Gonzalo Flores

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.

Prenatal Stress Alters Spine Density and Dendritic Length of Nucleus Accumbens and Hippocampus Neurons in Rat Offspring

Prenatal stress alters neuronal morphology of mesocorticolimbic structures such as frontal cortex and hippocampus in the adult offspring. We investigated here the effects of prenatal stress on the spine density and the dendrite morphology of hippocampal pyramidal neurons and medium spiny cells from nucleus accumbens in prepubertal and adult male offsprings. Sprague‐Dawley pregnant dams were stressed by restraining movement daily for 2 hours from gestational day 11 until delivery. Control mothers remained free in their home cage without water and food during the stressful event. Male offsprings from immobilized and control rats were left to grow until postnatal day (PD) 35 for the prepubertal group, and until PD 65 for the adult group. Spontaneous locomotor activity was assessed and then brains were removed to study the dendritic morphology by the Golgi‐Cox stain method followed by Sholl analysis. Prenatally stressed animals demonstrated increased locomotion and alterations in spine density in the hippocampus and nucleus accumbens at both ages. However, prepubertal males showed an increase in spine density in the CA1 hippocampus with a decrease in CA3 hippocampus, whereas the adult group showed a decrease in the spine density in both of the regions studied. These results suggest that prenatal stress carried out during the middle of pregnancy affect the spine density and basal dendrites of pyramidal neurons of hippocampus, as well as the dendritic morphology of nucleus accumbens which may reflect important changes in the mesocorticolimbic dopaminergic transmission and behaviors associated with the development of psychiatric diseases such as schizophrenia. Synapse 63:794–804, 2009.

Enhanced nucleus accumbens dopamine and plasma corticosterone stress responses in adult rats with neonatal excitotoxic lesions to the medial prefrontal cortex

The medial prefrontal cortex modulates the nucleus accumbens dopamine response to stress and has been implicated in feedback regulation of hypothalamic-pituitary-adrenal axis activation by stress. Here we report on the effects of bilateral neonatal (postnatal day 7) ibotenate-induced lesions to the medial prefrontal cortex on nucleus accumbens dopamine and neuroendocrine function in adult rats. Voltammetry was used to monitor the dopamine response to each of five, once-daily exposures to tail-pinch stress whereas alterations in neuroendocrine function were determined from the plasma corticosterone response to a single 20-min episode of restraint stress. Potential lesion-induced deficits in sensory-motor gating were assessed by measuring prepulse inhibition of the acoustic startle response before and after repeated stress. Our data show that each daily stress episode elicited larger and longer-lasting dopamine increases in prefrontal cortex-lesioned animals than in sham-lesioned controls. Furthermore, greater stress-induced elevations in plasma corticosterone were seen in lesioned animals than in their sham-lesioned counterparts. However, while repeated stress potentiated startle responses in animals of both groups, there was no effect of lesion on the amplitude or on prepulse inhibition of the startle response.Together, these findings indicate that neonatal prefrontal cortex damage can lead to changes in mesolimbic dopamine and neuroendocrine function during adulthood. They also add to a growing body of experimental and clinical evidence implicating abnormal prefrontal cortex neuronal development in the pathophysiology of schizophrenia and other disorders linked to central dopamine dysfunction.

Alteration in dendritic morphology of cortical neurons in rats with diabetes mellitus induced by streptozotocin.

The animal model of streptozotocin-induced diabetes mellitus is used to study the changes produced by an increase in glucemia. The morphology of the pyramidal neurons of the prefrontal cortex, occipital cortex, and hippocampus was investigated in rats. The level of glucose in the blood was evaluated at 2 months, and the animals that exhibited more than 200 mg/dL were used. After 2 months of increasing blood-glucose level, the animals were sacrificed by an overdose of sodium pentobarbital and perfused intracardially with a 0.9% saline solution. The brains were removed, processed by the Golgi-Cox stain method, and analyzed by the Sholl method. Clearly, the rats with diabetes mellitus induced by streptozotocin showed a decrease in the dendritic length of pyramidal cells from all the analyzed regions (20% to 45%). Furthermore, the density of dendritic spines was decreased in all the pyramidal cells from the diabetic animals (36% to 58%). However, the pyramidal neurons of the CA1 hippocampus region were the most affected (58%). In addition, the Sholl analyses showed that the diabetic rats exhibited a decrease in the number of Sholl intersections when compared with the control group. The present results suggest that diabetes mellitus may in part affect the dendritic morphology in the limbic structures, such as prefrontal cortex, occipital cortex, and hippocampus, which are implicated in cognitive disorders.

