was used to characterize the distribution of serotonin 5-HT1 and 5-HT2 receptors and uptake sites in 11 cortical areas of frontal, parietal, and occipital lobes in the rhesus monkey; 5-HT1 receptors were labeled with [3H]5-HT; 5-HT2 receptors were labeled with [3H]ketanserin; and 5-HT uptake sites were labeled with [3H]citalopram. Five-HT1 and 5-HT2 receptors and 5-HT uptake sites were found in every cortical area examined with the absolute concentration of 5-HT1 receptors higher than that of 5-HT2 receptors in all areas. In eight regions of prefrontal and parietal as well as in prestriate cortex, 5-HT1 and 5-HT2 receptors had complementary distribution profiles: 5-HT1 receptors were concentrated in layers I and II and the upper strata of layer III, while 5-HT2 receptors had their highest concentration throughout layers III and IV. Only the primary motor and visual cortex had receptor distributions different from that described above. Thus, in the primary visual cortex, both 5-HT1 and 5-HT2 receptors were found in high concentration in sublayer IVc beta, though the density of 5-HT1 receptor was also high in other subdivisions of layer IV and in layers III, V, and VI. In the primary motor cortex, both receptor subtypes were concentrated in layers I and II and the upper strata of layer III. The pattern of distribution of serotonin uptake sites did not match the patterns of distribution of either 5-HT1 or 5-HT2 receptors alone; rather it approximated the combined patterns of distribution of both receptor subtypes. The complementary patterns of distribution of 5-HT1 and 5-HT2 receptors in most areas of the monkey cerebral cortex suggest that these two receptor subtypes may make differential contributions to cortical functions.

Distribution of major neurotransmitter receptors in the motor and somatosensory cortex of the rhesus monkey

The in vitro quantitative autoradiographic technique was used to characterize the distributions of alpha 1, alpha 2, beta 1 and beta 2 adrenergic, D1 and D2 dopaminergic, 5-HT1 and 5-HT2 serotonergic, M1 and M2 cholinergic, GABAA and benzodiazepine receptors in the motor (Brodmann's area 4) and somatosensory (Brodmann's areas 3, 1 and 2) cortex of the adult rhesus monkey. All receptor subtypes studied were present throughout all layers of both areas. In the somatosensory cortex, each receptor had its own laminar distribution. Some subtypes of the same receptor (5-HT1 and 5-HT2; alpha 1 and alpha 2) had complementary distributions while others (beta 1 and beta 2; D1 and D2; M1 and M2) had largely overlapping distributions. In contrast, different receptors had remarkably coincidental distributions in the motor cortex. In this area, they all tended to concentrate in layers I, II and the upper part of layer III. However, such coextensive distribution of many types of neurotransmitter receptors is not observed in motor cortex of rats and humans and therefore may be a distinctive feature of motor cortex in the rhesus monkey. The findings described in this paper indicate that somatosensory and motor areas are distinct in their receptor architecture and that receptor autoradiography provides a useful complement to classical histological techniques in elucidating areal differences in the cortex.

Ontogeny of oxytocin receptors in rat forebrain: a quantitative study

The ontogeny of oxytocin receptors in rat forebrain was studied using the selective oxytocin receptor antagonist 125I-d(CH2)5[Tyr(Me)2, Thr4, Tyr-NH29]OVT [( 125I]-OTA). With in vitro receptor autoradiography, binding wa noted on the first postnatal day in dorsal subiculum and thalamus. On postnatal days 5-18, intense labeling was evident in posterior cingulate cortex, dorsal subiculum, lateral septum, and the CA1 subfield of hippocampus. Of these regions only the lateral septum expressed oxytocin receptors in adult brain. Competition studies on coronal sections through posterior cingulate, septum, and dorsal subiculum at P10 demonstrated that transient binding sites in these areas were indeed oxytocin selective (OXY greater than AVP greater tha V1 greater than V2). Result of saturation studies on cingulate membranes from 10-day-old pups agreed favorably with previous reports of the kinetics of [125I]-OTA binding to adult oxytocin receptors (Kd = 0.1 nM in P10 cingulate cortex vs. 0.07 nM for adult ventral subiculum). In contrast to these evanescent developmental sites, oxytocin receptors in the bed nucleus of the stria terminalis and the ventromedial nucleus of the hypothalamus only appeared in adulthood, presumably in response to the surge of gonadal steroids at puberty.