Types Of Neurosecretory Cells Research Articles

NEUROSECRETION IN OLIGOCHAETES - A LESS STUDIED SUBJECT IN INVERTEBRATE RESEARCH

The concept of neurosecretion was first developed by Ernst Scharrer (1905-1965) and Berta Scharrer (1906-1995) between 1928 and 1937. The neurosecretory cells are neuronal in structure and glandular in function. Typically, the neurosecretory cells are “tear drop” in appearance with a long axon. The neurosecretory products (neurosecretion/neurohormone) are proteinaeous in nature which is consistent with the ultrastructure of the cells
 In earthworm species, irrespective of their ecological categories, the neurosecretory cells in their distribution, structure and functions in the central nervous system are more or less similar in different species of earthworms. The central nervous system in tropical earthworms reveals mainly two types of neurosecretory cells: A type (outer cortical tier of deeply stained AF positive cells with distinct axonal processes) and B type (light stained cells lying in between A type cells and central fibrous neuropile). In addition to A and B cells, an “islet” of neurosecretory cells called S cells or Hubl cells are present at the base of circum esophageal connectives of subesophageal ganglia. Both A and B cells discharge their secretion (neurohormone) at the margin of highly vascularised fibrous neuropile called “zone of accumulation” which may be considered as “elementary neuro-haemal organ”. Neurosecretion in Oligochaetes has great role in food intake, osmoregulation, thermal acclimation, regeneration, copulation and cocoon production.

Histological, histochemical, ultrastructural and immunohistochemical identification and characterization of the neurosecretory cells of the adult rabbit's adrenal medulla.

The present investigation was conducted on the adrenal glands of 40 adult New Zealand rabbits of both sexes to characterize and identify the histological, histochemical, ultrastructural, and immunohistochemical features of the neurosecretory cells of the adrenal medulla. The obtained specimens of adrenal medulla were subjected to routine histological techniques and then stained with different histological stains, including general, non-specific, specific, and highly specific stains for neurosecretory cells, in addition to immunohistochemical reactions. The obtained results showed two types of adrenal medullary neurosecretory cells containing secretory granules (SGs) of different electron densities: adrenaline and noradrenaline (NA) secreting cells. These secretory granules showed a strong positive reaction to the Grimelius silver impregnation technique. Sections stained with Gomori's chrome alum haematoxylin stain, and the secretory granules showed a strong dark blackish-blue positive colour. The medullary cells showed typical chromaffin reactions when stained by H&E and Giemsa stains after formol dichromate 'Ortha's fluid' fixation. The noradrenaline secretory granules gave a strong positive Schmorl's test, while the adrenaline ones showed a moderate reaction. Immunohistochemically, the adrenal medullary cells were subjected to anti-chromogranin A (CHGA) antibody using the PAP technique, which gave positive reactions.

High Salt Intake Recruits Tonic Activation of NR2D Subunit-Containing Extrasynaptic NMDARs in Vasopressin Neurons.

