Colocalization of VIP with AVP in neurons of the human paraventricular, supraoptic and suprachiasmatic nucleus

Drastic decline in vasoactive intestinal peptide expression in the suprachiasmatic nucleus in obese mice on a long-term high-fat diet

The suprachiasmatic nucleus (SCN) is the main region for the regulation of circadian rhythms. Although the SCN contains a heterogeneous neurochemical phenotype with a wide variety of neuropeptides, a key role has been suggested for the vasoactive intestinal neuropeptide (VIP) as a modulator circadian, reproductive, and seasonal rhythms. VIP is a 28-amino acid polypeptide hormone that belongs to the secretin-glucagon peptide superfamily and shares 68 % homology with the pituitary adenylate cyclase-activating polypeptide (PACAP). VIP acts as an endogenous appetite inhibitor in the central nervous system, where it participates in the control of appetite and energy homeostasis. In recent years, significant efforts have been made to better understand the role of VIP in the regulation of appetite/satiety and energy balance. This study aimed to elucidate the long-term effect of an obesogenic diet on the distribution and expression pattern of VIP in the SCN and nucleus accumbens (NAc) of C57BL/6 mice. A total of 15 female C57BL/6J mice were used in this study. Female mice were fed ad libitum with water and, either a standard diet (SD) or a high-fat diet (HFD) to induce obesity. There were 7 female mice on the SD and 8 on the HFD. The duration of the experiment was 365 days. The morphological study was performed using immunohistochemistry and double immunofluorescence techniques to study the neurochemical profile of VIP neurons of the SCN of C57BL/6 mice. Our data show that HFD-fed mice gained weight and showed reduced VIP expression in neurons of the SCN and also in fibres located in the NAc. Moreover, we observed a loss of neuropeptide Y (NPY) expression in fibres surrounding the SCN. Our findings on VIP may contribute to the understanding of the pathophysiological mechanisms underlying obesity in regions associated with uncontrolled intake of high-fat foods and the reward system, thus facilitating the identification of novel therapeutic targets.

Vasopressin: a possible link between hypoxia and hypertension

Cardiovascular and respiratory diseases are frequently associated with transient and prolonged hypoxia, whereas hypoxia exerts pro-hypertensive effects, through stimulation of the sympathetic system and release of pressor endocrine factors. This review is focused on the role of arginine vasopressin (AVP) in dysregulation of the cardiovascular system during hypoxia associated with cardiovascular disorders. AVP is synthesized mainly in the neuroendocrine neurons of the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON), which send axons to the posterior pituitary and various regions of the central nervous system (CNS). Vasopressinergic neurons are innervated by multiple neuronal projections releasing several neurotransmitters and other regulatory molecules. AVP interacts with V1a, V1b and V2 receptors that are present in the brain and peripheral organs, including the heart, vessels, lungs, and kidneys. Release of vasopressin is intensified during hypernatremia, hypovolemia, inflammation, stress, pain, and hypoxia which frequently occur in cardiovascular patients, and blood AVP concentration is markedly elevated in cardiovascular diseases associated with hypoxemia. There is evidence that hypoxia stimulates AVP release through stimulation of chemoreceptors. It is suggested that acting in the carotid bodies, AVP may fine-tune respiratory and hemodynamic responses to hypoxia and that this effect is intensified in hypertension. There is also evidence that during hypoxia, augmentation of pro-hypertensive effects of vasopressin may result from inappropriate interaction of this hormone with other compounds regulating the cardiovascular system (catecholamines, angiotensins, natriuretic peptides, steroids, nitric oxide). In conclusion, current literature indicates that abnormal mutual interactions between hypoxia and vasopressin may significantly contribute to pathogenesis of hypertension.

