Golgi apparatus, GERL, and secretory granule formation within neurons of the hypothalamo-neurohypophysial system of control and hyperosmotically stressed mice.

The vasopressin-producing neurons of the hypothalamo-neurohypophysial system are a particularly good model with which to consider the relationship between the Golgi apparatus nd GERL and their roles in secretory granule production because these neurons increase their synthesis and secretion of vasopressin in response to hyperosmotic stress. Enzyme cytochemical techniques for acid phosphatase (AcPase) and thiamine pyrophosphatase (TPPase) activities were used to distinguish GERL from the Golgi apparatus in cell bodies of the supraoptic nucleus from normal mice, mice hyperosmotically stressed by drinking 2% salt water, and mice allowed to recover for 5-10 d from hyperosmotic stress. In nonincubated preparations of control supraoptic perikarya, immature secretory granules at the trans face of the Golgi apparatus were frequently attached to a narrow, smooth membrane cisterna identified as GERL. Secretory granules were occasionally seen attached to Golgi saccules. TPPase activity was present in one or two of the trans Golgi saccules; AcPase activity appeared in GERL and attached immature secretory granules, rarely in the trans Golgi saccules, and in secondary lysosomes. As a result of hyperosmotic stress, the Golgi apparatus hypertrophied, and secretory granules formed from all Golgi saccules and GERL. Little or no AcPase activity could be demonstrated in GERL, whereas all Golgi saccules and GERL-like cisternae were TPPase positive. During recovery, AcPase activity in GERL returned to normal; however, the elevated TPPase activity and secretory granule formation seen in GERL-like cisternae and all Golgi saccules during hyperosmotic stress persisted. These results suggest that under normal conditions GERL is the predominant site for the secretory granule formation, but during hyperosmotic stress, the Golgi saccules assume increased importance in this function. The observed cytochemical modulations in Golgi saccules and GERL suggest that GERL is structurally and functionally related to the Golgi saccules.

The spinal muscular atrophy disease gene product, SMN: A link between snRNP biogenesis and the Cajal (coiled) body.

The spliceosomal snRNAs U1, U2, U4, and U5 are synthesized in the nucleus, exported to the cytoplasm to assemble with Sm proteins, and reimported to the nucleus as ribonucleoprotein particles. Recently, two novel proteins involved in biogenesis of small nuclear ribonucleoproteins (snRNPs) were identified, the Spinal muscular atrophy disease gene product (SMN) and its associated protein SIP1. It was previously reported that in HeLa cells, SMN and SIP1 form discrete foci located next to Cajal (coiled) bodies, the so-called "gemini of coiled bodies" or "gems." An intriguing feature of gems is that they do not appear to contain snRNPs. Here we show that gems are present in a variable but small proportion of rapidly proliferating cells in culture. In the vast majority of cultured cells and in all primary neurons analyzed, SMN and SIP1 colocalize precisely with snRNPs in the Cajal body. The presence of SMN and SIP1 in Cajal bodies is confirmed by immunoelectron microscopy and by microinjection of antibodies that interfere with the integrity of the structure. The association of SMN with snRNPs and coilin persists during cell division, but at the end of mitosis there is a lag period between assembly of new Cajal bodies in the nucleus and detection of SMN in these structures, suggesting that SMN is targeted to preformed Cajal bodies. Finally, treatment of cells with leptomycin B (a drug that blocks export of U snRNAs to the cytoplasm and consequently import of new snRNPs into the nucleus) is shown to deplete snRNPs (but not SMN or SIP1) from the Cajal body. This suggests that snRNPs flow through the Cajal body during their biogenesis pathway.

Expression of G protein-coupled receptor-30, a G protein-coupled membrane estrogen receptor, in oxytocin neurons of the rat paraventricular and supraoptic nuclei.

