Β-endorphin-immunoreactive perikarya appear to receive innervation from NPY-immunoreactive fiber varicosities in the human hypothalamus.

Morphological and pharmacological studies indicate that hypothalamic neuropeptide Y (NPY) and proopiomelanocortin (POMC) neurons communicate with each other in rats and regulate a variety of hypothalamic and extrahypothalamic functions. Indeed, electron microscopic studies revealed NPY-immunoreactive (NPI-IR) synapses on ß-endorphin-IR neurons in the hypothalamus. However, no such connections have been reported in humans. Here, we studied the putative NPY-ß-endorphin associations with high-resolution light microscopic double-label immunocytochemistry in the human hypothalamus. The majority of ß-endorphin-IR perikarya appear to be innervated by abutting NPY-IR fibers in the infundibulum/median eminence, receiving more than 6 contacts (38% of the counted neurons) or three to six contacts (42% of the counted neurons). The rest of the ß-endorphin-IR neurons are lightly innervated by NPY fibers (14%, one-three contacts) or do not receive any detectable NPY-IR axon varicosities (6% of the counted neurons). Since ß-endorphin is cleaved from the proopiomelanocortin (POMC) precursor, the NPY-ß-endorphin connections also provide the foundation for NPY-α-MSH and NPY-ACTH connections and their subsequent physiology. The close anatomical connections between NPY-IR nerve terminals and ß-endorphin-IR neurons reported herein may represent functional synapses and provide the foundation for NPY-stimulated ß-endorphin release. By interacting with ß-endorphin, NPY may have a more widespread regulatory capacity than acting alone on different neurotransmitter systems.

Anatomy and cytoarchitectonics of the human hypothalamus.

Due to the complexity of hypothalamic functions, the organization of the hypothalamus is extremely intricate. This relatively small brain area contains several nuclei, most of them are ill-defined regions without distinct boundaries; these nuclei are often connected with each other and other distant brain regions with similarly indistinct pathways. These hypothalamic centers control numerous key physiological functions including reproduction, growth, food intake, circadian rhythm, behavior, and autonomic balance via neural and endocrine signals. To understand the morphology of the hypothalamus is therefore extremely important, though it remains a stupendous task due to the complex organization of neuronal networks formed by the various neurotransmitter and neuromodulator systems.

Morphology and distribution of hypothalamic peptidergic systems.

Neuropeptides participate in the regulation of numerous hypothalamic functions that are aimed for sustaining the homeostasis of the organism. These neuropeptides can act in two different levels. They can influence the release of hormones from the adenohypophysis via the portal circulation; in addition, they can act as neurotransmitters/neuromodulators modulating the functioning of numerous hypothalamic neurotransmitter systems. Indeed, most of these peptidergic systems form a complex network in the infundibular and periventricular nuclei of the human hypothalamus, communicating with each other by synaptic connections that may control fundamental physiologic functions. In the present chapter, we provide an overview of the distribution of neuropeptides in the human hypothalamus using immunohistochemistry and high-resolution, three-dimensional mapping.

Substance P-Immunoreactive Fiber Varicosities Appear to Innervate Galaninergic Perikarya in the Human Hypothalamus.

Introduction: Substance P (SP) is a member of the tachykinin family. In the central nervous system, SP participates among others, in the regulation of pain, learning, memory, emotion, and sexual functions. In the periphery, SP affects the gastrointestinal, cardiovascular, and urinary systems. Galanin, similarly to SP, appears to be involved in wide range of physiologic functions, including cognition, waking and sleep, feeding, mood, blood pressure, reproduction, and development, where acts as a trophic factor. The similar distribution of SP-immunoreactive (SP-IR) fibers and galanin-IR perikarya in the human hypothalamus suggests functional interaction between these neuropeptides. Methods: We have utilized double-label immunohistochemistry to reveal these putative juxtapositions. Results: The majority of galanin-IR neurons receive contacting SP-IR fibers that often cover a significant area of the galaninergic perikarya forming multiple en passant type contacts. These SP-galanin juxtapositions are located mainly in the basal part of the infundibulum/median eminence, populating the basal periventricular region as well as the basal perifornical area. Discussion: The density and the morphology of these associations suggest that these contacts are functional synapses and therefore may represent the morphological substrate of the control of SP on multiple functions regulated/modulated by galanin. SP via galanin may modulate anterior pituitary hormone secretion, as contrary to SP, high density of galanin immunoreactivity is present in the median eminence, and by innervating galanin-IR neurons projecting to other parts of the brain, SP can modulate indirectly their activities. Impact statement The present study is the first describing juxtapositions between the substance P (SP)-immunoreactive (IR) and galanin-IR neurons in the human hypothalamus. These juxtapositions may be functional synapses and they may represent the morphological substrate of the control of SP on the galaninergic system. SP via galanin may modulate anterior pituitary hormone secretion, as contrary to SP, high density of galanin immunoreactivity is present in the median eminence. Galanin, released into the hypothalamo-hypophyseal circulation, can reach the anterior pituitary and function as a hypophysiotropic substance and regulates anterior pituitary hormone secretion. SP by innervating galanin-IR neurons, which project to other parts of the brain, can modulate indirectly their activities.

