Herring bodies; an electron microscopic study of local degeneration and regeneration of neurosecretory axons

Roots and early routes of neuroendocrinology

Carl C. Speidel (1919) and Ernst Scharrer (1928) were privileged witnesses of the encounter between neurons and hormones, a biological phenomenon that had been occurring in nature during millions of years of evolution, as Berta Scharrer started to unfold since 1935 on. The story of neurosecretion is intimately associated to that of the hypothalamus, such a "marvellous region", as Wolfgang Bargmann (1975) called it. This story started more than two millennia ago. We have made an effort to trace the roots of the discoveries that gave rise to a medical discipline, neuroendocrinology. Our trip to the roots covers a period from the fourth century BC, when an extraordinary Medical School was founded in Alexandria, and extends into the late 1970s of the twentieth century, when neuroendocrine research had started to grow exponentially. An effort has been made to track back the origin of each piece of knowledge that was constructing, brick upon brick, the building of this new medical science, hoping that it would help neuroendocrinologists of the new era to find their own roots, to meet their ancestors. Tracking the roots of a particular phenomenon provides the opportunity to have an overview of the whole phenomenon, allowing comprehension rather than merely knowledge. An important purpose pursued throughout this article was to pay a tribute to all those who, in the early days, contributed to the brain-endocrine encounter. We have tried our best to bring back the achievements of most of them.

Localization of CGRP receptor components and receptor binding sites in rhesus monkey brainstem: A detailed study using in situ hybridization, immunofluorescence, and autoradiography

Functional imaging studies have revealed that certain brainstem areas are activated during migraine attacks. The neuropeptide calcitonin gene-related peptide (CGRP) is associated with activation of the trigeminovascular system and transmission of nociceptive information and plays a key role in migraine pathophysiology. Therefore, to elucidate the role of CGRP, it is critical to identify the regions within the brainstem that process CGRP signaling. In situ hybridization and immunofluorescence were performed to detect mRNA expression and define cellular localization of calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1), respectively. To define CGRP receptor binding sites, in vitro autoradiography was performed with [(3)H]MK-3207 (a CGRP receptor antagonist). CLR and RAMP1 mRNA and protein expression were detected in the pineal gland, medial mammillary nucleus, median eminence, infundibular stem, periaqueductal gray, area postrema, pontine raphe nucleus, gracile nucleus, spinal trigeminal nucleus, and spinal cord. RAMP1 mRNA expression was also detected in the posterior hypothalamic area, trochlear nucleus, dorsal raphe nucleus, medial lemniscus, pontine nuclei, vagus nerve, inferior olive, abducens nucleus, and motor trigeminal nucleus; protein coexpression of CLR and RAMP1 was observed in these areas via immunofluorescence. [(3)H]MK-3207 showed high binding densities concordant with mRNA and protein expression. The present study suggests that several regions in the brainstem may be involved in CGRP signaling. Interestingly, we found receptor expression and antagonist binding in some areas that are not protected by the blood-brain barrier, which suggests that drugs inhibiting CGRP signaling may not be able to penetrate the central nervous system to antagonize receptors in these brain regions.

Vesicle degradation in dendrites of magnocellular neurones of the rat supraoptic nucleus

The magnocellular neurones of the supraoptic nucleus (SON) and paraventricular nucleus release neuropeptide from their axon terminals and also from their dendrites. In the axon terminals, swellings known as Herring bodies are responsible for the degradation of aged, unreleased large dense-cored vesicles (LDCVs) by lysosomes. Dendrites of magnocellular neurones also contain a large number of LDCVs but specialised areas of vesicle degradation have yet to be discovered. Using immunofluorescence labelling for lysosomes in vasopressin-enhanced green fluorescent protein (vasopressin-eGFP) transgenic rats, we found that lysosomes are preferentially located in the centre of the dendrites where there was a high density of vasopressin-eGFP expression. These data suggest that there are local "hot spots", but not specific compartments for vesicle degradation in magnocellular dendrites.

The destination of the aged, nonreleasable neurohypophyseal peptides stored in the neural lobe is associated to the remodeling of the neurosecretory axon

The present investigation was designed to investigate the fate of the large pool of neurohypophyseal hormones that is never released into the blood. Normal Sprague-Dawley and taiep mutant rats were investigated under normal water balance, after dehydration and after dehydration-rehydration. Lectin histochemistry and light- and electron-microscopic immunocytochemistry using antibodies against vasopressin, oxytocin, and neurophysins used at low (1:1,000) and high (1:15,000) dilutions allowed to distinguish (1) recently packed immature granules, as those located in the perikaryon; (2) mature; and (3) aged granules. The distribution of these granules within the different domains of the neurosecretory axons located in the neural lobe, namely, undilated segments, swellings, terminals, and Herring bodies, and the response of these compartments to dehydration and dehydration-rehydration allowed to roughly follow the routing of the granules through such axonal domains. It is suggested that granules may move backward and forward between the terminals and the swellings. At variance, aged granules located in Herring body are retained in this compartment and would finally become degraded. Herring bodies displayed distinct lectin binding and immunocytochemical properties, allowing to distinguish them from axonal swellings. After a dehydration-rehydration cycle, immunocytochemistry and electron microscopy revealed that Herring bodies were no longer present in the neural lobe and that several terminals had degenerated. It is concluded that (1) the neurophysin axons may undergo remodeling under appropriate stimuli and (2) Herring bodies are a specialized and plastic domain of the magnocellular neurosecretory neuron involved in the disposal of aged neurosecretory granules. No differences were detected at the neural lobe level between normal and mutant rats subjected to the same experimental conditions.

