Localization of Insulin-Like Growth Factor-II Receptors in Rat Brain by in vitro Autoradiography and Immunohistochemistry

Insulin-like growth factor-ll (IGF-II) and its receptor, which is homologous with the mannose-6-phosphate (M6P) receptor, are found in high levels in adult rat and human brain, though their role remains unclear. In order to point to possible regional functions, we have mapped and quantified IGF-II/M6P receptors in sagittal sections of adult rat brain by in vitro autoradiography/computerized densitometry and immunohistochemistry. While in vitro autoradiography allowed mapping and quantitation, immunohistochemistry both confirmed mapping and allowed more detailed determination of cellular distribution of receptors. The two methods were generally in agreement with few areas of mismatching. By in vitro autoradiography, a discrete and characteristic distribution of IGF-II receptor binding was demonstrated, with specific binding representing 85% of total binding. Displacement and specificity competition curves in arcuate nucleus and choroid plexus were typical for authentic IGF-II receptors with half maximal displacement at 1 nM cold IGF-II. IGF-II receptor density, estimated by in vitro autoradiography, was very high in circumventricular organs, especially the median eminence, which had the highest binding in the brain. In the remainder of the brain there was concordance between the distribution of receptors identified by the two techniques, with greatest densities in the olfactory bulb and olfactory pathways, the hippocampus and discrete regions of the cerebral cortex, cerebellum, hypothalamus, thalamus and brainstem. There were however, some notable mismatches. Autoradiographic binding was high to very high in the median eminence, arcuate nucleus, suprachiasmatic nucleus and anterodorsal thalamic nucleus, whereas these areas were only poorly immunostained. Conversely, the septum showed moderate autoradiographic binding, but very prominent immunostaining of neurons in its dorsolat-eral aspect. Using the immunohistochemical technique IGF-II receptors were localized to specific neuronal groups such as the mitral cells of the olfactory bulb, Purkinje cells of the cerebellum and neurons in the red nucleus. Fibre pathways were not labelled by either technique. We conclude that IGF-II/M6P receptors are widespread throughout rat brain, specifically in neurons and blood vessels, with a similar, but distinct distribution to IGF-I and insulin receptors. Many of these regions have in common high rates of metabolic and synthetic activity, which may be mediated by IGF-II/M6P and their receptors.     

Insulin-like growth factor-I receptors in human brain and pituitary gland: An autoradiographic study

Insulin-like growth factor (IGF)-I receptors were studied in adult human postmortem brain and pituitary gland using quantitative autoradiography with human recombinant [¹²⁵I]IGF-I. The highest densities were found in the choroid plexus, pituitary gland-where IGF-I receptors were mainly concentrated in the anterior lobe, pineal gland, glomerular layer of the olfactory bulb, and the molecular layer of the cerebellar cortex. Moderate densities were present in cerebral cortex, caudate nucleus, putamen, accumbens, the CA1, CA2, CA3 fields and dentate gyrus of the hippocampus, the dendate nucleus of the cerebellum, amygdala, thalamus, pontine nuclei, and substantia nigra. All other brain areas, including white matter, contained low densities of IGF-I receptors. The finding that several well-defined brain structures are enriched with IGF-I receptors suggests a rieurotrophic/survival or neuromodulatory role of insulin-like growth factors on specific neuronal systems. IGF-I receptors observed in the white matter may be associated with oligodendrocytes. © 1994 Wiley-Liss, Inc.     

Localization of binding sites for insulin-like growth factor-I (IGF-I) in the rat brain by quantitative autoradiography

