Cross-talk between neurons and glia: highlights on soluble factors

The development of the nervous system is guided by a balanced action between intrinsic factors represented by the genetic program and epigenetic factors characterized by cell-cell interactions which neural cells might perform throughout nervous system morphogenesis. Highly relevant among them are neuron-glia interactions. Several soluble factors secreted by either glial or neuronal cells have been implicated in the mutual influence these cells exert on each other. In this review, we will focus our attention on recent advances in the understanding of the role of glial and neuronal trophic factors in nervous system development. We will argue that the functional architecture of the brain depends on an intimate neuron-glia partnership.

Gallbladder neuron count in cholelithiasis patients with and without Chagas disease

Various investigators agree that the incidence of cholelithiasis is greater in patients with Chagas disease. The most plausible explanation for this is based on the parasympathetic denervation that occurs over the whole digestive tract due to Chagas disease. In order to analyze the occurrence of this alteration, gallbladder neuron counts were performed on cholelithiasis patients with and without Chagas disease who were being treated at the Department of Digestive Surgery, Universidade Federal do Triângulo Mineiro, Uberaba, Brazil. In the present study, a notable reduction in the number of neurons in the gallbladder wall was observed in Chagas patients, in comparison with non-Chagas subjects.

Caracterização morfoanatômica do melão gália no ponto de colheita

O objetivo deste trabalho foi caracterizar morfoanatomicamente o melão 'Gália', com ênfase no exocarpo e mesocarpo, no ponto de colheita. Os frutos foram obtidos em propriedade comercial localizada no município de Mossoró-RN, aos 65 dias de cultivo após a semeadura. Em laboratório, realizou-se a caracterização morfológica através da determinação da massa, espessura da polpa, comprimento longitudinal e transversal, relação de formato e índice de rendilhamento. Análises em tomografia de ressonância magnética nuclear foram realizadas para a determinação da integridade dos tecidos. As análises anatômicas foram realizadas utilizando-se de microscopia de luz e eletrônica de varredura. O melão Gália, híbrido 'Solar King', foi caracterizado como fruto do tipo baga, de formato esférico, com massa média de 1.021 g. As imagens sugerem que, na região do mesocarpo, o metabolismo acentuado e o amadurecimento mais avançado nos tecidos do centro do fruto podem ser responsáveis pelo descolamento da placenta e o amaciamento mais rápido dos tecidos em volta da cavidade interna. As áreas rendilhadas, juntamente com as ceras epicuticulares e a estrutura adensada das primeiras camadas subepidérmicas podem contribuir para o controle da perda de umidade do fruto e a resistência às injúrias mecânicas.

Estrutura e diversidade do componente arbóreo da floresta na Estação Ecológica dos Caetetus, Gália, SP

O estudo fitossociológico, se realizado em diferentes estratos verticais da floresta, fornece dados de grande valia para a compreensão da dinâmica da comunidade. Efetuou-se levantamento das espécies arbóreas presentes em diferentes estratos, em área de 6.000 m² de floresta madura, na Estação Ecológica dos Caetetus, Gália, SP. Foram utilizadas 60 parcelas de 10 x 10 m, para indivíduos com diâmetro do caule a 1,30 m acima do nível do solo (DAP) a partir de 5 cm (estrato superior); 10 x 2 m, para indivíduos com DAP entre 1 e 5 cm (estrato intermediário) e 60 sub-parcelas de 2 x 2 m, para indivíduos menores que 1 cm de DAP (estrato inferior). Verificou-se que a diversidade, a composição florística e a densidade relativa das espécies variam entre estratos. No estrato superior, com 1.080 indivíduos.ha-1 e área basal de 31,2 m².ha-1, encontraram-se 62 espécies (28 famílias), tendo sido as mais importantes, em ordem decrescente de IVI: Metrodorea nigra, Savia dictyocarpa, Ocotea indecora, Aspidosperma polyneuron e Trichilia catigua. O estrato intermediário apresentou-se com densidade de 3.525 indivíduos.ha-1, pertencentes a 30 espécies (17 famílias), sendo as mais importantes em ordem decrescente de IVI: Metrodorea nigra, Actinostemon concolor, Trichilia catigua, Aspidosperma polyneuron e Trichilia clausenii. No estrato inferior a densidade foi de 28.875 indivíduos.ha-1, pertencentes a 37 espécies (19 famílias), sendo as mais abundantes, em ordem decrescente de densidade relativa: Metrodorea nigra, Actinostemon concolor, Trichilia catigua, Aspidosperma polyneuron e Eugenia blastantha. Constatou-se que há espécies do estrato superior da floresta que não foram observadas em regeneração, especialmente heliófitas de estádios sucessionais iniciais (p. ex. Croton floribundus). Outras ocorreram com densidade relativa decrescente nos estratos inferiores (p. ex. Savia dictyocarpa e Ocotea indecora). Para outras espécies, as sementes germinaram, mas não se desenvolveram à sombra, estando ausentes no estrato intermediário (p. ex. Cariniana estrellensis). Observou-se, ainda, um grupo de espécies, de estádios sucessionais mais avançados, que apresentaram a mesma densidade relativa em todos os estratos (p. ex. Metrodorea nigra e Aspidosperma polyneuron).

