RESUMO
We investigated the role of retinotectal projections on the distribution of nitric oxide synthase (NOS) in the retinoceptive layers of the rat superior colliculus (SC) using histochemical methods. Rats enucleated at birth showed no alteration in the temporal pattern of NOS expression. There was, however, a dramatic change in the NADPH-diaphorase staining pattern of NOS-positive cells. NOS was absent from the distal portions of the dendritic trees of the deafferented SC. Nevertheless, staining the dendritic trees of these cells with Lucifer yellow showed that they were not morphologically different from those of the ipsilateral SC of monoenucleated animals. The same results were obtained when enucleation was performed in adult rats. We conclude that NOS intracellular distribution in the SC cells can be regulated by retinotectal projections in both developing and adult animals.
Assuntos
Enucleação Ocular , Óxido Nítrico Sintase/análise , Retina/fisiologia , Colículos Superiores/enzimologia , Vias Visuais/fisiologia , Análise de Variância , Animais , Histocitoquímica , NADPH Desidrogenase , Ratos , Ratos Endogâmicos , Colículos Superiores/citologiaRESUMO
Methamidophos (O,S-dimethyl phosphoroamidothiolate, Tamaron), an organophosphate (OP) anticholinesterase of limited toxicity, is widely used as an insecticide and acaricide. To provide additional insight into the molecular basis of its action, we have used electrophysiological and biochemical techniques to study the effects of methamidophos on the neuromuscular junction of rat and frog and on the central nervous system of rat. Methamidophos has a relatively weak inhibitory action on cholinesterases in rat diaphragm muscle, brain and hippocampal homogenates, with IC50 values on the order of 20-20 microM. An even weaker anticholinesterase activity was found in frog muscle homogenates, with the IC50 being above 300 microM. As further evidence of anticholinesterase activity, methamidophos (1-100 microM) was able to reverse the blockade by d-tubocurarine (0.5-0.7 microM) of neuromuscular transmission in rat phrenic nerve-hemidiaphragm preparations. Inhibition of cholinesterase activity by methamidophos was long lasting, which is consistent with the formation by the agent of a covalent bond with the enzyme's active serine residue. The action was also slowly reversible, which suggests spontaneous reactivation of the enzyme. electrophysiological studies at the rat neuromuscular junction showed that, due to its anticholinesterase activity, methamidophos increased the amplitude and prolonged the decay phase of nerve-evoked and spontaneous miniature end-plate potentials. In contrast to other OP compounds, e.g., paraoxon (Rocha et al., 1996a), methamidophos did not affect neurotransmitter release, nor did it interact directly with the muscle nicotinic acetylcholine receptor. Moreover, it contrast to paraoxon, methamidophos did not affect the whole-cell currents induced by application of acetylcholine, glutamate or gamma-aminobutyric acid recorded to cultured hippocampal neurons. Based on these data, methamidophos appears to have a selective effect on cholinesterase.
Assuntos
Inibidores da Colinesterase/toxicidade , Inseticidas/toxicidade , Neurotransmissores/metabolismo , Compostos Organotiofosforados/toxicidade , Sinapses/efeitos dos fármacos , Animais , Diafragma/efeitos dos fármacos , Diafragma/inervação , Potenciais Evocados/efeitos dos fármacos , Técnicas In Vitro , Canais Iônicos/efeitos dos fármacos , Masculino , Placa Motora/efeitos dos fármacos , Contração Muscular/efeitos dos fármacos , Técnicas de Patch-Clamp , Ratos , Ratos Wistar , Sinapses/metabolismoRESUMO
Nitric oxide (NO) is synthesized in cells of both the central and peripheral nervous system and has been implicated in several forms of synaptic plasticity. The enzyme that produces NO, nitric oxide synthase (NOS), can be visualized in the brain by the reduced nicotinamide adenine dinucleotide phosphate diaphorase histochemistry technique (NADPH-d). We have used NADPH-d activity to detect the presence of NOS-positive cells in the developing rat superior colliculus. Our results showed that NOS is present in cells and neuropil in the developing and adult rat superior colliculus. The first NOS-positive cells appeared at postnatal day 7 and were weakly stained. The number and intensity of the NOS-positive cells increased progressively during the following days reaching a maximum at postnatal day 15. By the end of the third postnatal week, both the number and intensity of stained cells showed an adult-like pattern. The NOS-positive cells showed a Golgi-like morphology and we have found that all cell types present in the superior colliculus express the enzyme. The expression of NOS by tectal cells parallels the functional development of the retino-collicular and cortico-tectal projections and suggest that nitric oxide synthase-positive cells might be involved in this process. In this review we highlighted some of the recent descriptions of the expression of NOS in the mammalian visual system with emphasis in the superior colliculus and correlate these findings with several developmental events taking place in this structure.