In addition to producing a classical excitatory postsynaptic current via activation of synaptic NMDA receptors (NMDARs), glutamate in the brain also induces a tonic NMDAR current (INMDA) via activation of extrasynaptic NMDARs (eNMDARs). However, since Mg2+ blocks NMDARs in nondepolarized neurons, the potential contribution of eNMDARs to the overall neuronal excitatory/inhibitory (E/I) balance remains unknown. Here, we demonstrate that chronic (7 d) salt loading (SL) recruited NR2D subunit-containing NMDARs to generate an Mg2+-resistant tonic INMDA in nondepolarized [Vh (holding potential) -70 mV] vasopressin (VP; but not oxytocin) supraoptic nucleus (SON) neurons in male rodents. Conversely, in euhydrated (EU) and 3 d SL mice, Mg2+-resistant tonic INMDA was not observed. Pharmacological and genetic intervention of NR2D subunits blocked the Mg2+-resistant tonic INMDA in VP neurons under SL conditions, while an NR2B antagonist unveiled Mg2+-sensitive tonic INMDA but not Mg2+-resistant tonic INMDA In the EU group VP neurons, an Mg2+-resistant tonic INMDA was not generated by increased ambient glutamate or treatment with coagonists (e.g., d-serine and glycine). Chronic SL significantly increased NR2D expression but not NR2B expression in the SON relative to the EU group or after 3 d under SL conditions. Finally, Mg2+-resistant tonic INMDA selectively upregulated neuronal excitability in VP neurons under SL conditions, independent of ionotropic GABAergic input. Our results indicate that the activation of NR2D-containing NMDARs constitutes a novel mechanism that generates an Mg2+-resistant tonic INMDA in nondepolarized VP neurons, thus causing an E/I balance shift in VP neurons to compensate for the hormonal demands imposed by a chronic osmotic challenge.SIGNIFICANCE STATEMENT The hypothalamic supraoptic nucleus (SON) consists of two different types of magnocellular neurosecretory cells (MNCs) that synthesize and release the following two peptide hormones: vasopressin (VP), which is necessary for regulation of fluid homeostasis; and oxytocin (OT), which plays a major role in lactation and parturition. NMDA receptors (NMDARs) play important roles in shaping neuronal firing patterns and hormone release from the SON MNCs in response to various physiological challenges. Our results show that prolonged (7 d) salt loading generated a Mg2+-resistant tonic NMDA current mediated by NR2D subunit-containing receptors, which efficiently activated nondepolarized VP (but not OT) neurons. Our findings support the hypothesis that NR2D subunit-containing NMDARs play an important adaptive role in adult brain in response to a sustained osmotic challenge.

Histological investigation of the effects of fenoxycarb on neurosecretory cells in the silkworm, Bombyx mori brain.

Fenoxycarb 0-ethyl N-(2-(4-pheoxyphenoxy)-ethyl) carbamate is the most potent juvenile hormone analogue against a variety of insect species including the silkworm Bombyx mori. In this study, the effects of fenoxycarb on silkworm Bombyx mori brain neurosecretory cells in 5th instar were investigated. Fenoxycarb (1ng/10µl) was applied topically along the dorsa-medial line to the animals in the spinning behavior on day 1 of the experimental group. Brains removed by dissection were histologically examined by hematoxylin eosin (hem&eosin) and paraldehyde fuchsin staining. Three types of neurosecretory cells (NSCs) were identified, NSC-1, NSC-2 and NSC-3. It was determined that cell secretions were in different density on different days. It was shown that the secretion density of cells on different days was not the same as the experimental and control groups. The fenoxycarb was found to suppress the bombyxin (insulin-like peptides) secretion of cells in the spinning behavior on day 2. Also, it stimulated the division of NSCs on the spinning behavior on day 5.

Effects of dehydration and subsequent hydration stress on the cerebral neurosecretory cells of Eudrilus eugeniae (Kinberg, 1867)

Moisture is a limiting factor for the survival and distribution of earthworms. During rainy season earthworms come out from their water-filled burrows and during summer move deeper into the soil to prevent acute desiccational water loss. Moisture loving worms like Eudrilus eugeniae when subjected to the dry soil and then subsequently hydrated, both the types of neurosecretory cells (A and B cells) show contrasting neurosecretory changes. During dehydration stress (2, 4 & 6 hours), both A and B cells deplete, lose their cellular conformity with extensive vacuolation. But in subsequent hydration of desiccated worms for 4 hrs, there is accumulation of neurosecretory materials in both types of cells, chiefly in A cells. The result indicates involvement of both A and B neurosecretory cells during osmotic stress from the perspective of histomorphic variations and secretory dynamics.

Neuropeptides in modulation of Drosophila behavior: how to get a grip on their pleiotropic actions.

Neuropeptides constitute a large and diverse class of signaling molecules that are produced by many types of neurons, neurosecretory cells, endocrines and other cells. Many neuropeptides display pleiotropic actions either as neuromodulators, co-transmitters or circulating hormones, while some play these roles concurrently. Here, we highlight pleiotropic functions of neuropeptides and different levels of neuropeptide signaling in the brain, from context-dependent orchestrating signaling by higher order neurons, to local executive modulation in specific circuits. Additionally, orchestrating neurons receive peptidergic signals from neurons conveying organismal internal state cues and relay these to executive circuits. We exemplify these levels of signaling with four neuropeptides, SIFamide, short neuropeptide F, allatostatin-A and leucokinin, each with a specific expression pattern and level of complexity in signaling.

