Age-related changes in regional brain mitochondria from Fischer 344 rats.

Brain mitochondrial function has been posited to decline with aging. In order to test this hypothesis, cortical and striatal mitochondria were isolated from Fischer 344 rats at 2, 5, 11, 24 and 33 months of age. Mitochondrial membrane potential remained stable through 24 months, declining slightly in mitochondria from both brain regions at 33 months. The ability of calcium to induce mitochondrial swelling and depolarization, characteristics of the permeability transition, was remarkably stable through 24 months of age and increased at advanced ages only for cortical, but not striatal, mitochondria. Striatal mitochondria were more sensitive to calcium than were cortical mitochondria throughout the first 2 years of life. A two-fold increased resistance to calcium was observed in striatal mitochondria between 5 and 11 months. Although these measurements do demonstrate changes in mitochondrial function with aging, the changes in polarization are relatively small and the increased cortical susceptibility to the permeability transition only occurred at very advanced ages. Thus mitochondrial decline with advanced age depends upon brain region.

Age-dependent changes in the calcium sensitivity of striatal mitochondria in mouse models of Huntington's Disease.

Striatal and cortical mitochondria from knock-in and transgenic mutant huntingtin mice were examined for their sensitivity to calcium induction of the permeability transition, a cause of mitochondrial depolarization and ATP loss. The permeability transition has been suggested to contribute to cell death in Huntington's Disease. Mitochondria were examined from slowly progressing knock-in mouse models with different length polyglutarnine expansions (Q20, Q50, Q92, Q111) and from the rapidly progressing transgenic R6/2 mice overexpressing exon I of human huntingtin with more than 110 polyglutamines. As previously observed in rats, striatal mitochondria from background strain CD1 and C57BL/6 control mice were more sensitive to calcium than cortical mitochondria. Between 5 and 12 months in knock-in Q92 mice and between 8 and 12 weeks in knock-in Q111 mice, striatal mitochondria developed resistance, becoming equally sensitive to calcium as cortical mitochondria, while those from Q50 mice were unchanged. Cortical mitochondrial calcium sensitivity did not change. In R6/2 mice striatal and cortical mitochondria were equally resistant to Ca2+ while striatal mitochondria from littermate controls were more susceptible. No increases in calcium sensitivity were observed in the mitochondria from Huntington's Disease (HD) mice compared to controls. Neither motor abnormalities, nor expression of cyclophilin D corresponded to the changes in mitochondrial sensitivity. Polyglutamine expansions in huntingtin produced an early increased resistance to calcium in striatal mitochondria suggesting mitochondria undergo compensatory changes in calcium sensitivity in response to the many cellular changes wrought by polyglutamine expansion.

Reciprocal subtraction differential RNA display: an efficient and rapid procedure for isolating differentially expressed gene sequences.

A reciprocal subtraction differential RNA display (RSDD) approach has been developed that permits the rapid and efficient identification and cloning of both abundant and rare differentially expressed genes. RSDD comprises reciprocal subtraction of cDNA libraries followed by differential RNA display. The RSDD strategy was applied to analyze the gene expression alterations resulting during cancer progression as adenovirus-transformed rodent cells developed an aggressive transformed state, as documented by elevated anchorage-independence and enhanced in vivo oncogenesis in nude mice. This approach resulted in the identification and cloning of both known and a high proportion (>65%) of unknown sequences, including cDNAs displaying elevated expression as a function of progression (progression-elevated gene) and cDNAs displaying suppressed expression as a function of progression (progression-suppressed gene). Sixteen differentially expressed genes, including five unknown progression-elevated genes and six unknown progression-suppressed genes, have been characterized. The RSDD scheme should find wide application for the effective detection and isolation of differentially expressed genes.

Effects of prenatal protein malnutrition on hippocampal long-term potentiation in freely moving rats.

