Delayed neuronal migration of protein kinase Cgamma immunoreactive cells in hippocampal CA1 area after 48 h of moderate hypoxemia in the near term ovine fetus

Effects of gestational iron deficiency on fear conditioning in juvenile and adult rats

The hippocampus is especially sensitive to the effects of gestational and neonatal iron deficiency, even after iron repletion. This study compared the effects of iron deficiency, maintained from gestational day 2 to postnatal day (P)7, on "delay" and "trace" fear conditioning. Only the latter paradigm is critically dependent on the dorsal hippocampus. In different groups of rats, fear conditioning commenced either prior to puberty (P28 or P35) or after puberty (P56). Fear conditioning was measured using fear-potentiated startle. Both delay and trace fear conditioning were diminished by iron deficiency at P28 and P35. Hippocampal expression of the plasticity-related protein PKC-gamma was increased through trace fear conditioning, but reduced at P35 in the iron-deficient group. Trace fear conditioning was enhanced by prior iron deficiency in the P56 group. This unanticipated finding in iron-repleted adults is consistent with the effects of developmental iron deficiency on inhibitory avoidance learning, but contrasts with the persistent deleterious long-term effects of a more severe iron-deficiency protocol, suggesting that degree and duration of iron deficiency affects the possibility of recovery from its deleterious effects.

Neuronal migration is transiently delayed by prenatal exposure to intermittent hypoxia

BACKGROUND

Neonatal neurodevelopment is influenced by a variety of external factors, although the mechanisms responsible are poorly understood. Prenatal hypoxia, from physiological or chemical sources, can have no discernible effect, or can result in a broad spectrum of abnormalities.

METHODS

To mimic some of the maternal effects of smoking, we developed a model that investigates the effects of intermittent hypoxia (IH), with or without concurrent nicotine in timed pregnant Sprague-Dawley rats.

RESULTS

We found no significant differences between litter sizes or birthweight of pups from any treatment group, but animals exposed to IH (with or without nicotine) showed long term diminished body weights. Animals subjected to IH consistently showed a transient delay in neuronal migration early in the postpartum period, which was amplified by concurrent nicotine administration. We observed increased c-Abl protein levels in animals from the IH treatment groups. Multiple proteins involved in the intricate control of neuronal migration were also altered in response to this treatment, primarily the downstream targets of c-Abl: Cdk5, p25, and the cytoskeletal elements neurofilament H and F-actin and catalase. Catalase activity and protein levels, already elevated in response to IH, were further amplified by simultaneous nicotine exposure.

CONCLUSIONS

This new model provides a novel system for investigating the effects of low grade IH in the developing brain and suggests that concurrent nicotine further aggravates many of the deleterious effects of IH.

Prenatal hypoxia impairs circadian synchronisation and response of the biological clock to light in adult rats

The aim of this study was to test the hypothesis that prenatal hypoxia in rats might lead to consistent changes in the entrainment of the circadian clock by light. Pregnant female rats were placed in a chamber provided with hypoxic gas (10 % O2--90 % N2) at gestational day 5 and returned to normoxia before delivery. Once adult, rats born to hypoxic mothers had significant alterations in their circadian rhythm of locomotor activity (recorded in freely accessible running wheels). Under a regular 12/12 light/dark (LD) cycle, they showed a phase advance of their rhythm of activity (mean phase advance of 87 min) and were less active than control rats. After an abrupt 6 h phase delay in the LD cycle, rats from the prenatal hypoxic group (PNH) took significantly more time to resynchronise to the new LD cycle compared to controls (+53 %; 6.0 +/- 1.5 vs. 9.2 +/- 0.5 days respectively). Under constant darkness, PNH and control rats had a similar period of activity (24.27 +/- 0.20 vs. 24.40 +/- 0.13) but the response of PNH rats to a light pulse in the early subjective night was less marked than that of control rats (101 +/- 9 vs. 158 +/- 13 min). When submitted to acute restraint stress, PNH rats had a prolonged secretion of corticosterone compared to controls. These results indicate that prenatal hypoxia is a factor that has long lasting consequences for the functional output of the biological clock and the hormonal response to stress.

Hypoxia in fetal lambs: a study with (1)H-MNR spectroscopy of cerebrospinal fluid

In fetal lambs, severe hypoxia (SH) will lead to brain damage. Mild hypoxia (MH) is thought to be relatively safe for the fetal brain because compensating mechanisms are activated. We questioned whether MH, leading to mild acidosis, induces changes in cerebral metabolism. Metabolites in cerebrospinal fluid (CSF) samples, as analyzed by proton magnetic resonance spectroscopy, were studied in two groups of seven anesthetized near-term fetal lambs. In group I, SH leading to acidosis with an arterial pH <7.1 was achieved. In group II, MH with an intended pH of 7.23--7.27 was reached [start of MH (SMH)], and maintained during 2 h [end of MH (EMH)]. During SH, choline levels in CSF, a possible indicator of cell membrane damage, were increased. Both during SH and at EMH, CSF levels of lactic acid, alanine, phenylalanine, tyrosine, lysine, branched chain amino acids, and hypoxanthine were increased compared with control values and with SMH, respectively. At EMH, the hypoxanthine CSF-to-blood ratio was increased as compared with SMH. These results indicate that prolonged MH leads to energy degradation in the fetal lamb brain and may not be as safe as assumed.

Renal and cerebral responses to hypoxemia in the ovine fetus

Mild to moderate hypoxemia without major changes in pH and pCO(2) does not reduce fetal renal blood flow and fetal urine production rate. Other factors such as acidemia, hypercapnia or changes in lung liquid production or fetal swallowing are candidates for the reduced amniotic fluid in the growth retarded fetus. Mild hypoxemia influences the fetal brain development in that the migration of PKC immunoreactive cells is delayed after a period of 48 h of hypoxemia. This could be due to the fact that under these circumstances the expected compensatory increase in fetal cerebral blood flow was only significant 1 h after the onset of hypoxemia. Further research on the final position of the hippocampal neurons in term lambs, subjected to fetal mild hypoxemia, can give more information on the effects of hypoxemia on the fetal brain.