Avaliação dos efeitos do aspartame sobre a ingestão alimentar, os parâmetros físicos, bioquímicos e histopatológicos em ratos Wistar / Evaluation of aspartame effects on food intake, physical, biochemical, and histopatological parameters in rats

Nos últimos anos, tem-se observado um aumento no consumo de alimentos diet e light por adolescentes ou por aqueles que estão à procura de uma alimentação com baixo teor calórico, surgindo, assim, diversos edulcorantes, como o aspartame. Porém, seu consumo ainda gera polêmica, devido a muitos dados contraditórios e inconclusivos. Diante disso, objetivou-se avaliar os efeitos da suplementação de aspartame sobre ingestão alimentar, parâmetros físicos, bioquímicos e histopatológicos em 18 ratos machos da linhagem Wistar, com cinco semanas de vida (ratos jovens), tratados durante 21 dias. Os animais foram distribuídos aleatoriamente em dois grupos: grupo controle (GC) - tratados com água destilada por gavagem, e o grupo aspartame (GA) - tratados diariamente com 2mL/100g/dia de aspartame. Todos os animais receberam ração comercial (Essence(r)) e água ad libitum. O controle da ingestão alimentar foi registrado semanalmente. Foram aferidos os parâmetros físicos por meio da análise do peso corporal, da circunferência toráxica, da circunferência abdominal, do comprimento vértice-cóccix, da gordura abdominal total e do cálculo do índice de massa corporal; os parâmetros bioquímicos foram analisados por meio da glicemia, da lipoproteína de alta densidade e dos triglicerídeos; além de tais análises, foi realizado o estudo histopatológico do fígado. Durante todo o experimento, os ratos tratados com aspartame apresentaram um aumento significativo no peso corpóreo e na ingestão alimentar quando comparados ao grupo controle. Não houve diferença nas demais análises tanto físicas, quanto bioquímicas e histopatológicas comparando-se o GA com o GC (P<0,05). Com base nos resultados obtidos, é possível inferir uma maior chance de desenvolvimento da obesidade, oriunda do consumo regular desse tipo de adoçante, já que ele comprovou ser capaz de estimular o consumo de alimentos e, consequentemente, o ganho de peso corpóreo.(AU)

Recent years have seen an increase in consumption of diet and light foods by teenagers or those who are looking for a low-calorie diet, thus resulting in several sweeteners such as aspartame. However, their consumption still generates controversy due to many contradictory and inconclusive data. Thus, the aim of this study was to evaluate the effects of aspartame supplementation on dietary intake, physical, biochemical, and histopathological parameters in 18 male Wistar rats, at five weeks old (young mice) treated for 21 days. The animals were randomly assigned into two groups: control group (CG) - treated with distilled water by gavage and aspartame group (GA) - treated with 2ml/100g/day of aspartame. All animals received commercial feed (Essence (r)) and water ad libitum. The control of food intake was recorded weekly. The physical parameters were measured by analyzing the body weight, chest circumference, waist circumference, vertex-coccyx length, total abdominal fat and calculating the body mass index; biochemical parameters were analyzed by glucose, high-density lipoprotein and triglycerides. Apart from such analysis the histopathological study of the liver was conducted. Throughout the experiment the rats treated with aspartame showed a significant increase in body weight and food intake compared to the control group. There was no difference in other analyzes such physical, biochemical, and histopathological comparing GA to GC (P<0.05). From the results we can infer a greater chance of developing obesity, coming from the regular consumption of this type of sweetener, as it proved able to stimulate food intake, and hence the gain of body weight.(AU)

Cutaneous pythiosis in a donkey (Equus asinus) in Brazil.