It has been demonstrated that prenatal protein malnutrition significantly affects hippocampal plasticity, as measured by long-term potentiation, throughout development. This paper focuses on the hippocampal dentate granule cell population response to two separate paradigms of tetanization of the medial perforant pathway in prenatally protein-malnourished and normally nourished adult male rats. The 100-pulse paradigm consisted of the application of ten 25-ms-duration bursts of 400 Hz stimulation with an interburst interval of 10 s. The 1000-pulse paradigm consisted of the application of five 500-ms bursts of 400 Hz stimulation with an interburst interval of 5 s. No between-group differences were obtained for input/output response measures prior to tetanization. No between-group, nor between-paradigm, differences were obtained in the degree of population EPSP slope enhancement. However, in response to both paradigms, prenatally malnourished animals showed significantly less enhancement of the population spike amplitude (PSA) measure than normally nourished animals. Normally nourished animals showed a significantly greater level of PSA enhancement in response to the 100-pulse paradigm than the 1000-pulse paradigm. Prenatally malnourished animals showed no significant differences in the degree of PSA enhancement between the two paradigms. Results indicate that short duration bursts (< or = 25 ms) are more effective in inducing maximal PSA enhancement in normally nourished rats than longer duration stimulus bursts. The apparent inability of prenatally malnourished rats to transfer enhanced cellular activation (population EPSP slope enhancement) into enhanced cellular discharge (PSA enhancement) suggests that a preferential enhancement of GABAergic inhibitory modulation of granule cell excitability may result from the prenatal dietary insult. Such potentiation of inhibitory activity would significantly lower the probability of granule cell population discharge, resulting in the significantly lower level of PSA enhancement obtained from these animals.

Studies of dentate granule cell modulation: paired-pulse responses in freely moving rats at three ages.

Dentate granule cell population responses to paired-pulse stimulations applied to the perforant pathway across a range of interpulse intervals (IPI) were examined in freely moving rats at 15, 30, and 90 days of age. The profile of the paired-pulse index (PPI), a measure of the type and degree of modulation of dentate granule cell excitability, was shown to change significantly as a function of age.

Neonatal isolation alters LTP in freely moving juvenile rats: sex differences.

We have previously reported that neonatal isolation significantly enhanced the magnitude of hippocampal long-term potentiation (LTP) recorded from freely moving male rats tested at 30 days of age. The present study extends this work to examine the effects of neonatal isolation on hippocampal LTP in male and female juvenile rats. Changes in dentate granule cell population measures, i.e., EPSP slope and population spike amplitude (PSA), evoked by tetanization of the medial perforant pathway were used to assess the effects of neonatal isolation on LTP over a period of 96 hrs. Prior to tetanization, significant sex differences were obtained for input/output (I/O) response measures of EPSP slope and PSA, with males showing consistently higher values than females. No significant effect of treatment was obtained within either sex for baseline measures. Following tetanization significant sex differences were also obtained for both measures, with males showing significantly greater enhancement than females. Comparisons made at 1 hr post-tetanization (establishment of LTP) indicated that isolated males showed significantly greater enhancement than any other group. On the other hand, treatment differences were not obtained from females. At 96 hrs (maintenance of LTP), however, both neonatally isolated males and females showed significantly greater enhancement than either non-isolated siblings or unhandled controls. These results indicate that males and females exhibit different enhancement profiles with respect to both the magnitude and duration of LTP, and that neonatal isolation alters these profiles in a sex-specific manner.

Neonatal isolation enhances hippocampal dentate response to tetanization in freely moving juvenile male rats.

The impact of early neonatal isolation on measures of hippocampal neuronal plasticity was examined in freely moving male rats at 30 days of age. Beginning on Postnatal (PN) Day 2, one-half of pups from each experimental litter were individually isolated from the nest, dam, and siblings for a period of 1 h per day over PN Days 2-9, while their siblings remained in the nest. In addition, randomly selected litters served as unhandled controls. On PN Day 26 all pups were weaned and chronically implanted for recording of evoked field potentials and induction of hippocampal longterm potentiation. At 30 days of age, pups from the three treatment groups (isolated, nonisolated siblings, and unhandled controls) were tested for their ability to establish and maintain long-term potentiation across the perforant path/hippocampal dentate granule cell synapse. Changes in population EPSP slope and population spike amplitude (PSA) recorded following tetanization were used to assess the effects of neonatal isolation of hippocampal response measures. No significant between-group differences were obtained for input/output response curves constructed prior to tetanization. All three groups showed immediate and significant enhancement of the PSA measure at 15 min posttetanization. The level of PSA enhancement obtained from previously isolated pups was significantly greater than that obtained from both the nonisolated sibling and unhandled control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of long-term potentiation in the hippocampal dentate gyrus of the freely-moving 15-day-old rat.