In vitro quantitative autoradiography was used to localize IGF-I binding sites in rat brain. Slide-mounted sections of frozen rat brain were incubated in 0.01 nM ¹²⁵I[Thr⁵⁹]IGF-I, alone or mixed with 10 nM unlabeled [Thr⁵⁹]IGF-I or insulin, for 22 h at 4 °C and apposed to LKB Ultrofilm. Measurement of labeled [Thr⁵⁹]IGF-I binding by computer digital image analysis of the autoradiographic images indicated that high affinity IGF-I binding sites are widely distributed at discrete anatomical regions of the brain microarchitecture. The highest concentration of specific binding sites was in the choroid plexus of the lateral and third ventricles. Unlabeled porcine insulin was less potent than unlabeled IGF-I in competing for binding sites on brain slices. Regions of the olfactory, visual, and auditory, as well visceral and somatic sensory systems were labeled, in particular the glomerular layer of the olfactory bulb, the anterior olfactory nucleus, accessory olfactory bulb, primary olfactory cortex, lateral-dorsal geniculate, superior colliculus, medial geniculate, and the spinal trigeminal nucleus. High concentrations of IGF-I-specific binding sites were present throughout the thalamus and the hippocampus, (dentate gyrus, Ca1, Ca2, Ca3). The hypothalamus had moderate binding in the paraventricular, supraoptic, and suprachiasmatic nucleus. Highest binding in the hypothalamus was in the median eminence. The arcuate nucleus showed very low specific binding, approaching the levels found in optic chiasm and white matter regions. Layers II and VI of the cerebral cortex also had moderate IGF-I binding. The results suggest that the development and functions of brain sensory and neuroendocrine pathways may be regulated by IGF-I.     

Identification and Localization of Insulin-Like Growth Factor Receptors in Human Infant Pituitary Gland—Similar Distribution to Somatotrophs

Insulin-like growth factors(IGF) are involved in feedback regulation of growth hormone(GH) secretion from the pituitary. Though receptors for IGF-I and IGF-II have been identified on particulate preparations of rat pituitary, their localization and relationship to GH-secreting acidophils has not been determined. We used quantitative in vitro autoradiography and immunocytochemistry to simultaneously determine the distribution of IGF receptors and GH-secreting cells in human infant pituitary gland. Frozen or fixed post-mortem human infant pituitary glands were sectioned for binding studies, or immunocytochemistry. Binding for IGF-I and IGF-II showed characteristic specificity for respectively Type I and Type II receptors. Binding sites were visualized throughout the pituitary gland, with similar density and distribution for IGF-I and IGF-II receptor sites. Receptor density was two-fold higher in anterior than posterior pituitary, with highest density in the lateral horns of the anterior pituitary. The distribution of GH-containing cells (acidophils) was similar to IGF receptor distribution. Increased density of IGF receptors in regions of GH-secreting cells may point to the mechanism whereby IGF uniquely inhibits synthesis of human GH in contrast to its promotion of synthetic processes in other cells.     

Insulin receptors and insulin action in the brain: review and clinical implications

Insulin receptors are known to be located on nerve cells in mammalian brain. The binding of insulin to dimerized receptors stimulates specialized transporter proteins that mediate the facilitated influx of glucose. However, neurons possess other mechanisms by which they obtain glucose, including transporters that are not insulin-dependent. Further, insulin receptors are unevenly distributed throughout the brain (with particularly high density in choroid plexus, olfactory bulb and regions of the striatum and cerebral cortex). Such factors imply that insulin, and insulin receptors, might have functions within the central nervous system in addition to those related to the supply of glucose. Indeed, invertebrate insulin-related peptides are synthesized in brain and serve as neurotransmitters or neuromodulators. The present review summarizes the structure, distribution and function of mammalian brain insulin receptors and the possible implications for central nervous system disorders. It is proposed that this is an under-studied subject of investigation.     

Localization of angiotensin II receptor binding in rabbit brain by in vitro autoradiography

Binding of 125I-[Sar1,Ile8] angiotensin II (AII) to sections of brains from both wild and laboratory rabbits was determined by in vitro autoradiography. In the forebrain, specific high density binding was observed in the olfactory bulb, organum vasculosum of the lamina terminalis (OVLT), subfornical organ, median eminence, lateral septum, median preoptic nucleus and hypothalamic paraventricular, supraoptic and arcuate nuclei. In the midbrain, binding of the radioligand was observed in the interpeduncular and parabrachial nuclei, in the locus coeruleus, and ventrolateral pons. In the hind brain, there was dense binding of 125I-[Sar1,Ile8] AII to the nucleus of the solitary tract (NTS) and to both rostral and caudal parts of the reticular formation of the ventrolateral medulla oblongata. Weaker specific binding of the radioligand to the molecular layer of the cerebellum, to the nucleus of the spinal trigeminal tract, dorsal motor nucleus of the vagus, area postema, and to a band of tissue connecting the NTS to the ventrolateral medulla was also observed. Binding of the ligand to circumventricular organs such as the OVLT, subfornical organ, and median eminence suggests that these are sites in the brain of the rabbit at which blood-borne AII may exert influences on the central regulation of fluid balance and pituitary hormone secretion, although AII of neuronal origin could also act at these sites. Binding of the radioligand in several other brain regions suggests that angiotensin II of cerebral origin may be involved in a number of different aspects of brain function in the rabbit. The finding of dense binding in the NTS and ventrolateral medulla, which are involved in autonomic activity and are also sites of catecholamine-containing neurons, raises the possibility of angiotensin interaction with these neurons and involvement in autonomic function.     

