Characterization of a new neurosecretory cell type containing gastrin-cholecystokinin-like peptide in the locust pars intercerebralis: ultrastructural and immunocytochemical studies,in situ and in vitro

A new neurosecretory cell type of the locust pars intercerebralis, immunolabelled with an antiserum against a vertebrate peptide related to gastrin-cholecystokinin (CCK-8(s)), was characterized both in situ and in primary cell cultures. Semithin sections of pars intercerebralis were first immunostained in order to identify neurosecretory cells containing CCK-like material and then examined by electron microscopy. The neurosecretory cells containing CCK-like material were paraldehyde fuchsin negative and were unequivocally identified in ultrathin sections adjacent to immunostained semithin sections. They exhibited neurosecretory vesicles of variable electron density, ranging in diameter from 150 to 250 nm. Immunogold labelled ultrathin sections adjacent to unlabelled ultrathin sections allowed for the unambiguous localization of CCK-like immunoreactive material over the neurosecretory vesicles of the cells containing CCK-like material. Immunoreactivity towards CCK-8(s)-like peptide could also be detected in pars intercerebralis neurosecretory neurons grown in vitro. The CCK-like positive neurons showed a multipolar morphology with fine processes radiating from the cell body. The positive cells had the same ultrastructural characteristics as the in situ CCK-like neurons. The pattern of neurite outgrowth on reactive CCK-like neurosecretory cells in vitro and the neuroanatomical pathway of the CCK-like immunoreactive neurosecretory cells in situ could be correlated. On the basis of their number, size and localization in the locust pars intercerebralis, it is possible that the CCK-like neurosecretory cells correspond to neurosecretory cell type C, which has not, to date, been identified at the ultrastructural level.     

Ultrastructure of the corpus cardiacum and corpus allatum of the house cricket Acheta domesticus

Summary The ultrastructure of the corpus cardiacum (CC) and corpus allatum (CA) of the house cricket, Acheta domesticus, is described. Axon profiles within the CC contain neurosecretory granules 160–350 nm in diameter which are indistinguishable from those found in type I neurosecretory cells of the pars intercerebralis and in the nervus corporis cardiaci I. The CC itself contains two cell types: intrinsic neurosecretory cells and glial cells. Intrinsic NSC cytoplasm contains Golgi bodies and electron dense neurosecretory granules 160–350 nm in diameter. Synaptoid configurations with 20–50 nm diameter electron lucent vesicles were observed within axon profiles of the CC. The structure of the CA is relatively uniform with one cell type predominating. Typical CA cells possess large nucleoli, active Golgi complexes, numerous mitochondria, and occassional microtubules. Groups of dark staining cells scattered throughout the CA of some animals were interpreted as evidence of cellular death.This work was done while JTB was supported by USPHS Training Grant HD-0266 from NICHDI wish to express my thanks to Dr. Richard A. Cloney for sharing his expertise in electron microscopy     

Ultrastructural Analysis of the Neuroendocrine Apparatus of Oncopeltus fasciatus (Heteroptera)