Thyrotropin-releasing hormone axonal varicosities appear to innervate dopaminergic neurons in the human hypothalamus.

Thyrotropin-releasing hormone (TRH) has a critical role in the central regulation of thyroid-stimulating hormone (TSH) from the anterior pituitary, and subsequently, thyroid hormone secretion from the thyroid gland. In addition to its role in the regulation of HPT axis, TRH is a potent regulator of prolactin (PRL) secretion by stimulating PRL secretion either directly from lactotrophs or indirectly via its action on the tuberoinfundibular dopamine (TIDA) neurons. In rodents, the TRH neurons which regulate TSH and thyroid hormone secretion, called hypophysiotropic TRH neurons, are in the medial subdivision of the parvicellular paraventricular nucleus (PVN). In humans, the PVN also contains a large population of TRH neurons, especially in its medial part, but the location of hypophysiotropic TRH neurons is not yet known. In addition to regulating TSH and PRL secretion, TRH also functions as a neurotransmitter/neuromodulator. In rodents and teleosts, TRH axons densely innervate TIDA neurons to inhibit tyrosine hydroxylase (TH) biosynthesis, neuronal firing, and dopamine turnover which may contribute to increasing PRL secretion. No such connections have been reported in humans, although dopaminergic neurons express TRH receptors and TRH also regulates PRL secretion. The objectives of this study were to map TRH-IR and TH-IR structures in the human hypothalamus with single-label light microscopic immunocytochemistry and study their interaction with double-label light microscopic immunocytochemistry. We show that TRH-IR nerve terminals densely surround TH-IR neurons (perikarya and dendrites) in the infundibulum of the human hypothalamus. The micrographs illustrating these juxtapositions were taken by Olympus BX45 microscope equipped with a digital camera and with 100X oil immersion objective. Composite images were created from the consecutive micrographs if the neurons were larger than the frame of the camera, using Adobe Photoshop software. As no gaps between TRH-IR and TH-IR elements were seen, these contacts may be functional synapses by which TRH regulates the activity of dopaminergic neurons and subsequently TSH and PRL secretion.

Presence of substance P positive terminals on hypothalamic somatostatinergic neurons in humans: the possible morphological substrate of the substance P-modulated growth hormone secretion.

Substance P is an undecapeptide affecting the gastrointestinal, cardiovascular, and urinary systems. In the central nervous system, substance P participates in the regulation of pain, learning, memory, and sexual homeostasis. In addition to these effects, previous papers provided solid evidence that substance P exhibits regulatory effects on growth. Indeed, our previous study revealed that growth hormone-releasing hormone (GHRH) neurons appear to be densely innervated by substance P fibers in humans. Since growth hormone secretion is regulated by the antagonistic actions of both GHRH and somatostatin, in the present paper we have examined the possibility that SP may also affect growth via the somatostatinergic system. Therefore, we have studied the putative presence of juxtapositions between the substance P-immunoreactive (IR) and somatostatinergic systems utilizing double label immunohistochemistry combined with high magnification light microscopy with oil immersion objective. In the present study, we have revealed a dense network of substance P-IR axonal varicosities contacting the majority of somatostatin-IR neurons in the human hypothalamus. Somatostatinergic perikarya are often covered by these fiber varicosities that frequently form basket-like encasements with multiple en passant type contacts, particularly in the infundibular nucleus/median eminence and in the basal periventricular area of the tuberal region. In addition, numerous substance-P-somatostatinergic juxtapositions can be found in the basal perifornical zone of the tuberal area. If these contacts are indeed functional synapses, they may represent the morphological substrate of the control of substance P on growth. Indeed, the frequency and density of these juxtapositions indicate that in addition to the regulatory action of substance P on GHRH secretion, substance P also influences growth by regulating hypothalamic somatostatinergic system via direct synaptic contacts.

