Biomedical subjects

F Gonzalez-Lima

Publications and source records attributed to F Gonzalez-Lima.

At least 55 records · Page 3Linked to original sources

PubMed1999

Postnatal development of cytochrome oxidase activity in fiber tracts of the rat brain.

This paper describes postnatal changes in cytochrome oxidase (C.O.) activity in developing fiber tracts. Quantitative histochemistry was used to measure changes in C.O. activity in nine white matter regions at postnatal days (P) 7, 12, 17, 30, and 60 in the rat. At P7, enzyme activity was maximal in the spinal trigeminal tract, medial longitudinal fasciculus, and cerebellar white matter. At P12, maximal levels were measured in the medial lemniscus and cerebral peduncle. C.O. activity increased from low levels at P7 to maximal levels by P17 in the hippocampal commissure, posterior and anterior corpus callosum, and anterior commissure. In all nine regions, C.O. activity decreased by P60. Thus, peaks in C.O. activity shifted as a function of postnatal age in a caudo-rostral direction. The regional heterogeneity in the age of onset in C.O. fluctuations suggests that vulnerability to injury and metabolic dysfunction during the perinatal period will differentially affect white matter structures, depending on the age of onset of such disruptions.

Aging↗

PubMed1999

Extinction of behavior in infant rats: development of functional coupling between septal, hippocampal, and ventral tegmental regions.

Learning of a behavior at a particular age during the postnatal period presumably occurs when the functional brain circuit mediating the behavior matures. The inability to express a learned behavior, such as inhibition, may be accounted for by the functional dissociation of brain regions comprising the circuit. In this study we tested this hypothesis by measuring brain metabolic activity, as revealed by fluorodeoxyglucose (FDG) autoradiography, during behavioral extinction in 12- and 17-d-old rat pups. Subjects were first trained on a straight alley runway task known as patterned single alternation (PSA), wherein reward and nonreward trials alternate successively. They were then injected with FDG and given 50 trials of continuous nonreward (i.e., extinction). Pups at postnatal day 12 (P12) demonstrated significantly slower extinction rates compared to their P17 counterparts, despite the fact that both reliably demonstrated the PSA effect, i.e., both age groups distinguished between reward and nonreward trials during acquisition. Covariance analysis revealed that the dentate gyrus, hippocampal fields CA1-3, subiculum, and lateral septal area were significantly correlated in P17 but not P12 pups. Significant correlations were also found between the lateral septal area, ventral tegmental area, and the medial septal nucleus in P17 pups. Similar correlative patterns were not found in P12 and P17 handled control animals. Taken together, these results suggest that septal, hippocampal, and mesencephalic regions may be functionally dissociated at P12, and the subsequent maturation of functional connectivity between these regions allows for the more rapid expression of behavioral inhibition during extinction at P17.

Aging↗

PubMed1999

Metabolic activation of the subependymal zone after cortical injury.

The subependymal zone (SEZ) of the adult mammalian forebrain contains a population of progenitor cells that proliferate in response to brain injury. This study examined the effect of cortical injury on metabolic activity in the SEZ using quantitative histochemistry of cytochrome oxidase. The SEZ showed significantly enhanced cytochrome oxidase activity in rats with electrolytic cortical injuries relative to sham-operated controls, while other brain regions showed no such changes. The results indicate that the SEZ had increased oxidative energy demands, and thus provide metabolic evidence that SEZ cells are activated in response to brain injury.

Animals↗

PubMed1999

Extinction after regular and irregular reward schedules in the infant rat: influence of age and training duration.

