Vulnerability of developing brain. 3. Development of four enzymes in the brains of normal and undernourished rats

Maternal exposure to busulfan reduces the cell number in the somatosensory cortex associated with delayed somatic and reflex maturation in neonatal rats

Busulfan is a bifunctional alkylating agent used for myeloablative conditioning and in the treatment of chronic myeloid leukemia due to its ability to cause DNA damage. However, in rodent experiments, busulfan presented a potential teratogenic and cytotoxic effect. Studies have evaluated the effects of busulfan on fetuses after administration in pregnancy or directly on pups during the lactation period. There are no studies on the effects of busulfan administration during pregnancy on offspring development after birth. We investigated the effects of busulfan on somatic and reflex development and encephalic morphology in young rats after exposure in pregnancy. The pregnant rats were exposed to busulfan (10 mg/kg, intraperitoneal) during the early developmental stage (days 12-14 of the gestational period). After birth, we evaluated the somatic growth, maturation of physical features and reflex-ontogeny during the lactation period. We also assessed the effects of busulfan on encephalic weight and cortical morphometry at 28 days of postnatal life. As a result, busulfan-induced pathological changes included: microcephaly, evaluated by the reduction of cranial axes, delay in reflex maturation and physical features, as well as a decrease in the morphometric parameters of somatosensory and motor cortex. Thus, these results suggest that the administration of a DNA alkylating agent, such as busulfan, during the gestational period can cause damage to the central nervous system in the pups throughout their postnatal development.

Drinking desalinated seawater for a long time induces anomalies in the development of new-born albino rats

The present study aimed to elucidate the abnormalities in the development of rat brains, livers, kidney and behaviours after drinking desalinated seawater prenatally. Three types of drinking water were employed as an experimental probe (bottled water, filtered desalinated seawater and tap desalinated seawater) to investigate neurobehavioral and morphological changes in the development of pup rats. Female rats from each group were administered water from their birth until gestation and lactation. The 1st and 2nd generation pups were divided into three groups: Group C, mothers and pups administered with bottled drinking water (the control group); Group F, mothers and pups administered with filtered drinking water; Group T, mothers and pups administered with unfiltered desalinated seawater (tap water). Morphological changes (CNS aberration) and neurobehavioral changes were studied. The aberrations recorded in the tissues (brain, liver, kidney and spinal cord) of rats from groups T and F may be due to oxidative stress in these tissues such as reduced glutathione, lipid peroxidation, peroxidase and super oxide dismutase. In conclusion, drinking desalinated seawater for a long time may cause teratogenic effects in the development of New-born rats.

Effects of pre- and postnatal protein deprivation on rat's hard palatine mucosae: a scanning electron microscopic study of the connective tissue papillae

The primary (connective tissue papillae) and secondary projections of the subepithelial connective tissue of the lamina propria were studied in the hard palate of normal (control group), and in protein-deficient pups (experimental group) obtained through maternal protein deprivation during pregnancy and lactation. At birth, the primary projections in the control group are more developed in width whereas in the experimental group they are thin with a crest-like shape. On day 7 of lactation, the primary projections are abundant, well developed and regularly arranged in the control group. They are few in number and are irregular in shape and disposition in the experimental group. The secondary projections are located posterior to the primary ones in the control group and are intercalated with them in the experimental group. On day 21 of lactation, the characteristic foliate aspect of the primary projections are noted in the control group. In the experimental group they remain thin with a crest-like aspect.

Postnatal development of glycosidases and gangliosides in the rat central nervous system

The developmental profiles of sialidase, beta-galactosidase, beta-hexosaminidase and beta-glucosidase were compared to those of the gangliosides in rat brain and spinal cord. The glycosidase activities (enzyme units/g wet tissue), except beta-galactosidases, were found to be higher in brain than spinal cord, in adult rats. Among the hydrolases, beta-hexosaminidase showed a higher level of activity in both brain and spinal cord. In brain, the hydrolases, except beta-glucosidase, followed a similar developmental pattern, showing an increase from birth to 21 days, and then decreased to adult values by day 90. In the spinal cord, sialidase, beta-galactosidase, pH 3.1, and beta-hexosaminidase activities increased from birth to 21 days, reaching peak values. These activities then declined to adult values by 90 days of age. However, beta-galactosidase, pH 4.5, and beta-glucosidase activities showed a peak at day 14. Brain total ganglioside concentration (microgram N-acetylneuraminic acid/g tissue) increased slowly between birth and 7 days of age, followed by a rapid phase of increase to attain a peak value by day 21. The concentration of total gangliosides in the spinal cord is less when compared to the brain. The proportions of individual gangliosides in the central nervous system also vaired during development. The rapid phase of increase in enzyme activities between 0-7 and 14-21 days and a decrease thereafter is consistent with the turnover rate of gangliosides, which in rat brain is reported to be highest between 10 and 20 days.