• 1 In Oncopeltus fasciatus, the A-cells of the pars intercerebralis and their tracts are stainable in situ with the performic acid-victoria blue (PAVB) method. The axons from these cells, after traversing the corpus cardiacum, terminate in the anterior part of the aorta which thus serves as the neurohemal organ.
• 2 Ultrastructurally, four types of secretory neurons are distinguishable in the pars intercerebralis region: pic-I with granules measuring 1000–3000 Å in diameter; pic-II with granules of irregular size and shape, the elongate ones showing mean dimensions of 2400 × 1400 Å; pic-III with less electron-dense granules measuring 1000–2700 Å in diameter; pic-IV, present not only in the pars intercerebralis but also in adjacent regions of the brain, with variable proportions of granules measuring 700–1800 A and dense-cored vesicles measuring 1000–2400 Å.
• 3 The nervi corporis cardiaci contain at least three types of neurosecretory axons, based on granule content, presumably representing pic-I, pic-II and pic-III neurons.
• 4 The wall of the aorta contains endings of at least three distinct types, again representing pic-I, pic-II and pic-III neurons, and thus provides the neurohemal site for these three types of protocerebral neurosecretory cells. Axons of pic-IV neurons appear to enter the cerebral neuropil.
• 5 The corpus cardiacum is composed of two types of parenchymal secretory cells, with electron-dense granules measuring 1300–3000 Å and 1000–2300 Å in diameter, respectively. The corpus cardiacum also contains interstitial cells and some axons of extrinsic origin, with and without granules.
• 6 The corpus allatum may be paired or median, and receives a small number of at least two types of axons. The corpora allata of some reproducing females show a large number of PAVB-stainable inclusions which appear to be modified cytoplasmic organelles, but are definitely not neurosecretory material.
• 7 The hypocerebral ganglion is composed of two types of secretory-appearing neurons and glial cells. The two neuronal types contain secretory granules, 1000–3000 Å and 900–2100 Å in diameter, respectively. Axons of the recurrent nerve also may contain occasional granules.
• 8 In this heteropteran insect, the two principal functions of the corpus cardiacum appear to be spatially separated: the neurohemal function is subserved by the aortic wall, which permits release of material into both the aortic lumen and the hemocoel, and the intrinsic endocrine function is possessed by the parenchymal cells.

     

Neurons projecting to the retrocerebral complex of the adult blow fly, Protophormia terraenovae

Anatomical study of neurons projecting to the retrocerebral complex of the adult blow fly, Protophormia terraenovae, was done by NiCl2 filling and immunocytochemistry. Retrograde filling through the cardiac-recurrent nerve labeled three groups of neurons in the brain/subesophageal ganglion: (1) paramedial clusters of the pars intercerebralis, (2) neurons in each pars lateralis, and (3) neurons in the subesophageal ganglion. The pars intercerebralis neurons send prominent axons into the median bundle and exit from the brain via the contralateral nervus corporis cardiaci. Based on the projection pattern, two types of the pars lateralis neurons can be distinguished: the most lateral pairs of neurons contralaterally extend through the posterior lateral tract and the remainder ipsilaterally extend through the posterior lateral tract. The neurons in the subesophageal ganglion run through the contralateral nervus corporis cardiaci. The dendritic arborization of the pars intercerebralis and pars lateralis neurons is restricted to the superior protocerebral neuropil and to the anterior neuropil of the subesophageal ganglion where the neurons in the subesophageal ganglion also project. Retrograde filling from the corpus allatum indicated that the pars lateralis neurons and a few pars intercerebralis neurons project to the corpus allatum, but that the neurons in the subesophageal ganglion do not. Orthograde filling from the pars intercerebralis and staining by paraldehyde-thionin/paraldehyde-fuchsin indicated that the pars intercerebralis neurons project primarily to the corpus cardiacum/hypocerebral ganglion complex. Immunostaining with a polyclonal antiserum against diapause hormone, a member of the FXPRLamide family, suggests that some of the subesophageal ganglion neurons contain FXPRLamide-like peptides.     

Histology, histochemistry, and ultrastructure of neurosecretory cells in the optic lobe of the cockroach, Periplaneta americana

In the region of the distal optic chiasma of each optic lobe of Periplaneta americana, there is a group of about 120 monopolar neurosecretory cells. These cells do not stain with paraldehyde fuchsin but remain acidophilic after oxidation. They stain red or sometimes indigo with the azan technique. Histochemically, the neurosecretory material is positive for protein and the amino acids tryptophan and arginine but negative for 1, 2-glycols and strongly acidic groups. At the ultrastructural level, the cytoplasm of the cells contain many elementary neurosecretory granules 100 to 170 nm in dia. The cells also contain well-developed Golgi bodies and endoplasmic retieulum. The axons from these cells run toward the interior of the optic lobe. In this region, axons containing dense granules (mean diameter 70 nm) and synaptic vesicles synapse onto the axons from the neurosecretory cells. The neurosecretory axons then cross over to the anterior side of the optic lobe and run towards the brain. The function of these neurosecretory cells is unknown, but they may be involved with photoperiodically controlled activity rhythms.     

