Subcommissural organ–Reissner's fiber complex of the teleost Clarias batrachus responds to GABA treatment

Subcommissural organ (SCO) is a highly specialized ependymal gland located in the roof of the third ventricle. The secretory products of the SCO, which condense to form Reissner's fiber (RF), were recently found to cross-react with the anti-calcitonin antibody. To understand the mechanisms regulating the formation of the RF and the possible function of these discrete structures, we studied the response of the SCO–RF complex to intracranially administered GABA, using immunocytochemical labeling with anti-calcitonin antibody. Although the SCO–RF complex of control fish was intensely immunostained, 1 h after GABA treatment, the ependymal cells revealed partial loss of immunoreactivity; the RF showed occasional loss of immunoreactivity with its diameter increased by about 56% of the control value. Following 2 h of GABA treatment, the SCO revealed dramatic loss of calcitonin-like immunoreactivity from the ependymal cells. The RF showed a dual response in this group, while in some segments the RF appeared conspicuously thick, elsewhere it appeared thin. The mean diameter was, however, not significantly different from the normal. Following 4 h of GABA treatment, while calcitonin-like immunoreactive material made its reappearance in the SCO, the RF diameter was uniformly reduced to about 35% of the control value. The responses by the RF as well as the SCO to intracranially administered GABA were blocked by pretreatment with bicuculline, a GABA_A receptor antagonist. The results suggest that GABA, acting via GABA_A receptors, may trigger the release of secretory material from the SCO and induce histomorphological changes in the RF indicative of discharge of stored material.     

Distribution of monoamine oxidase (MAO) in relation to the hypothalamo-hypophyseal system of the teleost Clarias batrachus (L.)

Summary Varying degrees of monoamine oxidase (MAO) activity were noticed all along the hypothalamo-hypophyseal neurosecretory tract inC. batrachus. Intense activity was evident on the wall of the secretory cells of the adenohypophysis, neurons of the nucleus preopticus (NPO) and nucleus lateralis tuberis (NLT). However, MAO activity was also observed in the cytoplasm of some neurons in the ventromedian region of the NLT and groups of cells present in the neurohypophyseal ramifications of the pars intermedia. A strong accumulation of formazan granules in the median eminence (ME) and the neuroadeno interface lends further support to the view thatC. batrachus has a ME of both the tetrapodan and the teleostean type. The distributional pattern of MAO in the hypothalamus and hypophysis suggests that monoaminergic fibres are probably involved in the secretory mechanism of the releasing factors and pituitary hormones.Abbreviations AF Aldehyde fuchsin - CNST Common neurosecretory trunk - ME Median eminence - NH Neurohypophysis - NLT Nucleus lateralis tuberis - NPO Nucleus preopticus - NST Neurosecretory tract - PPD Proximal pars distalis - RPD Rostral pars distalis     

Cytoarchitectonic pattern of the hypothalamus in the catfish, Clarias batrachus (Linn.).

