Ismael Juárez

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.

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.

Chronic administration of the neurotrophic agent cerebrolysin ameliorates the behavioral and morphological changes induced by neonatal ventral hippocampus lesion in a rat model of schizophrenia.

Neonatal ventral hippocampal lesion (nVHL) in rats has been widely used as a neurodevelopmental model to mimic schizophrenia‐like behaviors. Recently, we reported that nVHLs result in dendritic retraction and spine loss in prefrontal cortex (PFC) pyramidal neurons and medium spiny neurons of the nucleus accumbens (NAcc). Cerebrolysin (Cbl), a neurotrophic peptide mixture, has been reported to ameliorate the synaptic and dendritic pathology in models of aging and neurodevelopmental disorder such as Rett syndrome. This study sought to determine whether Cbl was capable of reducing behavioral and neuronal alterations in nVHL rats. The behavioral analysis included locomotor activity induced by novel environment and amphetamine, social interaction, and sensoriomotor gating. The morphological evaluation included dendritic analysis by using the Golgi‐Cox procedure and stereology to quantify the total cell number in PFC and NAcc. Behavioral data show a reduction in the hyperresponsiveness to novel environment‐ and amphetamine‐induced locomotion, with an increase in the total time spent in social interactions and in prepulse inhibition in Cbl‐treated nVHL rats. In addition, neuropathological analysis of the limbic regions also showed amelioration of dendritic retraction and spine loss in Cbl‐treated nVHL rats. Cbl treatment also ameliorated dendritic pathology and neuronal loss in the PFC and NAcc in nVHL rats. This study demonstrates that Cbl promotes behavioral improvements and recovery of dendritic neuronal damage in postpubertal nVHL rats and suggests that Cbl may have neurotrophic effects in this neurodevelopmental model of schizophrenia. These findings support the possibility that Cbl has beneficial effects in the management of schizophrenia symptoms.

Enhanced dendritic spine number of neurons of the prefrontal cortex, hippocampus and nucleus accumbens in old rats after chronic donepezil administration

In Alzheimers disease brains, morphological changes in the dendrites of pyramidal neurons of the prefrontal cortex (PFC) and hippocampus have been observed. These changes are particularly reflected in the decrement of both the dendritic tree and spine number. Donepezil is a potent and selective acetylcholinesterase inhibitor used in the treatment of Alzheimers disease. We have studied the effect of oral administration of this drug on the morphology of neuronal cells from the brain of aged rats. We examined dendrites of pyramidal neurons of the PFC, dorsal or ventral hippocampus (VH), and medium spiny neurons of the nucleus accumbens (NAcc). Donepezil (1 mg/kg, vo) was administrated every day for 60 days to rats aged 10 and 18 months. Dendritic morphology was studied by the Golgi–Cox stain procedure followed by Sholl analysis at 12 and 20 months ages, respectively. In all Donepezil‐treated rats, a significant increment of the dendritic spines number in pyramidal neurons of the PFC and dorsal hippocampus was observed. However, pyramidal neurons of the VH and medium spiny cells of the NAcc only showed an increase in the number of their spines in 12‐month‐old rats. Our results suggest that Donepezil prevents the alterations of the neuronal dendrite morphology caused by aging. Synapse 64:786–793, 2010.

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.

Combined Administration of Cerebrolysin and Donepezil Induces Plastic Changes in Prefrontal Cortex in Aged Mice

Cerebrolysin (Cbl) shows neurotrophic and neuroprotective properties while donepezil (Dnp) is a potent acetylcholinesterase (AChE) inhibitor, both drugs are prescribed for Alzheimers disease (AD) treatment. Previous studies have shown that the Dnp and Cbl administered separately, modify dendritic morphology of neurons in the prefrontal cortex and hippocampus in senile rodents. Since the deficit of neurotrophic factor activity is implicated in the degeneration of cholinergic neurons of basal forebrain, a combination therapy of Dnp and Cbl has been tested recently in Alzheimers patients. However, the plastic changes that may underlie this combined treatment have not yet been explored. We present here the effect of the combined administration of Cbl and Dnp on dendritic morphology in brain regions related to learning and memory in aged mice. The Golgi‐Cox staining protocol and Sholl analysis were used for studying dendritic changes. Cbl and Dnp were administrated daily for 2 months to 9‐months‐old mice. Locomotor activity was assessed, as well as the dendritic morphology of neurons in several limbic regions was analyzed. Results showed that Cbl and Dnp induced an increase in locomotor activity without synergistic effect. The Cbl or Dnp treatment modified the dendritic morphology of neurons from prefrontal cortex (PFC), dorsal hippocampus (DH), dentate gyrus (DG), and the shell of nucleus accumbens (NAcc). These changes show an increase in the total dendritic length and spine density, resulting in an improvement of dendritic arborization. Prominently, a synergistic effect of Cbl and Dnp was observed on branching order and total dendritic length of pyramidal neurons from PFC. These results suggest that Dnp and Cbl may induce plastic changes in a manner independent of each other, but could enhance their effect in target cells from PFC. Synapse 66:938–949, 2012.

