Extracellular single unit activity in the intralaminar thalamic nuclei (ncl. centralis lateralis, CL, n = 77 and ncl. parafascicularis, Pf, n = 163) and in the pretectal area (Pt, n = 75) was examined following chronic electrolytic lesions of the nucleus reticularis thalami (nRT) in ketamine-anaesthetized rats after single electrical stimuli to the ventrobasal complex (VB). Extensive alterations of either the ongoing ("spontaneous") activity or the pattern of VB evoked responses were observed. Four major changes were observed in the activity of these intralaminar or pretectal neurones: 1) many neurones were silent, two times more frequently than in a parallel study with control intact rats; 2) the firing pattern of all the other neurones was in the form of tonic (stationary-like) discharge, without burst discharges as previously described in intact animals. They were ranked into classes according to their spontaneous discharge: class I, silent (no resting discharge) 12 %, class II (1-15 Hz), 54 % and class III (> 16 Hz), 34 %. Class III neurones were never found in intact rats; 3) electrical stimulation of the VB evoked a short latency orthodromic excitatory response in these neurones but this response was not followed by any slowing or depression of the spontaneous activity in more than 40 % of recorded cells. When it occurred, this pause was shorter than that always observed in intact rats by more than 35 % and longer in 7 % of the responsive cells. All these changes were correlated with the extent of damage to the ipsilateral nRT; 4) VB stimulation evoked prolonged excitatory responses lasting more than 150 ms in 13 % of the responsive cells, and nRT stimulation led to a short latency response followed by a pause of activity. These findings suggest that the nRT is involved in sensory integration and modulation.
The effects of phenytoin on threshold intensities of stimulation were studied in cortical epileptic afterdischarges (ADs) in 12-day-old and adult rats with implanted electrodes. Stimulation of the sensorimotor cortical area induced movements directly related to the stimulation as well as EEG afterdischarges (ADs) of the spike-and-wave type and of the limbic type. Rat pups exhibited lower thresholds for stimulation-bound movements and spike-and- wave ADs than adult animals. On the contrary, the limbic type of ADs was elicited with lower current intensity in adult than in immature rats. Phenytoin increased the threshold for stimulation-related movements only in adult rats, whereas threshold intensities for spike-and-wave ADs were increased and thresholds for limbic type of ADs remained uninfluenced in both age groups. The age-dependent effect on stimulation-related movements might be due to a maturation of connectivity in the motor system or to developmental changes in the voltage-gated sodium channels as the main target of phenytoin action.
Models of basic types of epileptic seizures are elaborated not only in adult but also in immature rodents. It is important because at least half of human epilepsies starts during infancy and childhood. This paper presents a review of chemically and electrically induced models of generalized convulsive and nonconvulsive (absence) seizures as well as models of partial simple (neocortical) and complex (limbic) seizures in immature rats. These models can also serve as a tool for study the development of central nervous system and motor abilities because the level of maturation is reflected in seizure semiology. Age-dependent models of epileptic seizures (absences and flexion seizures) are discussed. Models of seizures in immature animals should be used for testing of potential antiepileptic drugs., P. Mareš., and Obsahuje seznam literaury
Phosphene is the experience of light without natural visual stimulation. It can be induced by electrical stimulation of the retina, optic nerve or cortex. Induction of phosphenes can be potentially used in assistive devices for the blind. Analysis of phosphene might be beneficial for practical reasons such as adjustment of transcranial alternating current stimulation (tACS) frequency and intensity to eliminate phosphene perception (e.g., tACS studies using verum tACS group and sham group) or, on the contrary, to maximize perception of phosphenes in order to be more able to study their dynamics. In this study, subjective reports of 50 healthy subjects exposed to different intensities of retinal tACS at 4 different frequencies (6, 10, 20 and 40 Hz) were analyzed. The effectiveness of different tACS frequencies in inducing phosphenes was at least 92 %. Subject reported 41 different phosphene types; the most common were light flashes and light circles. Changing the intensity of stimulation often induced a change in phosphene attributes. Up to nine phosphene attributes changed when the tACS intensity was changed. Significant positive correlation was observed between number of a different phosphene types and tACS frequency. Based on these findings, it can be concluded that tACS is effective in eliciting phosphenes whose type and attributes change depending on the frequency and intensity of tACS. The presented results open new questions for future research.
Reciprocal interactions between intralaminar thalamic nuclei (ncl. centralis lateralis, CL, and ncl. parafascicularis, Pf), the pretectal area (Pt) and lateral thalamic nuclei (ventrobasal complex, VB, ncl. anterior ventralis, AV, and ncl. ventralis anterior, VA) have been observed in ketamine-anaesthetized rats. Extracellular single unit activity has been recorded after single electrical stimuli. Electrical stimulation of the VB evoked a short latency orthodromic response followed by a pause in spontaneous activity in neurones of medial thalamic nuclei. Lateral thalamic neurones responded to electrical stimulation of the intralaminar nuclei or the pretectal area with the same pattern of response. Striatal, sensorimotor cortical or peripheral electrical stimulation also evoked similar responses. The pauses in spontaneous activity were shown to be the result of inhibition since the responsiveness of the intralaminar nuclei or the lateral thalamic neurones to all inputs was abolished or reduced after a conditioning electrical singleshock stimulation in the VB or in the intralaminar nuclei, respectively. The two components of the response were of a different origin, since most of the short latency responses disappeared after medullary, upper cervical sections or large decortications, while the inhibitions persisted. These inhibitions were shown to be of thalamic origin since their duration was decreased after extensive decortications increased after medullary section. It is concluded that the neuroneal properties studied in this report are probably broadly represented throughout the thalamus and that thalamic neurones are under inhibitory control elicited by afferent volleys. This inhibitory control includes a relay in the nucleus reticularis thalami (nRT). The mechanisms of sensory interaction can be purely thalamic, but they can be modulated by suprathalamic and/or mesencephalic loops.