Our study describes the clinical, epidemiologic, pathologic, immunohistochemical, and molecular aspects PCR of a case of cutaneous pythiosis in a donkey (Equus asinus) from Brazil. During a dry period, the animal grazed for 4 months around a pond where the vegetation remained green. Skin lesions were nodular, multifocal, and disseminated, mainly involving the legs, ventral chest, and mammary gland. On cut surface, there were multifocal to coalescent discrete yellow foci, and occasional small cavitations with a few kunkers. Ulcerative nodular pyogranulomatous and eosinophilic dermatitis with folliculitis and furunculosis were observed histologically. Hyphae were observed in sections stained with Gomori methenamine silver. Immunohistochemistry with Pythium insidiosum antibodies yielded strong immunostaining of hyphae. P. insidiosum DNA was extracted from tissues in paraffin blocks by amplification of a fragment of 105 bp, which targets the 5.8S ribosomal gene. After the diagnosis of pythiosis, the larger skin lesions were excised and treated as second intention healing wounds, which were completely healed 30 days after resection. Small skin lesions regressed spontaneously in ~60 days. The granulomatous inflammation and outcome of the disease in this donkey were similar to cases of pythiosis in cattle.

Sonochemical assisted synthesis of SrFe12O19 nanoparticles.

We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe12O19) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe(3+), Fe(2+) and Sr(2+) ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe2O3) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe2O3) by a topotactic transition. The final product of strontium hexaferrite (SrFe12O19) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.

Undernutrition during early life alters neuropeptide Y distribution along the arcuate/paraventricular pathway.

Perinatal nutrient restriction exerts profound influences on brain development. Animals that suffer undernutrition during lactation also display impaired weight gain. Feeding behavior is mainly modulated by neural and hormonal inputs to the hypothalamus. The arcuate-paraventricular neuropeptidergic Y pathway has a prominent role in appetite regulation. The aim of this work was to study the effects of protein undernutrition during lactation on this hypothalamic pathway. We used rats from 5 to 60 postnatal (P) days whose dams were fed a 0% protein diet (PFG) or a normoprotein diet (CG) from P1 to P10. To reproduce the same amount of calorie ingested by the PFG we used an underfed group (UFG). Immunohistochemistry was performed to assess neuropeptide Y (NPY) distribution in the arcuate, periventricular and paraventricular nuclei. Our results showed a NPY immunostaining peak at P10 in all nuclei in CG animals. In UFG animals this peak was observed by P15, while, in the PFG animals only by P20. Our results suggest that the neuropeptidergic arcuate-paraventricular pathway suffered a delay in NPY distribution in undernourished animals, particularly those fed a 0% protein diet, reflecting an effect on this pathway maturation that could explain previously reported alterations on feeding behavior in these animals.

Glycogen stores are impaired in hypothalamic nuclei of rats malnourished during early life.

Perinatal nutrition has persistent influences on neural development and cognition. In humans and other animals, protein malnutrition during the perinatal period causes permanent changes, inducing to adulthood metabolic syndrome. Feeding is mainly modulated by neural and hormonal inputs to the hypothalamus. Hypothalamic glycogen stores are a source of glucose in high energetic demands, as during development of neural circuits. As some hypothalamic circuits are formed during lactation, we studied the effects of malnutrition, during the first 10 days of lactation, on glycogen stores in hypothalamic nuclei involved in the control of energy metabolism. Female pregnant rats were fed ad libitum with a normal protein diet (22% protein). After delivery, each dam was kept with 6 male pups. During the first 10 days of lactation, dams from the experimental group received a protein-free diet and the control group a normoprotein diet. By post-natal day 10 (P10), glycogen stores were very high in the arcuate nucleus and median eminence of control group. Glycogen stores decreased during development. In P20 control animals, glycogen stores were lower when compared to P10 control animals. Animals submitted to malnutrition presented a staining even lower than control ones. After P45, it was difficult to determine differences between control and diet groups because glycogen stores were reduced. We also showed that tanycytes were the cells presenting glycogen stores. Our data reinforce the concept that maternal nutritional state during lactation may be critical for neurodevelopment since it resulted in a low hypothalamic glycogen store, which may be critical for establishment of neuronal circuitry.

