Biomedical subjects

Joyel Almajano

Publications and source records attributed to Joyel Almajano.

3 recordsLinked to original sources

PubMed2005

Analysis of chronic seizure onsets after intrahippocampal kainic acid injection in freely moving rats.

PURPOSE: The goal of this study was to analyze the transition period between interictal and ictal activity in freely moving rats with recurrent spontaneous seizures after unilateral intrahippocampal kainic acid (KA) injection. METHODS: Pairs of tungsten electrodes (50 microm O/D) were implanted bilaterally under anesthesia at symmetrical points in the dentate gyrus (DG) and CA1 regions of anterior and posterior hippocampi and entorhinal cortex of adult Wistar rats. Stimulating electrodes were placed in the right angular bundle and KA was injected into the right posterior CA3 area of hippocampus after 1 week of baseline EEG recording. Beginning 24 h after injection, electrographic activity was recorded with video monitoring for seizures every day for 8 h/day for 60 days. RESULTS: Seventy percent of seizures started locally in the DG ipsilateral to injection, with an increase in frequency of interictal EEG spikes (hypersynchronous type, HYP), and 26% of seizures started with a decrease of EEG amplitude with parallel increase in frequency (low-voltage fast type, LVF). During HYP seizures, a significant increase was observed in amplitude of beta-gamma range frequencies, ripple frequency, and fast ripple (FR) frequency, whereas during LVF seizure, an increase was noted only in the beta-gamma range. In all cases but one, an EEG wave preceded ripple and FR oscillations. Before seizure onset, the amplitude of DG-evoked responses to single pulses decreased, whereas the amplitude of the response to the second pulse delivered at 30-ms interval increased. CONCLUSIONS: If ripple and FR oscillations indicate the seizure-generating neuronal substrate, these areas must be small and widespread, so that the probability of recording from them directly is very low. The decreased response to electrical stimulation before seizures could indicate a protective inhibitory mechanism that contains or prevents seizure occurrence. The presence of decreased paired-pulse suppression could indicate a network predisposition to follow an external input with a certain frequency.

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PubMed2004

Large-scale microarray gene expression analysis in discrete electrophysiologically identified neuronal clusters.

The normal processes of learning and memory as well as the pathological progress of various neurological diseases may result in changes in gene expression in small, local populations of neurons in any given brain area, leading to the occurrence of specific patterns of electrical activity without easily detectable changes in the morphology of this brain area. One way of identifying these changes might be the comparison of gene expression of areas which generate and areas which do not generate specific patterns of electrical activity. A method for microbiopsy of limited (0.5-1.0 mm3) tissue samples from electrophysiologically identified areas of neurons generating epileptiform activity in the rat brain is described. Here we demonstrate that total RNA isolated from individual microbiopsy samples might be successfully used for microarray based gene expression analysis of any discretely localized neuronal group which can be identified electrophysiologically, including neurons in cortical columns, cell assemblies or other functional units.

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PubMed2004

High-frequency oscillations after status epilepticus: epileptogenesis and seizure genesis.

PURPOSE: To investigate the temporal relation between high-frequency oscillations (HFOs) in the dentate gyrus and recurrent spontaneous seizures after intrahippocampal kainite-induced status epilepticus. METHODS: Recording microelectrodes were implanted bilaterally in different regions of hippocampus and entorhinal cortex. A guide cannula for microinjection of kainic acid (KA) was implanted above the right posterior CA3 area of hippocampus. After recording baseline electrical activity, KA (0.4 microg/0.2 microl) was injected. Beginning on the next day, electrographic activity was recorded with video monitoring for seizures every day for 8 h/day for > or = 30 days. RESULTS: Of the 26 rats studied, 19 revealed the appearance of sharp-wave activity and HFOs in the frequency range of 80 to 500 Hz in the dentate gyrus ipsilateral to the KA injection. In the remaining seven rats, no appreciable activity was noted in this frequency range. In some rats with recurrent seizures, HFOs were in the ripple frequency range (100-200 Hz); in others, HFOs were in the fast ripple frequency range (200-500 Hz), or a mixture of both oscillation frequencies was found. The time of detection of the first HFOs after status epilepticus varied between 1 and 30 days, with a mean of 6.3 +/- 2.0 (SEM). Of the 19 rats in which HFO activity appeared, all later developed recurrent spontaneous seizures, whereas none of the rats without HFOs developed seizures. The sooner HFO activity was detected after status epilepticus, the sooner the first spontaneous seizure occurred. A significant inverse relation was found between the time to the first HFO detection and the subsequent rate of spontaneous seizures. CONCLUSIONS: A strong correlation was found between a decreased time to detection of HFOs and an increased rate of spontaneous seizures, as well as with a decrease in the duration of the latent period between KA injection and the detection of spontaneous seizures. Two types of HFOs were found after KA injection, one in the frequency range of 100 to 200 Hz, and the other, in the frequency range of 200 to 500 Hz, and both should be considered pathological, suggesting that both are epileptogenic.

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