Impacto do fogo e dinâmica da regeneração da comunidade vegetal em borda de Floresta Estacional Semidecidual (Gália, SP, Brasil)

Bordas de fragmentos florestais são áreas sujeitas a uma série de fatores naturais e distúrbios, entre os quais o fogo, que acarretam modificações na comunidade vegetal. Estudou-se a natureza e dimensão dos danos causados pelo fogo e resiliência da comunidade vegetal após incêndio em borda de Floresta Estacional Semidecidual, na Estação Ecológica dos Caetetus, Gália, SP. Efetuou-se a amostragem da vegetação em duas áreas contíguas (queimada e não queimada), em cinco transectos, cada um formado por cinco parcelas de 10 × 10 m. Foram identificados e medidos todos os indivíduos do estrato arbóreo (altura > 1,7 m) e quantificou-se a cobertura de árvores, lianas e gramíneas invasoras. Foram realizadas medições aos seis, 15 e 24 meses após o incêndio e os dados obtidos foram agrupados em duas faixas de distância da borda: 0-20 m e 20-50 m. Alterações estruturais foram maiores na faixa mais externa, com perda total da biomassa e proliferação de lianas e gramíneas, enquanto na faixa mais interna houve perda de 89% da área basal arbórea. A área atingida pelo fogo apresentou 43 espécies a menos que a floresta não queimada na primeira avaliação após o fogo. Após 24 meses, esta diferença reduziu-se a 14 espécies, demonstrando alta resiliência, em termos de riqueza florística. A recuperação prevista da biomassa arbórea é mais lenta na faixa mais externa (11 anos) em comparação com a faixa mais interna (5 anos).

Localization of NMDA receptors in the cerebral cortex: a schematic overview

The fundamental role of N-methyl-D-aspartate (NMDA) receptors in many cortical functions has been firmly defined, as has its involvement in a number of neurological and psychiatric diseases. However, until recently very little was known about the anatomical localization of NMDA receptors in the cerebral cortex of mammals. The recent application of molecular biological techniques to the study of NMDA receptors has provided specific tools which have greatly expanded our understanding of the localization of NMDA receptors in the cerebral cortex. In particular, immunocytochemical studies on the distribution of cortical NMDA receptors have shown that NMDA receptors are preferentially localized on dendritic spines, have disclosed an unknown fraction of presynaptic NMDA receptors on both excitatory and inhibitory axon terminals, and demonstrated that cortical astrocytes do express NMDA receptors. These studies suggest that the effects induced by the activation of NMDA receptors are not due solely to the opening of NMDA channels on neuronal postsynaptic membranes, as previously assumed, but that the activation of presynaptic and glial NMDA receptors may mediate part of these effects

Facilitation of the main generator source of earthworm muscle contraction by a peripheral neuron

A constant facilitation of responses evoked in the earthworm muscle contraction generator neurons by responses evoked in the neurons of its peripheral nervous system was demonstrated. It is based on the proposal that these two responses are bifurcations of an afferent response evoked by the same peripheral mechanical stimulus but converging again on this central neuron. A single-peaked generator response without facilitation was demonstrated by sectioning the afferent route of the peripheral facilitatory modulatory response, or conditioning response (CR). The multipeaked response could be restored by restimulating the sectioned modulatory neuron with an intracellular substitutive conditioning stimulus (SCS). These multi-peaked responses were proposed to be the result of reverberating the original single peaked unconditioned response (UR) through a parallel (P) neuronal circuit which receives the facilitation of the peripheral modulatory neuron. This peripheral modulatory neuron was named "Peri-Kästchen" (PK) neuron because it has about 20 peripheral processes distributed on the surface of a Kästchen of longitudinal muscle cells on the body wall of this preparation as revealed by the Lucifer Yellow-CH-filling method.