Neurosecretory system of the earwig Labedura riparia, and the rôle of the aorta as a neurohaemal organ

The neurosecretory system of Labedura riparia has been described from sections and whole mounts using a variety of techniques. The pars intercerebralis contains two clusters of medial neurosecretory cells (MNC), each cluster consisting of 8 to 10 A-cells and occasional B-cells. The lateral sides of the brain have a few B-cells. The axons of the median neurosecretory cells terminate in the cephalic aorta (AO), whereas the axons of the lateral neurosecretory cells (LNC) terminate in the corpora cardiaca (CC). It appears that the neurosecretory material (NSM) elaborated in the MNC is stored in the cephalic aorta and that elaborated in the LNC is stored in the corpora cardiaca, which are two oval or elongate bodies composed of large chromophobe and small chromophil cells. Posteriorly there is the oval or elongate corpus allatum (CA) attached to the CC by thick nerves. The CA consists of one cell type only. Both CC and CA contain no A-cell neurosecretory material. It has been suggested that the neurosecretory system of L. riparia is composed of two complexes. One is formed by the medial neurosecretory cells for which the aorta functions as a neurohaemal organ, and the other is formed by lateral neurosecretory cells-lateral neurosecretory pathways-nervi corporis cardiaci-II in which the corpora cardiaca function as a neurohaemal organ.     

Postembryonic development of astrocyte-like glia of the central complex in the grasshopper Schistocerca gregaria

Central complex modules in the postembryonic brain of the grasshopper Schistocerca gregaria are enveloped by Repo-positive/glutamine-synthetase-positive astrocyte-like glia. Such cells constitute Rind-Neuropil Interface glia. We have investigated the postembryonic development of these glia and their anatomical relationship to axons originating from the w, x, y, z tract system of the pars intercerebralis. Based on glutamine synthetase immunolabeling, we have identified four morphological types of cells: bipolar type 1 glia delimit the central body but only innervate its neuropil superficially; monopolar type 2 glia have a more columnar morphology and direct numerous gliopodia into the neuropil where they arborize extensively; monopolar type 3 glia are found predominantly in the region between the noduli and the central body and have a dendritic morphology and their gliopodia project deeply into the central body neuropil where they arborize extensively; multipolar type 4 glia link the central body neuropil with neighboring neuropils of the protocerebrum. These glia occupy type-specific distributions around the central body. Their gliopodia develop late in embryogenesis, elongate and generally become denser during subsequent postembryonic development. Gliopodia from putatively type 3 glia within the central body have been shown to lie closely apposed to individual axons of identified columnar fiber bundles from the w, x, y, z tract system of the central complex. This anatomical association might offer a substrate for neuron/glia interactions mediating postembryonic maturation of the central complex.     

Morphology and distribution of the synapses to the spinal motoneuron of the frog

Summary Neurosecretory axons and their dilatations in the pars nervosa of the human neurohypophysis were studied electron microscopically. The axons are of two different types based on their content of neurosecretory granules (NSGs): (i) NSGs of Type A are 100–300 nm, and (ii) NSGs of type B are 50–100 nm in diameter.While fibers (or axons) of type B were scarce, showing simple swellings and terminal formations, fibers of type A were ubiquitous in the human pars nervosa, exhibiting numerous dilatations with a diversity of internal structure, apparently representing the ultrastructural manifestation of intraaxonal turnover of neurohypophysial hormones. Based on the predominating aspect of their internal structure, dilatations of type A-fibers were classified into six different types, with various transitional forms: Type I is characterized by abundant NSGs; type II by prominent mitochondria; type III by abundant lysosomal bodies; type IV by an electron-lucent matrix with few organelles; type V by prominent tubuloreticular profiles; and type VI by numerous microvesicles. The functional significance of each type is discussed and a scheme of possible interrelationships between these dilatations is proposed.     