Mapping of somatostatin receptor localization in rat brain: Forebrain and diencephalon

Using quantitative in vitro receptor autoradiography, minute distributions of 125I-Tyr11-somatostatin (SS)-14 binding sites were investigated in the rat forebrain and diencephalon. In the cerebral cortex, there was a high density of receptors observed in layers V-VI and a low density in layers I-IV. The entorhinal cortex displayed the highest receptor density of the cerebral cortices. The olfactory system had a high SS receptor density. The anterior olfactory nucleus, nucleus of the lateral olfactory tract, medial habenular nucleus and the basolateral amygdaloid nucleus showed moderate densities. In the limbic system, the CA1 and subiculum regions had high receptor densities. More detailed observations revealed high receptor densities in the oriens, radiatum and lacunosum layers and a much lower density in the pyramidal cell layer. The caudate putamen and substantia nigra showed low receptor densities, while the claustrum displayed the highest density of receptors in the rat brain. These data were not consistent with those of previous studies using 125I-SS-28 and 125I-201-995, which had shown that the high receptor density area in the basolateral amygdaloid group was identified as the lateral amygdaloid nucleus, and that the pyramidal cell layer in the hippocampus showed high receptor densities.     

Neurotensin-like immunoreactivity and neurotensin receptors in the rat hypothalamus and in the neurointermediate lobe of the pituitary gland

In the rat hypothalamus, cell bodies containing neurotensin-like immunoreactivity were mainly found in the medial preoptic area, the periventricular nucleus, the paraventricular nucleus, the supraoptic nucleus and the arcuate nucleus. [3H]neurotensin binding sites were observed throughout the hypothalamus with a dense accumulation of silver grains over the paraventricular nucleus, the arcuate nucleus and the median eminence region. By radioimmunoassay neurotensin-like immunoreactivity was also found in the neurointermediate lobe of the pituitary gland of various mammalian species and in human postmortem posterior pituitary glands. In the rat studies involving pituitary stalk transections and the neurotoxin monosodium glutamate indicated the presence of a neurotensinergic pathway from the arcuate nucleus to the neurointermediate lobe of the pituitary gland. [3H]neurotensin binding sites were found to be concentrated over the intermediate lobe of the pituitary gland and their presence was not affected by pituitary stalk transection, indicating their localization on endocrine cells of the intermediate lobe of the pituitary gland.     

Insulin-like growth factor I (IGF-I) distribution in the tissue and extracellular compartment in different regions of rat brain

The regional distribution of insulin-like growth factor I (IGF-I) was examined in the tissue and extracellular compartment of rat brain. The tissue content of IGF-I was the highest in the pituitary gland, followed by the olfactory bulb, upper brainstem, cerebellum, striatum, hippocampus, lower brainstem, and cerebral cortex. The extracellular concentration was studied by intracerebral microdialysis technique, and the highest content was found in the hippocampus, followed by the olfactory bulb, hypothalamus, cerebellum, striatum, and cerebral cortex. The tissue and extracellular contents were significantly correlated in the olfactory bulb, hypothalamus, cerebellum, striatum, and cerebral cortex. IGF-I might act by paracrine and/or autocrine regulatory mechanisms in these regions.     