Neonatal undernutrition and short term administration of hydrocortisone and thyroxine: effects on rat brain hydrolases

Brain enzymes activities that are likely to be involved in the catabolism of gangliosides were determined in controls (20% casein diet), postnatally undernourished (6.5% casein diet) and undernourished rats treated with either thyroxine or hydrocortisone, at 21 days of age. Postnatal undernutrition imposed by maternal protein deficiency during lactation resulted in a decrease in body weight and brain wet weight of the pups at 21 days of age. Administration of thyroxine or hydrocortisone to the undernourished pups every day between 16 and 21 days caused a further decrease in the body weight of the pups. On the other hand, the wet weight of brain showed a slight gain following hydrocortisone treatment. Postnatal undernutrition during lactation elevated the activities of beta-glucosidase, beta-galactosidase, beta-hexosaminidase and sialidase in rat brain. Short-term administration of thyroxine or hydrocortisone to the undernourished pups, every day between 16 and 21 days postnatal age decreased the enzyme activities. However, reversal of the increased enzyme activities to the normal lower level was completed only in the case of undernourished pups treated with hydrocortisone.

Undernutrition during the preweaning period changes calcium ATPase and ADPase activities of synaptosomal fractions of weanling rats

The presence of activities that hydrolyse externally added ATP to adenosine in synaptosomal preparations from various sources is well demonstrated. The hydrolysis of ATP to AMP can be mediated either by the concerted action of enzymes or by an ATP-diphosphohydrolase (EC 3.6.1.5; apyrase). Undernutrition during the preweaning period can delay the development of several enzymes involved in the metabolism of neurotransmitters or neuronal function. In young rats, the presence of an apyrase in synaptosomal preparations from cerebral cortex was investigated. The results suggested that the hydrolysis of externally added ATP and ADP can be mediated by a single enzyme. The effects of preweaning undernutrition on the hydrolysis of ATP and ADP were also investigated. In weanling rats, previous undernutrition caused a decrease of about 20% in the hydrolysis of both substrates in synaptosomal fractions.

Development of the cholinergic system in control and intra-uterine growth retarded rat brain

The activity of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and muscarinic receptors was studied in control rats and in rats growth-retarded in utero because of reduction of the blood supply 5 days before birth. The different markers of the cholinergic system were estimated at P (postnatal day) 6, 9, 12, 15, 22 and 60 in cerebellum, hypothalamus, septum, striatum and CA1, CA3 and fascia dentata of the hippocampus. In control rats, there was a transient increase in ChAT activity in the septum during the second week of postnatal development. In the intrauterine growth retarded rats there was a marked delay in this developmental rise in CA1, CA3 at P6 and P9 and in the fascia dentata at P14 respectively. This delayed rise enzyme activity was associated with a significant reduction of muscarinic binding sites [( 3H]QNB) in the hippocampus. AChE staining showed a similar development in both groups. Therefore, the undernutrition produced by a reduction of the blood supply 5 days before birth is associated with a delayed maturation of cholinergic functions.

Functional development of the visual system in normal and protein-deprived rats. V. Specific cortical response and repetitive stimulation in adult rats

Recent studies on the specific visual system have indicated that early induced protein deprivation results in an impaired transmission from cell to cell in the cortex. To further investigate cortical mechanisms the response to repetitive light flashes and to electrical stimulation of the optic tract (OT) and the dorsal lateral geniculate nucleus (dLGN) were examined. The first potential of the surface visual evoked response (VER) and the monosynaptic response to OT and dLGN stimulation showed similar sensitivity to repetitive stimulation in C and PD rats. In PD rats later activity was significantly more sensitive to repetitive stimulation than in controls. By using paired stimuli with a short inter-stimulus interval, similar inhibitory mechanisms in PD and C rats were demonstrated. The results support the view that protein deprivation results in impaired cortical synaptic activation. The results are discussed in relation to previously described impairment at the cortical level in malnourished animals.

Are the effects of gestational stress on motor development and cerebellar cholinesterase activity mediated prenatally?