Fine structure of neurosecretory cells and sinus gland in the eyestalk of the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae)

This study elucidated the fine structure of neurosecretory cells and sinus gland in the optic ganglia of the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae). The eyestalk ganglion showed the presence of four well defined ganglia arranged below the ommatidium: lamina ganglionaris, medulla externa, medulla interna and medulla terminalis of which the lamina ganglionaris, was devoid of neurosecretory cells. Groups of neurosecretory cells seen distributed along the medulla externa, interna and terminalis regions constitute the X-organs. Electron microscopic observations of the eyestalk ganglia revealed ten types of neurosecretory cells, mostly apolar with a few unipolar and bipolar cells classified according to the size, shape and density of the cell and nucleus, cell organelles/inclusions, together with the arrangement and properties of chromatin. These cells were characterized by the presence of large nuclei with unusually condensed chromatin, inclusions like vacuoles and vesicles of varying size, shape and density and organelles like Golgi, endoplasmic reticulum, ribosomes and mitochondria and neurosecretory material. The sinus gland of T. schirnerae was positioned laterally between the externa and interna regions, composed of axonal endings of the neurosecretory cells of the optic ganglia with interspersed glial cells. The axon terminals were enclosed with several small to large membrane bound homogenously dense neurosecretory granules which also occur in the preterminal areas of the axons. Based on size, shape and density of granules and axoplasmic matrix, seven terminal types could be distinguished in the sinus gland of T. schirnerae. Mostly, the granules contained in a terminal were of the same type; rarely, the same terminal enclosed granules of varying size, shape and density. The neurosecretory cell types and axon terminal types represent the types of neurohormones they contained. A precise knowledge of the morphology and cytology of neurosecretory cells in the XO-SG complex of the eyestalk that secrete neurohormones controlling major physiological processes such as growth and reproduction is imperative for successful captive breeding of a species of aquaculture potential.

Papillae revisited and the nature of the adhesive secreting collocytes

Ascidian papillae (palps) constitute a transient sensory adhesive organ that assures larval settlement and the onset of metamorphosis to the filterfeeding adult. Despite the importance of papillae for the ascidian development, their cellular composition is only roughly described. For Ciona intestinalis/robusta, a clear definition of cell numbers and discriminative molecular markers for the different cell types is missing. While some attention was given to neural cell types and their connectivity little is known about the adhesive producing collocytes. We converge serial-section electron microscopy and confocal imaging with various marker combinations to document the 3D organization of the Ciona papillae. We show the papillar development with 4 axial columnar cells (ACCs), 4 lateral primary sensory neurons (PSNs) and 12 central collocytes (CCs). We propose molecular markers for each cell type including novel ones for collocytes. The subcellular characteristics are suggestive of their role in papillar function: the ACCs featuring apical protrusions and microvilli, also contain neuroactive and endocytic vesicles indicative of a chemosensory role. They are clearly distinct from the ciliated glutamatergic PSNs. CCs encircle the ACCs and contain microvilli, small endocytic vesicles and notably a large numbers of adhesive granules that, according to element analysis and histochemistry, contain glycoproteins. Interestingly, we detect two different types of collocyte granules, one of them containing fibrous material and larger quantities of polysaccharides. Consistently, carbohydrate specific lectins label the papillar apex, the granules within CCs and the adhesive plaques upon larval attachment. We further propose CCs to derive from an evolutionary ancient neurosecretory cell type. Our findings contribute to understanding the development of the anterior (‘new head’) region of the Ciona larva and notably the adhesive secreting cells which has implications for developmental biology, cell differentiation and evolution, but also bioadhesion.