Localization and Characterization of Dopamine D1 Receptors in Sheep Hypothalamus and Striatum

Dopamine receptors are pharmacologically grouped as D₁ and D₂ receptors. Previous research in the ewe has shown that central D₁ receptors may have a role in facilitating prolactin release. The aims of this study were therefore to localize and characterize D₁ binding sites in the hypothalamus of sheep. For comparison, a known D₁ receptor-rich tissue (striatum) was also studied. The bioactivities of several D₁ analogues were also assessed for their efficacy in sheep tissue. In vitro autoradiography with [¹²⁵I]-SCH23982 was used to localize D₁ binding sites. The ventromedial hypothalamic nucleus (VMH) displayed moderate levels of specific binding, localized to the medial portion of the nucleus. Low levels of specific binding were seen in the preoptic area, supraoptic nucleus and anterior hypothalamic area. The suprachiasmatic nucleus, median eminence and arcuate nucleus did not show specific binding. As expected the striatum displayed high levels of specific binding. The VMH, preoptic area, median eminence, striatum and anterior pituitary were examined with radioligand binding studies to quantify and characterize D₁ binding sites. Scatchard analysis gave K_D 1.04 nM and B_max 127.4 fmol/mg protein for VMH and K_D 1.99 nM and B_max 454.6 fmol/mg protein for striatum. While specific binding occurred in the preoptic area and median eminence this binding did not show saturation characteristics. Specific binding was not observed in the anterior pituitary. Affinities determined by competitive binding studies showed that the binding sites in both VMH and striatum have the characteristics of a D₁ receptor, that is, high affinity for the D₁ agonists and antagonists, low affinity for dopamine and the serotonergic antagonist ketanserin and extremely low affinity for the D₂ agonists and noradrenaline. Adenylate cyclase studies showed that in the striatum dopamine and the D₁ agonists, fenoldopam and SKF38393, were able to cause significant dose-dependent increases in adenylate cyclase activity. In contrast the D₁ agonist, SKF82958, was inactive in this system. The D₁ antagonists SCH23390 and SCH39166, but not SKF83566, abolished the adenylate cyclase response to 50 μM dopamine. In the VMH the D₁ agonist SKF38393, but not dopamine, stimulated adenylate cyclase activity. In conclusion, these results demonstrate that D₁ binding sites exist within the hypothalamus in the VMH and that these binding sites have the characteristics of D₁ receptors. These receptors are a potential site of action for dopamine in facilitating prolactin release. In addition, the results show that at least for some dopamine analogues, receptor binding affinity does not always correlate with biological activity.     

Characterization and localization of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites in the brain of the frog Rana ridibunda.

The biochemical characteristics and the distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites have been investigated in the brain of the frog Rana ridibunda by using [(125)I]PACAP27 as a radioligand. Membrane-binding studies revealed the existence of high-affinity receptors for frog PACAP38 and PACAP27. In contrast, the [Des-His(1)]PACAP38 analogue had a much lower affinity and vasoactive intestinal polypeptide did not produce any displacement of the binding. Autoradiographic labeling of frozen brain sections revealed that the highest concentrations of PACAP receptors were located in the olfactory bulb, pallium, striatum, habenular nuclei, ventromedial thalamic nucleus, corpus geniculatum, posterior tubercle, dorsal part of the magnocellular preoptic nucleus, tectum, and the molecular cell layer of the cerebellum. Moderate binding was observed in the septum, in most parts of the thalamus, the dorsal hypothalamic nucleus, the median eminence, the ventral nuclei of the tegmentum, the torus semicircularis, and the interpeduncular and isthmi nuclei. The present data provide the first biochemical characterization and anatomic distribution of PACAP binding sites in the brain of a nonmammalian vertebrate species. The widespread distribution of specific PACAP receptors in the frog brain suggests that the peptide does not act solely as a hypophysiotropic factor, but likely fulfills neurotransmitter functions, neuromodulator functions, or both.     