Greater persistence in extinction is observed following inconsistent reward compared to that observed following consistent reward, an effect termed the partial reinforcement extinction effect (PREE). We report three experiments in which the extinction rates of random partially reinforced (PRF) or continuously reinforced (CRF) infant rat pups were compared to the extinction rate of pups trained with an alternative and regular schedule of partial reinforcement, known as patterned single alternation (PSA). In PSA, subjects learn to alternate speed of responding in anticipation of the regular alternation of reward and nonreward trials in the straight alley runway. In Experiment 1, 17-day-old PSA subjects showed CRF-like extinction rates; whereas in Experiment 2, in which extinction was initiated early in training prior to the onset of the PSA discrimination, PSA subjects showed prolonged, PRF-like extinction curves. In contrast, 12-day-old pups in Experiment 3 showed no reward-schedule-related differences in extinction, despite differences in behavior during acquisition. These results prompt a modification of Amsel's (1962) model of discrimination learning, and suggest the existence of a dissociation between different types of reward-related expectancies in the younger subjects.

Age Factors↗

PubMed1998

Classical conditioning modifies cytochrome oxidase activity in the auditory system.

The effects of excitatory classical conditioning on cytochrome oxidase activity in the central auditory system were investigated using quantitative histochemistry. Rats in the conditioned group were trained with consistent pairings of a compound conditional stimulus (a tone and a light) with a mild footshock, to elicit conditioned suppression of drinking. Rats in the pseudorandom group were exposed to pseudorandom presentations of the same tone, light and shock stimuli without consistent pairings. Untrained rats in a naive group did not receive presentations of the experimental stimuli. The findings demonstrated that auditory fear conditioning modifies the metabolic neuronal responses of the auditory system, supporting the hypothesis that sensory neurons are responsive to behavioural stimulus properties acquired by learning. There was a clear distinction between thalamocortical and lower divisions of the auditory system based on the differences in metabolic activity evoked by classical conditioning, which lead to an overt learned behavioural response versus pseudorandom stimulus presentations, which lead to behavioural habituation. Increases in cytochrome oxidase activity indicated that tone processing is enhanced during associative conditioning at upper auditory structures (medial geniculate nucleus and secondary auditory cortices). In contrast, metabolic activation of lower auditory structures (cochlear nuclei and inferior colliculus) in response to the pseudorandom presentation of the experimental stimuli suggest that these areas may be activated during habituation to tone stimuli. Together these findings show that mapping the metabolic activity of cytochrome oxidase with quantitative histochemistry can be successfully used to map regional long-lasting effects of learning on brain systems.

Acoustic Stimulation↗

PubMed1998

Large-scale functional connectivity in associative learning: interrelations of the rat auditory, visual, and limbic systems.

Large-scale functional connectivity in associative learning: interrelations of the rat auditory, visual, and limbic systems. J. Neurophysiol. 80: 3148-3162, 1998. Functional relations between specialized parts of the brain may be important determinants of learned behaviors. To study this, we examined the interrelations of the auditory system with several extraauditory structures in two groups of rats having different behavioral histories. Both groups were trained to associate a tone conditional stimulus (CS) with an aversive unconditional stimulus (US). For one group, a light presented with the tone predicted the absence of the US (group TL-). In the other group, the light was a neutral stimulus (group TL0). Fluorodeoxyglucose (FDG) incorporation was measured in the presence of the tone-light compound. Because the tone-light compound was physically identical for both groups, neural differences between groups reflected differences in the learned associative properties of the stimuli. Covariances of FDG uptake in the auditory system and extraauditory structures were examined using partial least squares. Three strong covariance or functional connectivity patterns were identified. The first pattern mainly reflected similarities between groups, with strong interrelations between the subcortical auditory system and the thalamocortical visual system, cerebellum, deep cerebellar nuclei, and midline thalamus. This pattern of interactions may represent part of a common circuit for relaying the associative value of the tone CS to the cerebellum and the midline thalamus. The external nucleus of the inferior colliculus and medial division of the medial geniculate nucleus were associated more strongly with this pattern for group TL-, which was interpreted as representing the change of the associative value of the tone by the light, mediated through extraauditory influences on these two regions. A second pattern involved midbrain auditory regions, superior colliculus, zona incerta, and subiculum and was stronger for group TL0. The relations between midbrain structures may represent the excitatory conditioned response (CR) evoked by the tone in this group. The final pattern was strongest in group TL- and involved interrelations of the thalamocortical auditory system with hippocampus, basolateral amygdala, and hypothalamus. This pattern may represent the learned inhibition of the CR to the tone in the presence of the light. These findings are consistent with behavioral studies suggesting that at least two types of associations are formed during associative learning. One is the sensory relation of the stimuli and another is the relation between the CS and the affective components of the US. These behavioral associations are mapped to the patterns of functional connectivity between auditory and extraauditory regions.