Distribution of neuropeptide Y immunoreactivity in the central and peripheral nervous systems of amphioxus (Branchiostoma lanceolatum Pallas)

Immunocytochemistry techniques were employed to investigate the distribution of neuropeptide Y-like-immunoreactive (NPY-ir) cells and fibers in the central and peripheral nervous systems of adult amphioxus. NPY-ir neurons of the commissural type were abundant in the brain and present but more scarce in the spinal cord. These neurons gave rise to conspicuous NPY-ir tracts that coursed along the entire length of the nerve cord. Some fibers exhibited conspicuous Herring body-like swellings. In the peripheral nervous system, small NPY-ir neurons and a large number of thin, beaded NPY-ir fibers were observed in the atrial region, indicating the involvement of this substance in visceral regulation. A few NPY-ir fibers, possibly afferent to the spinal cord, coursed in the ventral branches of the spinal nerves of this region, whereas no NPY-ir fibers coursed in the preoral or velar nerves or in the dorsal branches of the other spinal nerves. These results indicate that NPY is widely used as a neuroregulator/neurotransmitter in the central and peripheral nervous systems of this primitive chordate. In addition, this study demonstrates the presence of tall, thin NPY-ir cells in the putative adenohypophyseal homologue, the Hatschek's pit organ, which is located in the roof of the preoral cavity (vestibule).

The responses of vasopressin- and tyrosine hydroxylase-expressing neurons of the supraoptic nucleus in rats to chronic osmotic stimulation

The dynamics of intracellular contents of vasopressin and tyrosine hydroxylase in neuron bodies were studied in the supraoptic nucleus and the distant segments of their axons in the posterior lobe of the hypophysis in rats in conditions of salt loading lasting one, two, and three weeks. The number of vasopressin-immununoreactive neurons increased by the end of the second week of osmotic stimulation, due to the onset of vasopressin synthesis in neurons not synthesizing this hormone in normal physiological conditions. The vasopressin concentration decreased in cell bodies and axons during the first two weeks of salt loading, apparently because vasopressin release occurred at a greater level than vasopressin synthesis. During the third week, the intracellular vasopressin content remained essentially constant, demonstrating the establishment of dynamic equilibrium between the synthesis and release of the hormone. The number of tyrosine hydroxylase-immunoreactive neurons and the levels of tyrosine hydroxylase in neuron bodies and axons, at least in the largest swellings (Herring bodies), gradually increased, demonstrating that the rate of tyrosine hydroxylase was greater than its rate of enzymatic degradation. Thus, chronic stimulation of vasopressin neurons was accompanied by a series of adaptive reactions, the most important of which appears to be the expression of vasopressin and tyrosine hydroxylase synthesis by neurons which do not normally synthesize these compounds.

A mouse model of familial amyotrophic lateral sclerosis expressing a mutant superoxide dismutase 1 shows evidence of disordered transport in the vasopressin hypothalamo-neurohypophysial axis

Amyotrophic lateral sclerosis (ALS) is a fatal, paralytic disorder that primarily affects motoneurons. By combining physiological and morphological approaches, we examined the effect of a murine superoxide dismutase 1 (SOD1) mutation (G86R), which induces neurological disorders resembling human familial ALS (FALS), on the arginine vasopressin (AVP) hypothalamo-neurohypophysial axis, an unmyelinated tract poor in neurofilaments. First, we observed that G86R mice progressively consumed more water than wild-type littermates. Furthermore, levels of plasma AVP and neurohypophysial AVP content were decreased in the SOD1 mutant mice, whereas the amount of hypothalamic AVP increased in an age-dependent manner. However, hypothalamic AVP mRNA levels were not significantly modified in these animals. At the ultrastructural level, we found that the neurohypophysis of G86R mice had a decreased number of neurosecretory axons. Conversely, the presence of large axon swellings was more pronounced in the SOD1 mutant mice. In addition, the size of neurosecretory granules was higher in G86R than in wild-type animals. All these findings strongly suggest that the FALS-associated SOD1 mutation injures the hypothalamo-neurohypophysial axis by provoking early, progressive disturbances in the axonal transport of neurosecretory products from neuronal perikarya to nerve terminals. This blockade could ultimately result in degeneration of the tract, as proposed for the myelinated, neurofilament-enriched motor axons affected by ALS.

