RESUMEN

Many communication calls contain information about the physical characteristics of the calling animal. During maturation of the guinea pig purr call the pitch becomes lower as the fundamental frequency progressively decreases from 476 to 261 Hz on average. Neurons in the primary auditory cortex (AI) often respond strongly to the purr and we postulated that some of them are capable of distinguishing between purr calls of different pitch. Consequently four pitch-shifted versions of a single call were used as stimuli. Many units in AI (79/182) responded to the purr call either with an onset response or with multiple bursts of firing that were time-locked to the phrases of the call. All had a characteristic frequency ≤5 kHz. Both types of unit altered their firing rate in response to pitch-shifted versions of the call. Of the responsive units, 41% (32/79) had a firing rate locked to the stimulus envelope that was at least 50% higher for one version of the call than any other. Some (14/32) had a preference that could be predicted from their frequency response area while others (18/32) were not predictable. We conclude that about 18% of stimulus-driven cells at the low-frequency end of AI are very sensitive to age-related changes in the purr call.

Asunto(s)

Envejecimiento/fisiología , Corteza Auditiva/fisiología , Neuronas/fisiología , Discriminación de la Altura Tonal , Percepción de la Altura Tonal , Vocalización Animal , Estimulación Acústica , Factores de Edad , Animales , Audiometría de Tonos Puros , Corteza Auditiva/citología , Potenciales Evocados Auditivos , Femenino , Cobayas , Masculino , Espectrografía del Sonido , Factores de Tiempo

RESUMEN

Phase-locked responses to pure tones have previously been described in the primary auditory cortex (AI) of the guinea pig. They are interesting because they show that some cells may use a temporal code for representing sounds of 60-300 Hz rather than the rate or place mechanisms used over most of AI. Our previous study had shown that the phase-locked responses were grouped together, but it was not clear whether they were in separate minicolumns or a larger macrocolumn. We now show that the phase-locked cells are arranged in a macrocolumn within AI that forms a subdivision of the isofrequency bands. Phase-locked responses were recorded from 158 multiunits using silicon based multiprobes with four shanks. The phase-locked units gave the strongest response in layers III/IV but phase-locked units were also recorded in layers II, V and VI. The column included cells with characteristic frequencies of 80 Hz-1.3 kHz (0.5-0.8 mm long) and was about 0.5 mm wide. It was located at a constant position at the intersection of the coronal plane 1 mm caudal to bregma and the suture that forms the lateral edge of the parietal bone.

Asunto(s)

Estimulación Acústica , Audiometría/métodos , Corteza Auditiva/fisiología , Percepción Auditiva/fisiología , Animales , Corteza Auditiva/citología , Electrodos , Potenciales Evocados Auditivos/fisiología , Femenino , Cobayas , Audición , Masculino , Modelos Biológicos , Neuronas/fisiología , Tálamo/fisiología , Factores de Tiempo

RESUMEN

We wished to test the hypothesis that there are modules in low-frequency AI that can be identified by their responsiveness to communication calls or particular regions of space. Units were recorded in anaesthetised guinea pig AI and stimulated with conspecific vocalizations and a virtual motion stimulus (binaural beats) presented via a closed sound system. Recording tracks were mainly oriented orthogonally to the cortical surface. Some of these contained units that were all time-locked to the structure of the chutter call (14/22 tracks) and/or the purr call (12/22 tracks) and/or that had a preference for stimuli from a particular region of space (8/20 tracks with four contralateral, two ipsilateral and two midline), or where there was a strong asymmetry in the response to beats of different direction (two tracks). We conclude that about half of low-frequency AI is organized into modules that are consistent with separate "what" and "where" pathways.

Asunto(s)

Corteza Auditiva/fisiología , Percepción Auditiva/fisiología , Vocalización Animal , Estimulación Acústica , Potenciales de Acción , Animales , Femenino , Cobayas , Masculino , Microelectrodos , Movimiento (Física) , Espectrografía del Sonido , Percepción Espacial/fisiología