Acceso abierto y software libre: premisas para la independencia tecnológica / Open access and free software: premises for technological independence

El acceso abierto y el software libre se han convertido en premisas de la independencia tecnológica. Se estudian los principales aspectos que caracterizan a estos dos movimientos que, aún cuando se encuentran estrechamente relacionados, posee cada uno su propia existencia. Posteriormente, se estudia la organización de los textos digitales, así como diversos tipos de bibliotecas digitales: personales, personalizada y personalizable.

Open access and free software have become premises of technological independence. The main aspects characterizing these two movements that despite being closely interrelated, possess their own existence, are studied. Subsequently, the organization of the digital texts is studied; as well as diverse types of digital libraries: personal, personalized and personalizable.

Acceso abierto y software libre: premisas para la independencia tecnológica / Open access and free software: premises for technological independence

El acceso abierto y el software libre se han convertido en premisas de la independencia tecnológica. Se estudian los principales aspectos que caracterizan a estos dos movimientos que, aún cuando se encuentran estrechamente relacionados, posee cada uno su propia existencia. Posteriormente, se estudia la organización de los textos digitales, así como diversos tipos de bibliotecas digitales: personales, personalizada y personalizable(AU)

Open access and free software have become premises of technological independence. The main aspects characterizing these two movements that despite being closely interrelated, possess their own existence, are studied. Subsequently, the organization of the digital texts is studied; as well as diverse types of digital libraries: personal, personalized and personalizable(AU)

[Clinical trial comparing efficacy and safety of four highly active antiretroviral therapy (HAART) in antiretroviral-naive treatment with advanced HIV infection]. / Ensayo clínico comparativo de eficacia y seguridad de cuatro pautas de tratamiento antirretroviral de alta eficacia (TARGA) en pacientes naive con infección por VIH avanzada.

BACKGROUND: Comparison of efficacy and safety of four highly active antiretroviral therapy regimens (HAART) including two nucleoside analogues (NA) and a protease inhibitor (PI) in HIV positive patients with advanced infection and antiretroviral naive. PATIENTS AND METHODS: Multicenter, randomized and open labeled clinical trial in ten community hospitals of Castilla-La Mancha and Madrid. Regimen 1 contains zidovudine (AZT), lamivudine (3TC) and indinavir (IDV) regimen 2 includes AZT, 3TC and ritonavir (RTV), regimen 3 was didanosine (DDI), estavudine (D4T) and IDV, and regimen 4 included DDI, D4T and RTV. Decrease in viral load of HIV (VC) has been assessed as primary endpoint and as secondary one, the increase of the numbers of CD4 lymphocytes, percentage of disease progression, adverse reactions and adherence. Measurements were made at baseline visit and at 6, 12, 24, 36 and 48 weeks. RESULTS: A total of 98 patients with a mean baseline CD4 count of 122 x 10(6)/l (range of 5-340) and a baseline viral load of 5.1 log copies/ml were included. At 48 weeks, a mean increase of the CD4 and decrease of the viral load without significant difference between the 4 regimens (103 cells/2.62 log in regimen 1; 169 cells/2.86 log in regimen 2; 171 cells/2.56 log in regimen 3 and 141 cells/1.71 log in regimen 4) were observed in the analysis of the patients in treatment. Treatment was discontinued due to adverse reactions: 24% in regimen 1, 48% in regimen 2, 26% in regimen 3 and 32% in regimen 4, without significant difference. Analyzing by PI groups, 41% of the patients with RTV and 25% of those with IDV discontinued treatment due to adverse effects. There was withdrawal from treatment due to disease progression in 7% of the RTV patients and in 9% of IDV patients. CONCLUSIONS: In the HIV positive patients with advanced infection, efficacy between the four regimens of HAART is similar, but there is a tendency to require more withdrawal due to adverse effects in the RTV group than in those of IDV, the two used as single PI.