Fine structural and immunohistochemical studies of goat adenohypophysial cells

Summary The fine structure of each type of anterior pituitary cell in the male goat was studied through the application of a superimposition technique in which adjacent thick sections were used to identify individual cells beforehand by light-microscopic immunohistochemistry. A cone of the pars intermedia protrudes into the pars anterior, being surrounded by the narrow pituitary cleft; the immunohistochemical appearances of the cells forming the cone resemble those of the pars anterior. Several follicles appear in the pars anterior. Ultrastructurally GH cells resemble prolactin cells. The secretory granules of both types are spherical; the diameter of the former is about 340 nm, whereas that of the latter is about 440 nm. ACTH cells are polygonal in shape with secretory granules, about 180 nm in diameter, scattered throughout the cytoplasm. TSH cells, which are spherical in shape, contain the smallest secretory granules, 150 nm in diameter. The highly electron-dense LH cells contain numerous secretory granules about 210 nm in diameter. Their nuclei are irregular with incisures. Thus, the anterior pituitary cells of the goat are ultrastructurally characteristic and species-specific.     

In vitro peptidergic neurons from the adult locust pars intercerebralis: Morphological and immunocytological studies

Primary cell cultures were prepared from a major neurosecretory center of the adult locust brain, the pars intercerebralis, in order to characterize neurosecretory cells growingin vitro. Individual pars intercerebralis could be removed free of surrounding tissue and dissociated by mechanical treatment. Mature neurosecretory neurons of different sizes regenerate new neurites during the initial three daysin vitro in serum-free medium. They show a tendency to sprout one primary neurite from which fine processes develop. By means of electron microscopy, we observed the integrity of the cellular organelles, indicating that cultured neurons are healthy, and we were able to distinguish three types of neurosecretory neurons on the basis of the ultrastructural aspects of the neurosecretory material. These three types have the same ultrastructural characteristics asin situ neuroparsin, ovary maturing parsin and locust insulin related peptide neurons. Immunogold labelling at the electron microscopic level, using the two available specific antibodies, anti-neuroparsin and anti-ovary maturing parsin, confirms the morphological characterization of neuroparsin and ovary maturing parsin cells. These results show for the first time that cultured locust neurosecretory neurons behave like thosein vivo, in terms of their ultrastructure and immunocytochemistry. Moreover, the presence of recently-formed neurosecretory material both in the Golgi zone of the perikaryon and in the neuronal processes indicates that cultured neurons have functional capacity since they are able to synthesizede novo and to transport the neurosecretory material along the neurite. Thus our well-characterized culture system provides a suitable invitro model to investigate the secretory mechanism of locust neurosecretory neurons.     

Immunocytochemical localization of Bombyx-PTTH-like molecules in neurosecretory cells of the brain of the migratory locust,Locusta migratoria

Summary Using a monoclonal antibody directed against a synthetic pentadecapeptide corresponding to the N-terminus of the prothoracicotropic hormone (PTTH) of Bombyx mori, we report the presence of immunoreactive molecules in a large number of median neurosecretory cells of the pars intercerebralis of the migratory locust, Locusta migratoria. These cells correspond to the A₁ cell type which we show to contain also neuroparsins, a family of predominant neurohormones of the migratory locust. In contrast, PTTH-like molecules are absent from A₂ cells of the pars intercerebralis which contain Locusta insulin-related peptide (LIRP). Developmental studies show the presence of PTTH-related substances in neurosecretory cells of Locusta migratoria from late embryogenesis to adult development, including ageing vitellogenic female adults.     