RESUMEN

In visual and somatosensory cortex there are important functional differences between layers. Although it is difficult to identify laminar borders in the primary auditory cortex (AI) laminar differences in functional processing are still present. We have used electrodes inserted orthogonal to the cortical surface to compare the response properties of cells in all six layers of AI in anaesthetised guinea pigs. Cells were stimulated with short tone pips and two conspecific vocalizations. When frequency response areas were measured for 248 units the tuning bandwidth was broader for units in the deep layers. The mean Q (10) value for tuning in layers IV-VI was significantly smaller (Mann-Whitney test P < 0.001) than for layers I-III. When response latencies were measured, the shortest latencies were found in layer V and the mean latency in this layer was shorter than in any of the more superficial layers (I-IV) when compared with a Tukey analysis of variance (P < 0.005). There were also laminar differences in the best threshold with layer V having the highest mean value. The mean best threshold for layer V (32.7 dB SPL) was significantly different from the means for layers II (25.5 dB SPL) and III (26.3 dB SPL). The responses to two vocalizations also varied between layers: the response to the first phrase of a chutter was smaller and about 10 ms later in the deep layers than in layers II and III. By contrast, the response to an example of whistle was stronger in the deep layers. These results are consistent with a model of AI that involves separate inputs to different layers and descending outputs from layers V/VI (to thalamus and brainstem) that are different from the output from layers II/III (to ipsilateral cortex).

Asunto(s)

Potenciales de Acción/fisiología , Corteza Auditiva/fisiología , Percepción Auditiva/fisiología , Neuronas/fisiología , Estimulación Acústica , Animales , Corteza Auditiva/citología , Vías Auditivas/citología , Vías Auditivas/fisiología , Umbral Auditivo/fisiología , Mapeo Encefálico , Vías Eferentes/citología , Vías Eferentes/fisiología , Electrofisiología , Cobayas , Red Nerviosa/citología , Red Nerviosa/fisiología , Neuronas/citología , Discriminación de la Altura Tonal/fisiología , Tiempo de Reacción/fisiología , Transmisión Sináptica/fisiología , Vocalización Animal/fisiología

RESUMEN

The accurate and reliable identification of subdivisions within the auditory thalamus is important for future studies of this nucleus. However, in the guinea pig, there has been no agreement on the number or nomenclature of subdivisions within the main nucleus of the auditory thalamus, the medial geniculate body (MGB). Thus, we assessed three staining methods in the guinea pig MGB and concluded that cytochrome oxidase (CYO) histochemistry provides a clear and reliable method for defining MGB subdivisions. By combining CYO with acetylcholinesterase staining and extensive physiological mapping we defined five separate divisions, all of which respond to auditory stimuli. Coronal sections stained for CYO revealed a moderate to darkly-stained oval core. This area (the ventral MGB) contained a high proportion (61%) of V-shaped tuning curves and a tonotopic organisation of characteristic frequencies. It was surrounded by four smaller areas that contained darkly stained somata but had a paler neuropil. These areas, the dorsolateral and suprageniculate (which together form the dorsal MGB), the medial MGB and the shell MGB, did not have any discernable tonotopic frequency gradient and contained a smaller proportion of V-shaped tuning curves. This suggests that CYO permits the identification of core and belt areas within the guinea pig MGB.

Asunto(s)

Acetilcolinesterasa/análisis , Complejo IV de Transporte de Electrones/análisis , Cuerpos Geniculados/enzimología , Inmunohistoquímica/métodos , Neuronas/enzimología , Estimulación Acústica , Animales , Vías Auditivas/fisiología , Mapeo Encefálico/métodos , Potenciales Evocados Auditivos , Femenino , Cuerpos Geniculados/citología , Cuerpos Geniculados/fisiología , Cobayas , Procesamiento de Imagen Asistido por Computador , Masculino , Conducción Nerviosa , Neuronas/fisiología , Neurópilo/enzimología , Reproducibilidad de los Resultados