Neuropeptides of the human magnocellular hypothalamus

Hypothalamic magnocellular nuclei with their large secretory neurons are unique and phylogenetically conserved brain structures involved in the continual regulation of important homeostatic and autonomous functions in vertebrate species. Both canonical and newly identified neuropeptides have a broad spectrum of physiological activity at the hypothalamic neuronal circuit level located within the supraoptic (SON) and paraventricular (PVN) nuclei. Magnocellular neurons express a variety of receptors for neuropeptides and neurotransmitters and therefore receive numerous excitatory and inhibitory inputs from important subcortical neural areas such as limbic and brainstem populations. These unique cells are also densely innervated by axons from other hypothalamic nuclei. The vast majority of neurochemical maps pertain to animal models, mainly the rodent hypothalamus, however accumulating preliminary anatomical structural studies have revealed the presence and distribution of several neuropeptides in the human magnocellular nuclei. This review presents a novel and comprehensive evidence based evaluation of neuropeptide expression in the human SON and PVN. Collectively this review aims to cast a new, medically oriented light on hypothalamic neuroanatomy and contribute to a better understanding of the mechanisms responsible for neuropeptide-related physiology and the nature of possible neuroendocrinal interactions between local regulatory pathways.

At Term, XmO and XpO Mouse Placentas Show Differences in Glucose Metabolism in the Trophectoderm-Derived Outer Zone

Genetic mouse model (39,XO) for human Turner Syndrome (45,XO) harboring either a single maternally inherited (Xm) or paternally inherited (Xp) chromosome show a pronounced difference in survival rate at term. However, a detailed comparison of XmO and XpO placentas to explain this difference is lacking. We aimed to investigate the morphological and molecular differences between XmO and XpO term mouse placentas. We observed that XpO placentas at term contained a significantly larger area of glycogen cells (GCs) in their outer zone, compared to XmO, XX, and XY placentas. In addition, the outer zone of XpO placentas showed higher expression levels of lactate dehydrogenase (Ldha) than XmO, XX, and XY placentas, suggestive of increased anaerobic glycolysis. In the labyrinth, we detected significantly lower expression level of trophectoderm (TE)-marker keratin 19 (Krt19) in XpO placentas than in XX placentas. The expression of other TE-markers was comparable as well as the area of TE-derived cells between XO and wild-type labyrinths. XpO placentas exhibited specific defects in the amount of GCs and glucose metabolism in the outer zone, suggestive of increased anaerobic glycolysis, as a consequence of having inherited a single Xp chromosome. In conclusion, the XpO genotype results in a more severe placental phenotype at term, with distinct abnormalities regarding glucose metabolism in the outer zone.

Single-Cell Transcriptional Analysis Reveals Novel Neuronal Phenotypes and Interaction Networks Involved in the Central Circadian Clock

Single-cell heterogeneity confounds efforts to understand how a population of cells organizes into cellular networks that underlie tissue-level function. This complexity is prominent in the mammalian suprachiasmatic nucleus (SCN). Here, individual neurons exhibit a remarkable amount of asynchronous behavior and transcriptional heterogeneity. However, SCN neurons are able to generate precisely coordinated synaptic and molecular outputs that synchronize the body to a common circadian cycle by organizing into cellular networks. To understand this emergent cellular network property, it is important to reconcile single-neuron heterogeneity with network organization. In light of recent studies suggesting that transcriptionally heterogeneous cells organize into distinct cellular phenotypes, we characterized the transcriptional, spatial, and functional organization of 352 SCN neurons from mice experiencing phase-shifts in their circadian cycle. Using the community structure detection method and multivariate analytical techniques, we identified previously undescribed neuronal phenotypes that are likely to participate in regulatory networks with known SCN cell types. Based on the newly discovered neuronal phenotypes, we developed a data-driven neuronal network structure in which multiple cell types interact through known synaptic and paracrine signaling mechanisms. These results provide a basis from which to interpret the functional variability of SCN neurons and describe methodologies toward understanding how a population of heterogeneous single cells organizes into cellular networks that underlie tissue-level function.

Efferent projections of the suprachiasmatic nucleus based on the distribution of vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP) immunoreactive fibers in the hypothalamus of Sapajus apella