Expression of prokineticins and their receptors in the adult mouse brain

Prokineticins are a pair of regulatory peptides that have been shown to play important roles in gastrointestinal motility, angiogenesis, circadian rhythms, and, recently, olfactory bulb neurogenesis. Prokineticins exert their functions via activation of two closely related G-protein-coupled receptors. Here we report a comprehensive mRNA distribution for both prokineticins (PK1 and PK2) and their receptors (PKR1 and PKR2) in the adult mouse brain with the use of in situ hybridization. PK2 mRNA is expressed in discrete regions of the brain, including suprachiasmatic nucleus, islands of Calleja and medial preoptic area, olfactory bulb, nucleus accumbens shell, hypothalamic arcuate nucleus, and amygdala. PK1 mRNA is expressed exclusively in the brainstem, with high abundance in the nucleus tractus solitarius. PKR2 mRNA is detected throughout the brain, with prominent expression in olfactory regions, cortex, thalamus and hypothalamus, septum and hippocampus, habenula, amygdala, nucleus tractus solitarius, and circumventricular organs such as subfornical organ, median eminence, and area postrema. PKR2 mRNA is also detected in mammillary nuclei, periaqueductal gray, and dorsal raphe. In contrast, PKR1 mRNA is found in fewer brain regions, with moderate expression in the olfactory regions, dentate gyrus, zona incerta, and dorsal motor vagal nucleus. Both PKR1 and PKR2 are also detected in olfactory ventricle and subventricular zone of the lateral ventricle, both of which are rich sources of neuronal precursors. These extensive expression patterns suggest that prokineticins may have a broad array of functions in the central nervous system, including circadian rhythm, neurogenesis, ingestive behavior, reproduction, and autonomic function.     

Localization of [125I]IGF-I Binding on the Ovine Pars Tuberalis

In the sheep, it has been shown that the pars tuberalis of the pituitary may mediate the photoperiodic control of seasonal changes in prolactin secretion. High concentrations of melatonin receptors are present on the ovine pars tuberalis and melatonin is known to inhibit forskolin-stimulated cyclic AMP production in this tissue. Other hormonal inputs to the ovine pars tuberalis have not yet been identified. In the rat mRNA for the IGF-I receptor has been identified in the pars tuberalis using in situ hybridization. In order to define whether IGF-I may influence the function of the ovine pars tuberalis the presence of receptors for IGF-I has been investigated. Using in vitro autoradiography specific [¹²⁵I]IGF-I binding was found in high concentrations over the ovine pars tuberalis particularly associated with certain of the capillaries. Homogenate receptor assays showed saturable specific binding of [¹²⁵I]IGF-I with a mean dissociation constant (Kd) of 0.5 ± 0.1 nM (n=4). Competition studies revealed a rank order of potency of IGF-I>IGF-II> > >insulin, in displacing [¹²⁵I]IGF-I binding, indicative of a mixed population of IGF-I and IGF-II/rnannose-6-phosphate receptors and insulin-like growth factor binding proteins (IGFBPs). Cross-linking of [¹²⁵I]IGF-I to pars tuberalis membrane homogenates and analysis by SDS-PAGE under reducing conditions confirmed the presence of both IGF-I receptors and binding proteins. Autophosphorylation of a 97 kDa substrate, compatible with the β-sub-unit of the IGF-I receptor, was increased in the presence of IGF-I, indicating the existence of functional IGF-I receptors on the ovine pars tuberalis. In contrast in the rat [¹²⁵I]IGF-I binding was restricted to the median eminence region of the brain and was not detectable over the pars tuberalis.     

Localization and characterization of atrial natriuretic peptide binding sites in discrete areas of rat brain and pituitary gland by quantitative autoradiography

Atrial natriuretic peptide [rat (r) ANP6-33 or ANP99-126] binding sites were localized in discrete areas of rat brain and pituitary gland using quantitative autoradiographic techniques. High numbers of rANP6-33 binding sites were concentrated in the circumventricular organs (the organon vasculosum laminae terminalis, organon subfornicalis, and area postrema) and selected hypothalamic nuclei (the nucleus supraopticus, nucleus preopticus medianus and nucleus paraventricularis). High binding was also present in the choroid plexus and the bulbi olfactorii (laminae medullaris interna). A relatively low number of rANP6-33 binding sites was observed in other olfactory, limbic and brainstem areas (the nucleus tractus solitarii, nucleus motoris dorsalis vagii and nucleus hypoglossi), the eminentia mediana and the pituitary gland (anterior and posterior lobes). High-affinity rANP6-33 binding sites were demonstrated in the organon subfornicalis and the area postrema after incubation of consecutive sections from individual rat brains with 125I-rANP6-33 in concentrations from 20 to 400 pM. rANP6-33 binding sites were concentrated in areas associated with angiotensin II and/or vasopressin, suggesting an interaction among these peptides in the central nervous system.     

