Theta and gamma oscillations in the rat hippocampus during attentive lever pressing

The hippocampus is known to be pivotal for spatial memory but emerging evidence suggests its contribution to temporal memories as well. However, it is not clear how the hippocampus represents time and how it synchronizes spatial and temporal presentations into a coherent memory. We assessed the specific role of hippocampal theta and gamma oscillations and their interaction in short-term timing of motor reactions. Rats were trained to maintain lever pressing for 2.5 s and then to quickly release the lever and retrieve water reward from a nearby water port guided by a cue light. In essence, this task allows observation of hippocampal rhythms during timed anticipation when no overt movements take place. Then we implanted wire electrodes to five hippocampal layers for recording local field potentials during the task. Consistent with earlier reports, theta showed a declining trend during the lever press. We also found that fast-gamma declined in tandem with theta while slow-gamma showed an opposite trend. Theta-phase to gamma-amplitude cross-frequency coupling measured with modulation index (MI) varied significantly between the three task phases. Interestingly, also changes in MI were opposite for fast- and slow-gamma. The MI was also related to the task performance, so that during omission trials the MI for fast-gamma in CA1 was smaller than during trials with premature lever release. In addition, the MI in dentate hilus was higher during all error trials than during correctly performed trials. Collectively, these data suggest an important role of synchronization of hippocampal theta and gamma rhythms to timing of cued motor reactions.

2092

OBJECTIVES/SPECIFIC AIMS: We previously developed a translationally relevant model of temporal lobe epilepsy (TLE) in which glutamine synthetase is irreversibility inhibited by methionine sulfoximine (MSO), resulting in spontaneous seizures and dentate hilar neuron loss. The objective of this study was to determine the effects of chronic BCAA ingestion on neuronal viability in the dentate hilus in the MSO model of TLE. METHODS/STUDY POPULATION: Sixteen rats were randomly divided into 2 groups: 8 rats drank a 4% aqueous solution of all 3 BCAAs (BCAA group) ad libitum for 31 days, and the other 8 rats drank regular water (control group) for the same period. After 10 days of drinking, a microinfusion cannula (Alzet osmotic pump, model 2004) was surgically implanted in the right dentate gyrus to continuously infuse MSO at a rate of 0.625 g/hour for 28 days. After 31 days of drinking, rats were perfused transcardially with 0.9% NaCl followed by 4% paraformaldehyde in phosphate buffer. The brains were removed and fixed, sectioned on a Vibratome at 50-μm thickness, and were mounted on a gelatin-coated slides and stained with NeuN. Neuron counts in the hilar region were performed ipsilateral and contralateral to the infusion site using a stereological technique. RESULTS/ANTICIPATED RESULTS: Rats in the BCAA group had 37% fewer neurons in the ipsilateral dentate hilus than the control group (5.8×10−4±6.8×10−5 vs. 8.9×10−4±5.6×10−5 cells, respectively, p<0.01). Similarly, rats in the BCAA group had 39% fewer neurons in the contralateral dentate hilus than the control group (5.0×10−4±5.8×10−5 vs. 7.0×10−4±3.4×10−5 cells, respectively, p=0.01). DISCUSSION/SIGNIFICANCE OF IMPACT: This study demonstrates that chronic ingestion of BCAAs aggravates hilar neuronal loss in a translationally relevant rodent model of MTLE. This study gives important insight into how BCAAs may affect neuronal viability. Although the role of BCAAs on seizure activity is poorly understood, these results suggest that BCAAs may play an important role in neurochemical modulation and neurotoxicity.

Novel Surrogate Markers for Acute Brain Damage: Cerebrospinal Fluid Levels Corrrelate with Severity of Ischemic Neurodegeneration in the Rat

Previously, we identified proteins released from degenerating cultured cortical neurons as novel cerebrospinal fluid (CSF) markers for acute brain injury in the rat. Here, we investigate relationships between CSF changes in these novel markers and the severity of acute ischemic brain injury. Rats underwent sham surgery or 3,6,8, or 10mins of transient global forebrain ischemia. At 48 h after insult, CSF levels of 14-3-3β, 14-3-3ξ, and calpain cleavage products of α-spectrin and tau were quantified. Regional acute neurodegeneration was assessed by Fluoro-Jade and silver impregnation staining, and confirmed by immunohistochemical detection of the activation of calpain and caspase, cysteine proteases involved in neurodegenerative signaling. Ischemic neurodegeneration and activation of at least one cysteine protease were observed in the hippocampal CA1 sector, dentate hilus, caudate nucleus, parietal cortex, thalamus, and inferior colliculus. As expected, the total number of degenerating cells increased as a function of ischemia duration. Cerebrospinal fluid levels of the four marker proteins increased markedly after ischemia, and rose in proportion with its duration. Irrespective of the length of ischemia, CSF levels of the neuron-enriched proteins 14-3-3β and calpain-cleaved tau correlated significantly with the magnitude of acute ischemic neurodegeneration. Additionally, CSF levels of the two proteins correlated with one another. These results show that certain proteins released from degenerating neurons are CSF markers for brain injury in the rat whose levels reflect the severity of acute ischemic neurodegeneration. Measurement of 14-3-3β and calpain-cleaved tau may be useful for the minimally invasive diagnosis, prognosis, and therapeutic evaluation of acute brain damage.