Effects of a period of asphyxia during birth on spatial learning in the rat

Long-term reciprocal changes in dopamine levels in prefrontal cortex versus nucleus accumbens in rats born by Caesarean section compared to vaginal birth

Epidemiological evidence indicates a higher incidence of pregnancy and birth complications among individuals who later develop schizophrenia, a disorder linked to alterations in mesolimbic dopamine (DA) function. Two birth complications usually included in these epidemiological studies, and still frequently encountered in the general population, are birth by Caesarean section (C-section) and fetal asphyxia. To test the hypothesis that birth complications can produce long-lasting changes in DA systems, the present study examined the effects of Caesarean birth, with or without an added period of anoxia, on steady state monoamine levels and metabolism in various brain regions in a rat model. Pups born vaginally served as controls. At 2 months of age, in animals born by rapid C-section, steady state levels of DA were decreased by 53% in the prefrontal cortex and increased by 40% in both the nucleus accumbens and striatum, in comparison to the vaginally born group. DA turnover increased in the prefrontal cortex, decreased in the nucleus accumbens, and showed no significant change in the striatum, in the C-section group. Thus, birth by a Caesarean procedure produces long-term reciprocal changes in DA levels and metabolism in the nucleus accumbens and prefrontal cortex. This is consistent with the known inhibitory effect of increased prefrontal cortex DA activity on DA release in the nucleus accumbens. By contrast to birth by rapid C-section alone, young adult animals, that had been born by C-section with 15 min of added anoxia, showed no change in steady state DA levels in the prefrontal cortex, nucleus accumbens, or striatum and a significant decrease in DA turnover only in the nucleus accumbens, in comparison to the vaginally born group. Levels of norepinephrine, serotonin, and its metabolite, 5-hydroxyindole acetic acid, were unchanged in all groups, indicating relatively specific effects on DA systems. Although appearing robust at birth on gross observation, more subtle measurements revealed that rat pups born by C-section show altered respiratory rates and activity levels and increased levels of whole brain lactate, suggestive of low grade brain hypoxia, during the first 24 h of life, in comparison to vaginally born controls. Pups born by C-section with 15 min of added acute anoxia were pale, hypotonic, and inactive at birth and showed reduced respiration and high brain lactate levels. However, these alterations resolved by 1-5 h after birth and, with few exceptions, animals in the anoxic group remained normal with respect to these parameters during the remainder of the first 24 h of life. Immediately after birth, levels of plasma epinephrine, a hormone known to play a role in neonatal adaptation to extrauterine life and protection against hypoxia, were decreased in pups born by C-section but increased in pups born by C-section with 15 min added anoxia, in comparison to levels measured in vaginally born controls. These early developmental alterations could contribute to long-term alterations in dopaminergic parameters observed in rats born by C-section, with or without added anoxia. It is concluded that C-section birth is sufficient perturbation to produce long-lasting effects on DA levels and metabolism in the central nervous system of the rat. These findings highlight the sensitivity of DA pathways to variations in birth procedure and support the notion that birth complications might contribute to the pathophysiology of disorders involving central dopaminergic neurons, such as schizophrenia.

Influence of perinatal factors on the nucleus accumbens dopamine response to repeated stress during adulthood: an electrochemical study in the rat

Evidence from animal studies suggests that a period of anoxia to the fetus, a consequence common to many birth complications, results in long-term alterations in ventral mesencephalic dopamine function. Long-term functional changes in these dopamine neurons, in particular those that innervate the nucleus accumbens, also occur when animals are repeatedly stressed. In the present study, we examined the possibility that a period of anoxia during a Cesarean section birth can later alter the development of stress-induced sensitization of dopamine transmission in the nucleus accumbens. Dams were decapitated on the last day of gestation and the entire uterus was removed by Cesarean section. Pups were then delivered either immediately (Cesarean section group) or were immersed in a 37 degrees C saline bath for 3.5 or 13.5 min (Cesarean section+anoxia groups) before delivery of the pups. A fourth group of pups that were born vaginally served as controls (Vaginal group). Three to four months postnatally, animals from each group were implanted with monoamine-selective carbon-fiber electrodes into the nucleus accumbens. Voltammetry was used to monitor the dopamine response to each of five consecutive, once daily, 15-min exposures to tail-pinch stress. The results show that the first exposure to stress elicited dopamine signal increases of comparable amplitudes and durations in all animals. However, when compared to the initial stress response, the fourth and fifth exposures to tail-pinch elicited significantly longer-lasting dopamine responses in animals born by Cesarean section, either with or without added anoxia. In contrast, there was no significant day-to-day enhancement of the stress response in control, vaginally born animals. The findings reported here provide experimental support for the idea that birth complications may contribute to the pathophysiology of psychiatric disorders, in particular those that involve central dopamine dysfunction, such as schizophrenia. Specifically, our results suggest that subtle alterations in birth procedure may be sufficient to increase the sensitivity of mesolimbic dopamine neurons to the effects of repeated stress in the adult animal.