Neuroanatomy and morphological diversity of brain cells from adult crayfish Cherax quadricarinatus

As in vertebrates, brains play key roles in rhythmic regulation, neuronal maintenance, differentiation and function, and control of the release of hormones in arthropods. But the structure and functional domains of the brain are still not very clear in crustaceans. In the present study, we reveal the structural details of the brain in the redclaw crayfish using hematoxylin-eosin staining and microscopic examination, firstly. The brain of crayfish is consist of three main parts, namely, protocerebrum, deutocerebrum, and tritocerebrum, including some tracts and commissures, briefly. Secondly, at least 9 kinds of brain cells were identified on the basis of topology and cell shapes, as well as antibody labeling. We also provide morphological details of most cell types, which were previously un-described. In general, four types of glia and three types of neurosecretory cells were described except cluster 9/11 and cluster 10 cells. Glia were categorized into another three main kinds: (1) surface glia; (2) cortex glia; and (3) neuropile glia in addition to astrocytes identified by GFAP labelling. And neurosecretory cells were categorized into I, II and III types based on morphological observation. Finally, cluster 9/11 and 10 cells derived from the brain of crayfish, could be used for primary culture about 7–9 d under the optimized conditions. There results provide a resource for improving the knowledge of the still incompletely defined neuroendocrinology of this species. Using the crayfish as an animal model, we are easy to carry out further research in manipulating their endocrine system, exploring cellular and synaptic mechanisms so much as larval production on a small scale, such as in a cell or tissue.

Voltage-dependent calcium channels in the neurosecretory cells of cerebral ganglia of the mud crab, Scylla paramamosain.

Voltage-dependent calcium channels (VDCCs) play a critical role in stimulus-secretion coupling in neurosecretory cells (NSCs). The crustacean cerebral ganglion plays a crucial role in neuromodulation and controls neuropeptide release. The present study used patch-clamp and Illumina sequencing techniques to investigate the potential features of VDCC in the cerebral ganglia of the mud crab (Scylla paramamosain). The electrophysiological characteristics of VDCC were analyzed in three types of NSCs with a patch clamp. The thresholds for activation of Ca channel current recorded from all the three types of NSCs were all above -40 mV, with peak amplitudes occurring around 0 mV. Therefore, it was concluded that the currents recorded in NSCs were mediated by high-voltage-activated Ca channels. Ca channel current densities in I type NSCs were significantly lower than those in II and III type NSCs. Four VDCC subunits derived from three transcripts were predicted from a transcriptome database of the cerebral ganglia. Among these transcripts, Cavα1, Cavβ, and Cavα2/δ were predicted to encode 1674, 554, and 776 amino acids, respectively, and they shared conservative domains with VDCC subunits in other species. Overall, these findings provide an important basis for further studies on the neuroendocrine mechanisms in crustaceans.

Amyloid β42 peptide is toxic to non-neural cells in Drosophila yielding a characteristic metabolite profile and the effect can be suppressed by PI3K.

ABSTRACTThe human Aβ42 peptide is associated with Alzheimer's disease through its deleterious effects in neurons. Expressing the human peptide in adult Drosophila in a tissue- and time-controlled manner, we show that Aβ42 is also toxic in non-neural cells, neurosecretory and epithelial cell types in particular. This form of toxicity includes the aberrant signaling by Wingless morphogen leading to the eventual activation of Caspase 3. Preventing Caspase 3 activation by means of p53 keeps epithelial cells from elimination but maintains the Aβ42 toxicity yielding more severe deleterious effects to the organism. Metabolic profiling by nuclear magnetic resonance (NMR) of adult flies at selected ages post Aβ42 expression onset reveals characteristic changes in metabolites as early markers of the pathological process. All morphological and most metabolic features of Aβ42 toxicity can be suppressed by the joint overexpression of PI3K.

