Bindu M. Kutty

Short-term exposure to an enriched environment enhances dendritic branching but not brain-derived neurotrophic factor expression in the hippocampus of rats with ventral subicular lesions

Environmental enrichment promotes structural and behavioral plasticity in the adult brain. We have evaluated the efficacy of enriched environment on the dendritic morphology and brain-derived neurotrophic factor (BDNF) expression in the hippocampus of ventral subicular-lesioned rats. Bilateral ventral subicular lesion has significantly reduced the dendritic architecture and spine density of hippocampal pyramidal neurons. The lesioned rats exposed to enriched housing for 10 days showed a significant degree of morphological plasticity in terms of enhanced dendritic branching and spine density. However, the BDNF expression in the hippocampus remained unchanged following subicular lesion and following environmental enrichment. We suggest the participation of other neurotrophic factors in mediating the synaptic plasticity events following exposure to environmental enrichment in ventral subicular-lesioned rats.

Selective neurodegeneration of hippocampus and entorhinal cortex correlates with spatial learning impairments in rats with bilateral ibotenate lesions of ventral subiculum

Rats with bilateral ibotenic acid lesions of ventral subiculum were tested in an eight-arm radial maze task for spatial learning and memory functions. The performance of the lesioned rats was severely impaired relative to control rats in both acquisition and retention of the spatial task. Following subicular lesions, profound neurodegeneration of the CA1 and CA3 sub sectors of hippocampus and entorhinocortical layers I, II, III, V and VI was observed. These results support the concept that neurons in the ventral subiculum are a part of the neural network along with the above neurons, which could be involved in the processing of spatial information.

Exposure to enriched environment improves spatial learning performances and enhances cell density but not choline acetyltransferase activity in the hippocampus of ventral subicular-lesioned rats.

The authors demonstrated the efficacy of enriched housing conditions in promoting the behavioral recovery and neuronal survival following subicular lesion in rats. Chemical lesioning of the ventral subiculum impaired the spatial learning performances in rats. The lesion also induced a significant degree of neurodegeneration in the CA1 and CA3 areas of the hippocampus and entorhinal cortex. Exposure to enriched housing conditions improved the behavioral performance and partially attenuated the neurodegeneration in the hippocampus. The choline acetyl transferase (ChAT) activity in the hippocampus remained unchanged following ventral subicular lesion and also following exposure to an enriched environment. The study implicates the effectiveness of activity-dependent neuronal plasticity induced by environmental enrichment in adulthood following brain insult.

Stress-induced changes in sleep and associated neuronal activity in rat hippocampus and amygdala

Stress increases vulnerability to anxiety and depression. We have investigated the effect of acute immobilization stress in amygdalohippocampal circuits by measuring the electroencephalogram (EEG) in male Wistar rats during rapid eye movement (REM) sleep. Electrodes were implanted stereotaxically in the hippocampus (CA1 and CA3 subregions of the hippocampus) and the amygdala (lateral nucleus). Prior to the stress, two baseline recordings were taken. Twenty-four hours later rats were exposed once to acute immobilization stress (AIS) session for 2 h. After the release and on subsequent days, electrophysiological changes that occurred due to stress during REM sleep were analyzed by comparing them with baseline measurements. Our results suggest that acute immobilization stress induced significant increase in REM sleep in the first 24 h after the exposure. In addition to changes in the sleep patterns, we have observed increased theta oscillations in CA1 area of the hippocampus with decreased coherence at theta range (4-8 Hz) between hippocampus and amygdala. These results suggest that single exposure to aversive experience such as immobilization stress can lead to dynamic changes in neuronal activities with altered sleep morphology. The results obtained in the present study are comparable to those seen in human patients suffering from panic, and anxiety due to posttraumatic stress disorder (PTSD).

Post insult enriched housing improves the 8-arm radial maze performance but not the Morris water maze task in ventral subicular lesioned rats

The present study attempted to evaluate the efficacy of enriched housing conditions in promoting behavioral recovery following subicular lesion. Rats with bilateral ibotenic acid lesions of ventral subiculum were exposed to either enriched housing conditions or standard housing for 6 h daily for 10 days. The performance of the lesioned rats reared in standard housing conditions was severely impaired in both 8-arm radial maze and water maze tasks. Lesioned rats exposed to enriched housing showed behavioral recovery in the 8-arm radial maze but not in the water maze. Our study suggests the possibility that recovery may be based on the functional demand of spatial tasks and may require more appropriate environmental stimulation.

Assessing Neurocognition via Gamified Experimental Logic: A Novel Approach to Simultaneous Acquisition of Multiple ERPs.