Ensayo clínico comparativo de eficacia y seguridad de cuatro pautas de tratamiento antirretroviral de alta eficacia (TARGA) en pacientes naive con infección por VIH avanzada / Clinical trial comparing efficacy and safety of four highly active antiretroviral therapy (HAART) in antiretroviral-naive treatment with advanced HIV infection

Introducción. Comparación de la eficacia y seguridad de cuatro pautas de terapia antirretroviral de gran actividad (TARGA) incluyendo dos análogos de nucleósidos (AN) y un inhibidor de proteasa (IP) en pacientes con el virus de la inmunodeficiencia humana (VIH) con infección avanzada y naive a antirretrovirales. Pacientes y método. Ensayo clínico, multicéntrico, randomizado y abierto en diez hospitales comunitarios de Castilla-La Mancha y Madrid. La pauta 1 contenía zidovudina (ZDV), lamivudina (3TC) e indinavir (IDV); la pauta 2 incluía ZDV, 3TC y ritonavir (RTV); la pauta 3 era didanosina (DDI), estavudina (D4T) e IDV, y la pauta 4 incluía DDI, D4T y RTV. Se ha valorado como variable principal de respuesta el descenso de la carga viral del VIH (CV), y como variables secundarias: el aumento del número de linfocitos CD4, el porcentaje de progresión de la enfermedad, las reacciones adversas y la adherencia. Las determinaciones se realizaron en la visita basal y a las 6, 12, 24, 36 y 48 semanas. Resultados. Se incluyeron 98 pacientes con una media de CD4 basal de 122 x 106/l (rango de 5-340) y una carga viral basal de 5,1 log copias/ml. A las 48 semanas, en el análisis de los pacientes en tratamiento se observó un incremento medio de los CD4 y una disminución de la carga viral sin diferencia significativa entre las 4 pautas (103 células/2,62 log en la pauta 1, 169 células/ 2,86 log en la pauta 2, 171 células/2,56 log en la pauta 3 y 141 células/1,71 log en la pauta 4). Interrumpieron el tratamiento por reacciones adversas: el 24% en la pauta 1, el 48% en la pauta 2, el 26% en la pauta 3 y el 32% en la pauta 4, sin diferencias significativas. Analizando por grupos de IP el 41% de los pacientes con RTV y el 25% de los pacientes con IDV suspendieron el tratamiento por efectos adversos. Se produjo retirada del tratamiento por progresión de la enfermedad en el 7% de los pacientes con RTV y en el 9% de los pacientes con IDV. Conclusiones. En los pacientes VIH positivos con infección avanzada la eficacia entre cuatro pautas de TARGA es similar, pero existe una tendencia a precisar mayor retirada por efectos adversos en los grupos de RTV que en los de IDV, los dos usados como IP único

Background. Comparison of efficacy and safety of four highly active antiretroviral therapy regimens (HAART) including two nucleoside analogues (NA) and a protease inhibitor (PI) in HIV positive patients with advanced infection and antiretroviral naive. Patients and methods. Multicenter, randomized and open labeled clinical trial in ten community hospitals of Castilla-La Mancha and Madrid. Regimen 1 contains zidovudine (AZT), lamivudine (3TC) and indinavir (IDV) regimen 2 includes AZT, 3TC and ritonavir (RTV), regimen 3 was didanosine (DDI), estavudine (D4T) and IDV, and regimen 4 included DDI, D4T and RTV. Decrease in viral load of HIV (VC) has been assessed as primary endpoint and as secondary one, the increase of the numbers of CD4 lymphocytes, percentage of disease progression, adverse reactions and adherence. Measurements were made at baseline visit and at 6, 12, 24, 36 and 48 weeks. Results. A total of 98 patients with a mean baseline CD4 count of 122 x 106/l (range of 5-340) and a baseline viral load of 5.1 log copies/ml were included. At 48 weeks, a mean increase of the CD4 and decrease of the viral load without significant difference between the 4 regimens (103 cells/2.62 log in regimen 1; 169 cells/2.86 log in regimen 2; 171 cells/2.56 log in regimen 3 and 141 cells/1.71 log in regimen 4) were observed in the analysis of the patients in treatment. Treatment was discontinued due to adverse reactions: 24% in regimen 1, 48% in regimen 2, 26% in regimen 3 and 32% in regimen 4, without significant difference. Analyzing by PI groups, 41% of the patients with RTV and 25% of those with IDV discontinued treatment due to adverse effects. There was withdrawal from treatment due to disease progression in 7% of the RTV patients and in 9% of IDV patients. Conclusions. In the HIV positive patients with advanced infection, efficacy between the four regimens of HAART is similar, but there is a tendency to require more withdrawal due to adverse effects in the RTV group than in those of IDV, the two used as single PI

Myelin basic protein accumulation is impaired in a model of protein deficiency during development.