Assuntos
Plasticidade Neuronal/fisiologia , Óxido Nítrico Sintase/isolamento & purificação , Óxido Nítrico/biossíntese , Colículos Superiores/fisiologia , Córtex Visual/fisiologia , Animais , RatosRESUMO
1. We have shown that all cholinesterase (ChE) inhibitors, in addition to their well-known anti-ChE activity, have multiple effects on the nicotinic acetylcholine receptor-ion channel (AChR) macromolecule resulting from interactions with the agonist recognition site and with sites located at the ion channel component. Activation, competitive antagonism and different types of noncompetitive blockade occurring at similar concentration ranges and contributing in different proportions result in complex and somewhat unpredictable alterations in AChR function. The question is now raised as to how each effect of these compounds contributes to their antidotal property against organophosphorus (OP) poisoning, and what set of actions makes one reversible ChE inhibitor a better antidote. Many lines of evidence support the importance of direct interactions with various sites on the AChR: 1) morphological and toxicological studies with (+) physostigmine showed that anti-ChE activity is not essential to protect animals against toxicity by irreversible ChE inhibitors; 2) (-)physostigmine is far more effective against OP poisoning; 3) open channel blockers such as mecamylamine with no significant anti-ChE activity enhance the protective action of (-)physostigmine; 4) neostigmine, pyridostigmine, (-)physostigmine and (+)physostigmine showed qualitatively and quantitatively distinct toxicity and damage to endplate morphology and function. 2. In prophylaxis and during the very early phase of OP poisoning, carbamates, especially (-)physostigmine combined with mecamylamine and atropine, could protect almost 100% of the animals exposed to multiple lethal doses of OPs. Electrophysiological data showed that (-)physostigmine, among several reversible ChE inhibitors, showed greater potency in depressing both endplate current (EPC) peak amplitude and tau EPC. Therefore, concerning neuromuscular transmission, it seems that the higher the potency of a drug in reducing endplate permeability, the better is its protection against OP toxicity. A reversible open channel blockade combined with some agonist property helps to decrease the effect of ACh at its agonist site and to reduce the ion permeability of open channels. It should be pointed out that, during the later phase of OP poisoning, AChR desensitization should be most prevalent. Thus, a drug that can remove the AChR from this rather irreversible state to a more reversible blocked state should be a better protector. Indeed, oximes such as 2-PAM and a more potent analog, HI-6, produce multiple alterations in AChR function that comprise increased channel activation and open-channel blockade.(ABSTRACT TRUNCATED AT 400 WORDS)
Assuntos
Inibidores da Colinesterase/farmacologia , Intoxicação por Organofosfatos , Receptores Nicotínicos/efeitos dos fármacos , Animais , Sítios de Ligação , Fenômenos Químicos , Química , Inibidores da Colinesterase/metabolismo , Edrofônio/farmacologia , Contração Muscular/efeitos dos fármacos , Neostigmina/farmacologia , Fisostigmina/farmacologia , Brometo de Piridostigmina/farmacologia , Rana pipiens , Receptores Nicotínicos/metabolismo , Nervo Isquiático/efeitos dos fármacos , Relação Estrutura-AtividadeRESUMO
We have shown that alt cholinesterase (ChE) inhibitors, in addition to their well-known anti-ChE activity, have multiple effects on the nicotinic acetylcholine receptor-ion channel (AChR) macromolecule resulting from interactions with the agonist recognition site and with sites located at the ion channel component. Activation, competitive antagonism and different types of noncompetitive blockade occurring at similar concentration ranges and contributing in different proportions result in complex and somewhat unpredictable alterations inn AChR function. The question is now raised as to how each effect of these compounds contributes to their antidotal property against organophosphorus (OP) poisoning, and what set of actions makes one reversible ChE inhibitor a better antidote. Many lines of evidence support the importance of direct interactions with various sites on the AChR: 1) morphological and toxicological studies with (+) physostigmine showed that anti-ChE activity is not essential to protect animals against toxicity by irreversible ChE inhibitors; 2) (-) physostigmine is far more effective against OP poisoning; 3) open channel blockers such as mecamylamine with no significant anti-ChE activity enhance the protective action of (-) physostigmine; 4) neostigmine, pyridostigmine, (-) physostigmine and (+) physostigmine showed qualitatively and quantitatively distinct toxicity and damage to endplate morphology and function. In prophylaxis and during the very early phase of OP poisoning, carbamates, especially (-) physostigmine combined with mecamylamine and atropine, could protect almost 100% of the animals exposed to multiple lethal doses of OPs...
Assuntos
Animais , Inibidores da Colinesterase/farmacologia , Compostos Organofosforados/intoxicação , Receptores Nicotínicos/efeitos dos fármacos , Química , Contração Muscular/efeitos dos fármacos , Ácidos Nicotínicos , Rana pipiens , Nervo Isquiático/efeitos dos fármacos , Relação Estrutura-AtividadeRESUMO
Trypanosoma cruzi was cultured in spinal and sympathetic ganglion cells of chick embryos. The "Y" and the "CL" strains were used for comparison, showing no differences in their tropism for the different cell types of the ganglion cultures. Nerve cells as well as satellite and Schwann cells served as host for the parasite's intracellular cycle. No toxic effect on the nerve cells was observed in heavily infected cultures. The destruction of the nerve cells is due to the multiplication of the parasites in the cell's cytoplasm. Its structure in the non parasitized nerve cells, even in direct contact with parasites, looks normal under the optical microscope and also shows no alteration in its ultrastructure.
Assuntos
Gânglios Espinais/parasitologia , Gânglios Simpáticos/parasitologia , Neurônios/ultraestrutura , Trypanosoma cruzi/crescimento & desenvolvimento , Animais , Embrião de Galinha , Técnicas de CulturaRESUMO
Foi feita a inoculacao de Trypanosoma cruzi em culturas de celulas de ganglios espinais e simpaticos de embriao de galinha.Para comparacao, foram usadas as cepas "Y" e "CL", as quais nao mostraram diferencas em seu tropismo para os diversos tipos celulares das culturas. Tanto as celulas nervosas como os satelites e as de Schwann serviram de hospedeiro para o ciclo intracelular do parasito. Nao foi observado efeito toxico sobre as celulas nervosas, mesmo em culturas fortemente parasitadas.A destruicao das celulas nervosas se deve a multiplicacao dos parasitos no citoplasma das mesmas, finalizando com o rompimento total. A estrutura do citoplasma nas celulas nervosas nao parasitarias, mesmo havendo parasitos em vizinhanca proxima, se apresenta normal sob o microscopio optico, nao se notando, tambem, alteracao na sua ultra-estrutura