Prenatal random noise and light stress retards early motor development in the rat. To determine whether this delay is pre- or postnatally mediated and whether the developing cerebellum may play a role in the delay, rats were subjected to this form of stress and their offspring were fostered or cross-fostered onto control rats and vice versa. Their motor development was assessed by a series of behavioral tests between birth and day 10 of life. Prenatally stressed pups (Eo), whether reared by stressed (Em) or control mothers (Cm), showed a retardation in motor development. However, stressed pups matured earlier when reared by a control mother than by a stressed dam. Control pups (Co) raised by stressed mothers showed normal behavioral development. Cerebellar cholinesterase activity, which has been shown to undergo characteristic alterations with normal maturation, did not differ between stressed and control pups at birth. However, on day 10, cholinesterase activity was lower in EmCo than in CmCo pups, whereas that in CmEo and EmEo pups did not differ significantly from controls. It is concluded that three effects of random noise and light stress during pregnancy may be distinguished: (1) A prenatal effect as expressed by a delay in motor development, (2) a postnatal (rearing) effect on motor development and (3) a rearing effect expressed as a decrease in cerebellar ChE activity.

Undernutrition and the development of brain neurotransmitter systems

While there are homeostatic mechanisms to protect the brain against wide fluctuations in the availability of essential nutrients, food deprivation is known to influence brain neurochemistry. Given the growing problem of infant undernutrition and the fact that the developing nervous system appears to be especially vulnerable to this type of insult, numerous studies have been conducted to define the relationship between nutritional factors and cellular growth and maturation in the brain. The data suggest that the development of both neural and nonneural elements are significantly affected by undernutrition. This includes processes and substances important for neurotransmission such as transmitter synthesis, degradation and receptor sites. Because many neuropsychiatric conditions can be traced to dysfunctions in synaptic neurochemistry, it is possible that some of the central nervous system abnormalities which result from childhood undernutrition may be a consequence of a modification in synaptic biochemistry. The present report reviews data relating to this issue with the aim of assessing its relevance to developmental neurobiology.

Distribution and protein synthetic activities of neuronal free and membrane-bound ribosomes during postnatal development of rat cerebral cortex

The distribution and amino acid incorporative activities of free and membrane-bound ribosomes in neuronal perikarya of rat cerebral cortex at successive stages of postnatal development were investigated. The relative proportion of neuronal membrane-bound ribosomes increased significantly between 6 and 18 days of age, reaching 50% of the total ribosomal population around day 18. In contrast to the neuronal fraction, the membrane-bound ribosomes in unfractionated cerebral cortex decreased from 50% at birth to 35% in 18-day-old pups. When tested in a cell-free amino acid incorporation system the activities of both free and membrane-bound ribosomes increased up to day 10 post partum. However, whereas the activity of free ribosomes reached a constant level at this age, that of the membrane-bound fraction continued to rise until 18th day after birth. Crossover experiments employing homologous or heterologous cell sap fractions showed that the preparation from the 18-day-old animals was more efficient in supporting protein synthesis in vitro, if compared with similar preparation from the neonatal animals. This was attributed to an enhanced aminoacylation of transfer RNA in neuronal cell sap of older compared with younger rats. The observed developmental alterations in the distribution and activities of free and membrane-bound ribosomes are discussed in relation to changes that occur in morphology and function of brain during the early postnatal period.

Effect of undernutrition on DNA and RNA synthesis in subcellular fractions from different regions of the developing rat brain

The effect of undernutrition on the incorporation of [methyl-3H] thymidine into DNA and of 5-[3H] uridine into RNA of cerebral hemispheres, cerebellum, and brain stem was studied in vivo and in vitro in rats. The labeling of DNA from nuclei and mitochondria and of RNA from nuclei, mitochondria, microsomes, and soluble fractions, was also measured in vitro. The results demonstrate that nucleic acid synthesis is impaired and delayed during undernutrition. Specific effects were observed for the different brain regions and subcellular fractions: at 10 days nuclear and mitochondrial DNA and RNA synthesis was impaired, whereas at 30 days only the mitochondrial nucleic acid synthesis was affected. The delay of DNA and RNA labeling, caused by undernutrition, was most evident in the cerebellum, probably due to its intense cell proliferation during postnatal development. The specific sensitivity of mitochondria as compared to other subcellular fractions, may by due to the intense biogenesis and/or turnover of nucleic acids in brain mitochondria not only during postnatal development, but also in the adult animal.