The hypothalamus of the catfish, Clarias batrachus has been investigated to reveal the organization of various parvocellular (aldehyde fuchsin-negative) nuclear complexes and to suggest homologies. The hypothalamus of C. batrachus can be divided into the preoptic area, postoptic area, tuberal area and the laterally placed inferior lobes. Application of cytoarchitectonic criteria permits the delineation of 9 distinct nuclear complexes in the preoptic area extending along the periventricular margin of the preoptic recess. The postoptic area is represented by only two nuclear groups, the nucleus postopticus lateralis and the nucleus of the horizontal commissure. The tuberal area consists of as many as 14 nuclei, some are divisible into subnuclei, arranged in an elaborate pattern. The nucleus lateralis tuberis is located in the mid-ventral margin of the tuberal area and revealed two subdivisions, the pars anterior and pars posterior. At the mid-tuberal level, the nucleus anterior tuberis is well-developed and revealed dorsal, ventral and lateral subdivisions. The paraventricular organ is encircled by nucleus of the paraventricular organ. The conspicuous lateral recesses are flanked dorsally by nucleus recessus lateralis superior and ventrally by nucleus recessus lateral by nucleus recessus lateralis superior and ventrally by nucleus recessus lateralis inferior. In the caudal tuberal area, in close proximity of the pituitary, the nucleus arcuatus hypothalamicus is described for the first time. The recessus posterioris is encircled by nucleus recessus posterioris. The inferior lobes are massive and each consists of 7 well-defined nuclear complexes. The nucleus lobi inferioris centralis is represented by giant-sized cells clustered in the center of the lobes. The periventricular nucleus of the inferior lobes occupies the area surrounding the recesses of the inferior lobes. The hypothalamus shows 4 circumventricular organs. The organum vasculosum laminae terminalis is situated along the ventral wall of the preoptic recess. While the paraventricular organ is located in the dorsal wall of the third ventricle, the posterior recess organ is located in the postero-ventral wall of the third ventricle. The saccus vasculosus is small, capsule-like and located caudally in between the two mamillary nuclei.     

Subcommissural organ/Reissner's fiber complex: characterization of SCO-spondin, a glycoprotein with potent activity on neurite outgrowth

In the developing vertebrate nervous system, several proteins of the thrombospondin superfamily act on axonal pathfinding. By successive screening of a SCO-cDNA library, we have characterized a new member of this superfamily, which we call SCO-spondin. This extracellular matrix glycoprotein of 4,560 amino acids is expressed and secreted early in development by the subcommissural organ (SCO), an ependymal differentiation located in the roof of the Sylvian aqueduct. Furthermore, SCO-spondin makes part of Reissner's fiber (RF), a thread-like structure present in the central canal of the spinal cord. This novel protein shows a unique arrangement of several conserved domains, including 26 thrombospondin type 1 repeats (TSR), nine low-density lipoprotein receptor (LDLr) type A domains, two epidermal growth factor (EGF)-like domains, and N- and C-terminal von Willebrand factor (vWF) cysteine-rich domains, all of which are potent sites of protein-protein interaction. Regarding the huge number of TSR, the putative function of SCO-spondin on axonal guidance is discussed in comparison with other developmental molecules of the CNS exhibiting TSR. To correlate SCO-spondin molecular feature and function, we tested the effect of oligopeptides, whose sequences include highly conserved amino acids of the consensus domains on a neuroblastoma cell line B 104. One of these peptides (WSGWSSCSRSCG) markedly increased neurite outgrowth of B 104 cells and this effect was dose dependent. Thus, SCO-spondin is a favorable substrate for neurite outgrowth and may participate in the posterior commissure formation and spinal cord differentiation during ontogenesis of the central nervous system.     

Identification and partial characterization of the secretory glycoproteins of the bovine subcommissural organ-Reissner's fiber complex. Evidence for the existence of two precursor forms.