Acoustic Stimulation↗

PubMed1997

Effects of age and sociosexual experience on the morphology and metabolic capacity of brain nuclei in the leopard gecko (Eublepharis macularius), a lizard with temperature-dependent sex determination.

In vertebrates having sex chromosomes, sexual behavior is influenced by steroid hormones throughout life as well as by the cumulative experiences of the individual. Because males and females differ genetically as well as hormonally, it would be valuable to distinguish the contribution of sex-specific genes from hormones. In addition, since animals age as they gain sociosexual experience, but do not necessarily gain sociosexual experience as they age, it is important to separate the effects of age from those attributable to experience. The leopard gecko is a lizard lacking sex chromosomes, depending instead upon the temperature during incubation to establish gonadal sex. This effectively removes sex-specific genetic influences from any study of sexual differentiation. Eggs were incubated at either 26 degrees C or 32.5 degrees C, temperatures that produce only female hatchlings or a male-biased sex ratio, respectively. By raising geckoes in isolation and then housing some animals together in breeding groups at different ages after they attained sexual maturity, it was possible to assess the relative effects of age and sociosexual experience on the volume and metabolic capacity of limbic and non-limbic brain areas. In general, males showed more changes compared to females. For example, there was a decrease with age in the volume of the preoptic area and the ventromedial hypothalamus in males, but not in females. Both age and sociosexual experience influenced cytochrome oxidase activity in these and other brain areas. Experienced animals had greater metabolic capacity in nuclei functionally associated with sociosexual behavior in lizards and other vertebrates. For example, cytochrome oxidase activity was higher in the anterior hypothalamus of males, in the ventromedial hypothalamus of both males and females from the male-biased incubation temperature, and in the preoptic area of females from both incubation temperatures. These differences were not paralleled by differences in circulating levels of sex hormones; only plasma androgen levels differed as a function of experience in males. These data suggest that the volume and metabolic capacity of specific brain regions change as animals age and gain sociosexual experience, but the nature and degree of change depend upon prenatal events.

Age Factors↗

PubMed1997

Independent effects of incubation temperature and gonadal sex on the volume and metabolic capacity of brain nuclei in the leopard gecko (Eublepharis macularius), a lizard with temperature-dependent sex determination.

The extent to which variation within and between the sexes can be assigned to genes vs. environment is problematic, because, in most vertebrates, males and females differ genetically. However, factors other than sex chromosomes and the consequent sex-typical gonadal hormone secretions may play important roles in the differentiation of the neural mechanisms underlying individual and sex differences in aggressive and sexual behavior. The leopard gecko, like many oviparous reptiles, lacks sex chromosomes. Instead, gonadal sex is determined by temperature during embryogenesis, with low and high incubation temperatures producing females and intermediate temperatures producing mixed sex ratios. In essence, this allows for the study of individual and sex differences without the confounding variable of genetically determined gender. Experiments have shown that the temperature experienced during incubation plays a critical role in establishing the adult morphological, endocrinological, and behavioral phenotype. In this experiment, the independent effects of incubation temperature and gonadal sex on the morphology and metabolic capacity of specific brain nuclei were determined. Both individual and sex differences in the volume of the preoptic area and ventromedial nucleus of the hypothalamus are determined primarily by incubation temperature, not by gonadal sex. However, incubation temperature and gonadal sex are both important in determining the metabolic capacity in the anterior hypothalamus, external amygdala, dorsal lateral nucleus of the hypothalamus, dorsal lateral nucleus of the thalamus, dorsal ventricular ridge, habenula, lateral hypothalamus, nucleus rotundus, nucleus sphericus, periventricular nucleus of the hypothalamus, preoptic area, periventricular nucleus of the preoptic area, septum, striatum, torus semicircularis, and ventromedial nucleus of the hypothalamus. This is the first demonstration in a vertebrate that factors other than gonadal sex hormones, which arise from the individual's genetic constitution, can affect the sexual differentiation of the brain.