HISTOMORPHOLOGICAL CHANGES IN THE BRAIN IN RELATION TO OVARIAN CYCLE OF FRESHWATER CRAB, BARYTELPHUSA CUNICULARIS

Ovarian maturation by neurosecretory cells in the brain of freshwater crab, Barytelphusa cunicularis have been examined. The histological scrutiny of the brain of Barytelphusa cunicularis related with three types (A, B and C) of neurosecretory cells, which are classified on the basis of size, shape and tinctorial characters. All these types of cells marked annual cyclic changes of cytoplasmic material in association with ovarian cycle. The activity of these cells has been correlated with the ovarian cycle. They are distinguishable by their size, nature locations, shape, nucleus position, cell measure and the secretory product in the cytoplasm. The result indicates that the neurosecretory A, B and C cells of the brain seen involved in the process of mating ovulation. The neurosecretory materials staining intensity index of these cells is described.

From so simple a beginning - what amphioxus can teach us about placode evolution.

Cranial placodes are an evolutionary novelty of vertebrates that give rise to many cranial sense organs and ganglia, as well as to the neurosecretory anterior pituitary. Although amphioxus does not have placodes, it shares with vertebrates several of the ectodermal patterning mechanisms and cell types that are important in placode development. Comparisons between amphioxus, vertebrates and other groups provide us with important insights into what the last common chordate ancestor probably looked like and allow us to propose a scenario for how placodes evolved by rewiring of gene regulatory networks. After reviewing ectodermal patterning and the cytodifferentiation of neurosecretory and sensory cells in amphioxus, this review will argue that the evolutionary origin of cranial placodes involved 1) the concentration of sensory and neurosecretory cell types in the head by linking their development to ancient cranial ectodermal patterning mechanisms; and 2) the formation of high density arrays of sensorineural precursors by intercalating a progenitor expansion module into the gene regulatory network driving differentiation of sensory or neurosecretory cells.

Localization and identification of crustacean hyperglycemic hormone producing neurosecretory cells in the eyestalk of blue swimmer crab, Portunus pelagicus.

This study intensely focuses on to the localization and identification of crustacean hyperglycemic hormone (CHH) producing neurosecretory cells in the eyestalk of the blue swimmer crab Portunus pelagicus. Anti-Carcinus maenas-CHH was used to identify the location of CHH neurosecretory cells by immunohistochemistry. Ten pairs of eyestalks were collected from intact adult intermoult female crab and fixed in Bouin's fixative. Eyestalks were serially sectioned and stained with chrome-hematoxylin-phloxine stain. Histological studies show the presence of different types of neurosecretory cells namely A (multipolar), B (tripolar), C (bipolar), D (unipolar), E (oval), and F (spherical) in the medulla interna, externa, and terminalis regions based on their size, shape, and tinctorial properties. The neurohemal organ, sinus gland (SG) was observed laterally between medulla interna and terminalis regions. Immunohistochemical studies showed the presence of distinct CHH-like immunoreactivity in the optic ganglia. Divergent group of neurosecretory cells with varying degree of immunoreactivity with Anti-Carcinus maenas-CHH (low, moderate, and intense reactivity) were identified in medulla terminalis, medulla interna, medulla externa, and sinus gland. The present study maps the various types of neurosecretory cells in the optic ganglia and also shows the presence of CHH-like immunoreactivity in various regions of optic ganglia in P. pelagicus. The presence of these unique neurosecretory cell types with larger cell diameter in medulla terminalis, a region that bears the neurosecretory cell bodies, suggest high secretory activity.

C4-P-01Classification of Neurons in Major Ganglia ofPomacea canaliculata

Pomacae canaliculata was an economic species in terms of food consumption in Thailand [1]. However, at present, this snail becomes a cause of major problems in agriculture as a wetland pest [2]. Therefore, a basic knowledge of the snail biology is crucial for an initial attempt to understand how the snail successfully survives and reproduces. The objective of the present study was to categorize types of neurosecretory (NS) cells in major ganglia of this invasive mollusk. Based on cell sizes, neurons in the cerebral, buccal, and pleuropedal ganglia were classified into four NS cell types: NS1-NS4. Sizes of the NS1-NS4 cells were approximately 15-20, 31-35, 50-55, and 70-87 μm, respectively. Cytoplasm of the NS1 cells contained medium NS granules located close to the nucleus. In contrast, the NR2 cells contained large NS granules, which were observed near the nucleus. In the NR3 cells, small NS granules were scattered in the cytoplasm. In addition, the NS4 cells contained medium NS granules, which were clumped at one pole of the cytoplasm. This result was corresponded to those of closely related species [3]. However, function of the NS cells must be determined in further studies. [1] Naylor R, Ambio 25 (1996) 443-448 [2] Esbenet AL and Martin, PR, Biocell 26 (2002) 83-89. [3] Thongkukiatkul A, Sobhon P, Upatham ES, Kruatrachue M, Wanichanon C, Chitramvong YP, Pumthong T, Journal of Shellfish Research 20 (2001) 733-741. Figure: NS1-NS4 in the ganglia C4-P-01 doi:10.1093/jmicro/dfv319