The subcommissural organ (SCO) is a brain gland whose secretory material is released into the cerebrospinal fluid where it condenses into a thread-like structure known as Reissner's fiber (RF). This fiber extends along the aqueduct, fourth ventricle and central canal of the spinal cord. The present investigation was designed to identify and partially characterize the secretory products of the bovine SCO in their intracellular location and after they have been released and packed into RF form. 5,000 SCOs were dissected out under a microscope, whereas RF of 30,000 cows were collected by perfusing the central canal of the spinal cord with artificial cerebrospinal fluid. Extracts of SCO and RF were used for (i) raising polyclonal antibodies; (ii) immunoblotting; (iii) lectin binding on electrotransfers: concanavalin A (affinity = mannose, glucose) and Limax flavus agglutinin (affinity = sialic acid); (iv) immunoaffinity chromatography; (v) preparative SDS-PAGE and raising of polyclonal antibodies against each of the secretory glycoproteins identified in the immunoblots. All antibodies and the two lectins were also applied to tissue sections of the SCO and RF of several species. The immunocytochemical study of the bovine SCO using an anti-RF serum showed that the secretory material present in the rough endoplasmic reticulum (RER), secretory granules and in RF is strongly immunoreactive. Con A binding sites were only found in the endoplasmic reticulum, whereas Limax flavus agglutinin revealed secretory granules and RF, only. In the blots the immunostaining was used to identify secretory polypeptides. The glycosylated nature of the latter was established by their affinity for Con A and/or Limax flavus agglutinin. Furthermore, this latter lectin allowed us to distinguish whether the intracellular source of a secretory glycoprotein is from a pre-Golgi (RER) or a post-Golgi (secretory granules) compartment. Four glycoproteins were identified in the SCO with apparent molecular weights of 540, 450, 320 and 190 kDa. The three former were also purified by immunoaffinity chromatography. The 540 and 320 kDa forms are present in the SCO but missing in RF, have affinity for Con A, but not for LFA. It is suggested that these two compounds correspond to two precursor forms. The 450 and 190 kDa glycoproteins are present in both, the SCO and RF, and have affinity for Con A and Limax flavus agglutinin. These most likely correspond to processed forms. The presence of more than one precursor was further substantiated by immunocytochemical findings using antisera against the 540, 450 and 320 kDa forms.(ABSTRACT TRUNCATED AT 400 WORDS)     

The intrinsic organization of the nucleus preopticus in the catfish, Clarias batrachus (Linn.).

The organization of magnocellular neurons of the nucleus preopticus (NPO) of the catfisch, Clarias batrachus is described with the help of Nissl and aldehyde fuchsin stains and rapid Golgi technique. The NPO consists of a bilaterally located paraventricular group (PV) on either side of the preoptic recess and a supraoptic group (SO) dorsal to the optic tract. The PV shows a vertical laminar arrangement--smaller cells located adjacent to the ependyma and larger ones farther away. On the basis of the pattern of arrangement, the PV is divisible into 4 subdivisions-1: composed of small, spindle-shaped, bipolar, vertically oriented neurons characterized with short processes; subdivision 2: formed of large multipolar neurons with dendrites extending in different directions and some processes projecting into the cerebrospinal fluid (CSF); subdivision 3: consists of larger perikarya forming the lateral margin of the PV, characteristically, the processes of these neurons extend ventrolaterally and penetrate the optic tract; subdivision 4: situated posterodorsally to the above subdivisions of the PV and shows very large neurons, generally multipolar and exhibiting processes with projections to medial (MFB) and lateral (LFB) forebrain bundles, CSF, telencephalon, and towards the caudal diencephalon and tegmentum. The SO consists of three subdivisions, also arranged progressively lateralwards in order of increasing size. Processes of the lateral-most subdivision communicate with the MFB, LFB and extend into the optic tract. The NPO of C. batrachus seems comparable with the paraventricular and supraoptic nuclei of amniotes. Further the nucleus shows a complex organization and parcellation of SO and PV. By virtue of the occurrence of processes, connectivities and interneurons, the nucleus appears to play a pivotal role in receiving and integrating a wide spectrum of information to eventually influence a variety of neuroendocrine functions.     

Lead nitrate induced changes in the brain constituents of the freshwater fish Clarias batrachus (L)

Exposure of C batrachus to 5 ppm lead nitrate for 150 days resulted in the significant elevation of brain histamine and serotonin content, but Gamma aminobutyric acid level showed a decrease. Lead significantly reduced the brain monoamine oxidase and acetylcholinesterase activity. In addition, lead significantly lowered the brain lipid, cholesterol, protein and ascorbic acid contents. These findings suggest that lead significantly impairs the brain neurotransmitter function.     