RESUMEN

The auditory thalamus (medial geniculate body, MGB) receives its main ascending input from the inferior colliculus (IC), which was considered to be an obligatory relay for all auditory inputs to the MGB. However, recent anatomical evidence in the rat [ (Malmierca et al. 2002) J. Neurosci., 22, 10891-10897] has confirmed the presence of a direct pathway from the dorsal cochlear nucleus (DCN) to the medial MGB, bypassing the IC, as previously suggested in the chimpanzee [ (Strominger et al. 1977) J. Comp. Neurol., 172, 349-366]. We show that this direct pathway is also present in the guinea pig and apparently results in short latency responses in the thalamus. Injection of anterograde tracer into the DCN of five adult guinea pigs revealed terminal boutons and axonal swellings distributed throughout the medial MGB, but absent from all other MGB subdivisions. Electrophysiological recordings made from 39 adult guinea pigs (24 male & 15 female) showed neurons in the medial MGB responded with significantly shorter latencies to acoustic clicks (7.8 ms) than those from the ventral (11.0 ms), dorsal (14.4 ms), or shell (16.5 ms) MGB, consistent with the direct pathway from the DCN. The function of the direct pathway is not known but may be related to the fast responses and the role of the medial MGB in integrating combined somatosensory and auditory inputs. Short latency responses may be important in priming the auditory cortex to prepare it for rapid analysis and in recruiting the amygdala for rapid emotional responses such as fear.

Asunto(s)

Vías Auditivas/anatomía & histología , Percepción Auditiva/fisiología , Núcleo Coclear/anatomía & histología , Cuerpos Geniculados/anatomía & histología , Terminales Presinápticos/ultraestructura , Estimulación Acústica , Potenciales de Acción/fisiología , Amígdala del Cerebelo/fisiología , Animales , Corteza Auditiva/fisiología , Vías Auditivas/fisiología , Conducta Animal/fisiología , Biotina/análogos & derivados , Núcleo Coclear/fisiología , Dextranos , Miedo/fisiología , Femenino , Cuerpos Geniculados/fisiología , Cobayas , Masculino , Conducción Nerviosa/fisiología , Terminales Presinápticos/fisiología , Tiempo de Reacción/fisiología , Transmisión Sináptica/fisiología , Tacto/fisiología

RESUMEN

Stellate cells within the ventral cochlear nucleus (VCN) are a diverse cell group that have been classified according to their size and morphology. Some of these stellate cell types constitute major projection neurones into the brainstem and directly into the inferior colliculus, while others are implicated in more local processing. It is still not clear whether a specific physiological profile is uniquely associated with each distinct type of stellate cell. To investigate such associations, we have analysed 23 units with a battery of physiological stimuli in vivo and then examined their shape and outputs following juxtacellular labelling with biocytin. Five physiologically identified groups of cells were filled. These formed two major response classes: onset cells and chopper cells. The two classes could be separated purely on morphological grounds. The onset cells had large somata, large symmetrical dendritic trees and profuse axonal branches that were restricted to the cochlear nucleus on one (On-L) or both sides (On-C) of the brainstem. The chopper cells had smaller, asymmetric, dendritic trees, which were either planar or marginal, had smaller somata and an output axon that left via the trapezoid body. We have confirmed profuse projections into the dorsal cochlear nucleus from all onset cells, and more focal projections from some members of all three groups of chopper cells.

Asunto(s)

Vías Auditivas/citología , Percepción Auditiva/fisiología , Axones/ultraestructura , Núcleo Coclear/citología , Dendritas/ultraestructura , Lisina/análogos & derivados , Estimulación Acústica , Potenciales de Acción/fisiología , Animales , Vías Auditivas/fisiología , Axones/fisiología , Tamaño de la Célula/fisiología , Núcleo Coclear/fisiología , Dendritas/fisiología , Femenino , Cobayas , Masculino , Transmisión Sináptica/fisiología

RESUMEN

The organisation of guinea pig auditory cortex was studied by combining histological methods with microelectrode mapping. This allowed the location of seven auditory areas to be determined in relation to the visual and primary somatosensory areas. The auditory areas were identified by single-unit recordings and their borders defined by evoked potential mapping. The visual areas were identified by their relatively high densities of myelinated fibres, while the primary somatosensory cortex was identified by its characteristic barrels of high cytochrome oxidase (CYO) activity in layer IV. The auditory region had moderate levels of CYO and myelin staining. When staining was optimal, there was a clear edge to the moderate CYO activity, which apparently corresponds to the dorsal border of the primary auditory area (AI) and the other core field that lies dorsocaudal to it (DC). Thus the primary somatosensory area and the visual and auditory regions were separated from each other by a region with lower levels of CYO and myelin staining. The ventral borders of AI and DC could not be determined histologically as there were no sharp transitions in the levels of CYO or myelin staining. The two core areas were partially surrounded by belt areas. The dorsorostral belt and most of the belt around DC responded more strongly to broad-band stimuli than pure tones, while the ventrorostral belt, small field and a belt zone ventral to the rostral part of DC responded better to pure tones. Units in the small field (S) typically had higher thresholds and broader tuning to pure tones than AI, while units in the ventrorostral belt typically had longer onset latencies and gave more sustained responses than units in AI.