The regulatory actions of estrogens on magnocellular oxytocin (OT) neurons of the paraventricular and supraoptic nuclei are well documented. Although the expression and distribution of nuclear estrogen receptor-beta, but not estrogen receptor-alpha, in the OT neuron has been described, the nuclear receptors may not explain all aspects of estrogen function in the hypothalamic OT neuron. Recently a G protein-coupled receptor (GPR) for estrogens, GPR30, has been identified as a membrane-localized estrogen receptor in several cancer cell lines. In this study, we therefore investigated the expression and localization of GPR30 in magnocellular OT neurons to understand the mode of rapid estrogen actions within these neurons. Here we show that, in the paraventricular nucleus and supraoptic nucleus, GPR30 is expressed in magnocellular OT neurons at both mRNA and protein levels but is not expressed in vasopressin neurons. Specific markers for intracellular organelles and immunoelectron microscopy revealed that GPR30 was localized mainly in the Golgi apparatus of the neurons but could not be detected at the cell surface. In addition, the expression of GPR30 is also detected in the neurohypophysis. These results suggest that GPR30 may serve primarily as a nongenomic transducer of estrogen actions in the hypothalamo-neurohypophyseal system.

Structural-functional reorganization of nonapeptidergic neurosecretory hypothalamic nuclei in experimental acute pancreatitis.

Structures of the pancreas and magnocellular (supraoptic and paraventricular) nuclei of the hypothalamus of adult male rats were studied in conditions of acute pancreatitis at the light and electron microscopic levels. Histo-and organotypic changes in the parenchymatous and stromal elements of the pancreas were analyzed simultaneously with cytological assessment of the state of the nonapeptidergic neurosecretory centers of the hypothalamus. Blockade of the release of hypothalamic nonapeptides was found to occur at the level of axovasal complexes, and this aggravated the outcome of destructive and necrobiotic changes in the pathologically altered organ.

Plasticity of secretory neurons in the supraoptic and paraventricular nuclei of the hypothalamus on exposure to light.

Light and electron microscopic methods were used to analyze changes in secretory neurons in the supraoptic (SON) and paraventricular (PVN) nuclei in the hypothalamus in 100 adult male rats at time points from the first minutes to 180 days after 48 hours of full-time exposure to bright light. At the early time points after exposure, the cellular formulae of the SON and PVN shifted towards functionally active neurons with minimal quantities of secretory granules, large nuclei and nucleoli, low RNA contents, small numbers of rough endoplasmic reticulum cisterns, vacuoles, and lysosomes in the perikarya. The number of cells depositing secretion was greater than in controls at 24 h in the SON and PVN and at 10 days in the SON. Normalization of the cellular formula and the structural organization of the protein-synthesizing apparatus of PVN neurons occurred at 10-30 days, with normalization in the SON at 30-180 days. These data provide evidence that the range of plasticity of neurons in the PVN on exposure to full-time bright light was more significant than that in the SON.

Interplay between presynaptic and postsynaptic activities is required for dendritic plasticity and synaptogenesis in the supraoptic nucleus.

Developing oxytocin and vasopressin (OT/AVP) supraoptic nucleus (SON) neurons positively autocontrol their electrical activity via dendritic release of their respective peptide. The effects of this autocontrol are maximum during the second postnatal week (PW2), when the dendritic arbor transiently increases and glutamatergic postsynaptic potentials appear. Here, we studied the role and interaction of dendritic OT/AVP release and glutamate release in dendritic plasticity and synaptogenesis in SON. In vivo treatment with the peptides antagonists or with an NMDA antagonist suppressed the transient increase in dendritic arbor of SON neurons at the beginning of PW2. Incubation of acute slices with these compounds decreased the dendritic arbor on a short time scale (3-8 hr) in slices of postnatal day 7 (P7) to P9 rats. Conversely, application of OT/AVP or NMDA increased dendritic branches in slices of P3-P6 rats. Their effects were inhibited by blockade of electrical activity, voltage-gated Ca2+ channels, or intracellular Ca2+ mobilization. They were also interdependent because both OT/AVP and NMDA (but not AMPA) receptor activation were required for increasing the dendritic arbor. Part of this interdependence probably results from a retrograde action of the peptides facilitating glutamate release. Finally, blocking OT/AVP receptors by in vivo treatment with the peptides antagonists during development decreased spontaneous glutamatergic synaptic activity recorded in young adults. These results show that an interplay between postsynaptic dendritic peptide release and presynaptic glutamate release is involved in the transient increase in dendritic arbor of SON neurons and indicate that OT/AVP are required for normal synaptogenesis of glutamatergic inputs in SON.