Role of Isotocin in the Regulation of the Hypophysiotropic Dopamine Neurones in the Preoptic Area of the Catfish,Clarias batrachus

Dopamine (DA) has emerged as a potent inhibitory neuromodulator of luteinsing hormone (LH) secretion and reproduction in teleosts. The DA neurones located in the anterior subdivision of nucleus preopticus periventricularis (NPPa) in the preoptic area (POA) innervate the pituitary gland and regulate LH cells. Although a reduction in the inhibitory DAergic tone is crucial for stimulatory action of gonadotrophin‐releasing hormone (GnRH) on LH cells, the role of other hypothalamic factors is suggested but not fully understood. Nonapeptide, isotocin (IST) has emerged as a likely candidate that may also influence the LH cell function. IST neurones reside in the nucleus preopticus and innervate LH cells. While IST treatment dramatically elevated LH secretion, the IST levels in brain peaked during spawning. In a pilot study on the catfish, Clarias batrachus, we observed a dense network of IST‐immunoreactive (IST‐IR) fibres in the NPPa, the region known to harbour hypophysiotropic DA neurones. Application of the double immunofluorescence method showed a dense IST‐IR fibre network around the tyrosine hydroxylase‐immunoreactive (TH‐IR) neurones in the NPPa region. A great majority of the TH‐IR neurones in the NPPa were contacted by IST‐IR fibres during the spawning phase. The NPPa therefore appears to be a site for the intense interaction of DA and IST. IST‐IR fibre innervation in NPPa showed reproduction phase‐dependent changes. The percent fluorescent area of IST‐IR fibres showed a gradual increase from the resting through prespawning phases (resting: 7.5 ± 1.04; preparatory: 8.6 ± 0.8; prespawning: 15.5 ± 1.4), reaching a peak in the spawning phase (28 ± 2.3; P < 0.001). Compared to the spawning phase, a drastic reduction in IST‐IR fibres in the NPPa was observed during the postspawning phase (8.4 ± 0.9; P < 0.001). Superfused slices of the POA of C. batrachus treated with IST peptide resulted in a significant reduction in TH immunoreactivity in the NPPa (Control: 45.3 ± 4.2; IST peptide, 5 μm : 29.4 ± 4.7; P < 0.05). We suggest that the intense interaction between IST and DA in the NPPa, most probably of an inhibitory nature, may be critical for the regulation of LH cells and reproduction in teleosts.     

Executive dysfunction in hyperhomocystinemia responds to homocysteine-lowering treatment

An elevated serum homocysteine level is a risk factor for the development of cognitive impairment. Reported is a late-onset case of hyperhomocystinemia due to a vitamin B12 metabolic deficit (cobalamin C) with cognitive impairment, primarily in frontal/executive function. After homocysteine-lowering therapy, the patient's functional and neuropsychological status improved in conjunction with a decrease in leukoariosis on his MRI scan. These findings suggest that homocysteine-related cognitive impairment may be partially reversible.     

Modulation of the GABA receptor complex by a steroid anaesthetic

The interactions of a steroid anaesthetic, alphaxalone, with the GABA receptor-ionophore complex were investigated by two different experimental approaches. In the rat cuneate nucleus slice, alphaxalone (0.1-10 microM) potentiated depolarizing responses to superfused GABA and muscimol, but not those to glycine. The potentiating effect of alphaxalone was unaltered by the benzodiazepine antagonist Ro 15-1788. Alphaxalone (0.1-30 microM) also enhanced [3H]muscimol binding to rat brain membranes in the presence of Cl-ions; the enhancing effect on [3H]muscimol binding was abolished by Triton X-100. Analysis of binding curves for [3H]muscimol indicated that the steroid anaesthetic increases the affinity for [3H]muscimol of low affinity binding sites; this property is shared by pentobarbitone. The physiologically inactive beta-hydroxy isomer of the steroid was without activity in either of the experimental situations at 30 microM. It is suggested that alphaxalone and pentobarbitone share a common mode of action on the GABA system, which may be relevant to the mechanisms by which these drugs produce anaesthesia.     

Reproduction phase-related variations in neuropeptide Y immunoreactivity in the olfactory system, forebrain, and pituitary of the female catfish, Clarias batrachus (Linn.)

