Adriana B. Silva-Gómez

Decreased dendritic spine density on prefrontal cortical and hippocampal pyramidal neurons in postweaning social isolation rats

The effects of postweaning social isolation (pwSI) on the morphology of the pyramidal neurons from the medial part of the prefrontal cortex (mPFC) and hippocampus were investigated in rats. The animals were weaned on day 21 postnatal (P21) and isolated 8 weeks. After the isolation period, locomotor activity was evaluated through 60 min in the locomotor activity chambers and the animals were sacrificed by overdoses of sodium pentobarbital and perfused intracardially with 0.9% saline solution. The brains were removed, processed by the Golgi-Cox stain and analyzed by the Sholl method. The locomotor activity in the novel environment from the isolated rats was increased with respect to the controls. The dendritic morphology clearly showed that the pwSI animals presented a decrease in dendritic length of pyramidal cells from the CA1 of the hippocampus without changes in the pyramidal neurons of the mPFC. However, the density of dendritic spines was decreased in the pyramidal cells from mPFC and Hippocampus. In addition, the Sholl analyses showed that pwSI produced a decrease in the number of sholl intersections compared with the control group only in the hippocampus region. The present results suggest that pwSI may in part affect the dendritic morphology in the limbic structures such as mPFC and hippocampus that are implicated in schizophrenia.

Alterations in dendritic morphology of prefrontal cortical and nucleus accumbens neurons in post-pubertal rats after neonatal excitotoxic lesions of the ventral hippocampus

Neonatal ventral hippocampal (nVH) lesions in rats result in adult onset of a number of behavioral and cognitive abnormalities analogous to those seen in schizophrenia, including hyperresponsiveness to stress and psychostimulants and deficits in working memory, sensorimotor gating and social interaction. Molecular and neurochemical alterations in the prefrontal cortex (PFC) and nucleus accumbens (NAcc) of nVH-lesioned animals suggest developmental reorganization of these structures following neonatal lesions. To determine whether nVH lesions lead to neuronal morphological changes, we investigated the effect of nVH lesion on dendritic structure and spine density of pyramidal neurons of the PFC and medium spiny neurons of the NAcc. Bilateral ibotenic acid-induced lesion of the VH was made in Sprague-Dawley pups at postnatal day 7 (P7); and at P70, neuronal morphology was quantified by modified Golgi-Cox staining. The results show that length of basilar dendrites and branching and the density of dendritic spines on layer 3 pyramidal neurons were significantly decreased in rats with nVH lesions. Medium spiny neurons from the NAcc showed a decrease in the density of dendritic spines without significant changes in dendritic length or arborization. The data, comparable to those observed in the PFC of schizophrenic patients, suggest that developmental loss of excitatory projections from the VH may lead to altered neuronal plasticity in the PFC and the NAcc that may contribute to the behavioral changes in these animals.

Comparative behavioral changes between male and female postpubertal rats following neonatal excitotoxic lesions of the ventral hippocampus

Neonatal ventral hippocampal (nVH) lesioned male rat has been used as a model to test the hypothesis that early neurodevelopmental abnormalities lead to behavioral changes putatively linked to schizophrenia. There are significant gender differences in schizophrenia with male and female individuals differing in the age of onset, course and outcome of the disorder. In order to assess whether the behavioral effects of nVH lesions extend to or are different in female rats, we investigated spontaneous locomotion, grooming, social interactions and spatial memory in male and female rats post-pubertally at postnatal day (P) 56 following bilateral ibotenic acid of the ventral hippocampus at P7. The spontaneous locomotor activity in a novel environment of both male and female nVH lesioned rats was significantly enhanced compared to their respective sham-operated controls. In tests of social interactions, the number of encounters was significantly decreased in female lesioned rats, whereas the male nVH lesioned rats showed a significantly reduced duration of active social interactions. Furthermore, Morris water maze test showed a deficit of spatial learning/memory in only male lesioned rats with significant decrease in the latency to find hidden platform. These results suggest that while nVH lesions affect post-pubertal behavior in both sexes of rats, the males appear to be affected to a greater extent than the females underscoring the influence of sex differences in the development of behaviors in the nVH lesioned animals.