The suprachiasmatic nucleus (SCN), which is considered to be the master circadian clock in mammals, establishes biological rhythms of approximately 24 h that several organs exhibit. One aspect relevant to the study of the neurofunctional features of biological rhythmicity is the identification of communication pathways between the SCN and other brain areas. As a result, SCN efferent projections have been investigated in several species, including rodents and a few primates. The fibers originating from the two main intrinsic fiber subpopulations, one producing vasoactive intestinal peptide (VIP) and the other producing arginine vasopressin (AVP), exhibit morphological traits that distinguish them from fibers that originate from other brain areas. This distinction provides a parameter to study SCN efferent projections. In this study, we mapped VIP (VIP-ir) and AVP (AVP-ir) immunoreactive (ir) fibers and endings in the hypothalamus of the primate Sapajus apella via immunohistochemical and morphologic study. Regarding the fiber distribution pattern, AVP-ir and VIP-ir fibers were identified in regions of the tuberal hypothalamic area, retrochiasmatic area, lateral hypothalamic area, and anterior hypothalamic area. VIP-ir and AVP-ir fibers coexisted in several hypothalamic areas; however, AVP-ir fibers were predominant over VIP-ir fibers in the posterior hypothalamus and medial periventricular area. This distribution pattern and the receiving hypothalamic areas of the VIP-ir and AVP-ir fibers, which shared similar morphological features with those found in SCN, were similar to the patterns observed in diurnal and nocturnal animals. This finding supports the conservative nature of this feature among different species. Morphometric analysis of SCN intrinsic neurons indicated homogeneity in the size of VIP-ir neurons in the SCN ventral portion and heterogeneity in the size of two subpopulations of AVP-ir neurons in the SCN dorsal portion. The distribution of fibers and morphometric features of these neuronal populations are described and compared with those of other species in the present study.

Alterations of melatonin receptors MT1 and MT2 in the hypothalamic suprachiasmatic nucleus during depression

BACKGROUND

The pineal hormone melatonin regulates circadian rhythms, largely by feedback on the central biological clock of the brain, the hypothalamic suprachiasmatic nucleus (SCN). This feedback is mediated by the melatonin receptors, melatonin receptor 1 (MT1) and melatonin receptor 2 (MT2). The circadian system may play a role in the pathophysiology of mood disorders, and indeed, melatonin-receptor agonists are considered a potential therapy for depression.

METHOD

In order to investigate melatonin receptors in the SCN during depression, and their relationship to the major neuropeptides in the SCN, vasopressin (AVP) and vasoactive intestinal peptide (VIP), we studied the SCN in 14 depressed patients (five major depression and nine bipolar disorder) and 14 matched controls by immunocytochemistry.

RESULTS

We show here that hypothalamic MT2 receptor immunoreactivity was limited to SCN, the supraoptic nucleus and paraventricular nucleus. We found that numbers of MT1-immunoreactive (MT1-ir) cells and AVP and/or VIP-ir cells were increased in the central SCN in depression, but numbers of MT2-ir cells were not altered. Moreover, the number of MT1-ir cells, but not MT2-ir cells was negatively correlated with age at onset of depression, while positively correlated with disease duration. CONCLUSION AND LIMITATIONS: Although every post-mortem study has limitations, MT1 receptors appeared specifically increased in the SCN of depressed patients, and may increase during the course of the disease. These changes may be involved in the circadian disorders and contribute to the efficacy of MT agonists or melatonin in depression. Moreover, we suggest that melatonin receptor agonists for depression should be targeted towards the MT1 receptor selectively.

Suprachiasmatic nucleus neuropeptide expression in patients with Huntington's Disease

STUDY OBJECTIVE

To study whether sleep and circadian rhythm disturbances in patients with Huntington's disease (HD) arise from dysfunction of the body's master clock, the hypothalamic suprachiasmatic nucleus.

DESIGN

Postmortem cohort study.

PATIENTS

Eight patients with HD and eight control subjects matched for sex, age, clock time and month of death, postmortem delay, and fixation time of paraffin-embedded hypothalamic tissue.

MEASUREMENTS AND RESULTS

Using postmortem paraffin-embedded tissue, we assessed the functional integrity of the suprachiasmatic nucleus in patients with HD and control subjects by determining the expression of two major regulatory neuropeptides, vasoactive intestinal polypeptide and arginine vasopressin. Additionally, we studied melatonin 1 and 2 receptor expression. Compared with control subjects, the suprachiasmatic nucleus contained 85% fewer neurons immunoreactive for vasoactive intestinal polypeptide and 33% fewer neurons for arginine vasopressin in patients with HD (P = 0.002 and P = 0.027). The total amount of vasoactive intestinal polypeptide and arginine vasopressin messenger RNA was unchanged. No change was observed in the number of melatonin 1 or 2 receptor immunoreactive neurons.