In situ histochemical localization of type I interleukin-1 receptor messenger RNA in the central nervous system, pituitary, and adrenal gland of the mouse.

The cytokine interleukin-1 (IL-1) has a number of biologic activities, including pronounced effects on the nervous and neuroendocrine systems. In this study, in situ histochemical techniques were used to investigate the distribution of cells expressing type I IL-1 receptor mRNA in the CNS, pituitary, and adrenal gland of the mouse. Hybridization of 35S-labeled antisense cRNA probes derived from a murine T-cell IL-1 receptor cDNA revealed a distinct regional distribution of the type I IL-1 receptor, both in brain and in the pituitary gland. In the brain, an intense signal was observed over the granule cell layer of the dentate gyrus, over the entire midline raphe system, over the choroid plexus, and over endothelial cells of postcapillary venules throughout the neuraxis. A weak to moderate signal was observed over the pyramidal cell layer of the hilus and CA3 region of the hippocampus, over the anterodorsal thalamic nucleus, over Purkinje cells of the cerebellar cortex, and in scattered clusters over the external-most layer of the median eminence. In the pituitary gland, a dense and homogeneously distributed signal was observed over the entire anterior lobe. No autoradiographic signal above background was observed over the posterior and intermediate lobes of the pituitary, or over the adrenal gland. This study therefore provides evidence for discrete receptor substrates subserving the central effects of IL-1, thus supporting the notion that IL-1 acts as a neurotransmitter/neuromodulator in brain. It also supports studies suggesting that IL-1-mediated activation of the hypothalamic-pituitary-adrenal axis occurs primarily at the level of the brain and/or pituitary gland.     

Characterization and localization of cannabinoid receptors in rat brain: a quantitative in vitro autoradiographic study

A potent, synthetic cannabinoid was radiolabeled and used to characterize and precisely localize cannabinoid receptors in slide-mounted sections of rat brain and pituitary. Assay conditions for 3H-CP55,940 binding in Tris-HCl buffer with 5% BSA were optimized, association and dissociation rate constants determined, and the equilibrium dissociation constant (Kd) calculated (21 nM by liquid scintillation counting, 5.2 nM by quantitative autoradiography). The results of competition studies, using several synthetic cannabinoids, add to prior data showing enantioselectivity of binding and correlation of in vitro potencies with potencies in biological assays of cannabinoid actions. Inhibition of binding by guanine nucleotides was selective and profound: Nonhydrolyzable analogs of GTP and GDP inhibited binding by greater than 90%, and GMP and the nonhydrolyzable ATP analog showed no inhibition. Autoradiography showed great heterogeneity of binding in patterns of labeling that closely conform to cytoarchitectural and functional domains. Very dense 3H-CP55,940 binding is localized to the basal ganglia (lateral caudate-putamen, globus pallidus, entopeduncular nucleus, substantia nigra pars reticulata), cerebellar molecular layer, innermost layers of the olfactory bulb, and portions of the hippocampal formation (CA3 and dentate gyrus molecular layer). Moderately dense binding is found throughout the remaining forebrain. Sparse binding characterizes the brain stem and spinal cord. Densitometry confirmed the quantitative heterogeneity of cannabinoid receptors (10 nM 3H-CP55,940 binding ranged in density from 6.3 pmol/mg protein in the substantia nigra pars reticulata to 0.15 pmol/mg protein in the anterior lobe of the pituitary). The results suggest that the presently characterized cannabinoid receptor mediates physiological and behavioral effects of natural and synthetic cannabinoids, because it is strongly coupled to guanine nucleotide regulatory proteins and is discretely localized to cortical, basal ganglia, and cerebellar structures involved with cognition and movement.     