Neonatal ventral hippocampus lesion alters the dopamine content in the limbic regions in postpubertal rats.

The neonatal ventral Hippocampus (nVH) lesion in rats has been used as a model to test the hypothesis that early neurodevelopmental abnormalities lead to behavioral changes putatively linked to schizophrenia. The schizophrenic patients tend to social isolation. In addition, considerable evidence from behavioral and neurochemistry studies strongly implicate the dopamine (DA) system and the medial part of the prefrontal cortex (mPFC) in the pathophysiology of the social isolation syndrome. In order to assess effects of the postweaning social isolation (pwSI) on the DA system of the nVH lesions, we investigated the DA content and its metabolite, DOPAC in different limbic subregions in rats postpubertally at postnatal day (P) 78 following nVH lesions at P7 with and without pwSI for 8 weeks. The DA and DOPAC were measured by HPLC with electrochemical detection. The nVH lesion induces increase in the DA content in the hippocampus with no effect in the mPFC, nucleus accumbens and caudate‐putamen, while the pwSI induces major increase in the DA content in limbic subregions such as the mPFC, nucleus accumbens and hipocampus with opposite effect in the caudate‐putamen. These results suggest that while pwSI has an effect in the postpubertal content of DA in both sham and nVH lesions in rats, the nVH‐lesioned rats appear to be affected to a greater extent than the sham animals underscoring the influence of pwSI differences in the development of behaviors in the nVH‐lesioned animals.

Anoxia at birth induced hyperresponsiveness to amphetamine and stress in postpubertal rats

Several evidences suggest that transient global anoxia after Caeraean section birth in rats produces behavioral changes related to dopaminergic transmission. However, all of the reports tested the behavioral changes in adult rats. Here we investigated the role of perinatal anoxia on behavioral paradigms related to dopamine (DA) such as novel environment, saline injection, D-amphetamine, apomorphine and stress-induced changes in locomotor activity at prepubertal and postpubertal ages. All these dimensions of behavior can be affected in schizophrenia. Caesarean section birth with or without an additional period of anoxia was performed in Sprague-Dawley rats and their behaviors were studied at P35 and P56, respectively. In addition, a third group of animals born vaginally served as control. No significant differences in saline injection and D-amphetamine-induced locomotion were observed when the three groups of rats at P35 were compared. However, stress-induced locomotor activity was significantly increased in the Caesarean birth plus anoxia at P35, while after puberty (at P56), saline injection, D-amphetamine and stress-induced locomotion were significantly enhanced in the Caesarean birth plus anoxia compared to its control groups. The data suggests that anoxia at birth mediates differently the functional development and maturation of DA behaviors in adult rats.

Dexamethasone induces different morphological changes in the dorsal and ventral hippocampus of rats.

Dexamethasone (DEX), a synthetic glucocorticoid widely used in neurological illnesses because of its antiinflammatory properties, has many serious side effects, including severe psychiatric symptoms such as psychoses. The hippocampus is divided in the dorsal hippocampus (DH) and ventral hippocampus (VH) with each region having a subfield of CA1 and CA3 pyramidal layers. Great interest has recently emerged showing that the DH and VH are functionally different. In our work we determined whether, and what, changes occurred, after five days of DEX (0.2mg/kg) treatment, on the dendritic morphology of the CA1 and CA3 pyramidal neurons of the DH and VH of adult Sprague-Dawley rats. The dendritic morphology and characteristics were measured by using the Golgi-Cox procedure followed by a Sholl analysis. DEX decreased the number of dendritic spines of both apical and basolateral dendrites. Interestingly, this decrease was more pronounced in the VH. Only the VH neurons were affected by DEX with a decrease in their total dendritic length (TDL). An interesting point is that the VH neurons are longer that the DH neurons among the groups injected with saline only as the control. The length per branch order was only altered in the apical dendritic tree of the CA1 neurons. These data taken together show that the VH is more susceptible to DEX and its neurons are larger than the DH neurons. These results support previous observations related to differences between the DH and VH and suggest differences in the expression of the glucocorticoid receptors in connectivity and the space to elongate their dendritic arbor.