Asunto(s)

Corteza Auditiva/fisiología , Mapeo Encefálico , Complejo IV de Transporte de Electrones/metabolismo , Vaina de Mielina/metabolismo , Animales , Mapeo Encefálico/métodos , Potenciales Evocados/fisiología , Cobayas

RESUMEN

This study investigated the nature and topography of binaural interactions in the primary auditory field (AI) and dorsocaudal field (DC) of the urethane anaesthetised guinea pig auditory cortex. Single and multi-units were classified by their responses to monaural and binaural stimulation. In both AI and DC, units displayed binaural facilitation, binaural inhibition, or a level dependent mixture of facilitation and inhibition. There was a significant difference in the distribution of binaural response types between the two fields. Facilitated units predominated in DC (facilitated: 58%; inhibited: 24%; mixed: 6%; non-interacting: 12%), while inhibited units were the most common class in AI (facilitated: 15%; inhibited: 44%; mixed: 18%; non-interacting: 22%). It has previously been suggested that inhibited and facilitated units are concerned with processing different areas of space suggesting a possible separation of function between the two core fields. Topographically, the binaural response properties in AI and DC varied along isofrequency bands, with neurones displaying similar interactions aggregating in clusters. These clusters were similar in size for the two fields and often overlapped neighbouring isofrequency bands. However, their shape and position varied between different animals. This clustered organisation of binaural interactions is similar to that reported in recent studies of AI in other mammals.

Asunto(s)

Corteza Auditiva/fisiología , Oído/fisiología , Cobayas/fisiología , Estimulación Acústica/métodos , Animales , Umbral Auditivo , Mapeo Encefálico

RESUMEN

Phase-locked responses to pure tones are a characteristic of most auditory cells at the level of the brain stem and allow sophisticated analyses based on coincidence detection. Phase-locking to tones has not previously been shown at the level of the auditory cortex in single unit studies. We have now identified phase-locked responses in 10% of low-frequency (< 1 kHz) units in the ventrorostral belt, a strip of cortex immediately ventral to the primary auditory area. All of these units showed phase-locking in their response to binaural tone pips of 60-200 Hz and showed narrow band pass characteristics within this range.

Asunto(s)

Potenciales de Acción/fisiología , Corteza Auditiva/fisiología , Percepción Auditiva/fisiología , Neuronas/fisiología , Estimulación Acústica , Animales , Corteza Auditiva/citología , Cobayas , Neuronas/citología , Tiempo de Reacción/fisiología

RESUMEN

The previously defined anterior area (A) of guinea pig auditory cortex has been divided into a large dorsal portion identified as the primary area (AI) and a smaller ventrorostral belt (VRB). This division is based on: (1) the much longer response latency of units in VRB (21.7 ms) than AI (14.1 ms); (2) the absence of pure onset units in VRB (i.e. units that lacked a sustained response), which are common in AI; (3) the weakness of noise-induced evoked potentials in VRB compared to AI; (4) units in VRB had lower thresholds and stronger phase locking to amplitude modulated stimuli than in AI.

Asunto(s)

Corteza Auditiva/fisiología , Mapeo Encefálico , Animales , Potenciales Evocados Auditivos/fisiología , Cobayas , Microelectrodos , Tiempo de Reacción/fisiología

RESUMEN

The callosal connections of ferret auditory cortex were studied by making multiple injections of wheat germ agglutinin-horseradish peroxidase into the middle ectosylvian gyrus or by packing crystals of horseradish peroxidase into the transected corpus callosum. The primary area (AI) had strong callosal connections that arose from somata mainly located in layer III. Other layers contained sparsely distributed cells that projected across the midline. The projecting cells occurred over the whole extent of AI but were not homogeneously distributed in layer III. The axons from these cells terminated mainly in the upper layers of the contralateral cortex, where they converged onto three discrete bands. The three elongated bands lay in a dorsoventral orientation, parallel to the tonotopic axis. They were slightly curved and had a fairly uniform width. The posterior band had a width of about 200 microm, while the anterior and middle bands were more variable and had widths of 300-800 microm. The centre-to-centre distance between the posterior and middle bands was 520+/-60 microm and for the anterior to middle bands was 620+/-210 microm. The retrograde labelling produced by the same injections showed that the cell bodies had a higher density in the terminal bands than in the intervening spaces. The bands of dense callosal connections appear to correspond to the binaural summation columns, which have been clearly demonstrated in the ferret, but direct evidence of this will need to be sought in a future study. The discrete nature of the callosal bands in the ferret appears to make it a suitable species for studying the relationship between callosal terminals and those arising in other areas of the brain and for clarifying the possible existence of separate functional systems within the auditory cortex.