The effect of early postnatal undernutrition on the growth and development of the rat brain

1. Rat pups were undernourished during the period of the brain growth-spurt by feeding their mothers a low-protein diet from the third day post partum. 2. The pups were killed on days 5, 6, 9, 12, 16, 20 and 24 post partum, and their brains were analysed for protein, DNA, glycosides and glycoproteins. The activities of four enzymes involved in neurotransmission, and in the synthesis of glycolipids and myelin were also measured. Results of the analyses were compared with those obtained for pups that were suckled by well-nourished dams. 3. The brains of the undernourished pups contained substantially less protein and DNA; gangliosides and glycoproteins were also reduced. 4. All four enzymes showed lower peak activities in the nutritionally deprived animals, and the attainment of peak activity was retarded by several days. 5. These results suggest that undernutrition imposed during the brain growth-spurt leads to a deficit in the glial cell population and thus in the capacity to form myelin, and reduced development of cellular processes.

Effects of neonatal undernutrition on the lipid composition of gray matter and white matter in rat brain

Separate analyses were made of gray matter and white matter from rat brain after neonatal undernutrition. Newborn rats were redistributed into control, large-litter, and protein-deficient groups. Large litters had 16 rather than 8 pups with a dam. Protein-deficient dams were fed a 4%, instead of a 24%, casein diet. For controls at 21 days of age, the 2',3'-cyclic nucleotide-3'-phosphohydrolase activity was more than fivefold greater in white matter than in gray matter. Severe undernutrition (protein-deficient) gave 2',3'-cyclic nucleotide-3'-phosphohydrolase activities that were 36% lower in gray matter and 56% lower in white matter. Lipid galactose concentrations were 17% less than control in both gray matter and white matter. In protein-deficient white matter, phospholipid concentrations were 15% lower than control. Ethanolamine plasmalogens and phosphatidyl serine were affected most. Moderate nutrition (large litter) had no effect on 2',3'-cyclic nucleotide-3'-phosphohydrolase activity. A 14% deficit of galactolipids was the only difference from controls in large-litter white matter. In large-litter gray matter, phospholipid concentrations were 16% higher than controls. Nearly all glycerophospholipids, including plasmalogens, were affected. With the exception of the myelination markers, 2'3',-cyclic nucleotide-3'-phosphohydrolase and lipid galactose, the development of lipids in gray matter is almost completely spared from the effects of undernutrition. The primary effect of undernutrition is on myelination, especially in white matter.

The influence of protein restriction, rehabilitation and changing nutritional status on synaptic development: a quantitative study in rat brain

Quantitative ultrastructural technique were employed to compare the development and maturation of cortical synapses in rats subjected to protein deprivation, control diet, nutritional rehabilitation and a normal-low crossover diet. Osmicated preparations of the molecular layer of occipital cortex were prepared at 15, 20, 28, 75 and 224 days postnatal in male rats. At 15 and 30 days the values for mitochondrial and synaptic densities, vesicle number and packing per terminal, synaptic length, terminal area and brain weight were lower in the protein-deprived than in the control animals. These initial deficits were progressively transformed to excesses, with the most marked crossover period occurring between 20 and 28 days. By 224 days only brain weight and presynaptic terminal area were lower in the protein-deprived material. A further parameter, synaptic curvature, showed a decrease in negativity in protein-deficient junctions between 15 days (64%) and 224 days (41%). Well-nourished tissue had fewer negatively-curved synapses during early development. These data suggest that the morphological development of the presynaptic terminals is not simply delayed, but is ultimately different in the protein-deprived animals. The nature of these changes may facilitate an adaptation to provide more efficient functioning in the adverse condition. Nutritionally rehabilitated tissue ultimately approaches the control, although significant differences occur in synaptic and mitochondrial densities and in brain weight. The normal--low crossover procedure intensities the differences noted in animals subjected to continuous deprivation.

Ontogenetic alterations of the cerebral cortex in rat caused by a diet containing a lipid fraction extracted from yeast (Candida lipolytica) grown on N-alkanes

Several ontogenetic aspects of the cerebral cortex were studied in rats whose mothers were fed on a diet, the lipid fraction of which was extracted from yeast (Candida lipolytica) grown on N-alkanes, during part of pregnancy and throughout lactation. Measures of the heights of some cortical regions and specific layers, the maturation of mean cell volumes and of the cell/gray coefficient, especially in layers I, IV and VI, show that the diet affects cerebral cortex ontogeny. These effects on brain ontogeny and on intrinsic and extrinsic neuron connections may explain the electrophysiological and behavioural alterations observed in previous studies.

