Auditory Processing Deficits Are Selectively Associated with Medial Temporal Lobe Mnemonic Function and White Matter Integrity in Aging Macaques.

Deficits in auditory function and cognition are hallmarks of normative aging. Recent evidence suggests that hearing-impaired individuals have greater risks of developing cognitive impairment and dementia compared to people with intact auditory function, although the neurobiological bases underlying these associations are poorly understood. Here, a colony of aging macaques completed a battery of behavioral tests designed to probe frontal and temporal lobe-dependent cognition. Auditory brainstem responses (ABRs) and visual evoked potentials were measured to assess auditory and visual system function. Structural and diffusion magnetic resonance imaging were then performed to evaluate the microstructural condition of multiple white matter tracts associated with cognition. Animals showing higher cognitive function had significantly better auditory processing capacities, and these associations were selectively observed with tasks that primarily depend on temporal lobe brain structures. Tractography analyses revealed that the fractional anisotropy (FA) of the fimbria-fornix and hippocampal commissure were associated with temporal lobe-dependent visual discrimination performance and auditory sensory function. Conversely, FA of frontal cortex-associated white matter was not associated with auditory processing. Visual sensory function was not associated with frontal or temporal lobe FA, nor with behavior. This study demonstrates significant and selective relationships between ABRs, white matter connectivity, and higher-order cognitive ability.

Amygdala stimulation ameliorates memory impairments and promotes c-Fos activity in fimbria-fornix-lesioned rats.

Recently we provided data showing that amygdala stimulation can ameliorate spatial memory impairments in rats with lesion in the fimbria-fornix (FF). The mechanisms for this improvement involve early gene expression and synthesis of BDNF, MAP-2, and GAP43 in the hippocampus and prefrontal cortex. Now we have studied which brain structures are activated by the amygdala using c-Fos as a marker of neural activation. First, we studied neuronal activation after tetanic stimulation to the amygdala in intact rats. We then carried out a second study in FF-lesioned rats in which the amygdala was stimulated 15 min after daily spatial memory training in the water maze. Our results showed that amygdala stimulation produces widespread brain activation, that includes cortical, thalamic, and brain stem structures. Activation was particularly intense in the dentate gyrus and the prefrontal cortex. Training in the water maze increased c-Fos positive nuclei in the dentate gyrus of the hippocampus and in medial prefrontal cortex. Amygdala stimulation to trained FF-lesioned rats induced an increase of neural activity in the dentate gyrus and medial prefrontal cortex relative to the FF-lesioned, but not stimulated group, like the c-Fos activity seen in trained control rats. Based on these and previous results we explain the mechanisms of amygdala reinforcement of neural plasticity and the partial recovery of spatial memory deficits.

Glutathione Deficit Affects the Integrity and Function of the Fimbria/Fornix and Anterior Commissure in Mice: Relevance for Schizophrenia.

BACKGROUND: Structural anomalies of white matter are found in various brain regions of patients with schizophrenia and bipolar and other psychiatric disorders, but the causes at the cellular and molecular levels remain unclear. Oxidative stress and redox dysregulation have been proposed to play a role in the pathophysiology of several psychiatric conditions, but their anatomical and functional consequences are poorly understood. The aim of this study was to investigate white matter throughout the brain in a preclinical model of redox dysregulation. METHODS: In a mouse model with impaired glutathione synthesis (Gclm KO), a state-of-the-art multimodal magnetic resonance protocol at high field (14.1 T) was used to assess longitudinally the white matter structure, prefrontal neurochemical profile, and ventricular volume. Electrophysiological recordings in the abnormal white matter tracts identified by diffusion tensor imaging were performed to characterize the functional consequences of fractional anisotropy alterations. RESULTS: Structural alterations observed at peri-pubertal age and adulthood in Gclm KO mice were restricted to the anterior commissure and fornix-fimbria. Reduced fractional anisotropy in the anterior commissure (-7.5% ± 1.9, P<.01) and fornix-fimbria (-4.5% ± 1.3, P<.05) were accompanied by reduced conduction velocity in fast-conducting fibers of the posterior limb of the anterior commissure (-14.3% ± 5.1, P<.05) and slow-conducting fibers of the fornix-fimbria (-8.6% ± 2.6, P<.05). Ventricular enlargement was found at peri-puberty (+25% ± 8 P<.05) but not in adult Gclm KO mice. CONCLUSIONS: Glutathione deficit in Gclm KO mice affects ventricular size and the integrity of the fornix-fimbria and anterior commissure. This suggests that redox dysregulation could contribute during neurodevelopment to the impaired white matter and ventricle enlargement observed in schizophrenia and other psychiatric disorders.