[Plastisity of secreteory neurons of hypothalamic supraoptic and paraventricular nuclei during light exposure].

Changes of secreteory neurons of hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) were analyzed using light and electron microscopy in 100 adult male rats from the first minutes up to 180 days after their round-the-clock 48 hours-long exposure to bright light. At the early stages after the exposure, SON and PVN cellular formula was changed in favor of functionally active neurons containing few secretory granules, large nucleus and nucleoli, low RNA content, sparse complexes of rough endoplasmic reticulum, vacuoles and lysosomes in their perikarya. After 24 hours in both SON and PVN and after 10 days in SON the number of cells accumulating secretion was greater than that in control group. Normalization of the cellular formula and of the structural organization of protein-synthesis apparatus in PVN secretory neurons took place at days 10-30, while those ones in SON--at days 30-180. The results obtained suggest that the range of plasticity in PVN neurons in animals exposed to continuous bright light is larger than that in SON neurons.

[Structural and functional reorganization of the nonapeptidergic hypothalamic neurosecretory nuclei in experimental acute pancreatitis].

The structures of pancreas and hypothalamic magnocellular nuclei (supraoptic and paraventricular) were studied using light and electron microscopes in acute pancreatitis induced experimentally in mature male rats. Histo- and organotypic transformations of the pancreatic parenchymal and stromal elements were analyzed with a simultaneous cytological assessment of the hypothalamic nonapeptidergic neurosecretory centers. A phenomenon of the inhibition of hypothalamic nonapeptide release at the level in axo-vasal complexes was established, that aggravated the outcome of the destructive and necrobiotic processes in pathologically changed organ.

The hypothalamus in Alzheimer's disease: a Golgi and electron microscope study.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, characterized by irreversible decline of mental faculties, emotional and behavioral changes, loss of motor skills, and dysfunction of autonomic nervous system and disruption of circadian rhythms (CRs). We attempted to describe the morphological findings of the hypothalamus in early cases of AD, focusing our study mostly on the suprachiasmatic nucleus (SCN), the supraoptic nucleus (SON), and the paraventricular nucleus (PVN). Samples were processed for electron microscopy and silver impregnation techniques. The hypothalamic nuclei demonstrated a substantial decrease in the neuronal population, which was particularly prominent in the SCN. Marked abbreviation of dendritic arborization, in association with spinal pathology, was also seen. The SON and PVN demonstrated a substantial number of dystrophic axons and abnormal spines. Alzheimer's pathology, such as deposits of amyloid-ß peptide and neurofibrillary degeneration, was minimal. Electron microscopy revealed mitochondrial alterations in the cell body and the dendritic branches. The morphological alterations of the hypothalamic nuclei in early cases of AD may be related to the gradual alteration of CRs and the instability of autonomic regulation.

The V1a and V1b, but not V2, vasopressin receptor genes are expressed in the supraoptic nucleus of the rat hypothalamus, and the transcripts are essentially colocalized in the vasopressinergic magnocellular neurons.

We have identified and visualized the vasopressin (VP) receptors expressed by hypothalamic magnocellular neurons in supraoptic and paraventricular nuclei. To do this, we used RT-PCR on total RNA extracts from supraoptic nuclei or on single freshly dissociated supraoptic neurons, and in situ hybridization on frontal sections of hypothalamus of Wistar rats. The RT-PCR on supraoptic RNA extracts revealed that mainly V1a, but also V1b, subtypes of VP receptors are expressed from birth to adulthood. No V2 receptor messenger RNA (mRNA) was detected. Furthermore, the single-cell RT-nested PCR indicated that the V1a receptor mRNA is present in vasopressinergic magnocellular neurons. In light of these results, in situ hybridization was performed to visualize the V1a and V1b receptor mRNAs in supraoptic and paraventricular nuclei. Simultaneously, we coupled this approach to: 1) in situ hybridization detection of oxytocin or VP mRNAs; or 2) immunocytochemistry to detect the neuropeptides. This provided a way of identifying the neurons expressing perceptible amounts of V1a or V1b receptor mRNAs as vasopressinergic neurons. Here, we suggest that the autocontrol exerted specifically by VP on vasopressinergic neurons is mediated through, at least, V1a and V1b subtype receptors.