鳗鲡繁殖生物学研究 Ⅱ.下海雌鳗脑垂体超显微构造的研究

神经垂体主要由神经分泌纤维、脑垂体细胞和微血管组成。神经分泌纤维主要是无髓鞘神经纤维,也有一些是有髓鞘神经纤维。神经垂体中还有一些多层体构造。神经分泌纤维有两个基本类型:A型纤维含有直径为1250—1750Å的神经分泌颗粒;B型纤维含有直径为450—1000Å的颗粒状囊泡。腺垂体的分泌细胞按其超显微构造的特点和所含的分泌颗粒大小不同可以区分为六个类型:催乳激素分泌细胞、促甲状腺激素分泌细胞,促肾上腺皮质激素分泌细胞、促生长激素分泌细胞、促性腺激素分泌细胞和后腺垂体的分泌细胞。       

The ultrastructure of corpus allatum of the earwig Euborellia annulipes lucas (Dermaptera: Labiduridae)

The ultrastructure of corpus allatum of the earwig, Euborellia annulipes has been described. The corpus allatum (CA) is an oval body. The gland is covered by a thin stromal sheath which is wavey and acellular in composition. The gland consists of either parenchymal cells with distinct, double-layered, smooth or slightly undulated plasma-membranes. Golgi bodies and endoplasmic reticulum are poorly developed. The mitochondria are found in abundance and are oval, spherical, elongate, and Y-shaped, with oblique and longitudinal cristae. The gland is innervated by neurosecretory and non-neurosecretory axons. The neurosecretory axons are of two types. The type NS-II, contain electron dense granules of 40...120 nm in diameter and the type NS-I, small less electron dense granules (of mixed nature) 40...90 nm in diameter. Branches of tracheoles also occur that penetrate the gland. The large electron dense granules 100...220 nm in diameter occuring abundantly in aorta, and representing the secretions of the medial A-cells are absent in the CA.     

Central projections of first-order ocellar interneurons in the bug Triatoma infestans (Heteroptera: Reduviidae)

The projections of first-order ocellar interneurons were analyzed in the hematophagous bug Triatoma infestans by cobalt filling. The axons run between the calyces of the mushroom bodies and dorsal of the central body to different regions of the brain and the subesophageal and thoracic ganglia. The interneurons can be grouped into large L cells and small S cells. The L cells have cell bodies ranging from 11.5 to 25 μm and axons ranging from 8 to 25 μm diameter (measured in the ocellar nerve); the S cells have smaller cell bodies of 9 μm or less and axon diameters less than 5 μm. The projections of ten L cells are described in detail; they project to the protocerebral posterior slope (PS), the other ocellus (O), the optic neuropile, and the subesophageal, pro-, meso-, and metathoracic ganglia, either to ipsi- (PS I, II), or contra- (PS IV, V), or bilateral areas. In this case projections occur to the same areas (PSO, PS III) or different areas at each side (PSOE; E = eye). Large-descending (LD) first-order interneurons project to the contralateral posterior slope of the protocerebrum, the deutocerebrum, and subesophageal, pro-, mesa-, and metathoracic areas (LD I-III). Cell bodies are located in the dorsal protocerebral lobes and pars intercerebralis, except the PS II neuron and three LD cells, which are located in the ipsilateral posterior protocerebrum. This is the first report about ocellar pathways in Hemiptera. Their adaptive function is discussed with reference to the bugs' behavior as Chagas disease vectors. © 1996 Wiley-Liss, Inc.     

The neurosecretory cells of the brain and suboesophageal ganglion of Chironomus riparius

The neurosecretory cells of the supra- and suboesophageal ganglia of young, unmated, adult male midges, Chironomus riparius, have been examined by both light and electron microscopy. The 5 cell types recognized have been placed in three major categories on the basis of their ultrastructural characteristics:—α₁ cells, of which there are 8 in each medial neurosecretory cell (MNC) group and 3 in each group of ventral neurosecretory cells (VNC), contain electron-dense granules, 150 to 200 nm in diameter; α₂ cells containing irregular, electron-dense granules, 70 to 120 nm in diameter comprise the remaining 3 cells in each VNC group and the 2 or 3 cells in each outer neurosecretory cell (ONC) group; α₃ cells, of which there are 1 or 2 on each side of the midline in the ventral cortex of the sub-oesophageal ganglion (SNC₂), contain electron-lucent, spherical granules, 70 to 120 nm in diameter. The β cells contain spherical or ellipsoidal, electron-lucent granules, 80 to 100 nm in diameter, and make up the lateral neurosecretory cell (LNC) groups, each of three or four cells. The γ cells contain both spherical and flattened, electron-dense granules, 130 to 160 nm in diameter and 150 to 250 by 70 to 150 nm in size respectively, only 1 cell of this category being found in each half of the suboesophageal ganglion in the dorsal cortex (SNC₁). Axons from the MNC and VNC form the nervi corporis cardiaci I (NCCI) and those of the LNC and ONC, the nervi corporis cardiaci II (NCCII). Those of the SNC₁ appear to enter the wall of the stomodaeum but axons of the SNC₂ could not be traced.     