Orphan neurones and amine excess: the functional neuropathology of Parkinsonism and neuropsychiatric disease

The aetiology and treatment of Parkinsonism is currently conceptualised within a dopamine (DA) deficiency-repletion framework. Loss of striatal DA is thought to cause motor impairment of which tremor, bradykinaesia and rigidity are prominent features. Repletion of deficient DA should at least minimise parkinsonian signs and symptoms. In Section 2, based on extensive pre-clinical and clinical findings, the instability of this approach to Parkinsonism is scrutinised as the existing negative findings challenging the DA deficiency hypothesis are reviewed and reinterpreted. In Section 3 it is suggested that Parkinsonism is due to a DA excess far from the striatum in the area of the posterior lateral hypothalamus (PLH) and the substantia nigra (SN). This unique area, around the diencephalon/mesencephalon border (DCMCB), is packed with many ascending and descending fibres which undergo functional transformation during degeneration, collectively labelled 'orphan neurones'. These malformed cells remain functional resulting in pathological release of transmitter and perpetual neurotoxicity. Orphan neurone formation is commonly observed in the PLH of animals and in man exhibiting Parkinsonism. The mechanism by which orphan neurones impair motor function is analogous to that seen in the diseased human heart. From this perspective, to conceptualise orphan neurones at the DCMCB as 'Time bombs in the brain' is neither fanciful nor unrealistic [E.M. Stricker, M.J. Zigmond, Comments on effects of nigro-striatal dopamine lesions, Appetite 5 (1984) 266-267] as the DA excess phenomenon demands a different therapeutic approach for the management of Parkinsonism. In Section 4 the focus is on this novel concept of treatment strategies by concentrating on non-invasive, pharmacological and surgical modification of functional orphan neurones as they affect adjacent systems. The Orphan neurone/DA excess hypothesis permits a more comprehensive and defendable interpretation of the interrelationship between Parkinsonism and schizophrenia and other related disorders.

Cerebral and cerebellar gangliocytomas: a morphological study of nine cases

Hypothalamic gangliocytomas have been shown to contain immunoreactivity for hypophysiotropic peptides and some have been associated with endocrine dysfunction. Extrahypothalamic gangliocytomas are usually not associated with endocrine abnormalities. We studied nine cerebral or cerebellar gangliocytomas from six men and three women; none of the patients had detectable alterations of endocrine homeostasis. On histological examination, the tumor cells resembled hypothalamic neurons. Electron microscopy disclosed the presence of dense-core vesicles in neuronal cytoplasm and processes resembling Herring bodies, and there were synaptic contacts between tumor cells. All but two tumors contained immunocytochemical positivity for at least one peptide hormone or amine; these included somatostatin, corticotropin-releasing hormone, beta-endorphin, galanin, vasoactive intestinal peptide, calcitonin, serotonin, catecholamines or met-enkephalin. These tumors have been thought to represent neoplasms arising in ectopic autonomic neural tissue. Their morphological features, their similarity to hypothalamic gangliocytomas and the multiple immunoreactivities shown here suggest that they can be regarded as tumors of peptidergic neurons that are widely distributed throughout the central nervous system.

Compensatory sprouting of uninjured magnocellular neurosecretory axons in the rat neural lobe following unilateral hypothalamic lesion

Axonal sprouting of intact neurons of the magnocellular neurosecretory system was investigated using a unilateral hypothalamic knife cut of the hypothalamoneurohypophysial tract to partially denervate the rat neural lobe (NL). Densitometric, morphometric, ultrastructural, and metabolic measures were utilized to demonstrate the compensatory response to denervation in this system. Densitometric analysis revealed a transient reduction in the intensity of vasopressin staining in the NL at 10 days postsurgery (PS) with a subsequent recovery by 20 days PS. There was a comparable initial reduction in the cross-sectional area of the NL followed by a more gradual recovery to normal by 90 days PS. Ultrastructural investigation revealed a reduction in total axon number in the NL at 10 days PS similar to the declines in vasopressin immunoreactivity and size of the NL. A subsequent partial recovery of axon number occurred, paralleling the return to normal NL size between 30 and 90 days PS. Hypertrophy of both somata and cell nuclei of magnocellular neurons in the supraoptic and paraventricular hypothalamic nuclei contralateral to the lesion was also apparent during this period. Daily measurements of urine osmolality revealed an initial transient hypoosmolality followed by a chronic hyperosmolality which persisted throughout the 90 day postsurgical period. There was a concomitant chronic decrease in both daily drinking and urine excretion volumes which began immediately following surgery. These results suggest that intact, contralateral magnocellular vasopressinergic efferents undergo compensatory sprouting as a result of partial denervation of the NL in the absence of a functional deficit in vasopressin.

