Axons containing neuropeptide Y innervate arginine vasopressin-containing neurons in the rat paraventricular nucleus

Summary Synaptic connections between neurons immunoreactive for arginine vasopressin (AVP) and axon terminals immunoreactive for neuropeptide Y (NPY) were found in the magnocellular part of the paraventricular nucleus (PVN) in the rat hypothalamus. In pre-embedding double immunolabeling, NPY axon terminals labeled with diamin-obenzidine (DAB) reaction product established synaptic junctions on the perikarya and neuronal processes of AVP neurons labeled with silver-gold particles. Ultrastructural morphology of the neurons was more suitably preserved by a combination of pre- and post-embedding procedures. The presynaptic NPY terminals contained many small clear vesicles and a few cored vesicles, and DAB chromogen (immunoreaction product) was located on the surface of the vesicular profiles and on the core. The postsynaptic AVP neurons possessed many large secretory granules labeled with gold particles. At the synaptic junctions, small clear vesicles were accumulated at the presynaptic membrane, and the postsynaptic membrane was coated with a dense accumulation of fine electron dense particles. The perikarya also received synapses made by immuno-negative axon terminals containing many small clear vesicles and a few cored vesicles. These terminals were found more frequently than those containing NPY.     

Axons containing neuropeptide Y innervate arginine vasopressin-containing neurons in the rat paraventricular nucleus. Dual electron microscopic immunolabeling

Synaptic connections between neurons immunoreactive for arginine vasopressin (AVP) and axon terminals immunoreactive for neuropeptide Y (NPY) were found in the magnocellular part of the paraventricular nucleus (PVN) in the rat hypothalamus. In pre-embedding double immunolabeling, NPY axon terminals labeled with diaminobenzidine (DAB) reaction product established synaptic junctions on the perikarya and neuronal processes of AVP neurons labeled with silver-gold particles. Ultrastructural morphology of the neurons was more suitably preserved by a combination of pre- and post-embedding procedures. The presynaptic NPY terminals contained many small clear vesicles and a few cored vesicles, and DAB chromogen (immunoreaction product) was located on the surface of the vesicular profiles and on the core. The postsynaptic AVP neurons possessed many large secretory granules labeled with gold particles. At the synaptic junctions, small clear vesicles were accumulated at the presynaptic membrane, and the postsynaptic membrane was coated with a dense accumulation of fine electron dense particles. The perikarya also received synapses made by immuno-negative axon terminals containing many small clear vesicles and a few cored vesicles. These terminals were found more frequently than those containing NPY.     

Neurotensin immunoreactivity in the central nucleus of the rat amygdala: an ultrastructural approach

Neurotensin (NT) was demonstrated in the central nucleus of the rat amygdala (CNA) using a modification of the avidin-biotin complex immunohistochemical technique. Electron-dense reaction product (particles were 15-25 nm in diameter) was localized in perikarya, dendrites, axons, and axon terminals. It was found also associated with profiles of rough endoplasmic reticulum, mitochondria, microtubules, and small agranular as well as large granular vesicles. In distal dendrites, the reaction product was associated with microtubules, vesicles, and postsynaptic densities. Axon terminals of three types formed synaptic contracts with NT-immunoreactive neurons in the CNA: one was characterized by numerous round or oval agranular vesicles, the second by numerous pleomorphic vesicles, and the third by agranular vesicles that were loosely distributed and pleomorphic. All three types formed symmetric axosomatic and asymmetric axodendritic contacts. NT-immunoreactive axon terminals containing small round agranular vesicles stood out clearly from the intermingling profiles of immunonegative structures. We found numerous glomeruli, each consisting of a central NT-immunoreactive dendrite surrounded by all three types of axon terminals. We observed that some NT-immunoreactive terminals formed symmetric axoaxonal contacts with each other, providing evidence for the presence of local NT-to-NT circuits, whereas many others synapsed with axon terminals devoid of NT immunoreactivity.     