The aim of this study was to determine whether neuropeptide Y (NPY) immunoreactivity in the cells and fibers in the forebrain and pituitary of Clarias batrachus is linked to the annual reproductive cycle. A steady rise in luteinizing hormone (LH) immunoreactivity was seen in the pituitary through preparatory (February-April) and prespawning (May-June) phases; it was greatly reduced during spawning (July-August; P < 0.001) and partially replenished during postspawning (September-November; P < 0.01) through resting (December-January) phases. Although NPY immunoreactivity in olfactory receptor neurons and olfactory nerve layer in olfactory bulb was gradually augmented during resting through prespawning phases (P < 0.001), attaining a peak in spawning phase (P < 0.001), a dramatic decline was encountered during postspawning phase (P < 0.001). A similar pattern was also observed in NPY-containing fibers of the medial olfactory tract (MOT) and pituitary. However, a different pattern of NPY immunoreactivity was observed in the neurons of nucleus entopeduncularis (NE) and nucleus preopticus periventricularis (NPP). Whereas these neurons and fibers in the forebrain showed significant augmentation during the resting through prespawning phases (P < 0.001), the immunoreactivity dramatically declined during spawning (P < 0.001) and was partially replenished in the postspawning phase. Testosterone injection of juveniles significantly augmented (P < 0.001) NPY immunoreactivity in NE neurons. We suggest that NPY cells of NE and NPP, and related fiber systems, might be involved in processing of sex steroid-borne information and regulation of the gonadotropin-releasing hormone-LH axis.     

Interactions of etifoxine with the chloride channel coupled to the GABA(A) receptor complex

This study examined the nature of the interactions of etifoxine, an anxiolytic and anticonvulsant compound, with the GABA(A) receptor/chloride channel complex. In membrane preparations of Sprague-Dawley rat cerebral cortex, etifoxine competitively inhibited the binding of [35S]t-butylbicyclophosphoro-thionate (TBPS), a specific ligand of the GABA(A) receptor chloride channel site. In vivo studies demonstrated an anticonvulsant effect of etifoxine (50 and 75 mg/kg, i.p.) against the clonic convulsions induced by TBPS in CD1 mice. Flumazenil (10 and 40 mg/kg, i.p.), an antagonist of benzodiazepine sites at GABA(A) receptors, had no effect on the action of etifoxine. These findings suggest that etifoxine exerts its effect by interacting with the Cl- channel of GABA(A) receptors and probably by facilitating GABAergic inhibition.     

Anticonvulsant steroids and the GABA/benzodiazepine receptor-chloride ionophore complex

The ability of steroids to influence brain excitability is well documented. Certain 3 alpha-hydroxylated pregnanes are known to possess anticonvulsant and sedative-hypnotic/anesthetic properties. It has been observed that the seizure susceptibility in menstruating women with catamenial epilepsy appears to be correlated with changes in ovarian steroid levels. However, the underlying mechanism of these steroid influences on brain activity has only been recently revealed by pharmacological studies. These studies have provided compelling evidence for the presence of a novel steroid recognition site on the GABAA-benzodiazepine receptor complex (GBRC). Steroids may interact with this site with high affinity and stereospecificity to enhance chloride channel conductance in a manner similar to that produced by benzodiazepines (BZs) or barbiturates. The existence of such a steroid site on the GBRC is further supported by recent experiments involving the transfection of GABAA receptor cDNAs into a human embryonic kidney cell line. Based on the knowledge of the structure-activity requirements for the interaction of steroids with this novel recognition site, it is conceivable that the development of new anticonvulsant steroids with high therapeutic indices can be achieved.     

