An HRP study on cell types and their regional topography within the locus coeruleus innervating the supraoptic nucleus of the rat

Afferent connections of the rat's supraoptic nucleus

Neurons projecting to the supraoptic nucleus (SON) have been identified following stereotaxic injections of either horseradish peroxidase or fast blue into the SON region of adult rats. The subfornical organ, median preoptic nucleus, organum vasculosum of the lamina terminalis and medial septal nucleus were the source of the largest numbers of supraoptic-projecting neurons. Several smaller projections also originate from the ipsilateral locus coeruleus, preoptic area, lateral parolfactorial area, dorsomedial nucleus of the hypothalamus, lateral parabrachial nucleus and ventrolateral medulla. Several other areas appeared to project only to the region immediately dorsal to the SON: lateral septal nucleus, diagonal band of Broca, ventral tegmental nucleus, and the supramamillary nucleus. These areas may influence SON neurosecretory function by way of interneurons found immediately dorsal to SON. Additional areas were identified with retrograde fluorescent label only, and these projected to the area immediately dorsal to SON and/or to SON itself.

Emerging concepts of structure-function dynamics in adult brain: the hypothalamo-neurohypophysial system

As the first known of the mammalian brain's neuropeptide systems, the magnocellular hypothalamo-neurohypophysial system has become a model. A great deal is known about the stimulus conditions that activate or inactivate the elements of this system, as well as about many of the actions of its peptidergic outputs upon peripheral tissues. The well-characterized actions of two of its products, oxytocin and vasopressin, on mammary, uterine, kidney and vascular tissues have facilitated the integration of newly discovered, often initially puzzling, information into the existing body of knowledge of this important regulatory system. At the same time, new conceptions of the ways in which neuropeptidergic neurons, or groups of neurons, participate in information flow have emerged from studies of the hypothalamo-neurohypophysial system. Early views of the SON and PVN nuclei, the neurons of which make up approximately one-half of this system, did not even associate these interesting, darkly staining anterior hypothalamic cells with hormone secretion from the posterior pituitary. Secretion from this part of the pituitary, it was thought, was neurally evoked from the pituicytes that made the oxytocic and antidiuretic "principles" and then released them upon command. When these views were dispelled by the demonstration that the hormones released from the posterior pituitary were synthesized in the interesting cells of the hypothalamus, the era of mammalian central neural peptidergic systems was born. Progress in developing an ever more complete structural and functional picture of this system has been closely tied to advancements in technology, specifically in the areas of radioimmunoassay, immunocytochemistry, anatomical tracing methods at the light and electron microscopic levels, and sophisticated preparations for electrophysiological investigation. Through the judicious use of these techniques, much has been learned that has led to revision of the earlier held views of this system. In a larger context, much has been learned that is likely to be of general application in understanding the fundamental processes and principles by which the mammalian nervous system works.(ABSTRACT TRUNCATED AT 400 WORDS)

Efferent projections of nucleus locus coeruleus: morphologic subpopulations have different efferent targets

This study quantitatively addresses the hypothesis that there is a systematic relationship between the morphologic characteristics of locus neurons and the particular target regions they innervate. Following horseradish peroxidase injections into selected terminal fields, locus coeruleus cell bodies are heavily labeled by retrograde transport so that somata size and shape, and in many cases primary dendritic pattern can be observed. This allows the classification of neurons as one of six cell types: large multipolar cells within ventral locus coeruleus, large multipolar cells in the anterior pole of locus coeruleus, fusiform cells in dorsal LC, posterior pole cells, medium-sized multipolar cells (termed core cells in this report), and small round cells. It was found that while core cells contribute to the innervation of all terminal fields examined, other cell types project to more restricted sets of targets. The contributions of each type to selected efferents are presented in detail. In particular, fusiform cells project to hippocampus and cortex, large multipolar cells in ventral locus coeruleus project to spinal cord and cerebellum, and small round cells in central and anterior locus coeruleus, as well as large multipolar cells in anterior locus coeruleus, project to hypothalamus. These results, in conjunction with those described in the preceding report, indicate that locus coeruleus is intrinsically organized with respect to efferent projections with much more specificity than has previously been evident. This high degree of organization is consistent with other recent demonstrations of functional specificity exhibited by locus coeruleus neurons.

Characterization of hypothalamic noradrenaline receptors in the supraoptic nucleus and periventricular region of the paraventricular nucleus of mice in vitro