Dendritic regression dissociated from neuronal death but associated with partial deafferentation in aging rat supraoptic nucleus.

As neurons are lost in normal aging, the dendrites of surviving neighbor neurons may proliferate, regress, or remain unchanged. In the case of age-related dendritic regression, it has been difficult to distinguish whether the regression precedes neuronal death or whether it is a consequence of loss of afferent supply. The rat supraoptic nucleus (SON) represents a model system in which there is no age-related loss of neurons, but in which there is an age-related loss of afferents. The magnocellular neurosecretory neurons of the SON, that produce vasopressin and oxytocin for release in the posterior pituitary, were studied in male Fischer 344 rats at 3, 12, 20, 27, 30, and 32 months of age. Counts in Nissl-stained sections showed no neuronal loss with age, and confirmed similar findings in other strains of rat and in mouse and human. Nucleolar size increased between 3 and 12 months of age, due, in part, to nucleolar fusion, and was unchanged between 12 and 32 months of age, indicating maintenance of general cellular function in old age. Dendritic extent quantified in Golgi-stained tissue increased between 3 and 12 months of age, was stable between 12 and 20 months, and decreased between 20 and 27 months. We interpret the increase between 3 and 12 months as a late maturational change. Dendritic regression between 20 and 27 months was probably the result of deafferentation due to the preceding age-related loss of the noradrenergic input to the SON from the ventral medulla.

Organization of nucleoli and nuclear bodies in osmotically stimulated supraoptic neurons of the rat.

This study has analyzed variations in the number of nucleoli and nuclear bodies, as well as in their ultrastructural and cytochemical organization, after the osmotically induced activation of supraoptic nucleus (SON) neurons of the rat. The number of nucleoli and nuclear bodies and also the nucleolar size were determined on smear preparations of previously block-impregnated SON. The mean number of nucleoli per cell was 1.35 +/- 0.6 (mean +/- SDM) in control rats. No significant variations in this value were registered either in dehydrated or rehydrated rats. The mean nucleolar volume and the total nucleolar volume per cell showed a significant increase in dehydrated rats with respect to the controls, whereas these two parameters tended to return to control values in rats rehydrated after dehydration. The mean number of nuclear bodies per cell increased significantly from 0.56 +/- 0.50 (mean +/- SDM) in control rats to 1.54 +/- 1.1 after 6 days of dehydration. By electron microscopy, SON neurons displayed a reticulated nucleolar configuration. After the osmotically induced neuronal activation, there was an increase in the proportion of the total nucleolar area occupied by the granular component, and also a reduction in the mean fibrillar-center area. The most characteristic nucleolar features in rehydrated rats were the tendency for the granular component to be segregated and the occurrence of intranucleolar vacuoles. Ultrastructural cytochemistry with a specific silver method revealed a selective silver reaction on the coiled threads of the nuclear bodies--identified as "coiled bodies"--and on the nucleolar fibrillar components in all animal groups studied. Since nucleoli play a major role in ribosome biogenesis, a relationship between these nucleolar changes and the level of cellular activity of SON neurons is proposed. Furthermore, the response of nuclear "coiled bodies" to neuronal activation suggests their participation in the processing and transport of rRNA precursors.

Electron microscopic analysis of synaptic inputs from the median preoptic nucleus and adjacent regions to the supraoptic nucleus in the rat.

The median preoptic nucleus (MnPo) is critical for normal fluid balance, mediating osmotically evoked drinking and neurohypophysial hormone secretion. The influence of the MnPo on vasopressin and oxytocin release is in part through direct connections to the supraoptic and paraventricular nucleus. In the present investigation the synaptic contacts between the MnPo and supraoptic neurons were investigated in rats by ultrastructural examination of terminals labeled anterogradely with the tracers Phaseolus vulgaris-leucoagglutinin or biotinylated dextran. At the light microscopic level, labeled fibers within the supraoptic nucleus branched frequently, were punctuated by varicosities, and were distributed throughout the nucleus without preference for the known distributions of oxytocin and vasopressin neurons. At the ultrastructural level, synapses were associated with many of these varicosities. The ratio of labeled axodendritic to axosomatic synapses encountered was roughly consistent with a uniform innervation of dendrites and somata. The great majority of synapses were characterized by symmetrical contacts. Similar results were found for a few injections made in the organum vasculosum of the lamina terminalis, just rostral to the MnPo, and in the immediately adjacent periventricular preoptic area. Coupled with other recent anatomical and electrophysiological evidence, these results suggest there is a strong monosynaptic pathway from structures along the ventral lamina terminalis to the supraoptic nucleus.