CONCLUSIONS

These findings indicate posttranscriptional neuropeptide changes in the suprachiasmatic nucleus of patients with HD, and suggest that sleep and circadian rhythm disorders in these patients may at least partly arise from suprachiasmatic nucleus dysfunction.

Integration of the circadian and stress systems: influence of neuropeptides and implications for alcohol consumption

Disruptions in circadian rhythm and stress reactivity are associated with risks of developing neuropsychiatric disorders. The circadian system is organised in a hierarchical manner, whereby the master clock is located at the suprachiasmatic nucleus, a highly conserved brain region that coordinates the oscillations of peripheral clocks. Exposure to psychological stress leads to activation of the hypothalamic-pituitary-adrenal axis. There is growing evidence supporting the interactions between the circadian and stress systems. Anatomically, the circadian and stress signals converge at the paraventricular nucleus (PVN) in the hypothalamus. Genes that are involved in the operation of the circadian and stress systems, including Clock, Period and CRH are expressed in the PVN. In addition, several neuropeptides, including arginin-vasopressin, vasoactive intestinal polypeptide, pituitary adenylate cyclase-activating polypeptide and the neurotransmitter gamma-aminobutyric acid, are present in the PVN. In this review, we will discuss the interaction of circadian genes and stress-response genes at the molecular, neurotransmission and behavioural levels. We will place particular emphasis on the role of neuropeptides in mediating this interaction.

Circadian entrainment and its role in depression: a mechanistic review

The natural rotation of the earth generates an environmental day-night cycle that repeats every 24 h. This daily transition from dawn to dusk provides one of the most important time cues to which the majority of organisms synchronise their activity. Under these conditions, natural light, a photic stimulus, provides the principal entraining cue. In mammals, an endogenous circadian pacemaker located within the suprachiasmatic nucleus (SCN) of the hypothalamus acts as a coordinating centre to align physiological activity with the environmental light-dark cycle. However, the SCN also receives regulatory input from a number of behavioural, non-photic, cues such as physical activity, social interactions and feeding routines. The unique ability of the SCN to integrate both photic and non-photic cues allows it to generate a rhythm that is tailored to the individual and entrained to the environment. Here, we review the key neurotransmitter systems involved in both photic and non-photic transmission to the SCN and their interactions that assist in generating an entrained output rhythm. We also consider the impact on health of a desynchronised circadian system with a focus on depressive affective disorders and current therapies aimed at manipulating the relationship between photic and non-photic SCN regulators.

Neuroanatomy of the extended circadian rhythm system

The suprachiasmatic nucleus (SCN), site of the primary clock in the circadian rhythm system, has three major afferent connections. The most important consists of a retinohypothalamic projection through which photic information, received by classical rod/cone photoreceptors and intrinsically photoreceptive retinal ganglion cells, gains access to the clock. This information influences phase and period of circadian rhythms. The two other robust afferent projections are the median raphe serotonergic pathway and the geniculohypothalamic (GHT), NPY-containing pathway from the thalamic intergeniculate leaflet (IGL). Beyond this simple framework, the number of anatomical routes that could theoretically be involved in rhythm regulation is enormous, with the SCN projecting to 15 regions and being directly innervated by about 35. If multisynaptic afferents to the SCN are included, the number expands to approximately brain 85 areas providing input to the SCN. The IGL, a known contributor to circadian rhythm regulation, has a still greater level of complexity. This nucleus connects abundantly throughout the brain (to approximately 100 regions) by pathways that are largely bilateral and reciprocal. Few of these sites have been evaluated for their contributions to circadian rhythm regulation, although most have a theoretical possibility of doing so via the GHT. The anatomy of IGL connections suggests that one of its functions may be regulation of eye movements during sleep. Together, neural circuits of the SCN and IGL are complex and interconnected. As yet, few have been tested with respect to their involvement in rhythm regulation.

Pudendal afferent innervation of the guinea pig external anal sphincter

BACKGROUND

  Sensory nerves to the external anal sphincter (EAS) contribute to mechanisms promoting continence and defecation, yet we know little about their function. We investigated the function of pudendal mechanoreceptors to the guinea pig EAS.

