Divergent Pattern of Development in Rats and Humans.

Rattus norvegicus is the second most used laboratory species and the most widely used model in neuroscience. Nonetheless, there is still no agreement regarding the temporal relationship of development between humans and rats. We addressed this question by examining the time required to reach a set of homologous developmental milestones in both species. With this purpose, a database was generated with data collected through a bibliographic survey. This database was in turn compared with other databases about the same topic present in the literature. Finally, the databases were combined, covering for the first time the entire development of the rat including the prenatal, perinatal, and postnatal periods. This combined database includes 362 dates of 181 developmental events for each species. The developmental relationship between humans and rats was better fit by a logarithmic function than by a linear function. As development progresses, an increase in the dispersion of the data is observed. Developmental relationships should not be interpreted as a univocal equivalence. In this work is proposed an alternative interpretation where the age of one species is translated into a range of ages in the other.

Transition to extrauterine life and the modeling of perinatal asphyxia in rats.

Generation of murine models for the study of birth-related pathologies has proven to be a complex and controversial problem. Differences in the relative timing of developmental events of both species have led some researchers to suggest that the rat is born comparatively less developed than the human. The solution proposed to this problem would consist in the delay of the experiments of perinatal asphyxia (PA), usually up to 7-10 days, allowing developmental levels to "equalize" with the human at birth. This solution generates a new set of problems. The developmental milestones in both species follow a divergent temporal pattern. Increasing the age of the rat not only can improve resemblance with humans but also will make the model miss a crucial set of milestones related to birth. During this process, there are specific mechanisms to protect the fetus from neuronal damage, especially those caused by asphyxia. These factors are not present in models where the asphyxia is delayed. In these models, there will be more false positives and more damage that would not be present in humans exposed to PA. This article is categorized under: Cancer > Stem Cells and Development Congenital Diseases > Environmental Factors Neurological Diseases > Environmental Factors.

Deep hypothermia prevents striatal alterations produced by perinatal asphyxia: Implications for the prevention of dyskinesia and psychosis.

GABAergic medium spiny neurons are the main neuronal population in the striatum. Calbindin is preferentially expressed in medium spiny neurons involved in the indirect pathway. The aim of the present work is to analyze the effect of perinatal asphyxia on different subpopulations of GABAergic neurons in the striatum and to assess the outcome of deep therapeutic hypothermia. The uterus of pregnant rats was removed by cesarean section and the fetuses were exposed to hypoxia by immersion in water (19 min) at 37°C (perinatal asphyxia). The hypothermic group was exposed to 10°C during 30 min after perinatal asphyxia. The rats were euthanized at the age of one month (adolescent/adult rats), their brains were dissected out and coronal sections were immunolabeled for calbindin, calretinin, NeuN, and reelin. Reelin+ cells showed no staining in the striatum besides subventricular zone. The perinatal asphyxia (PA) group showed a significant decrease in calbindin neurons and a paradoxical increase in neurons estimated by NeuN staining. Moreover, calretinin+ cells, a specific subpopulation of GABAergic neurons, showed an increase caused by PA. Deep hypothermia reversed most of these alterations probably by protecting calbindin neurons. Similarly, there was a reduction of the diameter of the anterior commissure produced by the asphyxia that was prevented by hypothermic treatment.

Deep hypothermia reverses behavioral and histological alterations in a rat model of perinatal asphyxia.

The consequences of perinatal asphyxia (PA) include alterations which may manifest as schizophrenia. Characteristic features of this disease include a decrease in specific subpopulations of GABAergic cells and deterioration of social interaction. The purpose of this study is to assess if a deep and short-hypothermic treatment can ameliorate this damage in a model of PA. Rats offsprings were exposed to 19 min of asphyxia by immersing the uterus horns in water at 37 °C followed by 30 min in air at 10 °C that resulted in 15 °C body temperature. At postnatal day 36-38, the rats were tested in the open field and social interaction paradigms and processed for immunostaining of calbindin and reelin. A brief exposure to deep hypothermia reversed the deterioration produced by PA in play soliciting. PA decreased the density of calbindin neurons in layer II of the Anterior Insular Cortex, while deep hypothermia reversed this effect. Paradoxically, in AIC, there was a significant increase in the number of reelin-secreting neurons in layers II and III generated by PA and this increase was reversed by hypothermia. This suggests a compensatory mechanism, where reelin neurons trend to compensate for the loss of calbindin neurons, at least within Anterior Insular Cortex. Finally, the deep hypothermic shock might represent a valuable therapeutic alternative to treat PA.

Perinatal Asphyxia Reduces the Number of Reelin Neurons in the Prelimbic Cortex and Deteriorates Social Interaction in Rats.