Animals↗

PubMed1997

Quantitative cytochemistry of cytochrome oxidase and cellular morphometry of the human inferior colliculus in control and Alzheimer's patients.

Quantitative cytochemistry of cytochrome oxidase (C.O.) was implemented in human brains to measure C.O. activity in the 3 main divisions of the inferior colliculus (IC): central (ICC), dorsal (ICD), and external (ICE). Units of C.O. activity (micromol/min/g tissue wet weight) were quantified in cellular compartments (overall average, neuropil, perikaryon, and dendrites) at the light microscope level using microdensitometry calibrated with C.O. activity standards measured spectrophotometrically. In a non-AD (Alzheimer's disease) control group (mean age = 79.6 +/- 3.1 years, postmortem time = 6.9 +/- 1.6 h), the ICC and ICD demonstrated higher (p < 0.008) overall average activities (mean = 183.40 +/- 18.7 and 184.98 +/- 45.1 units, respectively) relative to the ICE (56.46 +/- 15.9 units). Comparison of cellular morphometry (soma and nucleus area, perimeter, and diameter) revealed that the ICC contained cells of significantly larger soma size than in both the ICD and ICE (p < 0.002). The distribution of soma diameters in the ICC of controls showed a clear bimodality, enabling the typing of the cells into larger and smaller than average soma diameter. Brains from patients with Alzheimer's disease (AD; mean age = 78.3 +/- 2.9 years, postmortem time = 6.5 +/- 1.3 h) were compared with the non-AD controls. Significant group differences were found only in the large cells of the ICC. The AD large cells showed a decrement in C.O. activity relative to the corresponding controls in overall average activity (p < 0.032) and in peak activity of neuropil near the soma (p < 0.012). These findings provide the first quantitative cytochemical data of C.O. activity in humans. They also suggest that cellular alterations in C.O. metabolism in AD affect predominantly specific groups of larger projection neurons while neighboring neurons are spared.

Aged↗

PubMed1997

Reduced cytochrome oxidase and memory dysfunction after chronic brain ischemia in aged rats.

The effects of chronic cerebrovascular ischemia on memory function and cytochrome oxidase (CO) activity were investigated. Cerebrovascular insufficiency was induced by permanent bilateral carotid artery ligation (2-VO) in 19 month old rats. Sham surgery in no-vessel occlusion (no-VO) rats were used for controls. Memory function was tested 1 week prior to surgery and then weekly for 21 days using the Morris water maze. Regional brain activity of CO was measured 4 weeks after surgery by quantitative histochemistry. Histologic examination of brain slices was used to evaluate any neuropathology present. Results showed that 2-VO rats were significantly impaired in the water maze task at each testing period with respect to no-VO controls. In addition, CO activity in 2-VO rats was markedly reduced only in the dorsal CA1 region of the hippocampus and in the posterior parietal cortex. These brain regions are involved in visuo-spatial memory mechanisms. Analysis of other brain regions in 2-VO rats did not reveal further CO activity changes. There were no damaged or loss of neurons in 2-VO or no-VO groups in any region examined, including CA1 and posterior parietal cortex. The CA1 region however, is known to undergo neuronal loss 25 weeks after chronic 2-VO suggesting that this vascular insult can induce a slowly-evolving cascade consisting of neuronal damage, atrophy and death. The present findings indicate that reduced CO activity in CA1 and posterior parietal regions can predict neural damage and atrophy prior to structural perikaryal pathology following chronic brain ischemia. In addition, the data shows that neuronal energy metabolic deficiency may initiate visuo-spatial memory impairment in this aging rat model.