METHODS

Extracellular recordings from pudendal nerve branches to 14 EAS preparations, in vitro, were used to characterize extrinsic primary afferent nerve endings activated by circumferential distension.

KEY RESULTS

All 42 pudendal nerve afferents were silent under non-distended conditions. Thirty-three of 42 afferents had slowly adapting, low-threshold responses to circumferential stretch that correlated with stretch length (R(2) = 0.40, P<0.001). Twenty of 20 slowly adapting afferents reduced firing when stretch was maintained for 60 s (P<0.0001). They had low thresholds to von Frey hairs (0.1-0.5mN). Firing frequency correlated with degree of compression (R(2) =0.40, P<0.0001). Nine of 42 afferents had rapidly adapting responses at the onset/offset of isometric stretch. During ramp stretch, small vibrations from the stepper motor evoked rapid bursts of firing at frequencies up to 200Hz. Instantaneous frequency was unrelated to either the rate or degree of stretch. Rapidly adapting units had low thresholds (0.1-0.2mN) to von Frey hairs and small punctate mechanotransduction sites. Responses to von Frey hair compression were also rapidly adapting, and instantaneous frequency was unrelated to the degree of compression.

CONCLUSIONS & INFERENCES

The EAS has two functional classes of mechanoreceptors: slowly adapting low-threshold and rapidly adapting low-threshold mechanoreceptors. These two classes of afferents are likely to be involved in the maintenance of continence, and the process of defecation.

Histaminergic and cholinergic neuron systems in the impairment of human thermoregulation during motion sickness

Motion sickness (MS) exaggerates body cooling during cold-water immersion. The aim of the present study was to investigate whether such MS-induced predisposition to hypothermia is influenced by two anti-MS drugs: the histamine-receptor blocker dimenhydrinate (DMH) and the muscarine-receptor blocker scopolamine (Scop). Nine healthy male subjects were immersed in 15 degrees C water for a maximum of 90min in five conditions: (1) control (CN): no medication, no MS provocation; (2) MS-control (MS-CN): no medication, MS provocation; (3) MS-placebo (MS-P): placebo DMH and placebo Scop, MS provocation; (4) MS-DMH: DMH and placebo Scop, MS provocation; (5) MS-Scop: Scop and placebo DMH, MS provocation. MS was induced by use of a rotating chair. Throughout the experiments rectal temperature (T(re)), the difference in temperature between the non-immersed right forearm and third finger (T(ff)) as an index of peripheral vasoconstriction, and oxygen uptake (VO(2)) as a measure of shivering thermogenesis, were recorded. DMH and Scop were similarly efficacious in ameliorating nausea. The fall in T(re) was greater in the MS-CN and MS-P conditions than in the CN condition. DMH, but not Scop, prevented the MS-induced increase in body-core cooling. MS attenuated the cold-induced vasoconstriction, an effect which was fully prevented by DMH but only partially by Scop. MS provocation did not affect VO(2) in any condition. The results suggest that the MS-induced predisposition to hypothermia is predominantly mediated by histaminergic mechanisms and that DMH might be useful in conjunction with maritime accidents or other scenarios where exposure to cold and MS are imminent features.

Vasoactive intestinal polypeptide immunoreactivity in the human cerebellum: qualitative and quantitative analyses