Development of blood-cerebrospinal fluid barrier to horseradish peroxidase in the avian choroidal epithelium

Summary Four neurons in the brain of the migratory locust were immunohistologically identified with an anti-met-enkephalin antiserum. The perikarya of two of these cells are located in the center of each of the two groups of lateral protocerebral neurosecretory cells. The fibres coming from these perikarya terminate in numerous immunoreactive ramifications visible at the periphery of both tractus I to the corpora cardiaca, through which pass the neurosecretory products of the pars intercerebralis. The other two cell bodies are located at the bases of the two optic lobes; their fibres enter the posterior part of the protocerebrum and ramify around the root of the nervus corporis cardiaci II, another area through which neurosecretory products pass. The topographic distribution of these met-enkephalin arborizations suggests that these four neurons may act as neuromodulators of the acitivity of the major neurosecretory cells in the brain of this insect.     

Structure of the neurohypophysis and the hypothalamo-hypophysial vascularization in the teleost Channa punctatus Bloch.

In C. punctatus the median eminence includes the subterminal region of the hypothalamus and the anterior neurohypophysis. It is formed of ependymal, fibrous and reticular layers as in the tetrapods. Primary capillary plexus extends from the subterminal region to the extremity of the anterior neurohypophysis. Only few portal vessels from the hypothalamus enter in the pars distalis. All the components of pituitary including the pars intermedia are irrigated by the secondary plexus formed from the portal vessels emerging out of the anterior neurohypophysis. The neurosecretory axons and the ependymal cells are in close morphological contact with the primary plexus. Several axons have perivascular endings at the median eminence. Some axons were found to be only silver or aldehyde fuchsin positive whereas some others take up both. The silver positive axons were abundant in the pars distalis and the AF positive ones were more concentrated in the pars intermedia with greater accumulation of neurosecretory material.     

Ultrastructural alterations of the paraventriculo-infundibular Corticotropin Releasing Factor (CRF)-immunoreactive neuronal system in long term adrenalectomized rats

The corticotropin releasing factor (CRF)-immunoreactive paraventriculo-infundibular neuronal system of long-term adrenalectomized and adrenalectomized-short term dexamethasone treated rats was analyzed at the ultrastructural level using the preembedding peroxidase anti-peroxidase complex (PAP)-immunohistological method. In both groups of animals, parvocellular neurons located in the medial and dorsal subnuclei of the paraventricular nucleus (PVN) showed CRF-like immunoreactivity. The perikarya contained hypertrophied rough endoplasmic reticulum (rER) with dilated cisternae, active Golgi-complexes and numerous neurosecretory granules. The majority of the neurosecretory granules measured 80–120 nm. Dendrites of CRF-immunoreactive neurons contained labeled vesicles, secretory granules, bundles of microtubules, a well-developed smooth endoplasmic reticulum (sER) complex and free ribosomes. Unlabeled terminal boutons of axons were observed to synapse on dendrites and somata of CRF-neurons. In addition, CRF perikarya were found in direct somato-somatic apposition with both CRF-immunopositive and immunonegative parvocellular cells. Retraction of glial processes and the existence of puncta adherentia between the cell membranes characterized these appositions. Varicose CRF axons within the median eminence contained hypertrophied sER, labeled vesicles and neurosecretory granules. The preterminal portions of the CRF-axons were dilated and possessed many labeled 80–120 nm diameter granules. CRF-terminals were greatly enlarged and established direct neurohemal contacts with the external limiting basal lamina of portal vessels without the interposition of tanycytic ependymal foot-processes. These tanycytes were not CRF immunopositive. CRF positive terminals contained clusters of microvesicles, labeled small vesicles and multivesicular bodies, but fewer granular elements than were observed within the preterminals. Many of the labeled organelles were attached to tubules of sER. Occasionally, CRF-axons were observed within the pericapillary space adjacent to portal vessels. The ultrastructural features of CRF-neurons, obtained from adrenalectomized and adrenalectomized plus short-term dexamethasone treated rats did not differ significantly from each other. The hormone content of the entire CRF-neuron was greater in the steroid treated group. Adrenocorticotrophic hormone (ACTH) synthesizing cells in the pars distalis of adrenalectomized-dexamethasone treated rats also showed increased numbers of immunopositive secretory granules (150–320 nm in diameter). These ultrastructural morphological results provide evidence that the function of the paraventriculo-infundibular CRF-system is adrenal steroid hormone dependent and suggest the participation of glial and ependymal elements in the regulation of the system in this hyperfunctional state. The observed membrane specializations are indicative of ephaptic interactions between CRF-neurons and may serve a synchronizing function in adrenalectomized animals.     