Substance P appears to affect growth via growth hormone-releasing hormone (GHRH) neurons in the human hypothalamus.

Substance P is an eleven-amino acid neuropeptide (undecapeptide) with multiple effects on the gastrointestinal, cardiovascular, and urinary systems as well as complex central nervous system functions such as pain, learning, memory, and sexual homeostasis. Previous studies also revealed that substance P exhibits regulatory effects on growth possibly via influencing hypothalamic GHRH release in human. However, the morphological substrate of this phenomenon has not been elucidated yet. In the present study, we examined the putative presence of juxtapositions between the substance P- and GHRH-immunoreactive (IR) systems using double-label immunocytochemistry. High-magnification light microscopy with oil immersion was used to identify putative juxtapositions between these systems. Our studies revealed substance P-IR fiber network abutting on the surface of the majority of GHRH-immunoreactive neurons in the human hypothalamus. These fiber varicosities often cover a significant surface area on the GHRH-IR neurons, forming basket-like encasements with multiple en passant type contacts. The majority of these densely innervated GHRH-IR neurons were found in the infundibular nucleus/median eminence, while substance P-IR fibers often abut on the GHRH-IR neurons in the periventricular zone and basal perifornical area of the tuberal region and in the dorsomedial subdivision of the ventromedial nucleus. The posterior hypothalamus did not contain observable substance P-GHRH associations. The density and the morphology of these intimate associations suggest that substance P influences growth by regulating hypothalamic GHRH release by direct synaptic contacts.

Accessory mammillary bodies formed by the enlarged lateral mammillary nuclei: cytoarchitecture.

Post mortem examination of the hypothalamus of a 79-year-old woman, deceased in cardiac arrest without recorded neurological symptoms, revealed well-defined spherical protrusions located rostro-laterally to the mammillary bodies that appear to be regular size when compared to normal. Cytoarchitectonically, these accessory mammillary bodies are formed by the enlarged lateral mammillary nucleus that is normally a thin shell over the medial. The mammillary nuclei appear to function synergistically in memory formation in rats; however, the functional consequences of the present variation are difficult to interpret due to lack of human data. Most importantly, in addition to the possible functional consequences, lateral mammillary bodies can be falsely identified as various neuropathological processes of the basal diencephalon including gliomas; therefore, it is extremely important to disseminate this unique morphological variant among clinicians.

Corticotropin-releasing hormone (CRH)-immunoreactive (IR) axon varicosities target a subset of growth hormone-releasing hormone (GHRH)-IR neurons in the human hypothalamus.

It is a general consensus that stress is one of the major factors that suppresses growth. Previous studies revealed that the catecholaminergic and neuropeptide Y (NPY) systems, involved in the activation of stress-related neuronal circuits, influence growth hormone (GH)-release via modulating growth hormone-releasing hormone (GHRH) secretion. Indeed, catecholaminergic and NPY-immunoreactive (IR) axon varicosities abut on the surface of the GHRH neurons forming contacts. These juxtapositions appear to be real synapses and may represent the morphological substrate of the impact of stress on growth. In addition to catecholamines and NPY, there is a vast amount of evidence that corticotropin-releasing hormone (CRH), a major stress hormone, also influences GH secretion. Whether this modulatory effect is direct, or indirect, via the hypothalamic GHRH system, has not been elucidated yet. In the present study, we examined the possibility that CRH influences GH secretion via modulating the GHRH release by direct synaptic mechanisms. Since the verification of these synapses by electron microscopy is problematic in human due to the long post mortem time, in order to reveal the putative CRH-GHRH juxtapositions, light microscopic double label immunohistochemistry was utilized. In the infundibular nucleus, a subset (6%) of the GHRH perikarya received abutting CRH fiber varicosities forming multiple contacts while passing by. No gaps appeared between the contacting elements. The morphology of these CRH-GHRH juxtapositions suggests that, among other neurotransmitters/neuromodulators, CRH influences growth by modulating the hypothalamic GHRH secretion via direct synaptic mechanisms.