Persistent attenuation and enhancement of the earthworm main muscle contraction generator response induced by repeated stimulation of a peripheral neuron

Responses evoked in the earthworm, Amynthas hawayanus, main muscle contraction generator M-2 (postsynaptic mechanical-stimulus-sensitive) neuron by threshold mechanical stimuli in 2-s intertrial intervals (ITI) were used as the control or unconditioned responses (UR). Their attenuation induced by decreasing these intervals in non-associative conditioning and their enhancement induced by associating the unconditioned stimuli (US) to a train of short (0.1 s) hyperpolarizing electrical substitutive conditioning stimuli (SCS) in the Peri-Kästchen (PK) neuron were measured in four parameters, i.e., peak numbers (N) and amplitude ()averaged from 120 responses, sum of these amplitudes (SAMP) and the highest peak amplitude (V) over a period of 4 min. Persistent attenuation similar to habituation was induced by decreasing the control ITI to 0.5 s and 2.0 s in non-associative conditioning within less than 4 min. Dishabituation was induced by randomly pairing one of these habituated US to an electrical stimulus in the PK neuron. All four parameters of the UR were enhanced by forward (SCS-US), but not backward (US-SCS), association of the US with 25, 100 and 250-Hz trains of SCS with 40-ms interstimulus intervals (ISI) for 4 min and persisted for another 4 min after turning off the SCS. The enhancement of these parameters was proportional to the SCS frequencies in the train. No UR was evoked by the SCS when the US was turned off after 4 min of classical conditioning.

Dietary sodium intake induced myenteric neuron hypertrophy in Wistar rats

In the present study we investigated the effect of salt intake on myenteric neuron size of the colon of adult male Wistar rats. The animals were placed on either a high-salt (HS; 8%; 12 animals) or a low-salt diet (LS; 0.15%; 12 animals) for 15 or 52 weeks and blood pressure was measured. The sizes of myenteric neurons of the distal colon from both groups were measured. No difference in neuron size was observed between the HS and LS groups after 15 weeks. After 52 weeks on HS, neuron size was increased (P<0.005) when compared with the LS group. The rats also presented hypertension, which was significantly different at 52 weeks (142 ± 11 vs 119 ± 7 mmHg). These results suggest that a long time on an HS diet can significantly increase myenteric nerve cell size.

Astroglial cells derived from lateral and medial midbrain sectors differ in their synthesis and secretion of sulfated glycosaminoglycans

Astroglial cells derived from lateral and medial midbrain sectors differ in their abilities to support neuritic growth of midbrain neurons in cocultures. These different properties of the two types of cells may be related to the composition of their extracellular matrix. We have studied the synthesis and secretion of sulfated glycosaminoglycans (GAGs) by the two cell types under control conditions and ß-D-xyloside-stimulated conditions, that stimulate the ability to synthesize and release GAGs. We have confirmed that both cell types synthesize and secrete heparan sulfate and chondroitin sulfate. Only slight differences were observed between the proportions of the two GAGs produced by the two types of cells after a 24-h labeling period. However, a marked difference was observed between the GAGs produced by the astroglial cells derived from lateral and medial midbrain sectors. The medial cells, which contain derivatives of the tectal and tegmental midline radial glia, synthesized and secreted ~2.3 times more chondroitin sulfate than lateral cells. The synthesis of heparan sulfate was only slightly modified by the addition of ß-D-xyloside. Overall, these results indicate that astroglial cells derived from the two midbrain sectors have marked differences in their capacity to synthesize chondroitin sulfate. Under in vivo conditions or a long period of in vitro culture, they may produce extracellular matrix at concentrations which may differentially affect neuritic growth.

Sulfated proteoglycans as modulators of neuronal migration and axonal decussation in the developing midbrain

Proteoglycans are abundant in the developing brain and there is much circumstantial evidence for their roles in directional neuronal movements such as cell body migration and axonal growth. We have developed an in vitro model of astrocyte cultures of the lateral and medial sectors of the embryonic mouse midbrain, that differ in their ability to support neuritic growth of young midbrain neurons, and we have searched for the role of interactive proteins and proteoglycans in this model. Neurite production in co-cultures reveals that, irrespective of the previous location of neurons in the midbrain, medial astrocytes exert an inhibitory or nonpermissive effect on neuritic growth that is correlated to a higher content of both heparan and chondroitin sulfates (HS and CS). Treatment of astrocytes with chondroitinase ABC revealed a growth-promoting effect of CS on lateral glia but treatment with exogenous CS-4 indicated a U-shaped dose-response curve for CS. In contrast, the growth-inhibitory action of medial astrocytes was reversed by exogenous CS-4. Treatment of astrocytes with heparitinase indicated that the growth-inhibitory action of medial astrocytes may depend heavily on HS by an as yet unknown mechanism. The results are discussed in terms of available knowledge on the binding of HS proteoglycans to interactive proteins, with emphasis on the importance of unraveling the physiological functions of glial glycoconjugates for a better understanding of neuron-glial interactions.