Aging↗

PubMed1997

Metabolic effects of blocking tone conditioning on the rat auditory system.

The Kamin blocking phenomenon occurs when behavioral expression of conditioning to a novel stimulus fails in the presence of a previously conditioned stimulus (CS). Neural metabolic effects of a tone conditioned as an excitor were compared to the effects of the same physical tone when excitatory conditioning was blocked by previous conditioning with a light. We examined the metabolic activity of the auditory system to test the hypothesis that auditory processing of a tone CS changes during blocking. Quantitative histochemistry of cytochrome oxidase (C.O.), the final mitochondrial enzyme for oxidative metabolism, was used to evaluate cumulative changes in the metabolic capacity of the auditory system resulting from blocking. Rats (Long-Evans) in the Blocking group received pairings of a light CS with a mild footshock unconditioned stimulus (US) during Phase 1 training. Rats in the Control group received random presentations of the same stimuli during Phase 1. Both groups then received the same Phase 2 training consisting of simultaneous tone and light presentations paired with footshock. The Control group exhibited significant suppression of drinking to tone alone presentations after training, whereas the Blocking group did not. Metabolic mapping results demonstrated that blocking effects were localized to auditory regions receiving direct US somatosensory projections. Significantly greater C.O. activity in the inferior colliculus and the dorsal cochlear nucleus was found for the Blocking group relative to the Control group. Input cell layers of secondary auditory cortex also demonstrated a group difference, in that layers II/III and IV had lower levels of C.O. activity in the Blocking group. These specific changes in C.O. activity linked to behavioral training demonstrated that the blocking phenomenon produced distinct neural metabolic changes in CS processing in the auditory system localized to regions with CS-US interactions.

Animals↗

PubMed1997

Effects of intrauterine position on the metabolic capacity of the hypothalamus of female gerbils.

The intrauterine position that a rodent fetus occupies relative to members of the same or opposite gender affects both its reproductive physiology and behavior when adult. Cytochrome oxidase histochemistry was used to assess regional differences in the oxidative metabolic capacity of the hypothalamus of female Mongolian gerbils that developed in utero between 2 female fetuses (n = 15) or between 2 male fetuses (n = 14). Cytochrome oxidase reactivity was measured densitometrically by experimenters unaware of subject intrauterine position. Gray-to-white matter ratios of optical density in 11 brain regions were used as a normalized index of metabolic capacity. Significant group differences in the metabolic capacity of the medial and the posterior parts of the anterior hypothalamus were revealed. Females that developed in utero between 2 male fetuses showed significant increases (19-22%) in cytochrome oxidase reactivity in these brain regions compared to that in females that developed between 2 female fetuses. The medial part of the anterior hypothalamus contributes to copulatory behavior, whereas the posterior part of the anterior hypothalamus may be involved in the control of pituitary gonadotropin secretion. Both these functions are influenced by intrauterine position during fetal life. To our knowledge, this is the first demonstration of metabolic changes in hypothalamic areas of the adult related to the differences in intrauterine position.

Animals↗

PubMed1996

Brain organization in a reptile lacking sex chromosomes: effects of gonadectomy and exogenous testosterone.

