Hyper-response to Novelty Increases c-Fos Expression in the Hippocampus and Prefrontal Cortex in a Rat Model of Schizophrenia.

Schizophrenia is a debilitating disorder that may have a neurodevelopmental origin. For this reason, animal models based on neonatal insults or manipulations have been extensively used to demonstrate schizophrenia-related behaviors. Among those, the neonatal ventral hippocampus lesion (nVHL) is largely used as a model of schizophrenia-related behavior as it mimics behavioral and neurochemical abnormalities often seen in schizophrenic patients including hyperlocomotion in a novel environment. To investigate the neuroanatomical basis of coding novelty in the nVHL rat, we assessed the behavioral locomotor activity paradigm in a novel environment and measured expression of c-Fos, a marker of neural activation, in brain regions involved in the process of coding novelty or locomotion. Upon reaching adulthood, nVHL rats showed hyperlocomotion in the novel environment paradigm. Moreover, in nVHL rats the expression of c-Fos was greater in the prefrontal cortex (PFC) and CA1 region of the dorsal hippocampus compared to sham rats. Whereas similar expression of c-Fos was observed in the basolateral amygdala, nucleus accumbens and dentate gyrus region of  hippocampus of nVHL and sham rats. These results suggest that the nVHL disrupts the neural activity in the PFC and CA1 region of hippocampus in the process of coding novelty in the rat.

Correction to: Hyper-response to Novelty Increases c-Fos Expression in the Hippocampus and Prefrontal Cortex in a Rat Model of Schizophrenia.

The original version of this article unfortunately contained a mistake. The spelling of the author Tommaso Ianniti was incorrect and has been corrected as Tommaso Iannitti. The original article has been corrected.

Progesterone treatment in rats after severe global cerebral ischemia promotes hippocampal dentate gyrus neurogenesis and functional recovery.

OBJECTIVE: Rats treated with progesterone (P4) after ischemia show an adequate functional performance despite a significant loss of hippocampal pyramidal neurons, suggesting that P4 could favour a permissive microenvironment for cerebral plasticity mechanisms. The possibility of P4 treatment promoting the survival of newly generated hippocampal neurons, in relation to the performance of ischemic rats in a spatial learning task, was assessed in this study. METHODS: Adult male rats were subjected to a severe global cerebral ischemia episode (30 min) and treated with P4 or its vehicle at 15 min, 2, 6, 24, 48 and 72 h of reperfusion. From day 4 to 8 post-ischemia 5-bromo-2-deoxyuridine (BrdU) was administered to label proliferating cells. Twenty-one days post-ischemia, the rats were exposed to the Morris water maze to assess behavioral parameters of spatial learning and memory. Subsequently, the brain was perfusion-fixed and immunofluorescence procedures were performed to quantify the number of new mature neurons (BrdU+/NeuN+) in the dentate gyrus (DG) of the hippocampus. RESULTS: Rats subjected to severe global cerebral ischemia and treated with P4 had a significantly better performance in spatial learning-memory tests, than those treated with vehicle, and a significantly higher number of new mature neurons (BrdU+/NeuN+) in the DG. CONCLUSION: These findings show that post-ischemia P4 treatment, following an episode of severe global cerebral ischemia, promotes the survival of newly generated hippocampal neurons in the DG, which may be one of the mechanisms of cerebral plasticity induced by the hormone, that underlie a successful functional performance in learning and memory tests.

Post-ischemic administration of progesterone reduces caspase-3 activation and DNA fragmentation in the hippocampus following global cerebral ischemia.

Delayed death of hippocampal CA1 pyramidal neurons following global cerebral ischemia/reperfusion may be mediated, in part, by caspase-3 activation resulting in DNA fragmentation. Progesterone (P4) is known to exert neuroprotective effects in several models of brain injury. This study was designed to assess the effect of P4 on caspase-3 levels and activation, and DNA fragmentation in the hippocampus following global cerebral ischemia/reperfusion. Adult male Sprague-Dawley rats were subjected to global ischemia by the four-vessel occlusion model. P4 (8 mg/kg), or its vehicle were administered i.v. at 15 min, 2, 6, 24, 48 and 70 h of reperfusion. Remaining pyramidal neurons were assesed by the Nissl staining technique, caspase-3 levels and activation by immunohistochemistry and an in situ activity assay, and DNA fragmentation by the TUNEL method. Post-ischemic progesterone treatment significantly reduced the ischemia/reperfusion-induced increase in caspase-3 levels and activation at 72 h, and DNA fragmentation and CA1 neuronal loss at 7 days. Present results suggest the reduction of caspase-3 levels/activation, and DNA fragmentation, as a part of the neuroprotective effects of progesterone against global cerebral ischemia/reperfusion injury.

Neuroprotective effects of progesterone and allopregnanolone on long-term cognitive outcome after global cerebral ischemia.

PURPOSE: To assess the longterm neuroprotective effects of progesterone (P4) and allopregnanolone (ALLO) on functional and morphological parameters of the integrity of the hippocampus, after global cerebral ischemia. METHODS: Adult male Sprague-Dawley rats were subjected to a transient severe (20 min) forebrain ischemia (Isch) episode and treated with P4 or ALLO (8 mg/kg i.v.) or its vehicle, at 20 min, 2, 6, 24, 48 and 72 h after ischemia. Rats subjected to Sham procedures, and intact rats were included as nonischemic controls. Three months after ischemia, both the functional (spatial learning and memory, and reference and working memory), and the morphological integrity (dimensions of the hippocampal formation, thickness of the CA1 subfield, and pyramidal neuron population) of the hippocampus and the medial prefrontal cortex(mPFC) were determined. RESULTS: Treatment with P4 or ALLO significantly reduced the impairment in spatial learning and memory, as well as in reference and working memory, and prevented the narrowing of the hippocampus, otherwise induced by ischemia. This better performance of P4 and ALLO treated rats than vehicle (Veh) treated rats, occurred in spite of a loss of pyramidal neurons in the CA1, CA2,CA3 and hilus subfields of the Ammon's horn (remaining neurons: Isch+Veh: 21.0, 35.6, 44.1, and 40.3%; Isch+P4: 19.9, 32.2,41.1, and 32.5%; Isch+ALLO: 25.5, 62.0, 73.7, and 56.7%), and nonsignificant changes in the mPFC, as compared to the Intact group (100%). CONCLUSIONS: Performance of P4 or ALLO treated rats in learning and memory tests suggests that these steroids promoted neural conditions accounting for adequate functioning long after ischemia, in spite of the loss of hippocampal pyramidal neurons.