Asunto(s)

Corteza Auditiva/fisiología , Cuerpo Calloso/fisiología , Hurones/fisiología , Animales , Vías Auditivas/fisiología , Femenino , Histocitoquímica , Masculino , Aglutinina del Germen de Trigo-Peroxidasa de Rábano Silvestre Conjugada

RESUMEN

This study provides the first evidence that nitric oxide is released by astrocytes surrounding beta-amyloid plaques. Nitric oxide is involved in many neuropathological conditions and can have either a neuroprotective or a neurotoxic function depending on its concentration and the redox state of the tissue. It is produced by the enzyme nitric oxide synthase, which can be located by a simple histochemical technique for demonstrating NADPH diaphorase. Using this method we examined tissue from 10 brains where there were varying numbers of beta-amyloid plaques in the cerebral cortex. In the 6 brains with moderate or high densities of plaques, primitive and cored plaques were associated with between 1 and 10 reactive astrocytes that contained NADPH diaphorase or were immunoreactive for the inducible form of nitric oxide synthase. In the 4 brains which had only low densities of plaques, the plaques were not associated with diaphorase-containing astrocytes. The percentage of plaques associated with 1 or more NADPH diaphorase-containing astrocyte varied between 1 and 21% and was correlated with the density of plaques. Astrocytes were the only form of NADPH diaphorase-positive glial cell associated with the plaques. There was no evidence of any nitric oxide synthase occurring in microglia.

Asunto(s)

Envejecimiento/patología , Enfermedad de Alzheimer/patología , Péptidos beta-Amiloides/análisis , Astrocitos/enzimología , Corteza Cerebral/patología , Demencia por Múltiples Infartos/patología , Proteínas del Tejido Nervioso/análisis , Óxido Nítrico Sintasa/análisis , Óxido Nítrico/biosíntesis , Anciano , Anciano de 80 o más Años , Envejecimiento/metabolismo , Enfermedad de Alzheimer/metabolismo , Corteza Cerebral/enzimología , Citocinas/fisiología , Demencia por Múltiples Infartos/metabolismo , Femenino , Humanos , Masculino , NADPH Deshidrogenasa/análisis , Oxidación-Reducción , Método Simple Ciego

RESUMEN

Histological methods and 2-deoxyglucose autoradiography were used in an attempt at finding distinguishing characteristics that would permit the clear definition of different auditory areas on the ectosylvian gyrus. This region was studied in both coronal and flattened tangential sections. In tangential sections a crescent-shaped region of high deoxyglucose uptake was identified. The centre of this crescent was in the position of the primary auditory area on the middle ectosylvian gyrus. The ventro-anterior arm of the crescent was on the surface of the anterior ectosylvian gyrus and the ventro-posterior arm on the posterior ectosylvian gyrus. All three parts of the crescent appear to have an auditory function, because ablating the inferior colliculus or inserting a contralateral earplug reduced their deoxyglucose uptake. This was shown by using two separately distinguishable forms of 2-deoxyglucose, incorporating the 18F and 14C isotopes. In addition, another area of high deoxyglucose activity was identified in the ventral wall of the suprasylvian sulcus, which seems to correspond to the anterior auditory field. These four areas with high deoxyglucose uptake also have high levels of succinate dehydrogenase activity and moderately high densities of myelinated fibres. Succinate dehydrogenase histochemistry provides a simple method for identifying auditory cortical areas and should be of use in future physiological studies. These results provide evidence that the ferret has four separate auditory areas with relatively high metabolic and functional activity.