Neurons without dendrites? – A novel type of neurosecretory cell in locusts

Small-diameter nerves were found that are associated with the lateral peripheral nerves of the unfused abdominal ganglia of locusts. Such small nerves were observed in about 30% of all cases in Locusta migratoria, more than 60% in Schistocerca gregaria. Retrograde staining of these small nerves showed two somata in the posterior, lateral, and ventral region of an abdominal ganglion. These cells give rise to the small nerves that accompany the big lateral nerves and, on their surface, form putative neurohaemal release sites. Astonishingly the cells do not form any dendritic ramifications within the neuropile of the ganglia.

Vertebrate cranial placodes as evolutionary innovations--the ancestor's tale.

Evolutionary innovations often arise by tinkering with preexisting components building new regulatory networks by the rewiring of old parts. The cranial placodes of vertebrates, ectodermal thickenings that give rise to many of the cranial sense organs (ear, nose, lateral line) and ganglia, originated as such novel structures, when vertebrate ancestors elaborated their head in support of a more active and exploratory life style. This review addresses the question of how cranial placodes evolved by tinkering with ectodermal patterning mechanisms and sensory and neurosecretory cell types that have their own evolutionary history. With phylogenetic relationships among the major branches of metazoans now relatively well established, a comparative approach is used to infer, which structures evolved in which lineages and allows us to trace the origin of placodes and their components back from ancestor to ancestor. Some of the core networks of ectodermal patterning and sensory and neurosecretory differentiation were already established in the common ancestor of cnidarians and bilaterians and were greatly elaborated in the bilaterian ancestor (with BMP- and Wnt-dependent patterning of dorsoventral and anteroposterior ectoderm and multiple neurosecretory and sensory cell types). Rostral and caudal protoplacodal domains, giving rise to some neurosecretory and sensory cells, were then established in the ectoderm of the chordate and tunicate-vertebrate ancestor, respectively. However, proper cranial placodes as clusters of proliferating progenitors producing high-density arrays of neurosecretory and sensory cells only evolved and diversified in the ancestors of vertebrates.

Differences in acid-induced currents between oxytocin-mRFP1 and vasopressin-eGFP neurons isolated from the supraoptic and paraventricular nuclei of transgenic rats

The hypothalamic supraoptic nucleus (SON) and paraventricular nucleus (PVN) consists of two types of magnocellular neurosecretory cells, oxytocin (OXT) and arginine vasopressin (AVP). We generated and characterized rats that express an OXT-monomeric red fluorescent protein 1 (mRFP1) and an AVP-enhanced green fluorescent protein (eGFP) fusion transgene. These transgenic rats enable the visualization of OXT or AVP neurons. Taking advantage of this, we examined the differences between OXT-mRFP1 neurons and AVP-eGFP neurons in response to acid. Acid-sensing ion channels (ASICs) are neuronal voltage-insensitive cationic channels that are activated by extracellular acidification. Although functional ASICs have been identified in AVP neurons, differences in acid-induced currents between OXT and AVP neurons in SON have not been reported. In the present study, we used the whole-cell patch-clamp technique to investigate differences between OXT-mRFP1 neurons and AVP-eGFP neurons reaction to acid in SON and PVN. In voltage clamp mode, lowering extracellular pH evoked inward currents in both OXT-mRFP1 neurons and AVP-eGFP neurons. In our findings, the acid-induced currents in the OXT-mRFP1 neurons were significantly smaller than those in the AVP-eGFP neurons. These acid-induced currents were inhibited by amiloride, a known blocker of ASICs. Further, to compare the response to acid between OXT-mRFP1 and AVP-eGFP neurons in the same transgenic rat, we used a double transgenic rat by mating an OXT-mRFP1 transgenic rat with an AVP-eGFP transgenic rat. The acid-induced currents of OXT-mRFP1 neurons were significantly smaller than those of AVP-eGFP neurons from the double transgenic rats. These currents were almost completely inhibited by amiloride. The difference of acid-sensitivity between OXT and AVP neurons might contribute to maintaining systematic order in hypothalamic function.