Scanning electron microscopy of the third ventricular floor of the rat.

By utilizing a horizontal dissection technique the entire floor of the third ventricle has been examined. When viewed in toto the ventricular floor was seen to have an hourglass shape with the supraoptic and infundibular recesses equalling the widened portions. Consistent regional differnces were also noted. The rostral half of the floor was densely ciliated while the caudal portion, containing ependymal elements of the underlying median emience, possessed few cilia. The ciliated cells ended in an abrupt transition zone located about halfway along the floor. The rostral portion of the infundibular recess had many more apical blebs and microvilli than did the caudal areas. Supraepen dymal cells of both the phagocyte-like and neuron-like variety were observed in all of the animals examined. In some animals, complex, branching, interconnecting networks of fine calibered fibers interconnected neuron-like cells that occurred singly and occasionally in clusters. Female rats examined at all phases of the estrus cycle demonstrated no cyclic alterations of the ependymal surface.

Local synaptic organization of cholinergic neurons in the basolateral hypothalamus.

A monoclonal antibody to choline acetyltransferase (ChAT) was utilized for immunocytochemical identification of cholinergic neurons in the basolateral hypothalamus. Light and electron microscopic examination revealed a network of cell bodies, dendrites, and axonal processes dorsolateral to the supraoptic nucleus. Within this region the cells immunoreactive for ChAT receive numerous unlabeled terminals which contact dendrites, cell soma, axons and occasional somatic spines. In a few cases, small ChAT-immunoreactive terminals were observed contacting a cholinergic cell soma or large dendrite. Many ChAT-immunoreactive fibers were directed toward the supraoptic nucleus forming a dense local network but very few of these fibers penetrated deeper than approximately 20 micron into the supraoptic nucleus. A total of 63 ChAT-immunoreactive terminals were mapped within the basal hypothalamus, of which the vast majority contacted unlabeled dendrites immediately dorsolateral to the supraoptic nucleus. Labeled terminals were rare or nonexistent in the medial portions of the hypothalamus or deep within the supraoptic nucleus. This pattern of ChAT terminal densities correlates with the distribution of binding for the muscarinic cholinergic probe, [3H]quinuclidinylbenzilate, but not the binding of the putative nicotinic cholinergic probe, [125I]alpha-bungarotoxin, which is high within the supraoptic nucleus. Thus, the cholinergic neurons of the basal hypothalamus appear to form a network of intrinsic connections which probably represent input to muscarinic cholinergic receptors. No evidence was found to suggest that cholinergic presynaptic terminals were colocalized with the alpha-bungarotoxin binding protein within the supraoptic nucleus.

Diagonal band projection towards the hypothalamic supraoptic nucleus: light and electron microscopic observations in the rat.