The present study describes the development of a neurocognitive paradigm: “Assessing Neurocognition via Gamified Experimental Logic” (ANGEL), for performing the parametric evaluation of multiple neurocognitive functions simultaneously. ANGEL employs an audiovisual sensory motor design for the acquisition of multiple event related potentials (ERPs)—the C1, P50, MMN, N1, N170, P2, N2pc, LRP, P300, and ERN. The ANGEL paradigm allows assessment of 10 neurocognitive variables over the course of three “game” levels of increasing complexity ranging from simple passive observation to complex discrimination and response in the presence of multiple distractors. The paradigm allows assessment of several levels of rapid decision making: speeded up response vs. response-inhibition; responses to easy vs. difficult tasks; responses based on gestalt perception of clear vs. ambiguous stimuli; and finally, responses with set shifting during challenging tasks. The paradigm has been tested using 18 healthy participants from both sexes and the possibilities of varied data analyses have been presented in this paper. The ANGEL approach provides an ecologically valid assessment (as compared to existing tools) that quickly yields a very rich dataset and helps to assess multiple ERPs that can be studied extensively to assess cognitive functions in health and disease conditions.

Meditation and Its Regulatory Role on Sleep

Intense meditation practices help to achieve a harmony between body and mind. Meditation practices influence brain functions, induce various intrinsic neural plasticity events, modulate autonomic, metabolic, endocrine, and immune functions and thus mediate global regulatory changes in various behavioral states including sleep. This brief review focuses on the effect of meditation as a self regulatory phenomenon on sleep.

Chronic stress-induced changes in REM sleep on theta oscillations in the rat hippocampus and amygdala

The present study investigated the effect of Chronic Immobilization Stress (CIS) on theta oscillations in the hippocampus and amygdala during Rapid Eye Movement (REM) sleep. Adult male Wistar rats were subjected to 2h of CIS daily for 10days. Polysomnographic recordings with electroencephalogram (EEG) from hippocampus (CA3 and CA1 subregion) and lateral nucleus of amygdala (LA) were carried out after termination of CIS protocol on the 7th, 14th and 21st day. The results showed a bimodal distribution on the total REM sleep duration in CIS rats: group of rats exhibited increased REM sleep duration considered as a stress-enhanced REM (SER) and rats with reduced REM sleep as stress-reduced REM sleep (SRR) group. The bimodal distribution in REM sleep was continued to exhibit even after 21 days of termination of stress, showing increased REM sleep in SER and reversible REM sleep in SRR rats. In addition to changes in sleep, increased REM sleep in SER rats was associated with attenuated theta activity in the hippocampus and amygdala, while the SRR rats did not show attenuated theta activities during the stress recovery period. Thus, the study demonstrates the dependence of synchronized amygdalo-hippocampal theta activity with the CIS-induced enhanced REM sleep duration. This raises the possibility that CIS-induced manifestations of the anxiety may be associated with synchronized theta oscillations in the hippocampus and amygdala.

Transplantation of Hippocampal Cell Lines Restore Spatial Learning in Rats With Ventral Subicular Lesions

We have demonstrated in our previous studies that ventral subicular lesion induces neurodegeneration of the hippocampus and produces cognitive impairment in rats. In the present study, the efficacy of transplanted green fluorescent protein (GFP)-labeled hippocampal cell line (H3-GFP) cells in establishing functional recovery in ventral subicular lesioned rats has been evaluated. The survival of H3-GFP transplants and their ability to express trophic factors in vivo were also investigated. Adult male Wistar rats were subjected to selective lesioning of ventral subiculum and were transplanted with H3-GFP cells into the cornu ammonis 1 (CA1) hippocampus. The transplants settled mainly in the dentate gyrus and expressed neurotrophic factors, brain-derived neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF). The ventral subicular lesioned (VSL) rats with H3-GFP transplants showed enhanced expression of BDNF in the hippocampus and performed well in eight-arm radial maze and Morris water maze tasks. The VSL rats without hippocampal transplants continued to show cognitive impairment in task learning. The present study demonstrated the H3-GFP transplants mediated recovery of cognitive functions in VSL rats. Our study supports the notion of graft meditated host regeneration and functional recovery through trophic support, although these mechanisms require further investigation.

Enriched environment attenuates behavioral seizures and depression in chronic temporal lobe epilepsy.

Temporal lobe epilepsy (TLE) is commonly associated with depression, anxiety, and cognitive impairment. Despite significant progress in our understanding of the pathophysiology of TLE, it remains the most common form of refractory epilepsy. Enriched environment (EE) has a beneficial effect in many neuropsychiatric disorders. However, the effect of EE on cognitive changes in chronic TLE has not been evaluated. Accordingly, the present study evaluated the effects of EE on chronic epilepsy–induced alterations in cognitive functions, electrophysiology, and cellular changes in the hippocampus.