Asunto(s)

Corteza Auditiva/fisiología , Percepción Auditiva/fisiología , Desoxiglucosa/metabolismo , Animales , Corteza Auditiva/citología , Corteza Auditiva/metabolismo , Corteza Auditiva/ultraestructura , Autorradiografía , Mapeo Encefálico , Radioisótopos de Carbono , Recuento de Células , Femenino , Hurones , Radioisótopos de Flúor , Histocitoquímica , Fibras Nerviosas Mielínicas/ultraestructura , Succinato Deshidrogenasa/metabolismo

RESUMEN

The enzyme nicotinamide adenine dinucleotide phosphate diaphorase (NADPH diaphorase) is widely used as a sensitive marker for indicating the presence of nitric oxide synthase in neurones. Pyramidal neurones in the healthy neocortex do not contain detectable levels of nitric oxide synthase. However, in the precentral gyrus of brains showing pathological damage, a high proportion of Betz cells (11-50%) and some smaller pyramidal neurones contained low to moderate levels of NADPH diaphorase. They were located in layers V and VI and were present in a newborn baby, older children and elderly adults. Thus, under pathological conditions, some pyramidal neurones are apparently capable of synthesising nitric oxide and this may have a neuroprotective function.

Asunto(s)

Corteza Motora/enzimología , Corteza Motora/patología , NADPH Deshidrogenasa/metabolismo , Óxido Nítrico Sintasa/metabolismo , Células Piramidales/enzimología , Síndrome de Inmunodeficiencia Adquirida/enzimología , Anciano , Anciano de 80 o más Años , Niño , Preescolar , Humanos , Lactante , Recién Nacido

Asunto(s)

Astrocitos/enzimología , Encéfalo/enzimología , NADPH Deshidrogenasa/análisis , Neuronas/enzimología , Óxido Nítrico Sintasa/análisis , Óxido Nítrico Sintasa/biosíntesis , Secuencia de Aminoácidos , Animales , Anticuerpos , Astrocitos/citología , Inducción Enzimática , Epítopos/inmunología , Histocitoquímica/métodos , Humanos , Inmunohistoquímica/métodos , Indicadores y Reactivos , Isoenzimas/análisis , Ratones , Neuronas/citología , Tractos Piramidales/enzimología , Conejos , Heridas Punzantes/enzimología

RESUMEN

Pyramidal cells in the mammalian neocortex do not normally contain detectable levels of the enzyme nitric oxide synthase. However one region of the human neocortex contains pyramidal neurones that express neuronal nitric oxide synthase activity. These neurons are mainly located in layer V of the precentral gyrus and frontal cortex and are predominantly Betz cells. The proportion of Betz cells stained in the eight brains examined varied from 5 to 80%. The brains of eight rats that had received a stab wound to the parietal cortex were also examined. Following a survival period of 7 or 14 days, small groups of pyramidal neurones surrounding the lesion contained moderate levels of neuronal nitric oxide synthase. We suggest that human pyramidal neurones may start expressing nitric oxide synthase as a response to damage or age-related stress and that the nitric oxide released may have a neuroprotective role.

Asunto(s)

Corteza Motora/enzimología , Óxido Nítrico Sintasa/metabolismo , Células Piramidales/enzimología , Anciano , Animales , Recuento de Células , Femenino , Histocitoquímica , Humanos , Persona de Mediana Edad , NADPH Deshidrogenasa/metabolismo , Óxido Nítrico Sintasa/química , Ratas , Ratas Sprague-Dawley

RESUMEN

Histochemical methods were used to assess the distribution of 4 neurotransmitters thought to be involved in cortical plasticity. They were measured in the primary auditory cortex of the ferret from just before the onset of hearing. Acetylcholinesterase staining was strongest in layers I, IV and VI and there was a gradual increase in the amount of staining from postnatal day (PND) 21 through to adulthood. Serotonin fibres were located mainly in layers I-III and their density increased gradually over the same time period. Noradrenergic fibres were sparsely scattered throughout the cortex but their density and distribution showed little change over the age range studied. Dopaminergic fibres were densest in layers V and VI at all ages. However, there was a transient doubling in their density that started round about the onset of hearing at PND 28, peaked at PND 35 and had returned to baseline levels by 2 wk later. This transient peak in density did not occur in the adjacent suprasylvian gyrus and did not appear to be a general phenomenon. The local transient increase in dopaminergic fibres implies that they may have an important role during a short period in auditory cortical development. This role may involve modifying the cortical circuitry that is involved in analysing the input from the auditory periphery.

