Journal of neurophysiology
-
The initiation site for triggering epileptiform activity was investigated via optical imaging using voltage-sensitive dyes in the neocortical slice perfused with artificial cerebral spinal fluid containing nominally zero magnesium. The neocortical slices (400-microm thick) were harvested from Sprague-Dawley rats (P21-28). Optical imaging was made by using a high speed photodiode array. ⋯ Because the timing for stimulation was arbitrary and the evoked events were initiated independent of discharges of neurons in any other layers, it is likely that the initiation site for epileptiform activity in various cortical layers is independent of the control of layer V pyramidal neurons. Together these finding suggest that the epileptiform focus is confined and can be formed in several (probably all) neocortical layers and in many cortical areas. The initiating neurons may be of different types because neuronal types in various cortical layers are different.
-
The purpose of the present investigation was to examine, in the primate, the role of the postsynaptic dorsal column (PSDC) system and that of the spinothalamic tract (STT) in viscerosensory processing by comparing the responses of neurons in these pathways to colorectal distension (CRD). Experiments were done on four anesthetized male monkeys (Macaca fascicularis). Extracellular recordings were made from a total of 100 neurons randomly located in the L(6)-S(1) segments of the spinal cord. ⋯ Of the unidentified neurons, 23 were excited by CRD, 7 were inhibited, and 5 did not respond. The average responses of STT and PSDC neurons excited by CRD were comparable in magnitude and duration. These results suggest that the major role of the PSDC pathway in viscerosensory processing may be due to a quantitative rather than a qualitative neuronal dominance over the STT.
-
The role of dendritic voltage-gated ion channels in the generation of action potential bursting was investigated using whole cell patch-clamp recordings from the soma and dendrites of CA1 pyramidal neurons located in hippocampal slices of adult rats. Under control conditions somatic current injections evoked single action potentials that were associated with an afterhyperpolarization (AHP). After localized application of 4-aminopyridine (4-AP) to the distal apical dendritic arborization, the same current injections resulted in the generation of an afterdepolarization (ADP) and multiple action potentials. ⋯ This suggest that the Ni-sensitive voltage-gated Ca(2+) channels have the most important role in action potential burst generation. In summary, these data suggest that the activation of dendritic voltage-gated Ca(2+) channels, by large-amplitude backpropagating spikes, provides a prolonged inward current that is capable of generating an ADP and burst of multiple action potentials in the soma of CA1 pyramidal neurons. Dendritic voltage-gated ion channels profoundly regulate the processing and storage of incoming information in CA1 pyramidal neurons by modulating the action potential firing mode from single spiking to burst firing.