The chronic administration of cerebrolysin induces plastic changes in the prefrontal cortex and dentate gyrus in aged mice

Cerebrolysin (Cbl) is a mixture of neuropeptides with effects similar to the endogenous neurotrophic factors and is considered one of the best drugs used in the treatment of dementias such as Alzheimers disease (AD). In brains with AD, morphological changes in the dendrites of pyramidal neurons of the prefrontal cortex (PFC) and hippocampus have been reported. These changes are reflected particularly in the decrement of both the dendritic tree and spine density. Here we evaluated the effect of this drug on the dendrites of pyramidal neurons of the PFC and CA1 dorsal hippocampus and granule cells from the dentate gyrus (DG) and medium spiny neurons of the nucleus accumbens (NAcc) of aged mice. Cbl (5 ml kg−1, i.p.) was administered daily for 60 days to 6‐month‐old mice. Dendritic morphology was studied by the Golgi‐Cox stain procedure followed by Sholl analysis at 8 months ages. In all Cbl‐treated mice a significant increase in dendritic spine density and dendritic length in pyramidal neurons of the PFC and granule cells of the DG was observed. Interestingly, the enhancement in dendritic length was close to the soma in pyramidal neurons of the PFC whereas in granule neurons of the DG the increase in dendritic length was further from the soma. Our results suggest that Cbl induces plastic modifications of dendritic morphology in the PFC and DG. These changes may explain the therapeutic effect seen in AD patients treated with Cbl. Synapse 2011.

Dendritic morphology of neurons in medial prefrontal cortex, hippocampus, and nucleus accumbens in adult SH rats

We have studied, in spontaneously hypertensive (SH) rats at different ages (2, 4, and 8 months old), the dendritic morphological changes of the pyramidal neurons of the medial prefrontal cortex (mPFC) and hippocampus and medium spiny neurons of the nucleus accumbens (NAcc) induced by the chronic effect of high‐blood pressure. As control animals, we used Wistar‐Kioto (WK) rats. Blood pressure was measured every 2 months to confirm the increase in arterial blood pressure. 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. SH animals at 4 and 8 months of age showed decreased spine density in pyramidal neurons from the mPFC and in medium spiny cells from the NAcc. At 8 months of age as well the pyramidal neurons from the hippocampus exhibited a reduction in the number of dendritic spines. An increase in locomotion in a novel environment at all ages in the SH rats was observed. Our results indicate that high‐blood pressure alters the neuronal dendrite morphology of the mPFC, hippocampus, and NAcc. The increased locomotion behavior supports the idea that dopaminergic transmission is altered in the SH rats. This could enhance our understanding of the consequences of chronic high‐blood pressure on brain structure, which may implicate cognitive impairment in hypertensive patients. Synapse, 2010.

Cerebrolysin reverses hippocampal neural atrophy in a mice model of diabetes mellitus type 1.

The animal model of streptozotocin‐induced diabetes mellitus type 1 (DM1) is used to study neuronal and behavioral changes produced by an increase in blood‐glucose levels. Our previous report showed that chronic streptozotocin administration induced atrophy of dendritic morphology of pyramidal neurons of the CA1 dorsal hippocampus. In addition, we showed that Cerebrolysin (Cbl), a neurotrophic peptide mixture, reduces the dendritic atrophy in animal models of aging. This study aimed to determine whether Cbl was capable of reducing behavioral and neuronal alterations, after 6 weeks of hyperglycemia in mice (streptozotocin‐induced DM1). The levels of glucose in the blood were evaluated before and after streptozotocin administration and only animals with more than 240 mg/dL of blood‐levels of glucose were used. After streptozotocin treatment, the mice received 6 weeks of Cbl, locomotor activity was measured and dendritic morphological changes were evaluated using Golgi‐Cox stain procedure, and analyzed by the Sholl method. In mice treated with streptozotocin there was a clear reduction in the dendritic length of pyramidal neurons of the CA1 and granular cells of the dental gyrus of the dorsal hippocampus. Interestingly, Cbl reversed the morphological changes induced by streptozotocin. Our results extend the list of abnormal morphological changes detected in this model of DM, and support the possibility that Cbl may have beneficial effects in the management of brain alterations induced by DM. Synapse 69:326–335, 2015.

Olfactory bulbectomy induces neuronal rearrangement in the entorhinal cortex in the rat

In humans, depression has been associated with disturbances in olfactory circuitry. Symptoms of depression can be mimicked in animals after olfactory bulbectomy (OBX). Animal models of depression-like behavior produce similar neuronal rearrangements in various brain regions as seen in patients affected by depression. We have recently observed that OBX produces neuronal hypotrophy in the piriform cortex (PirC) and CA1 hippocampus as well as decreased adult cell proliferation in the dentate gyrus (DG) of hippocampus. Thus we further evaluated the effects of OBX in neuronal arborization and spine density in brain regions involved in the control of circadian circle, emotion and memory processing such as the prefrontal cortex (PFC), nucleus accumbens (NAcc), infralimbic cortex (ILC), orbitolateral cortex (OLC) and entorhinal cortex (EC). Our present results show that along with severe behavioral deficits observed in these animals, OBX considerably decreased dendritic branching and the total dendritic length in the EC, a major interface of the hippocampus and neocortical regions. The remaining cortices and NAcc were not affected by OBX. Thus, we propose that the lack of input from the olfactory bulbs resulted in serial neuronal rearrangements in the PirC, EC, and hippocampus leading, at least partially, to behavioral deficits in emotion and memory processes.