Asunto(s)

Corteza Auditiva/crecimiento & desarrollo , Tronco Encefálico/crecimiento & desarrollo , Hurones/anatomía & histología , Acetilcolinesterasa/análisis , Animales , Corteza Auditiva/química , Dopamina beta-Hidroxilasa/análisis , Hurones/crecimiento & desarrollo , Inmunohistoquímica , Neuronas Aferentes/citología , Norepinefrina/análisis , Serotonina/análisis , Tirosina 3-Monooxigenasa/análisis

RESUMEN

In paraformaldehyde-fixed sections of healthy brain, glial cells at the light-microscope level do not contain measurable levels of NADPH-diaphorase. However, after a variety of lesions in the mouse brain, some reactive astrocytes express varying amounts of this enzyme. Following stab wounds, activated astrocytes or related glial cells surrounding the lesion, contained moderate to high levels of NADPH-diaphorase in the cerebellum, midbrain, thalamus, striatum, hippocampal formation and neocortex. Double-labelling experiments confirmed that this corresponds to an inducible form of nitric oxide synthase, similar to that found in activated macrophages. Within the lesion there were large numbers of macrophages which also contained NADPH-diaphorase. After 10 min of global hypoxic ischaemia, some reactive astrocytes also contained NADPH-diaphorase. These cells were confined to the dorsal part of the hippocampal formation (the dentate fascia and CA1 areas) and to the anterolateral striatum. More focal ischaemic damage, produced by dividing an arterial branch, also produced a rim of reactive astrocytes containing NADPH-diaphorase, that surrounded the area of necrosis. Low levels of NADPH-diaphorase were induced within one day of a stab wound and the enzyme activity reached near maximal levels by two days postlesion. Moderate NADPH-diaphorase activity was still present at 63 days postlesion, but only a small number of astrocytes were stained in the immediate vicinity of the lesion. These experiments confirm that NADPH-diaphorase activity represents inducible nitric oxide synthase in activated astrocytes and probably in inflammatory macrophages. We conclude that a high proportion of activated astrocytes and a small proportion of invading macrophages are induced to express moderate to high levels of nitric oxide synthase following neuronal damage. Our results indicate that following a variety of lesions reactive astrocytes are synthesizing significant levels of nitric oxide within 24 h. This nitric oxide may be involved in modulating the likelihood of epileptic seizures.

Asunto(s)

Aminoácido Oxidorreductasas/biosíntesis , Astrocitos/enzimología , NADPH Deshidrogenasa/biosíntesis , Proteínas del Tejido Nervioso/biosíntesis , Aminoácido Oxidorreductasas/análisis , Aminoácido Oxidorreductasas/genética , Secuencia de Aminoácidos , Animales , Biomarcadores , Lesiones Encefálicas/metabolismo , Isquemia Encefálica/metabolismo , Corteza Cerebral/lesiones , Corteza Cerebral/metabolismo , Inducción Enzimática , Femenino , Hipoxia Encefálica/metabolismo , Macrófagos/enzimología , Masculino , Ratones , Datos de Secuencia Molecular , NADPH Deshidrogenasa/análisis , NADPH Deshidrogenasa/genética , Proteínas del Tejido Nervioso/análisis , Proteínas del Tejido Nervioso/genética , Óxido Nítrico Sintasa , Células Piramidales/enzimología , Factores de Tiempo , Heridas Punzantes/metabolismo

RESUMEN

NADPH-Diaphorase has recently been shown to be identical to nitric oxide synthase in brain neurones. In the intact brain, NADPH-diaphorase is only present in selected populations of neurones and is not detectable in glia. However following a lesion in the mouse retrosplenial cortex, activated astrocytes display intense NADPH-diaphorase activity throughout their cytoplasm. After a control saline injection, NADPH-diaphorase-positive activated glia are only observed in damaged tissue immediately surrounding the injection site, but when kainic acid is injected unilaterally, activated astrocytes occur in the hippocampal formation bilaterally. This indicates that astrocytes activated by intense neuronal activity, as well as by direct mechanical damage, express high levels of NADPH-diaphorase.

Asunto(s)

Astrocitos/enzimología , Hipocampo/enzimología , NADPH Deshidrogenasa/metabolismo , Animales , Femenino , Hipocampo/citología , Histocitoquímica , Ácido Kaínico/metabolismo , Masculino , Ratones