Catecholaminergic axonal varicosities appear to innervate growth hormone-releasing hormone-immunoreactive neurons in the human hypothalamus: the possible morphological substrate of the stress-suppressed growth.

CONTEXT: Stress is considered to be a major factor in the regulation of growth. Psychosocial dwarfism, characterized with short stature, delayed puberty, and depression, is typically preceded by psychological harassment or stressful environment. It has been observed that stress suppresses GH secretion, possibly via the attenuation of GHRH secretion. However, the exact mechanism of the impact of stress on growth has not been elucidated yet. OBJECTIVE: Our previous studies revealed intimate associations between neuropeptide Y (NPY)-immunoreactive (IR) axonal varicosities and GHRH-IR perikarya in the human hypothalamus. Because NPY is considered to be a stress molecule, NPY-GHRH juxtapositions may represent an important factor of stress-suppressed GHRH release. In addition to NPY, catecholamines are among the major markers of stress. Thus, in the present study, we examined the putative juxtapositions between the catecholaminergic tyrosine hydroxylase (TH)-/dopamine-ß-hydroxylase-/phenylethanolamine N-methyltransferase-IR and GHRH-IR neural elements in the human hypothalamus. To reveal these juxtapositions, double-label immunohistochemistry was used. RESULTS: Our findings revealed that the majority of the GHRH-IR perikarya formed intimate associations with TH-IR fiber varicosities. The majority of these juxtapositions were found in the infundibular nucleus/median eminence. CONCLUSIONS: The lack of phenylethanolamine N-methyltransferase-GHRH associations and the small number of dopamine-ß-hydroxylase-GHRH juxtapositions suggest that the vast majority of the observed TH-GHRH juxtapositions represent dopaminergic associations. The density of the abutting TH-IR fibers on the surface of the GHRH perikarya suggests that these juxtapositions may be functional synapses, and thus, in addition to NPY, catecholamines may regulate GHRH secretion via direct synaptic mechanisms.

A putative morphological substrate of the catecholamine-influenced neuropeptide Y (NPY) release in the human hypothalamus.

Neuropeptide Y (NPY) is a 36 amino acid peptide, which among others, plays a pivotal role in stress response. Although previous studies confirmed that NPY release is increased by stress in several species, the exact mechanism of the stress-induced NPY release has not been elucidated yet. In the present study, we examined, with morphological means, the possibility that catecholamines directly influence NPY release in the human hypothalamus. Since the use of electron microscopic techniques is virtually impossible in immunostained human samples due to the long post mortem time, double-label immunohistochemistry was utilised in order to reveal the putative catecholaminergic-NPY associations. The present study is the first to demonstrate juxtapositions between the catecholaminergic, tyrosine hydroxylase (TH)/dopamine-beta hydroxylase (DBH)-immunoreactive (IR) and NPY-IR neural elements in the human hypothalamus. These en passant type associations are most numerous in the infundibular and periventricular areas of the human diencephalon. Here, NPY-IR neurons often form several contacts with catecholaminergic fibre varicosities, without any observable gaps between the contacting elements, suggesting that these juxtapositions may represent functional synapses. The lack of phenylethanolamine N-methyltransferase (PNMT)-NPY juxtapositions and the relatively few observed DBH-NPY associations suggest that the vast majority of the observed TH-NPY juxtapositions represent dopaminergic synapses. Since catecholamines are known to be the crucial components of the stress response, the presence of direct, catecholaminergic (primarily dopaminergic)-NPY-IR synapses may explain the increased NPY release during stress. The released NPY in turn is believed to play an active role in the responses that are directed to maintain the homeostasis during stressful conditions.

Distribution and morphology of the juxtapositions between growth hormone-releasing hormone-(ghrh)-immunoreactive neuronal elements.