The magnitude and duration of long-term potentiation (LTP) of perforant path/dentate granule cell synapses was examined in freely moving rats beginning at 15 days of age. Measures of dentate granule cell population EPSP slope and population spike amplitude (PSA) obtained before and after tetanization were used to evaluate the level of LTP. Tetanization resulted in significant enhancement of both the population EPSP slope (approximately +75%) and PSA (approximately +40%) measures. This enhancement was maintained without significant change for 18 h, after which both measures began a steady and continuous rise. Daily input/output response measures from age-matched nontetanized animals were used to factor out enhancement related to normal development. Under this schema, tetanization-induced enhancement of both EPSP slope and PSA measures decayed slowly, beginning 18-24 h after tetanization, returning to baseline 5 days after tetanization. Enhancement obtained from 90-day-old animals decayed to baseline 24 h after tetanization. The longer duration of LTP obtained from preweanlings is discussed with regard to the development of inhibitory systems modulating granule cell excitability.

Maturation of long-term potentiation in the hippocampal dentate gyrus of the freely moving rat.

The ability of the perforant path/dentate granule cell synapse of the hippocampal formation to establish and maintain enhanced levels of synaptic transmission in response to tetanization (long-term potentiation, LTP) was investigated in freely moving rats at 15, 30, and 90 days of age. Measures of 1) the slope of the population excitatory postsynaptic potential (EPSP), and 2) the population spike amplitude (PSA) obtained before, and at several times following tetanization, were used to evaluate the magnitude and duration of LTP as a function of age. Significant enhancement of both EPSP slope and PSA measures was obtained from animals of all three ages in response to perforant path tetanization. The initial degree of enhancement was essentially the same across the age groups, ranging from +27% to +38% of pretetanization levels for EPSP slope measures and +60% to +75% of pretetanization levels for PSA measures, obtained 15 min after tetanization. The duration of this enhancement obtained from animals of the preweaning group was significantly longer than that obtained from either 30- or 90-day-old animals. Enhanced measures of both EPSP slope and PSA decayed to baseline levels in these older animals 18 to 24 h after tetanization, while animals tetanized at 15 days of age maintained potentiated levels of both measures for a period of 5 days following tetanization. Tetanization of 15-day-old animals resulted in a significant reduction in the latency to EPSP onset without affecting the time-based relationships among the other measured parameters, which included latency of the population spike onset, population spike minimum, and population spike offset.(ABSTRACT TRUNCATED AT 250 WORDS)

Prenatal malnutrition and development of the brain.

In this review, we have summarized various aspects as to how prenatal protein malnutrition affects development of the brain and have attempted to integrate several broad principles, concepts, and trends in this field in relation to our findings and other studies of malnutrition insults. Nutrition is probably the single greatest environmental influence both on the fetus and neonate, and plays a necessary role in the maturation and functional development of the central nervous system. Prenatal protein malnutrition adversely affects the developing brain in numerous ways, depending largely on its timing in relation to various developmental events in the brain and, to a lesser extent, on the type and severity of the deprivation. Many of the effects of prenatal malnutrition are permanent, though some degree of amelioration may be produced by exposure to stimulating and enriched environments. Malnutrition exerts its effects during development, not only during the so-called brain growth spurt period, but also during early organizational processes such as neurogenesis, cell migration, and differentiation. Malnutrition results in a variety of minimal brain dysfunction-type syndromes and ultimately affects attentional processes and interactions of the organism with the environment, in particular producing functional isolation from the environment, often leading to various types of learning disabilities. In malnutrition insult, we are dealing with a distributed, not focal, brain pathology and various developmental failures. Quantitative assessments show distorted relations between neurons and glia, poor formation of neuronal circuits and alterations of normal regressive events, including cell death and axonal and dendritic pruning, resulting in modified patterns of brain organization. Malnutrition insult results in deviations in normal age-related sequences of brain maturation, particularly affecting coordinated development of various cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter systems. It is obvious that such diffuse type "lesions" can be adequately assessed only by interdisciplinary studies across a broad range of approaches, including morphological, biochemical, neurophysiological, and behavioral analyses.

Prenatal protein malnutrition alters behavioral state modulation of inhibition and facilitation in the dentate gyrus.