Maternal separation disrupts dendritic morphology of neurons in prefrontal cortex, hippocampus, and nucleus accumbens in male rat offspring

Neonatal maternal separation (MS) in rats has widely been used as a neurodevelopmental model to mimic mood-related disorders. MS produces a wide array of behavioral deficits that persist throughout adulthood. In this study we investigate the effect of MS and substitute maternal handling (human handling) on the dendritic morphology of neurons in the prefrontal cortex (PFC), the CA1 ventral hippocampus, and the nucleus accumbens (NAcc), brain regions in male rats that have been associated with affective disorders at pre-pubertal (postnatal day 35 (PND35)) and post-pubertal (PND60) ages. The morphological characteristics of dendrites were studied by using the Golgi-Cox staining method. MS induced decreases in total dendritic length and dendritic spine density in the neurons of the PFC, the CA1 ventral hippocampus, and the NAcc at a post-pubertal age. Conversely, human handling produced an increase in dendritic spine density in the pyramidal neurons of the PFC and the hippocampus at a pre-pubertal age, and a decrease in the dendritic length of the NAcc neurons at a post-pubertal age. These results suggest that the maternal care condition affects the dendritic morphology of neurons in the PFC, the CA1 ventral hippocampus, and the NAcc at different ages. These anatomical modifications may be relevant to altered behaviors observed in maternally separated animals.

Morphological reorganization after repeated corticosterone administration in the hippocampus, nucleus accumbens and amygdala in the rat.

Elevated levels of corticosteroids and stress play key roles in the pathophysiology of affective disorders. Corticosterone (CORT)-treated rats have emerged as a pharmacological model of depression-like behaviors. Previous studies have shown that CORT administration induces neuronal atrophy in the CA3 subfield of the hippocampus and laminae II/III of the prefrontal cortex. However, little attention has been given to other limbic structures such as the amygdala and the nucleus accumbens (NAcc). We investigated here whether 3 weeks of CORT administration in rats causes dendritic remodeling and spine density reorganization in the basolateral amygdala and pyramidal neurons of the CA1 subfield of the hippocampus as well as in spiny medium neurons of NAcc. Quantitative morphological analysis revealed retracted neuronal arborizations and modified configuration of length depending on branch order in medium spiny neurons of the NAcc of CORT-treated animals. Moreover, distal dendritic sections of the NAcc showed massive reductions in the number of spines caused by the CORT treatment. This treatment also induced a reduction in total dendritic length specific to fourth and sixth branch orders of pyramidal CA1 hippocampal neurons. These neurons also showed decreased branching and diminished number of spines. Finally, pyramidal neurons of the basolateral amygdala were apparently not significantly affected by the CORT treatment. Taken together, these data show for the first time neuronal morphological alterations in the NAcc in the CORT model of depression-like behaviors. Our results also add further information about the morphological reorganization occurring in CORT-sensitive regions of the limbic system.

Neonatal ventral hippocampal lesions attenuate the nucleus accumbens dopamine response to stress: an electrochemical study in the adult rat.