Use of neuron-specific enolase for assessing the severity and outcome of neurological disorders in patients

Neuron-specific enolase (NSE) is a glycolytic enzyme present almost exclusively in neurons and neuroendocrine cells. NSE levels in cerebrospinal fluid (CSF) are assumed to be useful to estimate neuronal injury and clinical outcome of patients with serious clinical manifestations such as those observed in stroke, head injury, anoxic encephalopathy, encephalitis, brain metastasis, and status epilepticus. We compared levels of NSE in serum (sNSE) and in CSF (cNSE) among four groups: patients with meningitis (N = 11), patients with encephalic injuries associated with impairment of consciousness (ENC, N = 7), patients with neurocysticercosis (N = 25), and normal subjects (N = 8). Albumin was determined in serum and CSF samples, and the albumin quotient was used to estimate blood-brain barrier permeability. The Glasgow Coma Scale score was calculated at the time of lumbar puncture and the Glasgow Outcome Scale (GOS) score was calculated at the time of patient discharge or death. The ENC group had significantly higher cNSE (P = 0.01) and albumin quotient (P = 0.005), but not sNSE (P = 0.14), levels than the other groups (Kruskal-Wallis test). Patients with lower GOS scores had higher cNSE levels (P = 0.035) than patients with favorable outcomes. Our findings indicate that sNSE is not sensitive enough to detect neuronal damage, but cNSE seems to be reliable for assessing patients with considerable neurological insult and cases with adverse outcome. However, one should be cautious about estimating the severity of neurological status as well as outcome based exclusively on cNSE in a single patient.

Differentiation of autonomic reflex control begins with cellular mechanisms at the first synapse within the nucleus tractus solitarius

Visceral afferents send information via cranial nerves to the nucleus tractus solitarius (NTS). The NTS is the initial step of information processing that culminates in homeostatic reflex responses. Recent evidence suggests that strong afferent synaptic responses in the NTS are most often modulated by depression and this forms a basic principle of central integration of these autonomic pathways. The visceral afferent synapse is uncommonly powerful at the NTS with large unitary response amplitudes and depression rather than facilitation at moderate to high frequencies of activation. Substantial signal depression occurs through multiple mechanisms at this very first brainstem synapse onto second order NTS neurons. This review highlights new approaches to the study of these basic processes featuring patch clamp recordings in NTS brain slices and optical techniques with fluorescent tracers. The vanilloid receptor agonist, capsaicin, distinguishes two classes of second order neurons (capsaicin sensitive or capsaicin resistant) that appear to reflect unmyelinated and myelinated afferent pathways. The differences in cellular properties of these two classes of NTS neurons indicate clear functional differentiation at both the pre- and postsynaptic portions of these first synapses. By virtue of their position at the earliest stage of these pathways, such mechanistic differences probably impart important differentiation in the performance over the entire reflex pathways.

Mapping and signaling of neural pathways involved in the regulation of hydromineral homeostasis

Several forebrain and brainstem neurochemical circuitries interact with peripheral neural and humoral signals to collaboratively maintain both the volume and osmolality of extracellular fluids. Although much progress has been made over the past decades in the understanding of complex mechanisms underlying neuroendocrine control of hydromineral homeostasis, several issues still remain to be clarified. The use of techniques such as molecular biology, neuronal tracing, electrophysiology, immunohistochemistry, and microinfusions has significantly improved our ability to identify neuronal phenotypes and their signals, including those related to neuron-glia interactions. Accordingly, neurons have been shown to produce and release a large number of chemical mediators (neurotransmitters, neurohormones and neuromodulators) into the interstitial space, which include not only classic neurotransmitters, such as acetylcholine, amines (noradrenaline, serotonin) and amino acids (glutamate, GABA), but also gaseous (nitric oxide, carbon monoxide and hydrogen sulfide) and lipid-derived (endocannabinoids) mediators. This efferent response, initiated within the neuronal environment, recruits several peripheral effectors, such as hormones (glucocorticoids, angiotensin II, estrogen), which in turn modulate central nervous system responsiveness to systemic challenges. Therefore, in this review, we shall evaluate in an integrated manner the physiological control of body fluid homeostasis from the molecular aspects to the systemic and integrated responses.

Cardiac plexus of dogs experimentally infected with Trypanosoma cruzi: inflammatory lesions and quantitative studies

Qualitative and quantitative aspects of the superficial and profound cardiac plexus of dogs experimentally infected with Be-62 and Be-78 strains of Trypanosoma cruzi were studied. Animals were autopsied in the acute phase of infection. The inflammatory process, lesions and number of parasites were more intense and frequent in animals infected with the Be-78 strain than in those infected with Be-62. Despite this, no statistically significant differences could be found between the number of neuron bodies in the ganglia of infected and control dogs.