大鼠孤束核内脑啡肽样免疫反应阳性结构及其轴突终末的突触联系

本文应用免疫细胞化学方法在光镜与电镜下观察了大鼠孤束核内脑啡肽样免疫反应（ＥＮＫ－ＬＩ）阳性结构的分布特征和ＥＮＫ－ＬＩ轴突终末的突触联系以及非突触性关系。结果表明：（１）经秋水仙素处理的大鼠,其孤束核内有许多ＥＮＫ－ＬＩ胞体的分布;而未经秋水仙素处理的大鼠,其孤束核内可见密集的ＥＮＫ－ＬＩ纤维与终末;ＥＮＫ－ＬＩ胞体、纤维和终末主要分布于锥体交叉平面至闩平面的孤束核内侧亚核与胶状质亚核。（２）ＥＮＫ－ＬＩ阳性产物主要定位于小圆形清亮囊泡外表面、大颗粒囊泡内和线粒体外表面等处。（３）ＥＮＫ－ＬＩ轴突终末主要与阴性树突形成轴－树突触。（４）阴性轴突终末终止于ＥＮＫ－ＬＩ轴突终末上,形成轴－轴突触。（５）ＥＮＫ－ＬＩ轴突终末与阴性轴突终末形成非突触性的轴－轴并靠。以上结果提示孤束核内的ＥＮＫ－ＬＩ神经成分主要通过突触后机制、也不排除突触前作用,参与孤束核中内脏信息的整合过程,而且这一作用又受到非ＥＮＫ－ＬＩ神经成分的调控。     

The distribution of neuropeptide Y and dynorphin immunoreactivity in the brain and pituitary gland of the platyfish,Xiphophorus maculatus,from birth to sexual maturity

Summary Immunoreactive neuropeptide Y and dynorphin have been localized in the brain and pituitary gland of the platyfish, Xiphophorus maculatus, at different ages and stages of development from birth to sexual maturity. Immunoreactive neuropeptide Y was found in perikarya and tracts of the nucleus olfactoretinalis, telencephalon, ventral tegmentum and in the neurohypophysis and in the three regions of the adenohypophysis. Immunoreactive dynorphin was found in nerve tracts in the olfactory bulb and in cells of the pars intermedia and the rostral pars distalis of the pituitary gland.     

Distribution of peptidyl-glycine alpha-amidating monooxygenase immunoreactivity in the brain,pituitary and islet organ of the anglerfish (Lophius americanus)

Peptidyl-glycine alpha-amidating monooxygenase (PAM; EC 1.14.17.3) is an enzyme that catalyzes conversion of glycine-extended peptides to alpha-amidated bioactive peptides. Two peptides that are processed at their carboxyl-termini by this enzyme are neuropeptide Y and anglerfish peptide Y, both of which possess a C-terminal glycine that is used as a substrate for amidation. Results from previous reports have demonstrated that neuropeptide Y-like and anglerfish peptide Y-like immunoreactivities are present in the brain of anglerfish (Lophius americanus). Furthermore, neuropeptide Y-like peptides, namely anglerfish peptide Y and anglerfish peptide YG (the homologues of pancreatic polypeptide) are present in the islet organ of this species. Neuropeptide Y has also been localized in the anterior, intermediated and posterior lobes of the pituitary gland in a variety of species. In order to learn more about the distribution of the enzyme responsible for alpha amidation of these peptides in the brain and pituitary and to specifically investigate the relationship of this enzyme to peptide synthesizing endocrine cells of the anglerfish islet, we performed an immunohistochemical study using several antisera generated against different peptide sequences of the enzyme. PAM antisera labeled cells in the islet organ, pituitary and brain, and fibers in the brain and pituitary gland. The PAM staining pattern in the brain was remarkably similar to the distribution of neuropeptide Y immunoreactivity reported previously. Clusters of cells adjacent to vessels in the anterior pituitary displayed punctate PAM immunoreactivity while varicose fibers were observed in the pituitary stalk and neurohypophysis. Endocrine cells of the islet organ were differentially labeled with different PAM antisera. Comparison of the staining patterns of insulin, glucagon, and anglerfish peptide Y in the islet organ to PAM immunoreactivity suggests a distribution of forms of PAM enzyme in insulin and anglerfish peptide Y-containing cells, but no overlap with glucagon-producing cells. The results also indicate that PAM immunoreactivity is widely distributed in the brain, pituitary and islet organ of anglerfish in cells that contain peptides that require presence of a C-terminal glycine for amidation.     