Obstetrical complications of perinatal asphyxia (PA) can often induce lesions that, in the long-term, manifest as schizophrenia. A deterioration of the medial prefrontal cortex (mPFC) and a reduction in the number of GABAergic neurons are commonly observed in the pathophysiology of schizophrenia. In this study, we investigated the link between PA, reelin and calbindin diminution and psychiatric diseases that involve social interaction deficits. This was achieved by observing the effect of 19 min of asphyxia on both subpopulations of GABAergic neurons. PA was produced by water immersion of fetus-containing uterus horns removed by cesarean section from ready-to-deliver rats. PA generated a significant and specific decrease in the number of reelin-secreting neurons in mPFC layer VI [F(2, 6) = 8.716, p = 0.016; PA vs. vaginal controls (VC), p = 0.03, and PA vs. cesarean controls (CC), p = 0.022]. This reduction reached approximately 60% on average. Changes in the percentage of reelin neurons including all the cortex layers did not achieve a significant outcome but a trend: CC % 10.61 ± 1.34; PA % 8.64 ± 1.71 [F(2, 6) = 1.299, p = 0.33]. In the case of calbindin, there was a significant decrease in cell density in the PA group [2-way repeated-measures ANOVA, F(1, 4) = 13.03, p = 0.0226]. The multiple-comparisons test showed significant differences in the superficial aspect of layer II (Sidak test for multiple comparisons CC vs. PA at 200 µm: p = 0.003). A small, but significant difference could be seen when the distance from the pia mater to the start of layer VI was analyzed (CC mean ± SEM = 768.9 ± 8.382; PA mean ± SEM = 669.3 ± 17.75; p = 0.036). Rats exposed to PA showed deterioration in social interactions, which manifested as a decrease in play soliciting. In this model, which involved severe/moderate asphyxia, we did not find significant changes in locomotive activity or anxiety indicators in the open field task. The loss of reelin neurons could be conducive to the shrinkage of the prelimbic cortex through the reduction in neuropil and the deterioration of the function of this structure.

Simultaneous projections from prefrontal cortex to dopaminergic and serotonergic nuclei.

Derangements of the prefrontal cortex (PFC) and of brainstem monoaminergic systems occur in depression and schizophrenia. Anatomical and functional evidence supports a PFC control of the brainstem monoaminergic systems. Similarly, the PFC contains a high density of monoamine receptors for which antipsychotic drugs exhibit high affinity. This raises the possibility that pathological or drug-induced changes in PFC may subsequently alter monoaminergic activity. Recent data indicate that a substantial proportion of PFC pyramidal neurons projecting to the ventral tegmental area (VTA) or the dorsal raphe nucleus (DR) express the 5-HT2A receptor mRNA, which suggests that atypical antipsychotic drugs affect serotonergic and dopaminergic function by targeting PFC 5-HT2A receptors. Using electrophysiological and tract-tracing techniques we examined whether PFC pyramidal neurons projecting to DR are segregated from those projecting to the VTA. Sequential electrical stimulation of these nuclei in anaesthetized rats evoked antidromic potentials from both areas in the same pyramidal neurons of the medial PFC (60%, n=30). A similar percentage of dual DR+VTA projection neurons (50%) was obtained using the reciprocal collision test (n=85). Similarly, tracer application (Fluoro-Gold in VTA and cholera toxin B in DR, or vice versa) retrogradely labelled pyramidal neurons in PFC projecting to VTA (81±18), to DR (52±9) and to both nuclei (31±4, n=5 rats). Overall, these results indicate that the PFC may simultaneously coordinate the activity of dopaminergic and serotonergic systems within a short temporal domain, supporting a concerted modulation of the ascending serotonergic and dopaminergic activity during antipsychotic drug treatment.

Pyramidal neurons in rat prefrontal cortex projecting to ventral tegmental area and dorsal raphe nucleus express 5-HT2A receptors.

The prefrontal cortex (PFC) is involved in higher brain functions altered in schizophrenia. Classical antipsychotics modulate cortico-limbic circuits mainly through subcortical D2 receptor blockade, whereas second generation (atypical) antipsychotics preferentially target cortical 5-HT receptors. Anatomical and functional evidence supports a PFC-based control of the brainstem monoaminergic nuclei. Using a combination of retrograde tracing experiments and in situ hybridization we report that a substantial proportion of PFC pyramidal neurons projecting to the dorsal raphe (DR) and/or ventral tegmental area (VTA) express 5-HT(2A) receptors. Cholera-toxin B application into the DR and the VTA retrogradely labeled projection neurons in the medial PFC (mPFC) and in orbitofrontal cortex (OFC). In situ hybridization of 5-HT(2A) receptor mRNA in the same tissue sections labeled a large neuronal population in mPFC and OFC. The percentage of DR-projecting neurons expressing 5-HT(2A) receptor mRNA was approximately 60% in mPFC and approximately 75% in OFC (n = 3). Equivalent values for VTA-projecting neurons were approximately 55% in both mPFC and ventral OFC. Thus, 5-HT(2A) receptor activation/blockade in PFC may have downstream effects on dopaminergic and serotonergic systems via direct descending pathways. Atypical antipsychotics may distally modulate monoaminergic cells through PFC 5-HT(2A) receptor blockade, presumably decreasing the activity of neurons receiving direct cortical inputs.