The ageing hypothalamo-neurohypophysial system. An analysis of the neurohypophysis in normal hydration, osmotic loading and rehydration

Age-associated changes in the structure and function of the neurohypophysis may contribute to the decreased ability to conserve water in older animals. We investigated the neurohypophyses of 6 and 28-month-old male mice using radioimmunoassay and quantitative morphological techniques. The dry-weight and volume of the neurohypophysis increased significantly with age but the quantity of vasopressin in the gland remained constant. Oxytocin levels decreased with age. A quantitative morphological analysis was performed on the compartments of the neurohypophysis from male mice of 6 and 28 months of age which were either normally hydrated, osmotically loaded, or osmotically loaded and rehydrated. The absolute volumes of the axon endings, swellings, their constituent organelles and the axon terminals containing degenerating subcellular components were determined. The design of the analysis allowed us to examine both age-related changes and statistical interactions between the age of the animal and the behaviour of a variable during the osmotic loading/rehydration phase of the experiment. There was a significant age-related reduction in the volume of the neurohypophysis occupied by the endings and swellings. The diameters of the neurosecretory granules found in the endings were significantly smaller than those in the swellings in both age groups but the size difference was greater in the young animals. Dehydration and subsequent rehydration of old male mice leads to extensive re-modelling of the neurohypophysial compartments and subcellular organelles to the configuration found in the adult animal.

Antibodies against specific membrane proteins of neurosecretory granules isolated from bovine neural lobes

Membrane proteins from bovine neurosecretory granules isolated by density gradient centrifugation were separated by polyacrylamide gel electrophoresis. A doublet of 120 kDa and and 67 kDa bands were identified as specific proteins of the neurosecretory granule membrane. Antibodies against the 120 kDa doublet were raised in rabbits and characterized by western blotting and immunocytochemistry. Analysis of the antiserum by western blotting showed that this recognizes mainly the 120 kDa doublet and some other minor components which seem to be degradation products. The antiserum against the 120 kDa proteins stained, by immunocytochemistry, specifically the supraoptic and paraventricular neurons of the rat hypothalamo-neurohypophysial system. In the neural lobe the immunoreaction was found around blood vessels on structures which appear to be nerve endings and on Herring bodies. Immunoelectron microscopy using protein A-gold showed that the 120 kDa antigens are located on the membrane of neurosecretory granules in sections of rat neural lobes. The presence of the 120 kDa antigens exclusively in the hypothalamo-neurohypophysial system suggests that these proteins are probably not involved in a general secretory mechanism and that they might be a result of the tissue-specific expression of proteins.

Correlative scanning-immunoelectromicroscopic analysis of neuropeptide localization and neuronal plasticity in the endocrine hypothalamus

Thirty-two Sprague-Dawley rats were divided into four groups, eight rats per group. Animals were hypophysectomized with removal of both the pars distalis and the neural lobe of the neurohypophysis. Groups of eight rats were euthanized 1, 2, 4 and 8 weeks following hypophysectomy and prepared for routine scanning electron microscopy (SEM) and correlative immunoelectron microscopy employing antisera against arginine vasopressin (AVP). Eight normal rats served as controls. In experimental rats that survived one to eight weeks posthypophysectomy, remarkable neuroanatomical alterations were notable in the median eminence and adjacent third cerebral ventricular lumen. In contrast to normal control rats, large numbers of neurites were observed with SEM to insinuate from the lateral recess into the cerebral ventricular lumen and as early as one week following hypophysectomy they overgrew the apical surfaces of ependymal cells that constitute the lining of the cerebral ventricle. Immunoelectron microscopy revealed that a significant proportion of these neurites were magnocellular in origin in that they harbored AVP-positive neurosecretory vesicles. In addition to large numbers of invading magnocellular neurites, neuronal perikayria with apparent axosomatic synapses were observed to emerge upon the thick feltwork of invading axons, the latter of which appeared to freely terminate within the ventricular lumen. AVP-positive axon profiles were, in addition, seen to terminate upon the basal lamina of portal perivascular spaces in the zona externa of the median eminence. These data are consistent with the idea that following hypophysectomy (to include high stalk section of the neurohypophyseal system), that there is rapid, and dynamic sprouting and regrowth of AVP-positive axons into the adjacent third cerebral ventricular lumen and to the contact zone of the median eminence as well. This phenomenon may represent a compensatory physiological response to injury of the neurohypophyseal system characterized by a highly plastic neuroanatomical reorganization of magnocellular elements which appear to utilize the CSF of the third cerebral ventricle as a functional terminus for the neurocisternal secretion of AVP which ultimately enters the systemic circulation.

Immunocytochemical localization of serotonin-containing neurons in the myelencephalon, brainstem and diencephalon of the sheep

Using immunocytochemistry, morphological characteristics and distribution of serotonin-containing neurons and fibers of the sheep myelencephalon, brainstem and diencephalon were studied, employing highly specific antibodies to serotonin. The immunocytochemical procedure described here allowed the visualization of endogenous, and thus presumably physiological, pools of serotonin, because no pharmacological treatments (colchicine, inhibitors of monoamine oxidase or 5-hydroxytryptophan) were used to increase the endogenous amount of antigen. The distribution of serotonin cell bodies observed in the study is in agreement with that described by other authors in the rat using a similar method. The present work also shows more numerous groups than the formaldehyde-induced fluorescence method, because five additional groups were revealed, designated S1 to S5. Compared with those in the rat, sheep serotonergic structures exhibit striking specific characteristics: (1) greater scattering of cell bodies within the different groups visualized, (2) absence of group B4 and hypothalamic groups, (3) only a weak serotonergic innervation of the suprachiasmatic nuclei area.

