ABSTRACT
Epileptiform potentials after the application of GABA A receptor antagonist first appeared in a local part of the cortex of anesthetized rats, and then with a small time lag appeared in other areas of the cortex. Externally, it looked like spreading. Potentials originally appeared at any point of recording, and then appeared (propagated) both in the rostral-caudal direction (forward) and reciprocally. The quantitative evaluation of this phenomenon showed that there are three periods of the epileptiform potential spreading. During the initial period, the epileptiform potentials appeared and spread relatively equally in rostrocaudal direction and backwards. In period 2 dominated potentials shift in rostrocaudal direction. After application of a sodium channel blocker epileptic activity significantly decreased. Frequency of initial appearance of potentials in the caudal areas increased. Propagation of the activity in one or another direction was observed. Obtained in this study quantitative characteristics of the initiation and spreading of epileptic activity suggest that in the cortex may exist independent generators, and distribution of the epileptiform potentials and the nature of this distribution implies that this process is based on direct and reciprocal functional connection of neurons.
Subject(s)
Evoked Potentials/physiology , GABA-A Receptor Antagonists/administration & dosage , Neocortex/physiopathology , Animals , Brain Mapping , Electric Stimulation , Epilepsy/physiopathology , Evoked Potentials/drug effects , Neocortex/drug effects , Neurons/drug effects , Rats , Receptors, GABA-A/metabolismABSTRACT
Long-term potentiation in the thalamo-cortical input to the somatosensory cortex barrel field has been reported to be inducible in vitro only during a narrow critical period of the first postnatal week. Here we explored whether this is due to inability of adult synapses to express LTP or lack of appropriate conditions for LTP induction in slice preparations. We recorded thalamo-cortical field potentials (FPs) from the barrel field of chronically prepared adult rats. In the first series, several parameters of conditioning tetanization of thalamus (T) have been tried. Statistically significant LTP of 135-150% relative to the baseline was observed only in rare cases (3/18) so that the mean changes were not statistically significant. In the second series, five trains of 100 Hz stimulation of T were paired with a "reinforcing" stimulation of the lateral hypothalamus (LH). In most cases (9/13), thalamo-cortical FPs were potentiated. The mean post-tetanic amplitude was 238 +/- 42% (+/- SEM) relative to the baseline (n = 13). The potentiation persisted for >1 h and typically even further increased when tested 24-48 h later. LTP magnitude strongly correlated with the initial paired-pulse ratio (PPR, coefficient of correlation r = 0.98) so that the LTP magnitude was larger (333 +/- 107, n = 6) in cases with PPR > 1.3. The mean PPR tended to decrease after LTP (from 2.05 to 1.65). Altogether the results suggest that LTP is inducible in the thalamo-cortical input to the barrel field of normal adult rats. The dependence of the LTP magnitude upon the initial PPR suggests that inputs with low initial release probability undergo larger LTP. Together with the tendency to a decrease in the PPR this suggests an involvement of presynaptic mechanisms in the maintenance of neocortical LTP.
Subject(s)
Hypothalamus/physiology , Long-Term Potentiation/physiology , Neural Pathways/physiology , Somatosensory Cortex/physiology , Thalamus/physiology , Wakefulness/radiation effects , Animals , Electric Stimulation/methods , Evoked Potentials/physiology , Evoked Potentials/radiation effects , Hypothalamus/radiation effects , Linear Models , Long-Term Potentiation/radiation effects , Neural Pathways/radiation effects , Rats , Rats, Wistar , Somatosensory Cortex/radiation effects , Time FactorsABSTRACT
Long-term potentiation in the thalamo-cortical input to the somatosensory cortex barrel field has been reported to be inducible in vitro only during a narrow critical period of the first postnatal week. Here we explored whether this is due to inability of adult synapses to express LTP or lack of appropriate conditions for LTP induction in slice preparations. We recorded thalamo-cortical field potentials (FPs) from the barrel field of chronically prepared adult rats. In the first series, several parameters of conditioning tetanization of thalamus (T) have been tried. Statistically significant LTP of 135-150% relative to the baseline was observed only in rare cases (3/18) so that the mean changes were not statistically significant. In the second series, five trains of 100 Hz stimulation of T were paired with a "reinforcing" stimulation of the lateral hypothalamus (LH). In most cases (9/13) thalamo-cortical FPs were potentiated. The mean post-tetanic amplitude was 238 +/- 42% (+/- SEM) relative to the baseline (n = 13). The potentiation persisted for > > 1 hr and typically even further increased when tested 24-48 hr later. LTP magnitude strongly correlated with the initial paired-pulse ratio (PPR, coefficient of correlation r = 0.98) so that LTP magnitude was larger (333 +/- 107, n = 6) in cases with PPR > 1.3. The mean PPR tended to decrease after LTP (from 2.05 to 1.65). Altogether the results suggest that LTP is inducible in the thalamo-cortical input to the barrel field of normal adult rats. The dependence of LTP magnitude upon the initial PPR suggests that inputs with low initial release probability undergo larger LTP. Together with the tendency to a decrease in the PPR this suggests an involvement of presynaptic mechanisms in the maintenance of neocortical LTP.