During the development of the central nervous system (CNS) there is a great possibility of permanent effects in consequence of environmental disturbances. Nutritional deficiency is one of the factors that impair the normal CNS formation. In general, the protein deficiency evokes, beyond the damages in the maturation of nervous system, several consequences in body growth, biochemical maturation, motor function and the major cognitive functions. These effects were observed in undernourished children all over the world. Even in a restricted period, the malnutrition status may evoke permanent impairments in feeding behavior and in metabolism. Rats submitted to malnutrition during development, showed a marked decrease in the number of myelinated fibers. This condition may reflect a failure in the beginning of the wrapping of axons by oligodendroglial processes and/or a delay in the myelin synthesis. Myelin basic protein (MBP) is an intracellular oligodendrocyte protein that is directly related to the formation of the myelin sheath. In this study we verified the temporal pattern of MBP expression, by immunohistochemical and immunoblotting analyses, in a model of protein malnutrition induced during the first half of the lactation period. We showed that MBP expression was impaired in our malnutrition model and that some of the effects were maintained in adulthood, with possible consequences in the maturation of myelin sheath.

Vasodilator activity of the aqueous extract of Viscum album.

The aqueous extract of Viscum album leaves showed a significant coronary vasodilator activity on the Langendorff's isolated and perfused heart model. The data obtained suggest that the aqueous extract of V. album contains some biologically active principles that may act as inducers of the nitric oxide/soluble guanylate cyclase pathway.

Hypothalamic nuclei nitric oxide synthase expression in rats malnourished during early lactation period.

In humans and other animals, it has been shown that protein malnutrition during the prenatal period leads to permanent changes, which in adulthood may cause chronic diseases. Molecules involved in the control of energy metabolism could be targets to alterations caused by nutritional status. Some hypothalamic nuclei as the paraventricular (PVN), ventro-medial and arcuate are related to energy metabolism regulation. Orexigenic and anorexigenic molecules are involved in this regulation. Some studies have showed that these nuclei present nitric oxide synthase (NOS) and that it is increased in obese rats. Recently it had been shown that rats malnourished during the lactation period presented metabolic alterations that persist in adulthood. The aim of this work was to study the expression of NOS in hypothalamic nuclei of rats submitted to malnutrition during the early lactation period. Rats from post-natal day (P10) to P90 were used. Control dams were fed with regular chow pellets and diet dams were fed with protein-free chow pellets during the first 10 days of lactation. NADPH-diaphorase or immunostaining techniques were used to access NOS expression in hypothalamic nuclei. Our results show a delay in NOS expression in the PVN and VMH of malnourished rats. It may affect the development of the hypothalamic circuitry, leading to a metabolic imprinting.

[Psychoanalysis, individualistic value shaping, and social ethics]. / Psicanalise, configuracao individualista de valores e etica do social.

Refuting the view now prevailing in social anthropology, the article seeks to offer a new outlook on relations between psychoanalysis and the individualistic shaping of values that characterizes modern Western society. According to current social anthropology, psychoanalysis embodies the promise of recouping a wholeness lost as a result of the world's process of de-sanctification. The self is seen as constituting this new wholeness value, while psychoanalysis, insofar as it proposes redemption through the self, is viewed as a modern religion with individualistic effects. In questioning this vision, the article offers as a counterpoint the idea that the Lacanian formalization of the subconscious through symbolic structure overcomes the dichotomy between subject and society. This leads Lacan to assert that analysis should lead the subject to dedicate his or herself to guaranteeing the workings of the great Other, which is understood to mean that psychoanalysis should lead the subject to assume his or her responsibility for the workings of the symbolic structure.