Although autoradiographic, reverse transcription-polymerase chain reaction and immunohistochemical studies have demonstrated receptors for vasoactive intestinal polypeptide (VIP) in the cerebellum of various species, immunohistochemistry has never shown immunoreactivity for VIP within cerebellar neuronal bodies and processes. The present study aimed to ascertain whether VIP immunoreactivity really does exist in the human cerebellum by making a systematic analysis of samples removed post-mortem from all of the cerebellar lobes. The study was carried out using light microscopy immunohistochemical techniques based on a set of four different antibodies (three polyclonal and one monoclonal) against VIP, carefully selected on the basis of control tests performed on human colon. All of the antibodies used showed VIP-immunoreactive neuronal bodies and processes distributed in the cerebellar cortex and subjacent white matter of all of the cerebellum lobes, having similar qualitative patterns of distribution. Immunoreactive neurons included subpopulations of the main neuron types of the cortex. Statistical analysis of the quantitative data on the VIP immunoreactivity revealed by the different antibodies in the different cerebellar lobes did not demonstrate any significant differences. In conclusion, using four different anti-VIP antibodies, the first evidence of VIP immunoreactivity is herein supplied in the human post-mortem cerebellum, with similar qualitative/quantitative patterns of distribution among the different cerebellum lobes. Owing to the function performed by VIP as a neurotransmitter/neuromodulator, it is a candidate for a role in intrinsic and extrinsic (projective) circuits of the cerebellum, in agreement with previous demonstrations of receptors for VIP in the cerebellar cortex and nuclei. As VIP signalling pathways are implicated in the regulation of cognitive and psychic functions, cerebral blood flow and metabolism, processes of histomorphogenesis, differentiation and outgrowth of nervous tissues, the results of this study could be applied to clinical neurology and psychiatry, opening new perspectives for the interpretation of neurodevelopment disorders and development of new therapeutic strategies in cerebellar diseases.

Neurotransmitters of the suprachiasmatic nuclei

There has been extensive research in the recent past looking into the molecular basis and mechanisms of the biological clock, situated in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. Neurotransmitters are a very important component of SCN function. Thorough knowledge of neurotransmitters is not only essential for the understanding of the clock but also for the successful manipulation of the clock with experimental chemicals and therapeutical drugs. This article reviews the current knowledge about neurotransmitters in the SCN, including neurotransmitters that have been identified only recently. An attempt was made to describe the neurotransmitters and hormonal/diffusible signals of the SCN efference, which are necessary for the master clock to exert its overt function. The expression of robust circadian rhythms depends on the integrity of the biological clock and on the integration of thousands of individual cellular clocks found in the clock. Neurotransmitters are required at all levels, at the input, in the clock itself, and in its efferent output for the normal function of the clock. The relationship between neurotransmitter function and gene expression is also discussed because clock gene transcription forms the molecular basis of the clock and its working.

Pin1 protein associates with neuronal lipofuscin: potential consequences in age-related neurodegeneration

Pin1 protein is a peptidyl-prolyl cis-trans isomerase that modulates the activity of a range of proteins involved in cell function. We and others have demonstrated neuronal Pin1 deficits in Alzheimer's disease (AD) and have shown similar deficits in frontotemporal dementia and in aging. Pin1 may, in fact, be a susceptibility factor; others have shown that Pin1 depletion causes apoptosis in HeLa cells. Further, patterns of AD pathology correlate with regions of lower Pin1 expression in normal human brain; Pin1 knockout mice suffer neurodegeneration; and Pin1 can ameliorate p-tau pathology by isomerizing p-tau, facilitating its trans-specific dephosphorylation and restoring its ability to bind to and restabilize microtubules and thence cytoskeletal integrity. Here, we report a novel localization of high levels of Pin1 with lipofuscin in aging neurons. This association could progressively drain available Pin1 and be deleterious to neuronal function during aging. We also show that Pin1 associates with lipofuscin when lipofuscin accumulations become marked and correlate with susceptibility to neurodegenerative disease. Our data are consistent with the possibility that neuronal Pin1 deficits may be a contributory factor in neurodegeneration associated with aging.

Beta-protein/A4 deposits are not associated with hyperphosphorylated tau in somatostatin neurons in the hypothalamus of Alzheimer's disease patients