The neuronal endoplasmic reticulum: its cytochemistry and contribution to the endomembrane system. II. Axons and terminals

The morphology and cytochemistry of the endoplasmic reticulum (ER) in axons and terminals of a number of different types of neurons in brains from mice were investigated ultrastructurally. The neurohypophysis received particular attention because the morphology and enzyme cytochemical activities of many of the preterminal swellings of hypothalamo-neurohypophysial axons are altered by chronic salt-stress. Membrane contrast and enzyme cytochemical staining techniques were employed to characterize the axonal reticulum and to determine if organelles representing the lysosomal system in the axon and the tubular profiles participating in the anterograde axonal transport of native horseradish peroxidase (HRP) are associated with the ER. Potential enzyme cytochemical markers for the axonal ER included glucose-6-phosphatase (G6Pase), thiamine pyrophosphatase, nucleoside diphosphatase, and acid hydroxylase activities. The anterograde transport of HRP was analyzed in undamaged hypothalamo-neurohypophysial neurons and in facial and hypoglossal motoneurons of mice receiving the protein in the lateral cerebral ventricle. The ER pervaded the axon and appeared as parallel, 20-40-nm-wide tubules interconnected by oblique anastomoses. Membrane thickness of the axonal reticulum measured 60-100 A, which is similar to that of the perikaryal ER. Enzyme cytochemical activities associated with the ER or lysosomes were not conspicuous in axons and terminals under normal conditions but became prominent in some axons and preterminal swellings manifesting an autophagic appearance within neurohypophyses from salt-stressed mice. Only G6Pase activity was a marker for the ER in these axons and preterminals. Many ER profiles in non-incubated sections and in G6Pase cytochemical preparations of salt-stressed neurohypophyses were wrapped around or interspersed among secretory granules, multilamellar bodies, and vacuoles that may represent forms of lysosomes involved in autophagy and crinophagy. Acid hydrolase activities were localized within the vacuoles as well as within 80-130-nm-wide, blunt-ended tubules in pituitary stalk axons; similar reactive tubules were confluent with large secondary lysosomes in neurosecretory cell bodies and may be derived from these lysosomes. Morphologically identical tubules transporting HRP in the anterograde direction were observed only in the salt-stressed hypothalamo-neurohypophysial neuron. The HRP-positive tubules very likely are affiliated with the lysosomal system.

Cell biology of synaptic plasticity

The nervous system of mammals retains throughout the animals' life-span the ability to modify the number, nature, and level of activity of its synapses. Synaptic plasticity is most evident after injury to the nervous system, and the cellular and molecular mechanisms that make it possible are beginning to be understood. Transplantation of brain tissue provides a powerful approach for studying mechanisms of synaptic plasticity. In turn, understanding the response of the central nervous system to injury can be used to optimize transplant survival and integration with the host brain.

Substance P-like immunoreactive neurons in the tuberoinfundibular area of rat hypothalamus. Light and electron microscopy

Immunoreactive substance P (ir SP) neurons were examined with special reference to their links with other neurons and blood vessels in the tuberoinfundibular hypothalamic area of normal and colchicine-treated male rats. On intraventricular administration of colchicine, ir SP neuronal cell bodies appeared in both the arcuate nucleus and the ventral portion of the ventromedial nucleus. These ir fibers were seen in the nuclei of untreated animals closely surrounding ir methionine-enkephalin and ACTH cell bodies, suggesting the presence of synaptic junctions. Electron microscopic examination of the arcuate nucleus stained with anti-SP serum showed synapses of ir SP fiber terminals on unlabeled neuronal cell bodies and fibers, some of which might be methionine-enkephalin and ACTH neurons. The ir fiber terminals contained numerous small clear and/or cored vesicles and a few large cored vesicles. Fiber terminals with the same ultrastructural characteristics were seen protruding into the pericapillary space in the external and subependymal layers of the median eminence. The possible role of the SP neurons in the tuberoinfundibular area is discussed.

Toxic effects of adriamycin on the central nervous system. Ultrastructural changes in some circumventricular organs of the mouse after intravenous administration of the drug

Recent experimental studies have shown that the cytotoxic antibiotic adriamycin (doxorubicin) after systemic administration can enter the so-called circumventricular organs (CVO) of the brain of the mouse. The present experiments were performed to find out whether such penetration of the brain is associated with signs of neurotoxic injury. For this purpose, light- and electron-microscopic observations were carried out on three of these organs: the neurohypophysis (NH), median eminence (ME), and postremal area (PA). Pronounced widening of the extracellular space indicating the presence of edema was present in all the regions, particularly in animals examined within 3 days of injection of the drug. Many degenerated axon terminals were observed in the NH and ME. The glial cells within these regions showed rarefaction of the nuclear chromatin, nucleolar segregation, and also cytoplasmic changes. The PA presented marked cellular changes resulting in degeneration of neurons, which was most evident 30 days after the injection. Hence, regions of the CNS outside the blood-brain barrier can be reached by adriamycin after systemic administration, and the drug can induce morphological changes there. The doses of the drug used in the present experiments were comparable to those given to patients for the treatment of malignant tumors.