Motor and cognitive functional deficits following diffuse traumatic brain injury in the immature rat

To determine the motor and cognitive deficits following a diffuse severe traumatic brain injury (TBI) in immature Sprague Dawley rats (17 days), four groups of animals were injured at different severity levels using a new closed head weight drop model: (sham, severe injury [SI: 100 g/2 m], SH [SI + hypoxemia (30 min of an FiO2 of 8% posttrauma)], and ultra severe injury [US: 150 g/2 m]). Latency on beam balance, grip test performance, and maintenance of body position on an inclined board were measured daily after injury to assess vestibulomotor function. Cognitive function was assessed on days 11-22 using the Morris water maze (MWM). Balance beam latency and inclined plane body position were reduced in both SI and SH rats (n = 20) (p < 0.05 vs. sham) (maximally at 24 h), and lasted 3-4 day postinjury; however, SH did not differ from SI. In the US group (n = 10), motor deficits were profound at 24 h (p < 0.05 vs. all other groups) and persisted for 10 days. The groups did not differ on grip test. In cognitive performance, there were no differences between sham, SI, and SH. US, however, produced significant cognitive dysfunction (vs. sham, SI, and SH), specifically, greater latencies to find the hidden platform through 22 days. Swim speeds were not significantly different between any of the injury groups and shams. These data indicate that (1) beam balance, inclined plane and MWM techniques are useful for assessing motor and cognitive function after TBI in immature rats; (2) SI produces motor but not cognitive deficits, which was not augmented by transient hypoxia; and (3) US created a marked but reversible motor deficit up to 10 days, and a sustained cognitive dysfunction for up to 22 days after TBI.

Animal models for the study of perinatal hypoxic-ischemic encephalopathy: a critical analysis

We critically evaluated various design features from 292 animal studies related to perinatal hypoxic-ischemic encephalopathy (HIE). Rodents were the most frequently used animals in HIE research (26%), followed by piglets (23%) and sheep (22%). Asphyxia with or without ischemia was the most predominant method of producing experimental brain damage, but there were significant variations in specific details, particularly regarding the method and duration of brain insult. In 71% (207/292) of studies the CNS outcomes were tested within 24 h of experimental insult and in 29% (85/292) they were tested 24 h or more after the insult. Acute CNS metabolic end-points were assessed in 82-100% of all studies. In 90% of studies the chronological age of the animal was equivalent to that of human term newborn infant. However, in only 23% (67/292) were clinical neurological, developmental or behavioral outcomes evaluated, and in only 26% (76/292) was neuropathology assessed. While no single animal model was found to be ideal for all HIE research, some models were distinctly superior to others, depending upon the specific research question. The fetal sheep, newborn lamb and piglet models are well suited for the study of acute and subacute metabolic and physiologic endpoints, whereas the rodent and primate models could be used for long-term neurological and behavioral outcome experiments as well. We also feel that standardizing the study design features, including an HI insult method that produces consistent and predictable brain damage is urgently needed. Studies in neuro-ethology should explore how well brains of various animals compare with that of the newborn human infant. There is also a need for developing animal models that mimic clinical entities in which long-term neuro-developmental and behavioral outcomes can be assessed.

Early developmental profiles of plasma corticosterone are altered by birth condition in the rat: a comparison of vaginal birth, cesarean section, and cesarean section with added anoxia

Circulating glucocorticoids play a role during the immediate postnatal period in adapting the neonate to extrauterine life and are also thought to influence tissue development and function in the later postnatal period. In the present study we have used a rat model to test whether birth by cesarean section (C-section), either alone or with an added period of acute anoxia, affects the development profile of basal corticosterone secretion during the first 5 wk of life. Plasma levels of total corticosterone and of corticosteroid-binding globulin were measured at various times after birth in rats born vaginally, by C-section, or by C-section with 15 min of added anoxia. These measures allowed for calculation of levels of free, biologically active, corticosterone. Under all conditions, total corticosterone appeared to accurately reflect levels of free corticosterone. Plasma corticosterone levels measured immediately (< 5 min) after birth were similar in male rat pups born vaginally, by C-section, or by C-section with added anoxia, whereas female pups born by C-section showed a significant increase in free corticosterone at birth, in comparison with vaginally born females. Both male and female animals born by C-section showed a reduction in plasma corticosterone at 1 h (male: 31% of control, p < 0.01; female: 45% of control, p < 0.05) and at 7 d (male: 61% of control, p < 0.01; female: 55% of control, p < 0.05) after birth, in comparison with vaginally born controls. In animals born by C-section with added anoxia, significant reductions in plasma corticosterone were observed for males at 1 h (58% of control; p < 0.05) and for females at 7 d (62% of control; p < 0.05) after birth. At 14 d of age, corticosterone levels were higher in male rats born by C-section either with (227% of control; p < 0.05) or without (239% of control; p < 0.05) added anoxia, in comparison with vaginally born controls. Thus C-section birth produces an early rise in plasma corticosterone on d 14 away from the low values associated with the adrenal quiescent period in the first 1-2 wk in the rat. By 35 d of age, there were no differences in plasma corticosterone attributable to C-section birth and/or acute birth anoxia, in either male or female rats. It is concluded that, in a rat model, birth by C-section has significant effects on the profile of plasma corticosterone during the early weeks of development, a period though to be critical for effects of corticosteroids on developing tissues. Because the rat at birth is developmentally less mature than is the term human neonate, these findings may have implications for development of the premature human neonate.