Supraoptic nucleus (SON) neurons receive a prominent gamma-amino-butyric acid (GABA) input. This study evaluated the hypothesis, partly on the basis of recent electrophysiological data, that this innervation might arise from GABAergic neurons located in the ventral diagonal band of Broca area. For retrograde transport studies, pentobarbital-anesthetized male Long-Evans rats received 0.03-0.20-microliter injections of a suspension of rhodamine tagged latex microspheres into the SON. In two cases where such injections were confined to the SON, less than 60 retrogradely labeled neurons were detected in the ipsilateral diagonal band. In three animals where injections extended into the perinuclear zone around the SON, more than 2,000 retrogradely labeled cells were counted in the ipsilateral diagonal band. For anterograde transport studies, another group of animals received either 30% horseradish peroxidase (HRP) in 0.5% poly-L-ornithine (0.05-0.10 microliter injections) or Phaseolus vulgarus (iontophoresed from a 2% solution) into the diagonal band. After survivals of 18-24 hours (HRP) or 5 days (PHAL-L) labeled axon terminals invested the perinuclear zone above the SON. The presence of just a single fiber within the nucleus indicated a minor projection to the SON itself. The HRP-injected material was processed for ultrastructural examination and revealed dense HRP-labeled axon terminals in this perinuclear zone, most often (98%) forming axodendritic appositions. A postembedding colloidal gold technique to visualize GABA-synthesizing terminals revealed that fewer than 5% of these perinuclear HRP-labeled terminals also exhibited GABA-like immunoreactivity. Within the SON, where GABAergic axon terminals are abundant, few (less than 5%) GABAergic terminals contained HRP.(ABSTRACT TRUNCATED AT 250 WORDS)

Volume densities and specific surfaces of neuronal and glial tissue elements in the rat supraoptic nucleus.

The present study was undertaken to provide an explanation for previous autoradiographic results suggesting a several times higher rate of synthesis of glycoconjugates per unit volume of hypothalamic glia than of neurons. Volume densities, specific surfaces (surface-volume ratios), and relative surfaces (contribution of the surface of a tissue element to the total surface of the tissue) were assessed. Neuronal elements occupy about 74% and glial elements about 8% of the total volume. The specific surface, i.e., the amount of plasma membrane per unit volume of structure, is more than 30 times higher in the neuropil than in the neuronal perikaryal fraction. The largest specific surface is found with (unmyelinated) axons and astroglial processes. The specific surface of the average astrocyte is about twice that of the average neuron. If the surface of the entire cell is considered in relation to the perikaryal volume only, this ratio is about seven times as large for glial cells as for neurons. It follows that an astrocyte perikaryon has to renew a several times larger plasma membrane than a neuron, which can account for the above differences in perikaryal synthesis rates of glycoconjugates.

Neuronal transport of acid hydrolases and peroxidase within the lysosomal system or organelles: involvement of agranular reticulum-like cisterns.

Neurosecretory neurons of the hyperosmotically stressed hypothalamo-neurohypophysial system have been a useful model with which to demonstrate interrelationships among perikaryal lysosomes, agranular reticulum-like cisterns, endocytotic vacuoles, and the axoplasmic transport of acid hydrolases and horseradish peroxidase. Supraoptic neurons from normal mice and mice given 2% salt water to drink for 5--8 days have been studied using enzyme cytochemical techniques for peroxidase and lysosomal acid hydrolases. Peroxidase-labeling of these neurons was accomplished by intravenous injection or cerebral ventriculocisternal perfusion of the protein as previously reported (Broadwell and Brightman, '79). Compared to normal controls, supraoptic cell bodies from hyperosmotically stimulated mice contained elevated concentrations of peroxidase-labeled dense bodies demonstrated to be secondary lysosomes and acid hydrolase-positive and peroxidase-positive cisterns either attached or unattached to secondary lysosomes. These cisterns were smooth-surfaced and 400--1,000 A wide. Their morphology was similar to that of the agranular reticulum. Some of the cisterns contained both peroxidase and acid hydrolase activities. The cisterns probably represent an elongated form of lysosome and, therefore, are not elements of the agranular reticulum per se. By virtue of their direct connections with perikaryal secondary lysosomes, these cisterns may provide the route by which acid hydrolases and exogenous macromolecules can leave perikaryal secondary lysosomes for anterograde flow down the axon. Very few smooth-surfaced cisterns were involved in the retrograde transport of peroxidase within pituitary stalk axons from normal and salt-treated mice injected intravenously with peroxidase. Peroxidase undergoing retrograde transport was predominantly in endocytotic structures such as vacuoles and cup-shaped organelles, which deliver this exogenous macromolecule directly to secondary lysosomes for degradation in the cell body. These observations extend our previously reported findings in the axon to the cell body and suggest that agranular reticulum-like cisterns in the perikaryon, like those in the axon, may be part of the lysosomal system rather than associated with the agranular reticulum. A diagram summarizing the lysosomal system of organelles and proposed transport of acid hydrolases and peroxidase in neurosecretory neurons specifically and in neurons in general is provided.