With respect to the pathogenesis of Alzheimer's disease (AD), it has been hypothesized that amorphous plaques containing beta-protein/A4 (Abeta) would locally induce cytoskeletal changes, and that neurons affected by neurofibrillary tangles (NFTs) lose their neuropeptide concentration and eventually die. To test this presumed cascade of events, the hypothalami of 14 non-demented subjects (Braak 0-III) and 28 AD patients (Braak IV-VI) aged 40-98 years were selected. The subject of our study was the nucleus tuberalis lateralis (NTL), which harbors a subpopulation of somatostatinergic neurons with extensive intrinsic interconnectivity. We used Gallyas silver staining, Congo staining, single- and double-staining with monoclonal antibody AT8 and polyclonal antibody anti-Abeta, and double-immunolabeling with AT8 and anti-somatostatin(1-12) with the following results: (1) Significant amounts of silver-staining NFTs were present in only three AD patients. (2) High densities of AT8-stained cytoskeletal changes were mainly found in aged, demented patients. (3) In contrast, large amounts of Abeta deposits were mainly observed in young and middle-aged (40-59 years) AD patients, and were very low or absent mainly in the older non-demented subjects and in AD patients. (4) Reduced anti-somatostatin staining was observed in the NTL of most AD patients, but anti-somatostatin/AT8 double-stained neurons were found virtually exclusively in aged AD patients. Thus, the occurrence of Abeta deposits and hyperphosphorylated tau formation in somatostatin cells are basically independent events, while decreased somatostatin staining only partly goes together with cytoskeletal changes in somatostatin cells in the NTL of AD patients. These observations cannot be explained by the amyloid cascade hypothesis.

Exposure of nuclear antigens in formalin-fixed, paraffin-embedded necropsy human spinal cord tissue: Detection of NeuN

Immunohistochemical and immunofluorescence staining approaches are powerful tools for characterization of the endogenous protein expression and subcellular compartmentalization. However, several technical problems hamper identification of low-abundance nuclear proteins in archival formalin-fixed, paraffin-embedded human neural tissue. These include loss of protein antigenicity during tissue fixation and processing, and intrinsic auto-fluorescence associated with the tissue related to its fixation and the presence of lipofuscin. We evaluated several antigen retrieval methods to establish a strategy for detection of neuronal nuclear proteins in human spinal cord formalin-fixed, paraffin-embedded tissue. Thus, using immunostaining of the neuron-specific nuclear protein NeuN as the outcome measure, we found that heating tissue sections in an alkaline pH buffer unmasked protein epitopes most effectively. Moreover, staining by immunohistochemistry with diaminobenzidine tetrahydrochloride chromagen was superior to immunofluorescence labeling, likely due to the signal amplification steps included in the former approach. Auto-fluorescence in the tissue sections can be effectively reduced, but a sufficient fluorescence signal associated with specific antibody labeling could not be detected above this background for NeuN in the nucleus.

Neurotensin expressing neurons developed earlier than vasoactive intestinal polypeptide and vasopressin expressing neurons in the human suprachiasmatic nucleus

Development of neurotensin (NT), vasoactive intestinal polypeptide (VIP), vasopressin (AVP) and neuropeptide-Y (NPY) expressing neurons was investigated in the human fetal suprachiasmatic nucleus of nine subjects ranging from 20-40 weeks of gestation using immunocytochemistry and morphometry. Results obtained showed that NT expressing neurons developed earlier than VIP, AVP and NPY expressing neurons. Consistent with results obtained from animal studies, we also found VIP expressing neurons were born earlier than AVP expressing neurons. Whether the NT expressing neurons play a role in generating circadian rhythms in the early life of humans needs to be further investigated.

A novel method for simultaneous anterograde and retrograde labeling of spinal cord motor tracts in the same animal

Examination of repaired spinal cord tracts has usually required separate groups of animals for anterograde and retrograde tracing owing to the incompatibility of techniques such as tissue fixation. However, anterograde and retrograde labeling of different animals subjected to the same repair may not allow accurate examination of that repair strategy because widely variable results can occur in animals subjected to the same strategy. We have developed a reliable method of labeling spinal cord motor tracts bidirectionally in the same animal using DiI, a lipophilic dye, to anterogradely label the corticospinal tract and Fluoro-Gold (FG) to retrogradely label cortical and brainstem neurons of several spinal cord motor tracts in normal and injured adult rats. Other tracer combinations (lipophilic dyes or fluorescent dextrans) were also investigated but were less effective. We also developed methods to minimize autofluorescence with the DiI/FG technique, and found that the DiI/FG technique is compatible with decalcification and immunohistochemistry for several markers relevant for studies of spinal cord regeneration. Thus, the use of anterograde DiI and retrograde FG is a novel technique for bidirectional labeling of the motor tracts of the adult spinal cord with fluorescent tracers and should be useful for demonstrating neurite regeneration in studies of spinal cord repair.(J Histochem Cytochem 49:1111-1122, 2001)

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.