Relationship Between Gonad Condition and Neurosecretory Cell Activity in the Green-Lipped Mussel, <i>Perna canaliculus</i>

The relationship between the activity of neurosecretory cells and gonad development of Perna canaliculus was investigated. The variation in staining intensity of the neurosecretory cells in different ganglia was evaluated. Changes in staining intensity of neurosecretory cells (NSC) were correlated with gonad development. The variation in colour intensity (CI) resulted from differences in the amount of secretory materials within the NSCs. The neurosecretory cell types A and B showed a similar pattern of staining intensity, and showed correlation with gametogenesis and spawning. At the beginning of gonad development, these cells possessed very few granules and the number of granules in the cells increased with gonad maturation. The staining intensity decreased in A and B- cells just after spawning. Cell types C and D did not show any substantial changes in colour intensity with gonad changes.DOI: http://dx.doi.org/10.3329/pa.v18i2.18169 Progress. Agric. 18(2): 135 - 148, 2007

Electrophysiological Effects of Kainic Acid on Vasopressin-Enhanced Green Fluorescent Protein and Oxytocin-Monomeric Red Fluorescent Protein 1 Neurones Isolated from the Supraoptic Nucleus in Transgenic Rats

The supraoptic nucleus (SON) contains two types of magnocellular neurosecretory cells: arginine vasopressin (AVP)-producing and oxytocin (OXT)-producing cells. We recently generated and characterised two transgenic rat lines: one expressing an AVP-enhanced green fluorescent protein (eGFP) and the other expressing an OXT-monomeric red fluorescent protein 1 (mRFP1). These transgenic rats enable the visualisation of AVP or OXT neurones in the SON. In the present study, we compared the electrophysiological responses of AVP-eGFP and OXT-mRFP1 neurones to glutamic acid in SON primary cultures. Glutamate mediates fast synaptic transmission through three classes of ionotrophic receptors: the NMDA, AMPA and kainate receptors. We investigated the contributions of the three classes of ionotrophic receptors in glutamate-induced currents. Three different antagonists were used, each predominantly selective for one of the classes of ionotrophic receptor. Next, we focused on the kainate receptors (KARs). We examined the electrophysiological effects of kainic acid (KA) on AVP-eGFP and OXT-mRFP1 neurones. In current clamp mode, KA induced depolarisation and increased firing rates. These KA-induced responses were inhibited by the non-NMDA ionotrophic receptor antagonist 6-cyano-7-nitroquinoxaline-2,3(1H4H)-dione in both AVP-eGFP and OXT-mRFP1 neurones. In voltage clamp mode, the application of KA evoked inward currents in a dose-dependent manner. The KA-induced currents were significantly larger in OXT-mRFP1 neurones than in AVP-eGFP neurones. This significant difference in KA-induced currents was abolished by the GluK1-containing KAR antagonist UBP302. At high concentrations (250-500 μm), the specific GluK1-containing KAR agonist (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA) induced significantly larger currents in OXT-mRFP1 neurones than in AVP-eGFP neurones. Furthermore, the difference between the AVP-eGFP and OXT-mRFP1 neurones in the ATPA currents was approximately equal to the difference in the KA currents. These findings suggest that the GluK1-containing KARs may be more highly expressed in OXT neurones than in AVP neurones. These results may provide new insight into the physiology and synaptic plasticity of SON neurones.