The supraoptic nucleus and the supraopticohypophysial tract in the monkey (Macaca mulatta).

The observations here on Golgi material are based on the study of fortunate impregnations in one horizontally sectioned and one frontally sectioned series found in the collection of Golgi preparations of the adult monkey brains (Macaca mulatta) available in this laboratory. The soma of the large supraoptic neurons have jagged protrusions and irregular crevices which give their surfaces a craggy appearance. Also they have a few somatic spines. Their dendrites, which usually arise from two or three dendritic trunks, emerging from the cell body, are moderately branched and have occasional dendritic spines. The axon emerges from a conical elevation either on the soma or a dendrite and is directed towards the supraopticohypophysial tract. In the present material there are a few neurons of the supraoptic nucleus impregnated that are definitely smaller than the larger neurons. They have short beaded axons, ending in the supraoptic nucleus a short distance from their point of origin. In the horizontal sections the supraopticohypophysial tract fibers can be seen passing over the posterior aspect of the optic tract. In the frontal sections, this fan-shaped tract, wide above and constricted below, can be followed into the median eminence. Some of these axons in their intrahypothalamic course have short beaded collaterals. Electron micrographs reveal: (1) endings with spherical synaptic vesicles and endings with flattened synaptic vesicles synapsing on neurosecretory axons in the supraoptic nucleus; (2) a few myelinated fibers containing neurosecretory granules in the intrahypothalamic portion of the supraopticohypophysial tract. As can be seen in both Golgi and electron microscopic preparations the presence of fibrous astrocytes in the supraoptic nucleus and their abundance in the hypothalamic portion of the supraopticohypophysial tract is characteristic of this neurosecretory system. In the nucleus and in the tract processes of the fibrous astrocytes are intimately associated with neurosecretory fibers.

Direct and indirect retinohypothalamic projections to the supraoptic nucleus in the female albino rat.

Earlier studies have shown that retinohypothalamic projections terminate extensively within the hypothalamus of the rat. Recently, we identified a light retinal projection to the supraoptic nucleus as well as a larger, well-focused projection resulting in a peri-supraoptic nucleus terminal field. In this study, we employed a double labeling method with cholera toxin conjugated to horseradish peroxidase (CT-HRP) and pseudorabies virus, a transsynaptic neural tracer, to evaluate retinorecipient neurons in both the supraoptic nucleus and peri-supraoptic nucleus terminal field. In addition, we looked for evidence that cells in the peri-supraoptic nucleus terminal field project into the supraoptic nucleus. Three strains of pseudorabies virus were compared. A direct retinosupraoptic nucleus circuit was confirmed with all three strains. Retinorecipient neurons in the peri-supraoptic nucleus terminal field were also confirmed. However, there was a strain-based difference in the identification of these neurons. The wild-type Becker strain labeled cells in the peri-supraoptic nucleus terminal field in a manner paralleling the early, intermediate and late stages of infection of the suprachiasmatic nucleus. This parallel time course suggests that retinal ganglion cells terminate directly on cells in the peri-supraoptic nucleus terminal field. Conversely, the Bartha and PRV-91 strains showed appreciable labeling of peri-supraoptic neurons only at long survival times. This longer time course suggests that these mutant strains label neurons in the peri-supraoptic nucleus terminal field indirectly, after passing through additional neurons. In addition, experiments with monocular injection of CT-HRP and posterior pituitary injection of pseudorabies virus showed retrogradely labeled second-order cells in the peri-supraoptic nucleus amidst the CT-HRP labeled terminal field of the retinohypothalamic tract. These results demonstrate a direct projection from the retina to the supraoptic nucleus and provide evidence for an indirect circuit from the retina to the supraoptic nucleus via neurons located in the peri-supraoptic nucleus terminal field. The strain-based differences imply that those retinal ganglion cells that project to the peri-supraoptic nucleus terminal field differ from those that project to the suprachiasmatic nucleus. In addition, these results suggest a neuroanatomic basis for photic effects on physiological mechanisms that are not mediated by the circadian timing system.