Ultrastructural parameters of GABA-ergic and non-GABA-ergic synaptic contacts on neurons of the catsubstantia nigra

Nigrothalamic neurons were identified in the reticular part of thesubstantia nigra using labelling by the retrograde axonal transport of horseradish peroxidase. Nine parameters of the synaptic contacts (n=195) were analyzed, including the size and shape of terminals and size and type of synaptic vesicies. Sixty-six percent of axon terminals studied formed symmetric contacts and contained large polymorphic vesicles (group I). Two-thirds of these synapses were located on the distal dendrites, while one-third was distributed on the perikarya and proximal dendrites. Synapses of group II (29% of all synapses analyzed) exhibited asymmetric contacts and contained round agranular vesicles. Among these synapses, 79% were located on the distal dendrites, 19% were located on the proximal dendrites, and only 2% were located on the neuronal perikarya. Axon terminals of group III (5% of total population) exhibited symmetric contact and contained small polymorphic vesicles. High-resolution immunogold EM histochemistry indicated that 63% of the group-I axon terminals were GABA-positive. The majority of synapses on the labelled nigrothalamic neurons (21 contacts of 25) belonged to group I. Among these 21 synapses, 19 were axo-somatic and mostly GABA-positive. Within group II, 30% of synapses showed slightly expressed GABA-positivity.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 147–157, March–April, 1995.     

Ultrastructural study of neurotensin immunoreactivity in the superficial laminae of the dorsal horn of the rat

Neurotensin immunoreactivity was identified in cell bodies, dendrites, spines, axons, terminals and varicosities in superficial laminae of rat spinal cord with the electron microscope. Unlabeled terminals synapsed with neurotensin-immunoreactive cell bodies, dendrites and spines. Presynaptic terminals contained round or pleomorphic vesicles and generally made symmetrical contacts with medium-sized neurotensin-containing dendrites in outer lamina II, and asymmetrical or symmetrical contacts with large and small dendrites and spines in inner lamina II. Neurotensin immunoreactive axons were unmyelinated, and their terminals were presynaptic to unlabeled dendrites and spines in laminae I and II. Terminals contained small, round, clear vesciles (31 nm) and occasional large granular vesicles (78 nm). Contacts in outer lamina II were evenly distributed among dendrites of various sizes and spines, whereas the majority of labeled terminals in inner lamina II made contacts onto small dendrites and spines. These findings indicate that neurotensin effects in rat spinal cord are mediated by axodendritic synapses, and that neurotensin cells at the inner and outer borders of lamina II contact dendrites of efferent neurons or other interneurons in the dorsal horn.     

Ultrastructural localization of RFamide-like peptides in neuronal dense-cored vesicles in the peduncle of Hydra

The presence of Arg-Phe-amide (RFamide)-like peptides in dense-cored vesicles in neurons of the peduncle of Hydra was demonstrated by immunogold electron microscopy. Thin sections of Lowicryl-embedded tissue labeled with antisera to RFamide and 5-nm gold-conjugated, secondary antibody and of Epon-Araldite-embedded tissue labeled with 15-nm gold particles revealed a concentration of RFamide-like immunoreactivity over the granular cores of vesicles in epidermal ganglion cells. Gold-labeled, dense-cored vesicles were present in the perikaryon, long thin neurites, and axon terminals of these neurons. The aggregation of labeled dense-cored vesicles in an axon terminal on the myoneme of an epitheliomuscular cell suggests a possible function of RFamide-like peptides in neuromuscular transmission. Gold staining of dense-cored vesicles completely disappeared when the RFamide antiserum was preabsorbed with 10 micrograms/ml RFamide. These results are the first demonstration that the dense-cored vesicles of Hydra neurons contain a neuropeptide.     