Tyrosine hydroxylase in the cerebral ganglia of the American cockroach (Periplaneta americana L.): an immunohistochemical study

We have investigated the distribution of tyrosine-hydroxylase-like immunoreactivity in the cerebral ganglia of the American cockroach, Periplaneta americana. Groups of tyrosine-hydroxylase-immunoreactive cell bodies occur in various parts of the three regions of the cerebral ganglia. In the protocerebrum, single large neurons or small groups of neurons are located in the lateral neuropil, adjacent to the calyces, and in the dorsal portion of the pars intercerebralis. Small scattered cell bodies are found in the outer layers of the optic lobe, and clusters of larger cell bodies can be found in the deutocerebrum, medial and lateral to the antennal glomeruli. Thick bundles of tyrosine-hydroxylase-positive nerve fibers traverse the neuropil in the proto- and deutocerebrum and innervate the glomerular and the nonglomerular neuropil with fine varicose terminals. Dense terminal patterns are present in the medulla and lobula of the optic lobe, the pars intercerebralis, the medial tritocerebrum, and the area surrounding the antennal glomeruli, the central body and the mushroom bodies. The pattern of tyrosine-hydroxylase-like immunoreactivity is similar to that previously described for catecholaminergic neurons, but it is distinctly different from the distribution of histaminergic and serotonergic neurons.     

The Sense Organs and Ventral Ganglion of Sagitta (Chaetognatha)

This paper describes some features of the chaetognath nervous system from ultrastructural observations and observations on material stained with specific techniques for nervous tissue, and from records of the activity of the locomotor muscles and ventral ganglion. Sensory cells grouped on the ventral surface of the head bear ciliary processes (some with multiple tubules), and are probably in connexion with the central nervous system by their own axons, unlike the sensory cells of the hair fan vibration receptors of head and body. The ventral ganglion is motor to the locomotor muscles of the body, and controls the rhythmic locomotor activity of the animal. Electrical events associated with contraction of these muscles are compound non-overshooting spike-like potentials. The ventral ganglion contains several large nerve fibres constant in position and connexions in different individuals. Some of these arise from cells in the ganglia of the head, and pass to the ventral ganglion, others from cells within the ventral ganglion, and probably supply the ciliary hair fan receptors of the body, whilst the motor axons issuing from the ventral ganglion are smaller in diameter. The ganglion is arranged on a ladder-like plan, and axons of the lateral cell bodies cross the central neuropil transversely before they contribute to the longitudinal tracts or pass out in the radial nerves. Synapses in the neuropil contain 30–40 nm electron lucent vesicles; the transmitter is unknown, but is unlikely to be either acetylcholine or l -glutamate. Occasional larger electron dense vesicles up to 70 nm in diameter are also found within nerve fibres of the neuropil. It is concluded that the arrangement of the peripheral nervous system is unlike that of several groups which have been suggested as related to chaetognaths.