Gamma-vinyl GABA treatment of Huntington's disease

In a double-blind, crossover study gamma-vinyl GABA, 2 g/day, and placebo were administered orally for 2 weeks each to six patients with Huntington's disease. Five patients were treated concomitantly with a neuroleptic maintained at constant dose. No consistent beneficial effects on the hyperkinetic movements, abnormal motor function, or ability to carry out normal activities were evident with gamma-vinyl GABA treatment. Treatment was tolerated without clinically significant alterations in the physiologic or biochemical tests used for monitoring. These results suggest that increasing CNS GABAergic function is unlikely to ameliorate Huntington's disease.     

Chronic benzodiazepine treatment and cortical responses to adenosine and GABA

The effects of chronic treatment of mice with clonazepam have been examined on the responses of neocortical slices to adenosine, 5-hydroxytryptamine (5-HT) and γ-aminobutyric acid (GABA). Responses to these agonists were measured as changes in the depolarisation induced byN-methyl-d-aspartate (NMDA). Added to the superfusion medium diazepam blocked responses to adenosine but not 5-HT; this effect was not observed with 2-chloroadenosine or in the presence of 2-hydroxynitrobenzylthioguanosine. GABA was inactive in control slices but chronic treatment with clonazepam induced responses to GABA and enhanced responses to adenosine but not 5-HT. It is suggested that the induction of GABA responses may reflect the up-regulation of GABA receptors, but the increase of adenosine responses by clonazepam implies that there is no simple relationship between adenosine receptor binding and functional responses.     

How the brain recognizes and responds to shock

The rat that wishes to reach the goal of his learning and attain the reward, his very own mountain of cheese, must be able to navigate through the maze (Figure One). So the nurse, to reach the goal of understanding why the outward manifestations of shock occur must learn to navigate through the physiological maze of the body. After considering some general information on shock, we will embark on a tour through the maze created by the shock syndrome.     

GABA and glycine immunoreactivity in the guinea pig superior olivary complex

Immunoperoxidase immunocytochemistry was employed to examine the distribution of gamma-aminobutyric acid (GABA)-and glycine (GLY)-immunoreactive cells, fibers, and terminals in the guinea pig superior olivary complex. The nuclei studied were the lateral superior olive (LSO), medial superior olive (MSO), superior paraolivary nucleus (SPN), and the medial, ventral, and lateral nuclei of the trapezoid body (MNTB, VNTB, and LNTB, respectively). The majority of LSO neurons exhibited GABA-immunoreactive (+) labeling. These same neurons were also lightly GLY+. Extensive perisomatic punctate GLY + labeling was observed on most LSO neurons; these puncta most likely correspond to synaptic terminals. A very small number of MSO fusiform neurons were GABA +, and none were GLY +. The GLY positive perisomatic punctate labeling around most MSO neurons, although abundant, was not as profuse as that observed in the LSO. The MNTB neurons corresponding to the principal and elongate types were intensely GLY + and were contacted by small numbers of GLY + puncta. There was extensive GLY + punctate labeling in the SPN that surrounded the cell bodies of most of its large, radiate neurons and many of the smaller, fusiform neurons. The few large, radiate neurons that were lightly GLY + possessed far fewer GLY + puncta on their perikarya. The distribution of GABA + puncta was generally diffuse and scattered throughout the nuclei described above. In the VNTB and LNTB, several large neurons of various shapes were GLY + as were the small, oval neurons. The extent of GLY + punctate labeling was quite variable in both nuclei. The majority of perikarya in the VNTB and LNTB were GABA +. A light distribution of GABA + puncta was observed on most cell bodies in both nuclei. Peridendritic GABA + punctate labeling was dense in the VNTB neuropil. Two small populations of GLY + neurons were observed outside of the named nuclei of the SOC; one was located dorsal to the LSO, near its dorsal hilus, and the other was identified near the medial pole of the LSO. The somata of both populations possessed extremely sparse GLY + punctate labeling. In general, these results agree with and expand on findings in rodents from previous studies. There appears, however, to be differences between the guinea pig and cat with regard to the proportions of GABA + neurons in the LSO and GLY + punctate labeling in the MSO.