Expression of a novel angiotensin II receptor subtype in gerbil brain

Angiotensin II receptors are highly localized in adult gerbil brain. Apparent receptor number is high in subfornical organ, vascular organ of the lamina terminalis, nucleus of the solitary tract, hippocampus, and in the anterior pituitary gland. In the hippocampus, binding is localized to the stratum oriens, radiatum, the lacunar molecular layers of the CA1 subfield, and the molecular layer of the gyrus dentatus, with a medial to lateral and anterior to posterior gradient in receptor expression. Binding is absent from the pyramidal layer of the CA1 subfield and from the granular cell layer of the gyrus dentatus, areas rich in angiotensin IV binding. Characterization in the hippocampus revealed the presence of a high affinity receptor, sensitive to incubation with the guanine nucleotide GTPγS, and displaced by angiotensin II = angiotensin III < Sar¹-Ile⁸-angiotensin II, but not by angiotensin IV or other angiotensin fragments, the AT₁ receptor antagonist losartan, or the AT₂ ligands CGP 42112 or PD 123177. In other brain areas, binding was equally insensitive to displacement by AT₁ or AT₂ ligands, with the exception of binding in the olfactory bulb, which was totally displaced by CGP 42112 and PD 123177, but not by losartan. In the gerbil, most of the brain and pituitary angiotensin II receptors are different from the AT₁ AT₄ and AT₄ subtypes, and should be considered ‘atypical’ until further characterization.     

Periventricular hypothalamic cells in the rat brain contain insulin mRNA

In situ hybridization histochemistry with a 35S-labeled oligodeoxyribonucleotide probe for insulin was performed in the rat. Labeled cells were observed in the pancreas and in the periventricular nucleus of the hypothalamus. No labeling was seen elsewhere in the brain, including the olfactory bulb, the choroid plexus, and the tissue adjacent to the lateral ventricles. This finding suggests that insulin may be released from cells in the periventricular nucleus for transport via cerebrospinal fluid to other brain regions.     

Distribution of immunoreactive dynorphin B in discrete areas of the rat brain and spinal cord

The distribution of immunoreactive (ir)-dynorphin B in 101 microdissected rat brain and spinal cord regions was determined using a specific radioimmunoassay. The highest concentration of dynorphin B in brain was found in the substantia nigra (1106.2 fmol/mg protein). Very high concentrations of ir-dynorphin B (> 400 fmol/mg protein) were also found in the lateral preoptic area, parabrachial nuclei and globus pallidus. Relatively high concentrations of ir-dynorphin B (250–400 fmol/mg protein) were found in 19 nuclei, including the periaqueductal gray matter, anterior hypothalamic nucleus, median eminence, nucleus accumbens and hippocampus. Moderate levels of the peptide (between 100 and 250 fmol/mg protein) were found in 42 brain nuclei such as the perifornical nucleus, nucleus of the diagonal band, medial forebrain bundle, and dorsal premamillary nucleus. Low concentrations of ir-dynorphin B (< 100 fmol/mg protein) were found in 28 brain areas, e.g. cerebral cortical structures (parietal, cingulate, frontal), claustrum, olfactory bulb, lateral and periventricular thalamic nuclei. The cerebellar cortex has the lowest dynorphin B concentration (53.7 fmol/mg protein). Spinal cord segments exhibit low or moderate (cervical segment) levels of the peptide. The neurointermediate lobe of the pituitary gland is extremely rich in ir-dynorphin B (11,047.1 fmol/mg protein).     

Distribution of immunoreactive substance P neurons in the hypothalamus and pituitary of the rhesus monkey

The distribution of immunoreactive substance P (IR-SP) neurons was examined in the hypothalamus and pituitary gland of the rhesus monkey by using the peroxidase-antiperoxidase immunocytochemical technique. Immunoreactive SP cell bodies were observed in the arcuate nucleus, in the region lateral to the arcuate nucleus, and in the median eminence (ME). Immunoreactive SP cells were also seen in the periventricular area of the dorsal tuberal region. A rich network of SP fibers was concentrated in the arcuate region, and the fiber stain was particularly dense in the external zone of the median eminence and in the external layer of the infundibular stalk. Also, substance P fibers were seen in the internal layer of the pituitary stalk and in the neural lobe of the pituitary gland. Outside the hypothalamus a dense network of IR-SP fibers was observed in the globus pallidus.