Fine structural characteristics and synaptic connections of trigeminocerebellar projection neurons in rat trigeminal nucleus oralis

In order to classify the presynaptic terminals contacting trigeminocerebellar projection neurons (TCPNs) in rat trigeminal nucleus oralis (Vo), electron-microscopic examination of sequential thin sections made from TCPNs located in the border zone (BZ) of Vo, labeled by the retrograde transport of horseradish peroxidase, was undertaken. The use of BZ TCPNs, labeled in Golgi-like fashion so that many of their dendrites and axons were visible, allowed for the determination of the distribution of each bouton type along the soma and dendrites, as well as for the characterization of the morphology and synaptic relations of the labeled axon and its terminals. Three types of axon terminals contacting labeled BZ TCPNs have been recognized, depending upon whether they contain primarily spherical-shaped, agranular synaptic vesicles (S endings); predominantly flattened, agranular synaptic vesicles (F endings); or a population of pleomorphic-shaped, agranular synaptic vesicles (P endings). The S endings represent the majority of axon terminals contacting labeled BZ TCPNs and establish asymmetrical axosomatic and axodendritic synaptic contacts. Many S endings are situated in one of two types of synaptic glomeruli. One type of glomerulus has a large S ending at its core, whereas the other contains a small S ending. Large-S-ending glomeruli include only labeled distal dendrites of BZ TCPNs; small-S-ending glomeruli contain either a labeled soma, proximal dendrite, or distal dendritic shaft. The remaining S endings are extraglomerular, synapsing on distal dendrites. P endings are less frequently encountered and establish intermediate axosomatic and axodendritic synapses. These endings exhibit a generalized distribution along the entire somatodendritic tree. F endings make symmetrical axodendritic synapses with distal dendrites, are only found in glomeruli containing small S endings, and are the least frequently observed ending contacting labeled BZ TCPNs. The majority of axonal endings synapsing on labeled BZ TCPNs are located along distal dendrites, with only a relatively few synapsing terminals situated on proximal dendrites and somata. The axons of labeled BZ TCPNs arise from the cell body and generally give rise to a single short collateral near their points of origin. This collateral remains unbranched and generates several boutons within BZ, while the parent axon acquires a myelin sheath and, without branching further, travels dorsolaterally toward the inferior cerebellar peduncle. The collateral boutons resemble extraglomerular S endings. They contain agranular, spherical-shaped synaptic vesicles and make asymmetrical axodendritic synapses with small-diameter unlabeled dendritic shafts in the BZ neuropil.     

A new case for a presynaptic role of dendrites: An immunocytochemical study of the N. Raphé Dorsalis

The distribution of serotonin (5-HT) was determined by the application of the prembedding peroxidase-anti-peroxidase (PAP) technique in vibratome and ultrathin sections of the brain stem. The antiserum stained the neuronal groups B₁ to B₉. Somata, dendrites and axons of multipolar and bipolar neurons were recognized in the usual locations. The most commonly found profiles in the area of the n.raphe dorsalis were dendrites. The search for axon terminals was unsuccesful. The labeled dendrites appear in synaptic contact with unlabeled endings containing round or pleomorphic vesicles, and occasionally some large dense core vesicles. Contacts between two labeled dendrites or processes were not found. Occasionally a dendrodendritic junction between a 5-HT labeled dendrite and an unlabeled dendrite has been found. There are areas of the dendritic membrane free of synaptic junctions and free of glial insulation. Results are discussed in relation with the previously proposed presynaptic role of the dendrites in the neuronal circuitry of then. raphé dorsalis.Special Issue dedicated to Prof. Eduardo De Robertis.Research supported by grants from the CONICET and SECYT, Argentina.     