Sensory input to growth stimulating neuroendocrine cells of Lymnaea stagnalis

Several environmental factors influence the growth of the basommatophoran freshwater snail Lymnaea stagnalis. Growth is hormonally controlled by 4 cerebral clusters of ca 50-75 peptidergic, neuroendocrine Light Green Cells (LGC). The present light, transmission, and scanning electron microscopic study shows that the LGC are synaptically contacted by a tentacle sensory system (TSS). The TSS consists of 2 types of primary sensory neurone, viz. ca 150 S1-cells and ca 50-100 S2-cells. A S1-cell has a non-ciliated dendrite and an axon branch that synaptically contacts the soma of a S2-cell. A S2-cell has a branching, ciliated dendrite. Probably, S1- and S2-cells have different sensory modalities and can integrate sensory information by intersensory interaction. The S2-axons run through the tentacular nerves, the cerebral ganglia, and the intercerebral commissure. In each ganglion S2-axons branch and form synaptic contacts on the axons and somata of the LGC and on glial cells that surround the LGC. In an LGC-cluster, 1-3 LGC-somata are particularly strongly innervated. Probably, the TSS is involved in the environmental control of growth in L. stagnalis.

Are large, fluorescent spots in aged mouse brain due to lesioning of catecholamine neurons?

Age-related, large intensely fluorescent (LIF) catecholamine-containing spots were discovered in mouse brain. The similarity of their appearance to "piled-up" fluorescent material observed in catecholamine (CA) nerve tracts after 6-hydroxydopamine (6-OHDA) lesions suggests that LIF spots may be due to accumulation of CA in neurons whose distal portions are undergoing degeneration. When senescent mouse brain were examined longitudinal to monoaminergic tracts by the Falck-Hillarp histofluorescence method, some elongated, large fluorescent structures were observed. This suggests an axonal swelling and accumulation of CA proximal to a lesion. One month after lesioning by intraventricular injections of 6-OHDA, the number of large fluorescent accumulations was significantly reduced. CA accumulations due to lesioning, thus, do not generally remain for the life of the animal. Hence if LIF spots are caused by lesioning, they may be turning over, and the number of LIF spots present at any one time represents only newly formed spots.

A new type of lesion-induced synaptogenesis: I. Synaptic turnover in non-denervated zones of the dentate gyrus in young adult rats

It is well established that partial denervation causes the formation of new synapses within denervated areas. It is also possible that synapse formation and remodeling occurs outside denervated zones. In this study we evaluate this possibility by examining the effect of a unilateral entorhinal lesion on the number and characteristics of synapses in non-denervated zones of the dentate gyrus within the hippocampal formation. A unilateral entorhinal lesion massively denervates the outer two-thirds of the ipsilateral dentate molecular layer and also causes a minor loss of synapses in the outer two-thirds of the contralateral dentate molecular layer. The inner one-third of the molecular layer is not denervated on either side. In the ipsilateral inner molecular layer the number of synapses rapidly decreases by about 20% and recovers by 10 days post-lesion. Similarly, in the contralateral inner molecular layer, synapses are lost and replaced, but the time course is slower. Loss is maximal at 60 days post-lesion and this recovers by 180 days post-lesion. Thus, a complete cycle of turnover occurs in both of the inner molecular layers. No degenerating terminals of any type were seen throughout the time course in these layers. Small synapses with non-complex synaptic junctions appear to account for most of the changes. Also the outer two-thirds of the contralateral molecular layer, which has lost less than 5% of its input, loses about 37% of its synapses and replaces the majority of them over time. However, the total number of synapses in the contralateral molecular layer never fully attains the value of unoperated animals. The total synaptic population reaches a value such that the ipsilateral and contralateral molecular layers are nearly equivalent. These changes, achieved through synaptic turnover, may represent a homeostatic response to nearby denervation which may facilitate restoration of bilateral function in the dentate gyrus.

The hypothalamo-hypophysial system of hypophysectomized rats. II. Structure and ultrastructure of the median eminence

The median eminence (ME) of hypophysectomized rats was studied by means of light and electron microscopy. Paraldehyde-fuchsin (PAF)-positive material is seen in the external zone (EZ) of the ME 2--5 days after the operation. Its amount gradually increases especially in the caudal part of the ME during the following few days. Some PAF-positive fibers make contact with the subependymally located blood capillaries. In the most caudal region of the recessus infundibuli they penetrate into the third ventricle. PAF-positive material decreases markedly from the ME of rats two months after hypophysectomy and exposure to a 1% salt load. Fibers of types A1, A2 and B containing granules of 120--220 nm, 100--150 nm and 80--100 nm in diameter, respectively, are seen in the EZ of the ME in hypophysectomized rats, although almost exclusively A2- and B-type structures make contact with the primary portal capillaries in intact animals. All types of neurosecretory fibers establish contact with the subependymal nonfenestrated blood capillaries and penetrate the recessus infundibuli. Some neurosecretory terminals of different types make direct contact with the glandular cells of the pars tuberalis or are separated from them by a thin basal lamina. It is assumed that mainly neurosecretory fibers of types A2 and B are permanently connected with the primary portal capillaries in the EZ of the ME in intact mammals, while the overwhelming majority of fibers of A1-type shows ingrowth during the course of postoperative reparation. The possible physiological significance of the described changes is discussed.