Previous studies revealed that growth hormone-releasing hormone (GHRH)-immunoreactive (IR) neurons form a circumscribed cell group in the basal infundibulum/median eminence of the human hypothalamus. GHRH from these neurons is released into the hypothalamo-hypophyseal portal circulatory system in a pulsatile manner. It is a common consensus that the pulsatile release of GHRH is the main driving force behind the pulsatile release of growth hormone (GH) and may contribute to the regulation of other hypothalamic functions. The pulsatile release of GHRH requires synchronized activity of GHRH-IR neurons. However, the morphological basis of this synchronization between the GHRH-IR neural elements has not been elucidated yet. Since the utilization of electron microscopy combined with immunohistochemistry is virtually impossible in the human brain due to the long post mortem period, immunohistochemistry, evaluated with oil immersion light microscopy, was used in order to reveal the associations between the GHRH elements. Numerous GHRH-GHRH juxtapositions have been detected in the infundibular area/median eminence, where GHRH-IR axonal varicosities often formed multiple contacts with GHRH-IR perikarya. Examination of these associations with high magnification oil immersion light microscopy revealed (1) axonal swellings at the site of the contacts and (2) no gaps between the contacting elements suggesting that these juxtapositions may be functional synapses. The large number of GHRH-GHRH juxtapositions in the infundibular area/median eminence suggests that these synapse-like structures may represent the morphological substrate of the synchronized activity of GHRH neurons that in turn may result in the pulsatile release of GHRH in human.

Morphology and distribution of neurons expressing serotonin 5-HT1A receptors in the rat hypothalamus and the surrounding diencephalic and telencephalic areas.

Disorders of serotonergic neurotransmission are involved in disturbances of numerous hypothalamic functions including circadian rhythm, mood, neuroendocrine functions, sleep and feeding. Among the serotonin receptors currently recognized, 5-HT(1A) receptors have received considerable attention due to their importance in the etiology of mood disorders. While previous studies have shown the presence of 5-HT(1A) receptors in several regions of the rat brain, there is no detailed map of the cellular distribution of 5-HT(1A) receptors in the rat diencephalon. In order to characterize the distribution and morphology of the neurons containing 5-HT(1A) receptors in the diencephalon and the adjacent telencephalic areas, single label immunohistochemistry was utilized. Large, multipolar, 5-HT(1A)-immunoreactive (IR) neurons were mainly detected in the magnocellular preoptic nucleus and in the nucleus of diagonal band of Broca, while the supraoptic nucleus contained mainly fusiform neurons. Medium-sized 5-HT(1A)-IR neurons with triangular or round-shaped somata were widely distributed in the diencephalon, populating the zona incerta, lateral hypothalamic area, anterior hypothalamic nucleus, substantia innominata, dorsomedial and premamillary nuclei, paraventricular nucleus and bed nucleus of stria terminalis. The present study provides schematic mapping of 5-HT(1A)-IR neurons in the rat diencephalon. In addition, the morphology of the detected 5-HT(1A)-IR neural elements is also described. Since rat is a widely used laboratory animal in pharmacological models of altered serotoninergic neurotransmission, detailed mapping of 5-HT(1A)-IR structures is pivotal for the neurochemical characterization of the neurons containing 5-HT(1A) receptors.

Topography and associations of leu-enkephalin and luteinizing hormone-releasing hormone neuronal systems in the human diencephalon.

Although several studies indicated that leu-enkephalin controls gonadal function, the morphological substrate of this modulation is unknown. To reveal potential interaction sites between leu-enkephalin and LH-releasing hormone (LHRH) in the hypothalamus, the distribution and connections of leu-enkephalin-immunoreactive (IR) and LHRH-IR systems were examined in the human diencephalon using double-label immunohistochemistry. First the leu-enkephalin-IR and LHRH-IR neural elements were mapped, then the maps of the two different neurotransmitter systems were superimposed unveiling the overlapping areas. The putative juxtapositions between leu-enkephalin-IR and LHRH-IR structures were revealed with double label immunocytochemistry. Close contacts were detected in the medial preoptic area and in the infundibulum/median eminence. In these areas, diaminobenzidine-silver-intensified, black leu-enkephalin-IR fibers abutted fusiform, brown, diaminobenzidine-labeled LHRH neurons often forming multiple contacts. Examination of semithin sections of these close associations with the aid of oil immersion revealed no cleft between the contacting LHRH-IR and leu-enkephalin-IR elements. Our findings indicate that the juxtapositions between LHRH-IR and leu enkephalin-IR neurons may be functional synapses forming the morphological substrate of the leu-enkephalin-modulated LHRH secretion in the human diencephalon. Moreover, the wide distribution of leu-enkephalin-IR elements suggests leu-enkephalin control of other diencephalic functions as well.