Synaptic interactions between ghrelin- and neuropeptide Y-containing neurons in the rat arcuate nucleus

Morphological relationships between neuropeptide Y- (NPY) like and ghrelin-like immunoreactive neurons in the arcuate nucleus (ARC) were examined using light and electron microscopy techniques. At the light microscope level, both neuron types were found distributed in the ARC and could be observed making contact with each other. Using a preembedding double immunostaining technique, some NPY-immunoreactive axon terminals were observed at the electron microscope level to make synapses on ghrelin-immunoreactive cell bodies and dendrites. While the axo-somatic synapses were mostly symmetric in nature, the axo-dendritic synapses were both symmetric and asymmetric. In contrast, ghrelin-like immunoreactive (ghrelin-LI) axon terminals were found to make synapses on NPY-like immunoreactive (NPY-LI) dendrites although no NPY-like immunoreactive perikarya were identified receiving synapses from ghrelin-LI axon terminals. NPY-like axon terminals were also found making synapses on NPY-like neurons. Axo-axonic synapses were also identified between NPY- and ghrelin-like axon terminals. The present study shows that NPY- and ghrelin-LI neurons could influence each other by synaptic transmission through axo-somatic, axo-dendritic and even axo-axonic synapses, and suggests that they participate in a common effort to regulate the food-intake behavior through complex synaptic relationships.     

Monoamine-synthesizing enzymes in central dopaminergic, noradrenergic and serotonergic neurons. Immunocytochemical localization by light and electron microscopy.

The monoamine-synthesizing enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and tryptophan hydroxylase (TrH) were immunocytochemical localized in dopaminergic, noradrenergic and serotonergic neurons of rat brain by light and electron microscopy. In dopaminergic and serotonergic neurons, the respective synthesizing enzymes. TH and TrH, were distributed throughout the cytoplasm of the neuronal perikarya, dendrites, axons and terminals. The most selective accumulation of reaction product for the specific enzyme was associated: (a) in perikarya with endoplasmic reticulum, Golgi apparatus and microtubules, (b) in processes with microtubules, and (c) in terminals with dense granules or clear vesicles. The labeled terminals were characterized by their content of labeled organelles and the absence of synaptic junctions. In noradrenergic neurons, both TH and DBH were localized in the perikarya, similar to TH in dopamine neurons. TH and DBH differed in their localization within proximal axons and dendrites in that TH was associated with microtubules but DBH was not. These results provide ultrastructural evidence to suggest that monoamines may be: (a) synthesized by enzymes which are associated with different organelles depending on the portion of the neuron and the type of enzyme; (b) synthesized in both axons and dendrites and (c) released from terminals without postsynaptic membrane specializations.     

Characterization of orexin A immunoreactivity in the rat area postrema

The distribution of orexin A immunoreactivity and the synaptic relationships of orexin A-positive neurons in the rat area postrema were studied using both light and electron microscopy techniques. At the light microscope level, numerous orexin A-like immunoreactive fibers were found within the area postrema. Using electron microscopy, immunoreactivity within fibers was confined primarily to the axon terminals, most of which contained dense-cored vesicles. Both axo-somatic and axo-dendritic synapses made by orexin A-like immunoreactive axon terminals were found, with these synapses being both symmetric and asymmetric in form. Orexin A-like immunoreactive axon terminals could be found presynaptic to two different immunonegative profiles including the perikarya and dendrites. Occasionally, some orexin A-like immunoreactive profiles, most likely to be dendrites, could be seen receiving synaptic inputs from immunonegative or immunopositive axon terminals. The present results suggest that the physiological function of orexin A in the area postrema depends on synaptic relationships with other immunopositive and immunonegative neurons, with the action of orexin A mediated via a self-modulation feedback mechanism.     