The influence of age on the hypothalamo-neurohypophyseal system of the mouse: a quantitative ultrastructural analysis of the posterior pituitary

A quantitative ultrastructural study of the posterior pituitary was undertaken. The posterior pituitary is the storage of the hormones vasopressin and oxytocin. Female C57BL/Icrfat mice which were under conditions of normal hydration were sampled at 8 and 32 months of age. There was a slight age-related decline in the volume fraction of cellular components with a corresponding increase in perivascular space. The proportion of neurosecretory endings and swellings showing autophagic activity (Dellman type II Herring bodies) increased significantly in the senescent mouse. The total pituicyte population showed a significant decrease in volume fraction, but with a significant increase in electron-dense types. Of the subcellular parameters examined, only the diameter of the neurosecretory granules showed a significant age-related decrease, the volume fraction remaining unaltered. The animals used in this study were from stocks found to be in a constant oestrus-metoestrus-like state unlikely to obscure changes in pituitary morphology. Over-all, the morphology of the posterior pituitary of the senescent female mouse under physiologically defined resting conditions indicates maintenance of the status quo.

Aging and unusual catecholamine-containing structures in the mouse brain

Brains of C57BL/6J mice, aged 4, 8 and 20--29 months, were examined by the Falck-Hillarp histochemical fluorescence technique. Numerous large, intensely fluorescent green to yellow-green spots (LIFS) were observed in the brains of senescent mice. LIFS were generally round to ovoid in shape and ranged in size from about 10 micrometer to about 30 micrometer. Histochemical and pharmacological procedures and spectral analysis indicated that the formaldehyde-induced fluorescence of the LIFS was due to the presence of catecholamines (CA) rather than aging pigment. Their distribution in the brain suggests an association with nerve axons or terminals rather than cell bodies. The number of LIFS in the hypothalamus increased progressively during aging. It is proposed that LIFS may represent age-related, unusual CA accumulation in enlargements proximal to axonal or terminal portions undergoing spontaneous degeneration.

Degeneration and regeneration of autonomic nerve endings in the anterior part of rhesus monkey ciliary muscle

The autonomic nerve plexus of the ciliary muscle was examined with the electron microscope in normal rhesus monkeys of different ages. In the anterior region of the muscle, at the boundary with the poorly innervated scleral spur and trabecular meshwork, 3.8-7.1% of the axons exhibit either degenerative or regenerative features. The cytoplasm of degenerating axons contains lamellated, dense and multivesicular bodies, vesicles, whorls of filaments, and membranous debris. The plasma membrane is often discontinuous and, on occasion, axonal debris and degenerative organelles are freely dispersed in the connective tissue spaces of the muscle. Degenerating axons contain a granular reaction product when stained for acid phosphatase activity. Regenerating axons are characterized by tightly packed mitochondria, glycogen particles, and aggregates of synaptic vesicles; they synapse with muscle cells and are negative to the acid phosphatase reaction. A quantitative analysis showed that in the anterior region of the ciliary muscle degenerating and regenerating axons increase in number with age, although the total number of axonal profiles remains constant. In the age groups examined, degenerating axons occurred with the same frequency as regenerating axons, thus, the age-dependent increase in axonal degeneration is accompanied by a parallel increase in axonal regeneration. We conclude that autonomic nerve endings in the anterior part of the ciliary muscle undergo a continuous process of renewal that is more prominent in old age.

The development of monamine-containing neurons in the brain and spinal cord of the salamander, Ambystoma mexicanum

The distribution of monoamine-containing neurons in the CNS of the developing and adult axolotl, Ambystoma mexicanum, has been investigated using the histochemical fluorescence technique of Falck and Hillarp combined with microspectrofluorimetry. The earliest catecholamine-containing neurons to be detected are located in the ventral ependymal zone of the spinal cord at the time of hatching (Stage 41). Between stages 43 and 46, catecholamine fluorescence can be detected in neurons in the following regions: nucleus preopticus, the hypothalamic-infundibular region, and the brain stem reticular formation. 5-HT-containing neurons are only observed in the midbrain raphe region and are first detected at stage 44. In contrast to these early monoamine fluorescing groups, catecholamine-containing neurons are not routinely detectable in the nucleus interpeduncularis until six months of age. All monoamine-containing neuronal groups detected in developing axolotls are also present in both sexes of the adult. However, the fluorescence intensity is less in monoamine-containing neurons observed in adults than in early developing subjects. All catecholamine-containing neuronal groups, with the exception of those located in the midbrain region (nucleus interpeduncularis, reticular zone) have fluorescent processes that contact the cerebrospinal fluid (CSF). The presence of CSF-contacting processes in the hypothalamic and spinal cord regions suggest that the CSF may act as a medium through which bioactive substances are transported from one brain region to another. Intense catecholamine fluorescence is observed in cells of the notochord prior to the detection of the monoamine-containing neurons in the CNS. A possible involvement of catecholamines in the inductive effects of the notochord during development is discussed.