In mammals, males and females differ both genetically and hormonally, making it difficult to assess the relative contributions of genetic constitution and fetal environment in the process of sexual differentiation. Many reptiles lack sex chromosomes, relying instead on the temperature of incubation to determine sex. In the leopard gecko (Eublepharis macularius), an incubation temperature of 26 degrees C produces all females, whereas 32.5 degrees C results in mostly males. Incubation temperature is the primary determinant of differences both within and between the sexes in growth, physiology, and sociosexual behavior, as well as the volume and metabolic capacity of specific brain nuclei. To determine if incubation temperature organizes the brain directly rather than via gonadal sex hormones, the gonads of male and female leopard geckos from the two incubation temperatures were removed and, in some instances, animals were given exogenous testosterone. In vertebrates with sex chromosomes, the size of sexually dimorphic nuclei are sensitive to hormone levels in adulthood, but in all species studied to date, these changes are restricted to the male. Therefore, after behavior tests, morphometrics of certain limbic and nonlimbic brain areas were determined. Because nervous system tissue depends on oxidative metabolism for energy production and the level of cytochrome oxidase activity is coupled to the functional level of neuronal activity, cytochrome oxidase histochemistry also was performed on the same brains. Hormonal manipulation had little effect on the volume of the preoptic area or ventromedial hypothalamus in geckos from the all-female incubation temperature, but significantly influenced the volumes of these brain areas in males and females from the male-biased incubation temperature. A similar relationship was found for cytochrome oxidase activity of the anterior hypothalamus, amygdala, dorsal ventricular ridge, and septum. The only sex difference observed was found in the ventromedial hypothalamus; males showed no significant changes in cytochrome oxidase activity with hormonal manipulation, but females from both incubation temperatures were affected similarly. The results indicate that incubation temperature organizes the brain directly rather than via hormones arising from its sex-determining function. This is the first demonstration in a vertebrate that factors other than steroid hormones can modify the organization and functional activity of sexually differentiated brain areas.

Animals↗

PubMed1995

Functional network interactions between parallel auditory pathways during Pavlovian conditioned inhibition.

Using covariance structural equation modeling and fluorodeoxyglucose (FDG) autoradiography this study examined auditory system interactions when the learned associative effects of a tone were inhibited by a light. Two groups of rats received pairings of a tone (conditioned excitor: T+) with a mild footshock. Group TL- was trained in a Pavlovian conditioned inhibition paradigm (T+/TL-) where the tone-light compound signaled the absence of footshock, making the light the inhibitor (L-). Group TL degree was trained with the tone as the excitor and the light as a 'neutral' stimulus. After FDG injection, all rats were presented with the tone-light compound. Group differences in auditory system FDG uptake were observed only in the ventral division medial geniculate nucleus (MGV), where group TL- had relatively lower incorporation. Structural equation modeling was used with the covariances of FDG activity to determine the functional influences through the auditory system anatomic connections. Differences were noted mainly at the level of the inferior colliculus (IC) and medial geniculate, possibly reflecting the unique anatomic relation of these regions with extraauditory areas. Ascending and descending influences from the IC differed with stronger influences for group TL-. Intracollicular and the ascending influence influences of MGV and medial division of the medial geniculate nucleus (MGM) on the auditory cortex also differed mainly in the sign of the functional interaction. These results demonstrate how interactions among parallel auditory pathways can code the behavioral significance of auditory stimuli and emphasize that a full appreciation of neural operations underlying learning can only be gained through examination of both regional activity and interregional interactions.

Animals↗

PubMed1995

A landscape parametric profile approach for rat brain image analysis.

This paper develops the use of the landscape parametric profile as a descriptive and interpretative method of analyzing metabolic activity data obtained by neuroimaging techniques such as 2-deoxyglucose autoradiography. The method is suggested as an initial survey-type approach that can be used to map regional activity throughout the coronal planes of a rat brain and to compare relative differences in the patterns of activity between different brains. Images are acquired using preexisting image analysis software and then transformed to landscape parametric profiles derived from each matrix array. The image profile analysis tasks are done using commercially available software for matrix computations such as MATLAB. An effective way of interpreting activity differences between brains is presented by plotting the results from a randomized blocks ANOVA significance test combined with the average profiles of different subjects within the same experimental group. The method greatly reduces the computational burden associated with image averaging and statistical comparison of brains from different subjects while preserving the richness in topographic metabolic information. One significant advantage of the method is that it results in figures that are readily depicted and interpretable in black and white.