GABA-immunoreactive neurons and terminals in the cat periaqueductal gray matter: A light and electron microscopic study

Immunocytochemical and electron microscopic methods were used to study the GABAergic innervation in adult cat periaqueductal gray matter (PAG). A mouse monoclonal antibody against γ -aminobutyric acid (GABA) was used to visualize the inhibitory neuronal system of PAG. At light microscopy, GABA-immunopositive (GABA_IP) neurons formed two longitudinally oriented columns in the dorsolateral and ventrolateral PAG that accounted for 36% of the neuronal population of both PAG columns; their perikaryal cross-sectional area was smaller than that of unlabeled (UNL) neurons found in the same PAG subdivisions. At electron microscopic level, patches of GABA immunoreactivity were readily detected in neuronal cell bodies, proximal and distal dendrites, axons and axon terminals. Approximately 35–36% of all terminals were GABA_IP; they established symmetric synapses with dendrites (84.72% of the sample in the dorsolateral PAG and 86.09% of the sample in the ventrolateral PAG) or with cell bodies (7–10% of the sample). Moreover, 49.15% of GABA_IP axon terminals in the dorsolateral and 52.16% in the ventrolateral PAG established symmetric synapses with GABA_IP dendrites. Immunopositive axon terminals and unlabeled terminals were also involved in the formation of a complex synaptic arrangment, i.e. clusters of synaptic terminals in close contact between them that were often observed in the PAG neuropil. Moreover, a fair number of axo-axonic synapses between GABA_IP and/or UNL axon terminals were present in both PAG subdivisions. Several dendro-dendritic synapses between labeled and unlabeled dendrites were also observed in both PAG subdivisions. These results suggest that in the cat PAG there exist at least two classes of GABArgic neurons. The first class could exert a tonic control on PAG projecting neurons, the second could act on those GABAergic neurons that in turn keep PAG projecting neurons under tonic inhibition. The functional implications of this type of GABAergic synapse organization are discussed in relation to the dishinibitory processes that take place in the PAG.     

Electron-microscopic investigations of vasoactive intestinal peptide (VIP)-like immunoreactive terminal formations in the lateral septum of the pigeon

Vasoactive intestinal peptide (VIP)-like immunoreactive terminal fields were examined in the lateral septum of the pigeon by means of immunocytochemistry. According to light-microscopic observations, these projections originated from VIP-like immunoreactive cerebrospinal fluid (CSF)-contacting neurons, which are located in the ependymal layer of the lateral septum and form a part of the lateral septal organ. The processes of these cells gave rise to dense terminal-like structures in the lateral septum. Pre-embedding immuno-electron microscopy revealed that VIP-like immunoreactive axon terminals had synaptoid contacts with perikarya of small VIP-immunonegative neurons of the lateral septum, which were characterized by an invaginated nucleus, numerous mitochondria, a well-developed Golgi apparatus, endoplasmic reticulum and a small number of dense-core vesicles (about 100 nm in diameter). VIP-like immunoreactive axons were also seen in contact with immunonegative dendrites in the lateral septum. In both axosomatic and axodendritic connections, VIP-like immunoreactive presynaptic terminals contained large dense-core vesicles, clusters of small vesicles and mitochondria. These findings suggest that VIP-immunoreactive neurons of the lateral septal organ project to small, presumably peptidergic nerve cells of the lateral septum and that the VIP-like neuropeptide serves as a neuromodulator (-transmitter) in this area.     

Enzymatic cleavage prior to antibody incubation as a method for neuropeptide immunocytochemistry