Neuroimaging and electroencephalographic changes after vagus nerve stimulation in a boy with medically intractable myoclonic astatic epilepsy.

Myoclonic astatic epilepsy (MAE) is characterized by multiple seizure types, which are often refractory. Although vagus nerve stimulation (VNS) is an alternative treatment for medically intractable seizures, its exact mechanism of action remains unclear. Herein, we report the case of a 4-year-old boy with intractable MAE who has been in a seizure-free status for 2 years and 3 months since 6 months after the implantation of a vagus nerve stimulator (Model 103, Cyberonics, Inc., Houston, TX). Various test results 6 months after VNS were compared with those before VNS. Results of an electroencephalograph revealed disappearance of epileptiform discharges and an increased beta-gamma spectrum rhythm. The brain diffusion-tensor imaging showed an increased ratio of fraction anisotropy in the right fimbria-fornix, indicating improved diffusion of the white matter tract, and (18)F-fluorodeoxyglucose positron emission tomography revealed globally improved cerebral glucose metabolism. His cognitive and social-emotional performances also improved at 2 years after VNS. To the best of our knowledge, this is the first report to describe the effects of VNS on fimbria-fornix and glucose metabolism in MAE.

Fimbria-Fornix Volume Is Associated With Spatial Memory and Olfactory Identification in Humans.

White matter pathways that surround the hippocampus comprise its afferent and efferent connections, and are therefore crucial in mediating the function of the hippocampus. We recently demonstrated a role for the hippocampus in both spatial memory and olfactory identification in humans. In the current study, we focused our attention on the fimbria-fornix white matter bundle and investigated its relationship with spatial memory and olfactory identification. We administered a virtual navigation task and an olfactory identification task to 55 young healthy adults and measured the volume of the fimbria-fornix. We found that the volume of the right fimbria-fornix and its subdivisions is correlated with both navigational learning and olfactory identification in those who use hippocampus-based spatial memory strategies, and not in those who use caudate nucleus-based navigation strategies. These results are consistent with our recent finding that spatial memory and olfaction rely on similar neural networks and structures.

Effects of the dimeric PSD-95 inhibitor UCCB01-144 on functional recovery after fimbria-fornix transection in rats.

Pharmacological inhibition of PSD-95 is a promising therapeutic strategy in the treatment of stroke, and positive effects of monomeric and dimeric PSD-95 inhibitors have been reported in numerous studies. However, whether therapeutic effects will generalize to other types of acute brain injury such as traumatic brain injury (TBI), which has pathophysiological mechanisms in common with stroke, is currently uncertain. We have previously found a lack of neuroprotective effects of dimeric PSD-95 inhibitors in the controlled cortical impact model of TBI in rats. However, as no single animal model is currently able to mimic the complex and heterogeneous pathophysiology of TBI, it is necessary to assess treatment effects across a range of models. In this preliminary study we investigated the neuroprotective abilities of the dimeric PSD-95 inhibitor UCCB01-144 after fimbria-fornix (FF) transection in rats. UCCB01-144 or saline was injected into the lateral tail vein of rats immediately after sham surgery or FF-transection, and effects on spatial delayed alternation in a T-maze were assessed over a 28-day period. Task acquisition was significantly impaired in FF-transected animals, but there were no significant effects of UCCB01-144 on spatial delayed alternation after FF-transection or sham surgery, although decelerated learning curves were seen after treatment with UCCB01-144 in FF-transected animals. The results of the present study are consistent with previous research showing a lack of neuroprotective effects of PSD-95 inhibition in experimental models of TBI.