Fine structural features of adrenergic nerve fibers and endings in the pineal gland of the rat, ground squirrel and chinchilla

The ultrastructural features of the adrenergic nerve fibers in the pineal glands of the rat, ground squirrel and chinchilla are described. Frequency distribution histograms of diameters of granulated and non-granulated vesicles in the adrenergic nerve endings demonstrate that the pineal nerve endings in the chinchilla contain a considerable number of large granulated and non-granulated vesicles, in contrast to those in the rat and ground squirrel. Synaptic ribbons seen in the pinealocytes of the ground squirrel were often localized near that plasma membrane which lay in close proximity to the axolemma of adrenergic nerve fibers. This observation may indicate that the synaptic ribbons are involved in the functional interconnection between pinealocytes and adrenergic nerve fibers. Localized dilations of the adrenergic nerve fibers were commonly observed in the pineal glands of all species examined. In addition to a variety of axonal constituents, various forms of inclusion bodies were tightly packed within these axonal dilations. The accumulation of the inclusion bodies may represent degenerative changes which occur in the pineal adrenergic nerve fibers in relation to the functional activity of the pineal gland.

Neurophysin in the brain and pituitary gland of normal and scrapie-affected sheep—I

By use of an immunofluorescence histochemical technique with a cross-species reactive antiserum to porcine neurophysin-II the precise localization of neurophysin in the pituitary gland and the hypothalamic area of the brain of the sheep has been determined. Neurophysin was confined to neurosecretory pathways originating from the supraoptic and paraventricular hypothalamic nuclei. The major pathway terminates in the neurohypophysis but in addition a second neurophysin-containing pathway proceeds in the external infundibular zone of the median eminence-pituitary stalk and is associated with the presence of vasopressin. In sheep affected with the hereditary degenerative disease known as natural scrapie, this supraoptico-paraventriculo-infundibular pathway is preserved and hypertrophied, while the major pathway to the posterior lobe of the pituitary degenerates. The supraoptic and paraventricular nuclei in the sheep comprise at least two distinct but morphologically similar neuronal populations affected differently by the natural scrapie genome, one undergoing dissolution by middle-age and one surviving and becoming hyperactive. This premature ageing is probably associated with a primary biochemical lesion affecting the rate of the axonal flow of neurosecretory vesicles and of their discharge at synaptic terminals. Possible metabolic and circulatory bases for such an anomaly are considered. The presence of neurophysin in the rostral and caudal adenohypophysis supports the view that vasopressin is acting directly as a trophic-hormone releasing factor, possibly for the quick release of adrenocorticotropic hormone and of growth hormone. The relation of neurophysin-rich aggregations in the neurohypophysis to Herring bodies and the turnover of neurosecretory material are discussed.

Ultrastructural comparisons of neurons of supraoptic and circularis nuclei in normal and dehydrated rats

A quantitative ultrastructural investigation was undertaken to compare the nucleus circularis (NC) and supraoptic nucleus (SON) of the rat both under normal and water-deprived conditions. NC was found to have dramatically more of its cells and membrane surface involved in direct soma-somatic contact than the SON. Water deprivation, even for one day, brought about a significant increase in both percentage of cells and membrane surface in contact in both nuclei, apparently by the retraction of fine glial processes from between the somata. The normal NC was made up of only one ultrastructurally identifiable cell type. The normal NC had no cells showing expanded endoplasmic reticulum, although these were seen following 5 days (but not 1 day) of water deprivation. The normal SON did have 4.4% of its cells showing expanded endoplasmic reticulum. This percentage significantly increased following water deprivation. The vesicle population per area of cytoplasm was very similar between the two normal nuclei. One day of water deprivation brought about a significant increase in less than 800 A vesicles in NC but not the SON. Five days of water deprivation resulted in a significant decrease in the lysosomal population per unit area in both nuclei. Vesicle changes have been discussed in relation to the volume changes in the cells.

Autolysis in axon terminals of a new neurohaemal organ in the cockroach Periplaneta americana

An ultrastructural investigation showed that there was a neurohaemal organ in the wall of the ampulla of the antennal pulsatile organ. The neurosecretory axon terminals occurred singly or in small groups, rather than closely packed together as in other neurohaemal organs. All axons contained the same type of neurosecretory granule. The granules had varying electron density and a diameter in the range 1000-2500 A. Some terminals contained small, elliptical electron-transparent vesicles and the axolemma was apposed to the stroma. Other terminals were large and enveloped by glial tissue and the contents of the terminals exhibited varying degrees of autolytic degeneration. Autolysis was characterized by the occurrence of dense bodies and multilaminate bodies which enclosed mitochondria and neurosecretory granules. It was suggested that the neurosecretory material affects antennal function.