When deplasticized Epon sections were treated with endo- and/or exopeptidases prior to incubation with antibodies, the neuropeptide immuno-reactivity of secretory nerves was often altered in a predictable way. Cleavage of neurosecretory material in octopus nerves by trypsin and carboxypeptidase-B enhanced enkephalin-like immunoreactivity, while Molluscan neuropeptide-like immunoreactivity was prevented by tryptic cleavage. The enzyme effects indicated the occurrence of a heptapeptide (Tyr-Gly-Gly-Phe-Met/Leu-Arg-Phe) that contains both the enkephalin and the Molluscan neuropeptide sequence. Vasopressin terminals of the rat neurohypophysis, which presumably contain enkephalin precursor sequences, exhibited enkephalin-like immunostaining after tryptic cleavage. ACTH/beta-endorphin cells of the rat intermediate pituitary, which synthesize the enkephalin sequence at the N-terminus of Beta-endorphin, exhibited enkephalin=like immunoreactivity when sections were treated with alpha-chymotrypsin or trypsin, but not after incubation with leucine-aminopeptidase or carboxypeptidase-B. Enkephalin-like immunostaining could not be induced in any way in ACTH/beta-endorphin cells of the anterior pituitary. Enzymatic cleavage may give additional information in immunocytochemical localization studies on neuropeptide sequences in secretory nerves and hormonal granules.     

An immunohistochemical and electron microscopic study of the peri-ureteric ganglia of the guinea-pig

Summary The neuropeptide- and catecholamine-synthesizing enzyme content and ultrastructure of the peri-ureteric ganglia of guinea-pigs were investigated. Small numbers of neuronal perikarya were present at frequent intervals forming ganglia close to, and along the entire length of, the ureter. Each of these ganglia was surrounded by a connective tissue capsule, and was located in the peri-ureteric connective tissues. Within each ganglion were typical nerve terminals and varicosities containing small, clear synaptic vesicles or synaptic vesicles with an electron-dense core, or a mixture of the two. In the ganglia, immunoreactivity to tyrosine hydroxylase, dopamine hydroxylase, neuropeptide tyrosine, or vasoactive intestinal peptide was present in neuronal perikarya; immunoreactivity to substance P or leucine enkephalin was present in nerve terminals and varicosities. Electron-microscopic immunogold studies indicated that there was no coexistence of substance P and enkephalin in the nerve terminals, unlike related ganglia in the pelvis of guinea-pigs.     

Neurotensin-like immunoreactivity in the pituitary and hypothalamus of bony fishes

Using an antiserum raised against synthetic neurotensin (NT), the distribution of immunoreactivity in the pituitary and hypothalamus has been examined by immunocytochemistry at light and electron microscope level in a number of species of bony fishes. In most species immunoreactive perikarya were found in the preoptic region of the hypothalamus, with fibres throughout the tuberal hypothalamus and neurohypophysis (neural lobe and median eminence). In the neurohypophysis of teleosts NT-like immunoreactivity was seen in a dense band of fibres bordering the ACTH cells of the rostral pars distalis: absorption controls showed that this was due to the presence of an NT(8-13)-like or xenopsin-like sequence, which, according to electron microscopic observations, was contained in small dense cored vesicles. The antiserum also stained the pituitary ACTH cells of some species, apparently due to cross-reaction with the 17-19 sequence of ACTH. These results suggest that an NT-like peptide may have a role in control of the adenohypophysis in fishes.     

Synaptic relationships between proopiomelanocortin- and ghrelin-containing neurons in the rat arcuate nucleus

Both proopiomelanocortin (POMC) and ghrelin peptides are implicated in the feeding regulation. The synaptic relationships between POMC- and ghrelin-containing neurons in the hypothalamic arcuate nucleus were studied using double-immunostaining methods at the light and electron microscope levels. Many POMC-like immunoreactive axon terminals were found to be apposed to ghrelin-like immunoreactive neurons and also to make synapses with ghrelin-like immunoreactive neuronal perikarya and dendritic processes. Most of the synapses were symmetrical in shape. A small number of synapses made by ghrelin-like immunoreactive axon terminals on POMC-like immunoreactive neurons were also identified. Both the POMC- and ghrelin-like immunoreactive neurons were found to contain large dense granular vesicles. These data suggest that the POMC-producing neurons are modulated via synaptic communication with ghrelin-containing neurons. Moreover, ghrelin-containing neurons may also have a feedback effect on POMC-containing neurons through direct synaptic contacts.