Mild membrane depolarization in neurons induces immediate early gene transcription and acutely subdues responses to successive stimulus

The transcriptional profile of immediate early genes (IEGs) is indicative of the duration of neuronal activity, but it is unknown whether it affected by the strength of depolarization. Also unknown is whether an activity history of graded potential changes influences further neuronal activity. In this work with dissociated rat cortical neurons, we found mild depolarization – mediated by elevated extracellular KCl – not only induces a wide array of rapid IEGs, but also transiently depresses transcriptional and signaling responses to a successive stimulus. This latter effect was independent of de novo transcription, translation, calcineurin (CaN) signaling, and MAPK signaling downstream of PKC. Furthermore, as measured by multiple electrode arrays, mild depolarization acutely subdues subsequent spontaneous and bicuculline-evoked activity. Collectively, this work suggests that a recent history of graded potential changes acutely depresses neuronal intrinsic properties and subsequent responses. Such effects may have several potential downstream implications, including reducing signal-to-noise ratio during Hebbian plasticity processes.

Changing Role of Stimulus Intensity as a Determinant of Infants' Attention

When pairs of stimuli which varied in size or brightness and in pattern were presented to 6-, 9- and 24-wk.-olds, the visual attention of the younger infants appeared to be more influenced by size or brightness than by pattern, while the opposite was the case for the oldest infants. The results of another study suggested that the effects of size and brightness were additive for 9-wk.-olds. Finally, a third study using a subject-control procedure with successive stimulus presentation yielded results which were essentially the same as those of the first study. The results were interpreted as supporting the hypothesis that amount of stimulation is a major determinant of attention in the first 2 mo. and that its effectiveness decreases with age.

A progressive and cumulative suppression of the activity of spinal neurones in the nonspinal rat

Electrical stimulation of the skin of the hindpaw of the rat, at frequencies ranging from 2 to 0.2 s−1, halted the tonic or evoked activity of spinal neurones. The duration of this effect increased with each successive stimulus until it outlasted the interstimulus interval. Tonic activity did not return immediately following termination of the stimulation, and activity was often depressed for periods of up to 5 min. Neurones displaying this behaviour were found in laminae 1 and 4–7 of the cord. Some neurones failed to demonstrate this behaviour following the administration of strychnine. This phenomenon provides a possible substrate for habituation of the flexor reflex that occurs with repetitive and noxious stimulation of the skin.