Neonatal damage to the ventral hippocampus (VH) can lead, during adulthood, to behaviours that are believed to reflect enhanced mesocorticolimbic dopamine (DA) transmission. In the present study, the effects of neonatal excitotoxic lesions to the VH on spontaneous locomotor activity and stress-elicited increases in extracellular nucleus accumbens (NAcc) DA levels were examined in adult rats. Male pups received, on postnatal day 7, bilateral injections of either an ibotenic acid solution (lesioned) or vehicle (sham-lesioned) into the VH. At 3-4 months of age, animals were assessed during five daily sessions for changes in spontaneous locomotor activity associated with habituation to a novel environment. Voltammetry was used in separate groups of sham- and VH-lesioned animals to monitor the NAcc DA response to each of five once-daily exposures to tail-pinch stress. The results indicate that while VH-lesioned animals seem to habituate to novelty, they remain hyperactive relative to sham-lesioned controls. In contrast, however, stress consistently elicited in VH-lesioned animals smaller and shorter-lasting increases in NAcc DA than in sham-lesioned controls. These data suggest that neonatal excitotoxic damage to VH leads to changes in DA function that persist into adulthood. The blunted response to stress seen in VH-lesioned animals indicates that one consequence of such damage is a functional hyporeactivity in meso-NAcc DA neurons. The fact that these animals are spontaneously more active suggests compensatory changes in DA function that are efferent to DA terminals in NAcc.

Postweaning social isolation enhances morphological changes in the neonatal ventral hippocampal lesion rat model of psychosis

Neonatal ventral hippocampal (nVH) lesions in rats have been widely used as a neurodevelopmental model that mimics schizophrenia-like behaviors. Recently, we reported that nVH-lesions result in significant decreases in both length of dendrites and dendritic density of spines of pyramidal neurons of the prefrontal cortex (PFC) and in the density of dendritic spines of medium spiny neurons of the nucleus accumbens (NAcc). Moreover, postweaning social isolation induces major decreases in dendritic spiny density of PFC neurons. We investigated here the comparative dendritic morphology of PFC pyramidal neurons and NAcc medium spiny neurons in nVH rats, following social isolation after weaning (8 weeks). Morphological characteristics of dendrites were measured using the Golgi-Cox procedure followed by a Sholl analysis. Social isolation (SI) by itself induced decreases in dendritic length and dendritic spine density of the NAcc. In socially isolated nVH-lesion rats decrease in dendritic length in PFC and NAcc neurons were exacerbated whereas an increase in spine density of medium spiny neurons was observed in the NAcc. These results indicate that nVH-lesions alter dendritic morphology of NAcc and PFC neurons. These anatomical modifications in both structures may be relevant to behaviors observed in schizophrenia.

Ontogeny of altered dendritic morphology in the rat prefrontal cortex, hippocampus, and nucleus accumbens following Cesarean delivery and birth anoxia

We used a delayed Cesarean birth model and the Golgi–Cox staining method to investigate the effects of perinatal anoxia on prefrontal cortex (PFC) and hippocampal (CA1) pyramidal neurons as well as nucleus accumbens (NAcc) medium spiny neurons. Dendritic morphology in these regions was studied on postnatal days (P) 2, 7, 14, 21, 35, and 70 in male Sprague–Dawley rats born either vaginally (VAG) or by Cesarean section either with (C + anoxia) or without (C‐only) anoxia. The most striking birth group differences seen were at the level of dendritic spine densities on P35. During this postnatal period the dendritic spine density of PFC neurons was significantly lower in C + anoxia and C‐only animals than in VAG controls; however, by P70 PFC spine densities in all birth groups were comparable. In contrast, hippocampal spine densities on P35 were comparably greater in C + anoxia animals than in VAG controls, whereas in C‐only animals spine densities were lower than controls; here again, by P70 all groups had comparable hippocampal spine densities. In NAcc greater spine densities were seen on medium spiny neurons of C + anoxia animals on P35. These findings provide evidence that perinatal insult in the form of Cesarean birth with or without anoxia alters the dendritic development of PFC and hippocampal pyramidal neurons and to some extent also of NAcc medium spiny neurons. They also suggest that perinatal anoxia can alter the neuronal development of key structures thought to be affected in such late‐onset dopamine‐related disorders as schizophrenia and Attention Deficit Hyperactivity Disorder (ADHD). J. Comp. Neurol. 507:1734–1747, 2008.

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.