We have examined the effects of prenatal protein malnutrition on interneuronally mediated inhibition and facilitation in the dentate gyrus of the rat using the paired-pulse technique. Field potentials were recorded in the dentate gyrus in response to paired stimuli delivered to the perforant path. The paired-pulse index (PPI) was used as a measure of the net short-term facilitation or interneuronally mediated inhibition effective at the time of the paired-pulse test and was computed by dividing the amplitude of the second population spike (p2) by the amplitude of the first population spike (p1). PPIs were classified according to p1 in order to compare PPIs between behavioral states and dietary treatments since population spike amplitudes in the dentate gyrus vary in relation to behavioral state. Testing was performed during 4 behavioral states: slow-wave sleep (SWS), paradoxical sleep (REM), immobile waking (IW) and exploratory locomotion (AW) using interpulse intervals (IPI) from 20 to 400 ms. The magnitude and duration of interneuronally mediated inhibition was significantly increased in prenatal protein malnourished animals when compared with controls. Paired-pulse tests performed using an IPI of 20 ms under the high p1 (p1 greater than median) condition showed significantly smaller PPIs in prenatal protein malnourished rats regardless of behavioral state. For IPIs greater than 20 ms PPIs were consistently smaller in prenatal protein malnourished rats during SWS and IW. These data indicate that both the magnitude and duration of interneuronally mediated inhibition are increased in prenatally malnourished rats. No consistent diet-related differences were found during AW and REM using IPIs greater than 20 ms because interneuronally mediated inhibition was relatively suppressed during these behavioral states for both dietary groups. There was no consistent behavioral state modulation of paired-pulse facilitation (IPI = 40 to 80 ms) or late inhibition (IPI = 400 ms) in either diet group. In addition, a new relation between PPI and IPI was found under the low p1 (p1 greater than median) condition. During AW the PPIs observed using IPIs of 40 and 50 ms were smaller than those observed using IPIs of 30 and 60 ms. This depression interrupts what is generally considered the "facilitatory" phase of paired-pulse response and may indicate an interaction between perforant path stimulation and hippocampal theta rhythm which is masked when p1 amplitude is high.(ABSTRACT TRUNCATED AT 400 WORDS)

Prenatal protein malnutrition and hippocampal function: rapid kindling.

A stimulation paradigm evoking rapidly recurring seizure activity from the hippocampal dentate gyrus was used to examine perforant path kindling in prenatally protein malnourished adult rats. Biphasic electrical stimulations (50 Hz) of five s duration were applied to the perforant path every five min for one hour over five consecutive days. Behavioral manifestations of seizure activity were assessed using the standard 0-5 scale. Prenatally malnourished rats exhibited significantly fewer convulsive seizures (stage 5) and required significantly more stimulations to attain the first stage 5 seizure than controls. Animals of the malnourished group also exhibited significantly more stage 1 seizures than control animals, indicating a significant retardation in the kindling rate of these animals. Additionally, 3 of the 11 malnourished animals failed to exhibit a single stage 5 seizure during the 60 stimulation test period. These findings parallel previous results reported for prenatally protein malnourished rats using the traditional one stimulation-per-day kindling paradigm and indicate that this rapid kindling paradigm can be effectively used to study the impact of various insults on seizure susceptibility and development in a shortened time frame.

Effects of prenatal protein malnutrition on kindling-induced alterations in dentate granule cell excitability. II. Paired-pulse measures.

The effects of prenatal protein malnutrition on kindling-induced changes in inhibitory modulation of dentate granule cell activity were examined by analysis of extracellular field potentials recorded from the granule cell layer of the dentate gyrus in response to paired-pulse stimulation of the perforant pathway in freely-moving rats. Since we have shown that kindling results in enhanced synaptic transmission at the level of the perforant path/granule cell synapse (see preceding paper), we sought to determine if the kindling process might induce changes in inhibitory modulation of granule cell excitability which could be involved in the slower acquisition of the kindled state we have previously reported in malnourished animals. Beginning at 120-150 days of age, the response of dentate granule cells to paired-pulse stimulation of the perforant path was examined at interpulse intervals (IPIs) ranging from 20-1000 ms. A paired-pulse index (PPI) was constructed based on the mean percent change in population spike amplitudes of the two responses resulting from application of the pulse pair. PPI measures obtained during the kindling process were compared with individual prekindling measures to determine the mean percent change in excitatory/inhibitory modulation of granule cell activity. Significant inhibition of the second population response was apparent at all IPIs tested for both diet groups following the first kindled afterdischarge.(ABSTRACT TRUNCATED AT 250 WORDS)