Effects of perinatal asphyxia on the mesostriatal/mesolimbic dopamine system of neonatal and 4-week-old male rats

The present study was undertaken in order to study the effects of perinatal asphyxia on tyrosine hydroxylase (TH) activity, dopamine levels and turnover, and dopamine metabolites (3,4-dihydroxyphenylacetic acid, DOPAC, homovanillic acid, HVA, and 3-methoxytyramine, 3-MT, analyzed by high-performance liquid chromatography, HPLC) measured in the basal ganglia of the 20- to 40-min-old newborn and 4-week-old male rat. Asphyxia was induced in pups by placing the fetuses, still in their uterus horns removed by hysterectomy from pregnant rats at full term, in a 37 degrees C water bath for 15-16 min or 19-20 min. Following asphyxia, the uterus horns were opened, and the pups were removed and stimulated to breathe. A 100% and 50-80% pup survival was obtained following 15-16 min and 19-20 min of asphyxia, respectively. Acute changes were studied in brains from newborn pups 20-40 min after delivery, and long-term changes were studied in brains from 4-week-old rats. No changes in TH-activity could be observed in the substantia nigra/ventral tegmental area (SN/VTA), the striatum, or the accumbens nucleus/olfactory tubercle (ACC/TUB), in the newborn or the 4-week-old rat. In the newborn rat, 19-20 min of asphyxia increased (as compared to controls) dopamine levels in the SN/VTA to 136 +/- 14% and in the ACC/TUB to 160 +/- 10%, indicating an increased synthesis and/or release of dopamine. DO-PAC levels were increased in the SN/VTA to 150 +/- 14% and in the ACC/TUB to 151 +/- 10%, and HVA levels were increased to 152 +/- 16% in the striatum and to 117 +/- 4% in the ACC/TUB. Following 15-16 min of asphyxia, dopamine levels were increased to 130 +/- 12% in the ACC/TUB, and DOPAC levels were increased to 135 +/- 6% and 130 +/- 12% in the SN/VTA and the ACC/TUB, respectively. This suggests that the increased dopamine levels may preferably reflect an increased release of dopamine following perinatal asphyxia. In the 4-week-old rat, dopamine levels were decreased in the SN/VTA to 71 +/- 4%, in the striatum to 52 +/- 8%, and in the ACC/TUB to 53 +/- 7%, following 19-20 min of perinatal asphyxia as compared to controls. No changes were observed in DOPAC, HVA, or 3-MT levels, indicating that the reduced dopamine levels reflect a reduced dopamine synthesis following perinatal asphyxia. A decrease in dopamine utilization was observed in the striatum to 15 +/- 8% and in the ACC/TUB to 9 +/- 13% following 19-20 min of perinatal asphyxia as compared to controls. This indicates that perinatal asphyxia produced long-lasting reductions in activity in the mesostriatal/mesolimbic dopamine systems in the 4-week-old rat.

The effects of perinatal hypoxia on the behavioral, neurochemical, and neurohistological toxicity of the metabolic inhibitor 3-nitropropionic acid

3-nitropropionic acid (3-NPA) neurotoxicity and long-term effects of perinatal hypoxia were evaluated in 18 adult rats. Hypoxia-insulted (I) and noninsulted (NI) rats were delivered by cesarean section. Hypoxic insult was effected by submerging dissected uterine horns in warmed saline for 15 min. NI rats were delivered from the adjacent nonsubmerged horns. At postnatal day 90, I and NI rats were trained to perform tasks thought to measure behaviors dependent upon aspects of time estimation (TE), motivation, and learning. At 12 months of age, rats were injected i.p. with escalating doses of 3-NPA (5 mg/kg/day to a maximum of 30 mg/kg/day) immediately after each test session and sacrificed at the end of treatment. Additional male rats were used as untreated controls. Although 3-NPA produced a dose-dependent impairment of performance in each task, the effects were qualitatively similar for each group. A significant difference between I and NI rats was, however, observed in the TE task where NI rats completed less of the task at high doses of 3-NPA compared to I rats. Compared to untreated controls, dopamine concentrations were decreased in caudate nucleus of both I and NI rats after 3-NPA. Specific areas most frequently damaged included cerebral cortex, hippocampal subfield CA1, thalamus, caudate nucleus, and the cerebellum. Lesions usually were less extensive in the I rather than NI members of a littermate pair, suggesting a possible protective effect of perinatal hypoxia against subsequent 3-NPA neurotoxicity.