Ontogeny of short- and long-term memory capacities for passive avoidance training in undernourished mice

To assess the effects of early postnatal undernutrition upon the developing abilities of infant and juvenile mice to acquire and retain a passive-avoidance response, we reared mice following birth in either "normally nourished" or "undernourished" conditions by maintaining litter sizes of 6 or 16, respectively. At ages ranging from 7 to 21 days, mice from each nutritional condition were trained to withhold stepping off from a small vibrating platform in order to avoid shock. Following training to a common criterion, separate groups of mice were retained to the same criterion either 1 or 24 hr later. From the comparisons with yoked control groups at each age and retention interval, we conclude that although undernutrition results in some age-related differences in the ability to withhold responding, these are quite small during acquisition within each age group. In contrast, the retention data suggest that undernutrition delayed the development of both short- and long-term memory abilities on this task. In general, these results are similar to earlier data involving discriminated shock-escape wherein undernutrition had little apparent effect upon acquisition at the early ages but rather marked effects upon developing memory system.

Impeded cerebellar development and reduced serum thyroxine levels associated with fetal alcohol intoxication

Pregnant albino rats were placed on a complete liquid diet (Ensure) containing either 9% ethanol or an isocaloric amount of sucrose between the third and twentieth day of gestation. The pups born to these rats were sacrificed either day 11 or day 14 postnatum and morphometrical, histological and biochemical analyses were done on their cerebellums and cerebrums. Pups that were exposed to ethanol in utero had significantly smaller body weights, cerebrums and cerebellums than pair-fed controls. The cerebellar mass was reduced by 10% and the cerebral weight by 3% in the pups exposed to alcohol when body weights were normalized to that of pair-fed controls. Cerebellar aspartyl aminotransferase (EC 2.6.1.1) activity was reduced at day 11 and 14 in ethanol treated pups compared with controls. Serum T4 levels were also reduced in the ethanol treated group. Histological analyses revealed that the external granule cell (EGC) layer of ethanol treated pups was significantly thicker at 11 and 14 days postnatum than that of pair-fed control pups. Cerebellar ornithine decarboxylase (ODC, EC 4.1.1.17) activity was higher at day 11 in the ethanol treated pups than in controls. The reduced mass, AAT activity, T4 serum levels and the increased thickness of the ECG layer indicate a delayed or impeded maturation of cerebellum in ethanol treated pups. These data are considered from the viewpoint that ethanol, other drugs such as methadone and prenatal stress (malnutrition) may cause delayed cerebellar maturation by reducing serum T4 levels in the early postnatal period (day 5-14).

Tissue culture analysis of neurogenesis: myelination and synapse formation are retarded by serum deprivation

Explants from newborn mouse cerebellum were cultured in nutrient media containing either adequate (30%) or low (15% or 7.5%) serum content. By light microscopic observation, delayed and inhibited myelination was detected in cultures fed with low serum media (experimental cultures). Specific activities of two enzymes related to myelin synthesis, 2',3'-cyclic nucleotide-3'-phosphohydrolase and 3-hydroxy-3-methylglutaryl coenzyme A reductase, were also reduced in experimental cultures. Morphometric analysis of electron micrographs showed that the size of presynaptic endings and total area occupied by synapses in experimental cultures were substantially reduced, while synaptic density per unit area increased. Reflecting the results of synaptic underdevelopment, the levels of two neurotransmitter enzymes, choline acetyltransferase and glutamic acid decarboxylase, were also decreased in experimental cultures.

Lysosomal properties during thyroxine-induced lateral motor column neurogenesis

This investigation illustrates that thyroid hormones and not prolactin regulate lysosomal activity during hormone-stimulated lateral motor column (LMC) development in Rana pipiens larvae. Administering a single dose of DL-thyroxine to normal or hypophysectomized larvae induces a 4-8 fold increase in lysosomal acid hydrolase activity within 5 or 6 days. During this interval, the physical properties of lysosomes are dramatically altered with the granules becoming extremely labile to treatments known to disrupt membranes. Nevertheless, thyroxine does not directly influence lysosomal stability; it apparently induces the synthesis and packaging of enzymes through a mechanism requiring de movo production of RNA and protein. The subcellular distribution and physical characteristics of the enzymes are then modified during neuronal death. Such information suggests that changes in lysosomal activity which accompany LMC neurogenesis are indicative of neuronal death, and that these events are controlled by thyroid hormones.