Amygdala electrical stimulation inducing spatial memory recovery produces an increase of hippocampal bdnf and arc gene expression.

Amygdala seems to promote the consolidation of plastic modification in different brain areas and these long-term brain changes require a rapid de novo RNA and protein synthesis. We have previously shown that basolateral amygdala electrical stimulation produces a partial recovery of spatial memory in fimbria-fornix lesioned animals and it is also able to increase the BDNF protein content in the hippocampus. The emerging question is whether these increased BDNF protein content arises from previously synthesized RNA or from de novo RNA expression. Now we address the question if amygdala electrical stimulation 15min after daily water maze training produces a rapid de novo RNA synthesis in the hippocampus, a critical brain area for spatial memory recovery in fimbria-fornix lesioned animals. In addition, we also study RNA arc expression, a gene which is essential for memory and neural plasticity processes. To this purpose, we study amygdala stimulation effects on the expression of plasticity related-early-genes bdnf and arc in the hippocampus of fimbria-fornix lesioned animals trained in a water-maze for 4days. We also checked on the expression of both genes in non-lesioned, untrained animals (acute condition) at 0.5, 1, 2 and 24h after basolateral amygdala electrical stimulation. Our data from trained animals confirm that daily amygdala electrical stimulation 15min after water maze training produces a partial memory recovery and that is coupled to an increase of bdnf and arc genes expression in the hippocampus. Additionally, the acute study shows that a single session of amygdala stimulation induces a transient increase of both genes (peaking at 30min). These results confirm the memory improving effect of amygdala stimulation in fimbria-fornix-lesioned animals and sustain the assumption that the memory improving effect is mediated by newly synthetized BDNF acting on a memory relevant structure like the hippocampus. The increased amount of BDNF within the hippocampus seems to be locally synthetized by mechanisms activated by the amygdala stimulation.

Implementation of a Functional Observation Battery for the Assessment of Postoperative Well-being in Rats Subjected to Fimbria-Fornix Transection.

The postoperative well-being of Wistar rats subjected to fimbria-fornix transections was assessed using a functional observational battery (FOB), including observations of relative body weight change, general condition, fur quality, body posture and movement, appetite, and pica behavior. Fimbria-fornix transected animals (FF), sham-operated animals (Sham), and two non-operated control groups with and without administration of buprenorphine (+BUP and -BUP, respectively) were observed twice daily for seven days after surgery. Buprenorphine (0.4 mg/kg) mixed in a nut paste for voluntary ingestion was supplied twice daily for 84 h to all groups except the -BUP control group starting on the day of surgery. Body weight was slightly decreased postoperatively in both surgical groups (FF and Sham) compared to control groups. The +BUP control group lost weight starting at day four after discontinuation of buprenorphine. Furthermore, the FF group exhibited significantly reduced general condition one day after surgery, with significantly affected body posture and movement for two days after surgery. In addition, mild pica behavior was observed in the FF group during the first postsurgical day. In conclusion, the FOB implemented in the present study appears to be a sensitive and accurate protocol for assessing animal well-being in the experimental setup applied. It is apparent that the FF transection is an invasive procedure that causes mildly adverse postoperative effects on the rats' well-being. We therefore recommend that this FOB is applied as a routine welfare monitoring protocol in experiments using mechanical central nervous system injury models, such as FF transection.

Denervated hippocampus provides a favorable microenvironment for neuronal differentiation of endogenous neural stem cells.

Fimbria-fornix transection induces both exogenous and endogenous neural stem cells to differentiate into neurons in the hippocampus. This indicates that the denervated hippocampus provides an environment for neuronal differentiation of neural stem cells. However, the pathways and mechanisms in this process are still unclear. Seven days after fimbria fornix transection, our reverse transcription polymerase chain reaction, western blot assay, and enzyme linked immunosorbent assay results show a significant increase in ciliary neurotrophic factor mRNA and protein expression in the denervated hippocampus. Moreover, neural stem cells derived from hippocampi of fetal (embryonic day 17) Sprague-Dawley rats were treated with ciliary neurotrophic factor for 7 days, with an increased number of microtubule associated protein-2-positive cells and decreased number of glial fibrillary acidic protein-positive cells detected. Our results show that ciliary neurotrophic factor expression is up-regulated in the denervated hippocampus, which may promote neuronal differentiation of neural stem cells in the denervated hippocampus.