Loss of NADPH diaphorase-positive neurons in the hippocampal formation of chronic pilocarpine-epileptic rats.

Recent evidence suggests an important role for NO in cholinergic models of epilepsy. Nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd), a marker of NO containing neurons, was shown to intensely colocalize with GABA in double-labeling studies performed in the hippocampal formation (exception made for the pyramidal cell layer) (Valtschanoff et al., J Comp Neurol 1993:331:111-121). In this sense, it further characterizes an extremely important cell category due to the relevant involvement of inhibitory systems in the mechanisms of genesis and propagation of seizures. Here, we assessed the histochemistry for NADPHd in the hippocampal complex of chronic pilocarpine-epileptic animals. NADPHd-positive cells were lost in almost every hippocampal subfield in pilocarpine-treated rats. The central portion of the polymorphic layer of the dentate gyrus (hilus) presented one of the highest losses of NADPHd-positive cells (55-79%) in the hippocampus. A significant loss of NADPHd-positive cells was seen in strata oriens, pyramidale, and radiatum CA1, CA2, and CA3 subfields. NADPHd staining in the subicular pyramidal cell layer was not different from that observed in controls. A significant loss of NADPHd-stained cells was observed in entorhinal cortex layers II and III in the epileptic group. For entorhinal cortex layers V and VI, however, results varied from an almost complete tissue destruction to an overexpression of NADPHd-positive cells, as well as an increase in neuropil staining. In summary, loss of NADPHd staining was not uniform throughout the hippocampal formation. There has been a growing support for the notion that GABAergic neurons in the hippocampal formation are not equally sensitive to insults. Our results suggest that, as a marker for a subpopulation of GABAergic neurons, NADPHd helps in further refining the characterization of the different neuronal populations sensitive to epileptic activity.

Expression of nitric oxide synthase in the developing rat hippocampus.

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry was used to study the development of neurons synthesizing nitric oxide (NO) in the postnatal rat hippocampus. We show that NADPH-d reactive somata and processes are present from the day of birth until adulthood in the Ammon's horn. The dentate gyrus, however, has a more delayed period of nitric oxide synthase (NOS) expression with the staining appearing only by the end of the first postnatal week. Our results suggest that the time course of NOS expression correlates with the developmental sequence of events described in the hippocampus and that NO could be involved in the development of connections in this structure.

Nitric oxide synthase expression in the opossum superior colliculus: a histochemical, immunohistochemical and biochemical study.

The expression of neuronal nitric oxide synthase (nNOS) in the superior colliculus (SC) of the opossum Didelphis marsupialis was studied by NADPH diaphorase (NADPH-d) histochemistry and nNOS immunohistochemistry. In addition, the activity of nNOS was quantified by measurement of [(3)H]-L-arginine conversion to [(3)H]-L-citrulline in tissue extracts from SC superficial layers in opossums and rats. Our results show that the number of NADPH-d stained cells was small and virtually identical in stratum opticum (SO) and stratum griseum superficiale (SGS) and their staining was very light, particularly in SGS. Neuropil staining was heavier in the stratum zonale (SZ) than in SGS or SO. The intermediate and deep layers contained heavily stained cells and moderate neuropil staining. Surprisingly, nNOS-immunoreactive cells were far more numerous than NADPH-d+ cells in every layer. The production of [(3)H]-L-citrulline from [(3)H]-L-arginine in tissue extracts enriched in superficial layers indicated that nNOS specific activity is as high in the opossum as in the rat. Our results suggest that the location of nNOS-expressing neurons in retino-receptive layers may be related to inter-specific differences in the processing of visual information.

Eye enucleation alters intracellular distribution of NO synthase in the superior colliculus.

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.

Patterns of nitric oxide synthase expression in the developing superior colliculus.

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.