Impaired development of the rat perineurium by undernutrition. An enzyme histochemical study

Enzyme activity of adenosinetriphosphatase, NADH2-tetrazolium reductase and lactate dehydrogenase was studied in the rat perineurium 10, 20, 30, and 90 days post partum. The effect of under-nutrition was shown by a lack of enzyme activity in rats 30 days post partum in contrast to control animals, 30 days also corresponds to the time when, in normal rats, the perineurial diffusion barrier to exogenous macromolecules becomes established. In undernourished rats this diffusion barrier does not appear. At 90 days post partum raised enzyme activities indicate a high metabolic turnover in the perineurium even in animals with undernutrition.

Some effects of undernutrition on synaptic development -- a quantitative ultrastructural study

The development of synaptic junctions in rat occipital cortex has been studied at 7 and 20 days postnatal in control and undernourished animals. In addition, adult control cortex has been compared with cortex derived from animals undernourished until 35 days postnatal and then nutritionally rehabilitated. Emphasis has been placed on material stained with phosphotungstic acid (E-PTA technique) although osmicated material has been examined. The body weights of the undernourished animals were lower than those of their age-matched controls, the deficit at 20 days being 55%. The number of synaptic junctions per unit area of the molecular layer was lower in the undernourished animals at 7 and 20 days, the most prominent deficit being at 20 days. In an attempt to detect ultrastructural correlates of undernutrition, E-PTA stained synaptic junctions were divided into 5 types (A-E), based upon their presynaptic characteristics are reflecting varying degrees of maturity. During normal development the immature synaptic types, particularly type E, are predominant, giving way to the more mature types (A-C) as development proceeds. Undernutrition however, appears to disrupt this developmental sequence, with a higher than normal percentage of immature synaptic types present at the age studied. Nutritional rehabilitation rectifies the imbalance to a degree, the adult rehabilitated pattern resembling the 20-day control pattern. Preliminary examination of the 20-day osmicated material confirmed the deficit of synapses per area of tissue in the undernourished cortex. It also revealed decreases in the number of vesicles per terminal unit area and in the internal area of the synaptic vesicles in the undernourished tissue.

The effect of a low-fat maternal diet on neonatal rats

1. Rats were raised on a low-fat diet containing 6 g fat/kg. Females of the second generation were bred and only 11% of their pups survived to weaning age compared with a 66% survival for control pups. Pups were killed 8–12 h after birth and their tissues were analysed.

2. Pups in the low-fat group had smaller body, brain and liver weights than control pups; the lipid contents of body, brain and liver were also significantly less.

3. In the liver triglycerides from the control group the C20and C22polyenoic fatty acids constituted 33% of the total fatty acids. The liver triglyceride concentration in the low-fat group was lower and the concentration of the long-chain polyenoic fatty acids in this fraction was 20% of the control value. The milk fatty acids from the low-fat group contained only 33% as much of the C18to C22polyenoic fatty acids compared with the control group.

4. In the brain lipids from the low-fat group, changes in the fatty acid composition were less marked than in the liver lipids. In these experiments there were only small amounts of 20:3ω9 in the tissue lipids; the ratio to 20:4ω6 was less than 1.

5. These changes are discussed in relation to the influence of dietary lipids on tissue growth especially of lipid-rich tissues such as the brain.

The effect of anoxia on cerebral acid hydrolases in the five-day-old rat

1. Five-day-old anaesthetized rats subjected to slow, prolonged asphyxia (50-55 min) were either allowed to die or resuscitated when at the point of death. Activities of various cerebral acid hydrolases known to be associated with lysosomes were determined in these animals and in littermate controls. 2. Asphyxia to death resulted in a significant increase in the activities of acid phosphatase, cathepsin (pH5.0) and beta-glucuronidase in whole-brain homogenates. 3. The effect of asphyxia on beta-glucuronidase activity was not apparent when the assay was performed in the presence of Triton X-100 (0.1%, v/v). 4. In resuscitated animals whole-brain-homogenate beta-glucuronidase activity showed the greatest increase (31%) 15 min after recovery. After a 60 min recovery period differences between control and asphyxiated animals were no longer apparent. 5. In animals anoxiated to death activities of acid phosphatase and beta-N-acetylglucosaminidase in brain high-speed supernatants were significantly higher than in controls. Acid phosphatase activity was similarly increased in asphyxiated animals resuscitated for 5 or 60 min. 6. It is suggested that the response of the immature rat brain to asphyxia involves a disruption or increased fragility of lysosomal particles.