In an attempt to determine the basis for apparently conflicting reports of the effects of noradrenaline (NA) on the neurohypophyseal system and its effects on the parvocellular periventricular region of the paraventricular nucleus (PVN), recordings were made from the neurons in the supraoptic nucleus (SON) and the periventricular region in the mouse hypothalamic slice preparation. Of 47 SON neurons, 43 (91%) were excited and two (4%) were inhibited by NA. Seven SON neurons increased the firing rate with increase of NA concentration (10(-7)-10(-4) M). Both the alpha 1-agonists phenylephrine and methoxamine also increased the activity of all SON neurons tested whereas application of the alpha 2-agonist clonidine and the beta-agonist isoproterenol had weak and inconsistent effects. While the alpha 2-antagonist yohimbine had no consistent influence, the alpha 1-antagonist prazosin blocked or reversed the effects of NA. Another group of 37 neurons in the periventricular region of the PVN was also tested; 13 (35%) were excited and 22 (59%) inhibited by application of NA (10(-5) M). When tested with phenylephrine or methoxamine, 6 of the 7 neurons were excited and one inhibited but all the 4 neurons tested were excited by isoproterenol. Clonidine strongly depressed the activity of all 12 neurons tested. The NA-induced excitatory effects were suppressed or reversed by pre-application of prazosin and the beta-antagonist propranolol while the inhibitory ones were suppressed or reversed by yohimbine. Synaptic blockade did not affect the excitatory responses of SON cells to NA nor the inhibitory responses of periventricular neurons to NA or clonidine. We conclude that SON neurons receive adrenergic excitatory effects mainly through alpha 1-receptors. The periventricular neurons receive the excitatory effects through alpha 1- or beta-receptors and receive the inhibitory effects through alpha 2-receptors.

Anatomy of brain alpha 1-adrenergic receptors: in vitro autoradiography with [125I]-heat

Much useful information on the localization of alpha 1-adrenergic binding sites has been gained by using tritiated radioligands for in vitro autoradiography. However, the iodinated alpha 1-adrenergic antagonist HEAT [( 2-beta (4-hydroxyphenyl)-ethylaminomethyl)-tetralone], BE 2254), a radioligand with high affinity and specificity, provides autoradiographs with a higher signal to noise ratio. This has allowed us to describe the anatomy of these binding sites in much greater detail than previously possible. Regions showing the highest levels of binding include external plexiform layer of the olfactory bulb, layers Va and Vc of frontoparietal cortex, lateral and central amygdaloid nuclei, thalamus, and inferior olive. Other regions were generally less intensely labeled, with the least evidence of labeling in white matter, such as corpus callosum. Some regions (e.g., hippocampus) had only moderate labeling, but the binding appeared in a discrete pattern that reflected the functional organization of the structure. Although the [125I]-HEAT binding sites were distributed in a pattern similar to that previously reported for [3H]-WB 4101 and [3H]-prazosin, the anatomical detail seen with the iodinated ligand is greater. As a result, an association of alpha 1-adrenergic antagonist binding sites with specific layers in the cortex and with some catecholamine-containing nuclei in the brainstem, such as the locus coeruleus, have been seen for the first time.

Simultaneous monoamine histofluorescence and neuropeptide immunocytochemistry: VI. Catecholamine innervation of vasopressin and oxytocin neurons in the rhesus monkey hypothalamus

The co-localization patterns of catecholamine varicosities and peptide-specific neuronal perikarya were assessed within the supraoptic and paraventricular nuclei in the rhesus monkey, Macaca mulatta. Formaldehyde-induced histofluorescence was coupled with the unlabelled antibody technique for the demonstration of neuropeptides. Hormone-specific neurophysin staining served to identify vasopressin and oxytocin-containing neurons in these hypothalamic nuclei. Catecholamine varicosities were seen in juxtaposition to vasopressin- and oxytocin-containing perikarya and proximal dendrites. The densest catecholamine innervation patterns were seen in the ventrolateral portion of the supraoptic nucleus; the dorsomedial portion of this nucleus received a considerably less dense innervation pattern. Oxytocin neurons were clustered in this relatively catecholamine poor region, whereas the vasopressin-containing neurons were more abundantly found in the catecholamine rich region. The paraventricular nucleus presented a considerably more complex pattern, perhaps reflecting the more diverse organization of this nucleus. Nevertheless, some separation of the oxytocin neurons, in a region less densely innervated by catecholamine varicosities, was noted. These observations confirm our earlier reports, in rat hypothalamus, that the norepinephrine innervation of the hypothalamic magnocellular neurons as seen with catecholamine histofluorescence favors the vasopressin-containing neurons over those located within the same nuclei which synthesize another neurohyphysial principal, oxytocin.

An HRP study on the distribution of all nuclei innervating the supraoptic nucleus in the rat brain

Detailed histochemical studies have been performed on the distribution of the nuclei innervating the supraoptic nucleus (SO) in the whole brain after horseradish peroxidase (HRP) injections through fine glass micropipettes (2 to 8 micrograms ) into the SO of 39 Wistar strain rats. The chromatogenic reaction was carried out according to the Mesulam's (1976) No. 8 procedure. Successful HRP injections resulted in labeling in various regions of the brain. The following conclusions were drawn from the analysis of these successful cases. All the nuclei of the subthalamus and posthypothalamus innervate the SO whereas only a few neurons of the hypothalamic arcuate and ventromedial nuclei probably send axons to it. The afferent monoaminergic fibers arise largely from the B7 and B8, and to a certain extent from the A6 and A10 cell groups. The septum, diagonal band nucleus and amygdala project directly to the SO while the olfactory tubercle and pyriform cortex may not. The mesencephalic central gray has a high possibility to project directly to it. The possibility that the hippocampus sends axons to the SO remains to be fully proven. A few small multipolar cells clearly revealed by the test in the SO should be non-secretory intercalated neurons.