NEONATAL OLFACTORY BULBECTOMY ENHANCES LOCOMOTOR ACTIVITY, EXPLORATORY BEHAVIOR AND BINDING OF NMDA RECEPTORS IN PRE-PUBERTAL RATS

In this study, we investigated the effect of neonatal olfactory bulbectomy (nOBX) on behavioral paradigms related to olfaction such as exploratory behavior, locomotor activity in a novel environment and social interaction. We also studied the effect of nOBX on the activity of the N-methyl-d-aspartate (NMDA) subtype of glutamate receptors during development. The behavioral effects of nOBX (postnatal day 7, PD7) were investigated in pre- (PD30) and post-pubertal (PD60) Wistar rats. NMDA receptor activity was measured with [(125)I]MK-801 in the brain regions associated with the olfactory circuitry. A significant increase in the novelty-induced locomotion was seen in the pre-pubertal nOBX rats. Although the locomotor effect was less marked than in pre-pubertal rats, the nOBX rats tested post-pubertally failed to habituate to the novel situation as quickly as the sham- and normal- controls. Pre-pubertally, the head-dipping behavior was enhanced in nOBX rats compared with sham-operated and normal controls, while normal exploratory behavior was observed between groups in adulthood. In contrast, social interaction was increased in post-pubertal animals that underwent nOBX. Both pre- and post-pubertal nOBX rats recovered olfaction. Interestingly, pre-pubertal rats showed a significant increase in the [(125)I]MK-801 binding in the piriform cortex, dorsal hippocampus, inner and outer layers of the frontal cortex and outer layer of the cingulate cortex. At post-pubertal age, no significant differences in [(125)I]MK-801 binding were observed between groups at any of the brain regions analyzed. These results suggest that nOBX produces pre-pubertal behavioral disturbances and NMDA receptor changes that are transitory with recovery of olfaction early in adulthood.

Neonatal prefrontal cortex lesion using CO2 laser technique

Prefrontal cortex (PFC) is a large area of the brain and its neonatal lesion with ibotenic or kainic acid is used to study the early abnormalities in neurodevelopment that lead to behavioral changes linked to schizophrenia. However, these exitotoxic drugs produce a large and asymmetric damage in the PFC. We produced the bilateral lesions of the dorsal part of the PFC of neonatal Sprague-Dawley rats (postnatal day 7, P7) at the anteroposterior +2.5 mm and mediolateral +/-0.4 coordinates by the new laser technique that employ the confined radiation of the CO(2) laser in the pulsed mode. The laser was used because its coherent radiation can be focused in a very small spot and as small as of several tens of micrometers in diameters. The CO(2) laser radiation is strongly absorbed by water that is present in any soft tissue. Thereafter, the configuration of the heated zone and, consequently, that of the lesion does not depend on the morphological non-homogeneity of particular structures. We obtained the symmetric, conical in shape and small-size bilateral lesions of the PFC. The size of the lesion depended on the beam spot-size and could be as small as several dozens of micrometers in diameter. Our data suggests that the laser technique will be used for the anatomical-functional studies of the PFC in the brain.

Juvenile Taiep rats have shorter dendritic trees in the dorsal field of the hippocampus without spatial learning disabilities

Myelin mutant taiep rats show a progressive demyelination in the central nervous system due to an abnormal accumulation of microtubules in the cytoplasm and the processes on their oligodendrocytes. Demyelination is associated with electrophysiological alterations and the mutant had a progressive astrocytosis. The illness is associated with change in cytokine levels and in the expression of different nitric oxide synthase and concomitantly lipoperoxidation in several areas of the brain. However, until now there has been no detailed anatomical analysis of neurons in this mutant. The aim of this study was to analyze the dendritic morphology in the hippocampus using Golgi‐Cox staining and spatial memory through Morris water maze test in young adult (3 months old) taiep rats and compare them with normal Sprague‐Dawley. Our results showed that taiep rats have altered dendritic tree morphology in pyramidal neurons in the CA1 field of the hippocampus, but not in the CA3 region. These morphological changes did not produce a concomitant deficit in spatial memory acquisition or recall at this early stage of the disease. Our results suggest that impairment of dendritic morphology in the CA1 field of the hippocampus is a landmark of the pathology of this progressive multiple sclerosis model.