Analysis of Variance↗

PubMed1995

Regional brain effects of sodium azide treatment on cytochrome oxidase activity: a quantitative histochemical study.

The objective of the present study was to determine if regional variation in brain cytochrome oxidase activity was observed following systemic administration of sodium azide. An image analysis system calibrated with internal standards of known cytochrome oxidase activity was used to quantify cytochrome oxidase in histochemically stained brain sections. Rats receiving chronic infusion of sodium azide (400 micrograms/hr), which were sacrificed after two weeks, showed a substantial decrease in brain cytochrome oxidase activity over those infused with saline. All of the 22 regions sampled from telencephalic, diencephalic, and mesencephalic levels, showed a significant activity reduction which ranged between 26% and 37%. The regions that appeared significantly more vulnerable to the sodium azide effects were the mesencephalic reticular formation and the central amygdala, which displayed the largest decrease in activity. In addition, interregional correlations of activity showed a deeply modified pattern of correlative metabolic activity between hippocampal, amygdaloid and cortical areas after azide treatment. The regional effects found were consistent with azide-induced learning and memory dysfunctions.

Animals↗

PubMed1994

Quantitative mapping of cytochrome oxidase activity in the central auditory system of the gerbil: a study with calibrated activity standards and metal-intensified histochemistry.

The objective was to obtain detailed topographic determinations of cytochrome oxidase activity in the gerbil central auditory system at the light microscopic level. Quantitative techniques were developed using (1) tissue standards calibrated to express histochemical measures as actual enzyme activity units, (2) densitometry and image analysis of histochemical reaction product formation, (3) spectrophotometry of cytochrome oxidase activity, and (4) a cobalt-intensified staining procedure compatible with autoradiography and other techniques requiring fresh-frozen brains without perfusion-fixation. Linear relationships between incubation time, section thickness, and activity of dissected brain regions, with their reaction product measured densitometrically were determined. Auditory structures with the high activities showed about 8 times the labeling intensity of the white matter or control sections inhibited with cyanide, glutaraldehyde, or heat. This indicated the high sensitivity of the method without loss of specificity. Specific activity for each of the 18 auditory structures measured were all above the units measured for whole brain homogenates, supporting the notion that basal levels of oxidative metabolism are greater for the auditory system. There was a progressive decrement in activity from brain stem to forebrain auditory structures. The more peripheral nuclei also showed a higher proportion of somatic as compared to neuropil reactivity. In contrast, auditory midbrain and thalamocortical regions were characterized primarily by neuropil reactivity. Comparison of intrinsic patterns of activity with morphological schemes to subdivide nuclei, showed a good correspondence with classical subdivisions derived from Golgi studies. The reported activities may provide a base of normative data in the gerbil for subsequent studies of central auditory functions. The method presented fulfilled established quantitative criteria and provided a more sensitive approach for regional mapping studies of brain cytochrome oxidase activity.

Animals↗

PubMed1994

Metabolic activation of the brain of young rats after exposure to environmental complexity.

Autoradiography with 14C-2-deoxyglucose was used to determine brain metabolic activity during the quiet period that follows after daily exploratory experiences in new complex environments. Eight 1-month-old, male Tryon rats were selected from two litters. Pairs of littermates matched by body weight were assigned to one of two conditions: rats housed individually in small home cages as the "impoverished condition," or rats exposed twice daily to changing and complex environments of two large cages with inanimate objects and conspecifics as the "enriched condition." After 4 days, rats were injected with 2-deoxyglucose, placed individually in a home cage and left undisturbed for 90 min until sacrificed. The brains of "enriched" rats were heavier than their "impoverished" littermates, and showed a global trend for metabolic enhancement. They also showed significantly greater amounts of 2-deoxyglucose in occipital cortex (27%), hippocampal subiculum (36%), and nucleus accumbens (40%).

Aging↗