Erythropoietin Promotes Neural Plasticity and Spatial Memory Recovery in Fimbria-Fornix-Lesioned Rats.

BACKGROUND: Erythropoietin (EPO) upregulates the mitogen activated protein kinase (MAPK) cascade, a central signaling pathway in cellular plastic mechanisms, and is critical for normal brain development. OBJECTIVE: We hypothesized that EPO could modulate the plasticity mechanisms supporting spatial memory recovery in fimbria-fornix-transected animals. METHODS: Fimbria-fornix was transected in 3 groups of rats. Seven days later, EPO was injected daily for 4 consecutive days within 10 minutes after training on a water maze task. RESULTS: Our results show that EPO injections 10 minutes after training produced a substantial spatial memory recovery in fimbria-fornix-lesioned animals. In contrast, an EPO injection shortly after fimbria-fornix lesion surgery does not promote spatial-memory recovery. Neither does daily EPO injection 5 hours after the water maze performance. EPO, on the other hand, induced the expression of plasticity-related genes like arc and bdnf, but this effect was independent of training or lesion. CONCLUSIONS: This finding supports our working hypothesis that EPO can modulate transient neuroplastic mechanisms triggered by training in lesioned animals. Consequently, we propose that EPO administration can be a useful trophic factor to promote neural restoration when given in combination with training.

Efectos del tratamiento con Compvit B, ácido orótico o la combinación de ambos sobre la recuperación de la memoria espacial en ratas con lesión de fimbria-fornix / Effects of treatment with Compvit B, orotic acid or their combination on the recovery of spatial memory in rats with fimbria-fornix lesion

Las vitaminoterapias han sido ampliamente utilizadas en neurología para el tratamiento de neuritis o la correción de déficit metabólicos. En Cuba, se produce desde hace algunos años el preparado vitamínico Compvit®, que contiene vitaminas B1, B6 y B12. El ácido orótico, también llamado vitamina B13, es un producto natural que ha mostrado acciones como nootrópico en estudios con animales jóvenes y viejos que acusan deterioro cognitivo. En el presente trabajo se reportan los resultados de un estudio realizado para evaluar las potencialidades terapéuticas del Compvit® y del ácido orótico, empleando la lesión del sistema fimbria-fornix, que afecta severamente las capacidades de aprendizaje de los animales. Los resultados confirman un efecto positivo de cada uno de los tratamientos vitamónicos mejorando las capacidades cognitivas afectadas por la lesión. Aunque ninguno de los productos empleados o su combinación fue capaz de elevar el rendimiento cognitivo al nivel de los animales sanos, todos logran mejorías signficativas en comparación con el placebo. Este trabajo constituye una evidencia adicional en favor del uso terapéutico de compuestos vitamínicos como parte del tratamiento neurorrestaurativo

Vitamin therapies have been widely used in Neurology for the treatment of neuritis or the correction of metabolic deficits. In Cuba, Compvit® (B1, B6 and B12 vitamins) have been produced since several years. Orotic acid, also called vitamin B13 is a natural product showing nootropic actions in studies with young and old cognitively impaired animals. The present paper reports the results of a study conducted to assess the therapeutic potentials of Compvit® and orotic acid, in the recovery of cognitive abilities in fimbria-fornix lesioned animals, a lesion known to severely impair learning abilities. The results confirm positive effects of each vitamin treatment to improve the cognitive abilities affected by lesion. Although none of the products used, neither their combination, was able to raise the cognitive performance to the level of non-lesioned animals, both of them achieve significant improvement compared to placebo. The present paper constitutes additional evidence favoring the therapeutic use of vitamin compounds as part of neurorestorative treatments