Preface .............................................................. 649

The functional states of the thalamus and the associated neuronal interplay.

A monograph communicating the current realities and future possibilities of unifying basic studies on anatomy and cellular physiology with investigations of the behavioral and physiological events of waking and sleep. Steriade established the Laboratory of Neurophysiology at Laval U., Quebec; McCarl

Brainstem control of wakefulness and sleep

1. Intracellular recordings were obtained from neurons of the guinea pig sensorimotor cortical slice maintained in vitro. Under control recording conditions input resistances, time constants, and spiking characteristics of slice neurons were well within the ranges reported by other investigators for neocortical neurons in situ. However, resting potentials (mean of -75 mV) and spike amplitudes (mean of 93.5 mV) were 10-25 mV greater than has been observed in intact preparations. 2. Current-voltage relationships obtained under current clamp revealed a spectrum of membrane-rectifying properties at potentials that were subthreshold for spike generation. Ionic and pharmacologic analyses suggest that subthreshold membrane behavior is dominated by voltage-sensitive, very slowly inactivating conductances to K+ and Na+. 3. Action potentials were predominantly Na+ dependent under normal conditions but when outward K+ currents were reduced pharmacologically, it was possible, in most cells, to evoke a non-Na+-dependent, tetrodotoxin-(TTX) insensitive spike, which was followed by a prominent depolarizing after-potential. Both of these events were blocked by the Ca2+ current antagonists, Co2+ and Mn2+. 4. A small population of neurons generated intrinsic, all-or-none burst potentials when depolarized with current pulses or by synaptic activation. These cells were located at a narrow range of depths comprising layer IV and the more superficial parts of layer V. 5. Spontaneous excitatory synaptic potentials appeared in all neurons. Spontaneous inhibitory events were visible in only about 10% of the cells, and in those cases apparently reversed polarity at a level slightly positive to resting potential. Stimulation of the surface of the slice at low intensities evoked robust and usually concurrent excitatory and inhibitory synaptic potentials. Unitary inhibitory postsynaptic potentials (IPSPs) reversed at levels positive to rest. Stronger stimulation produced a labile, long-duration, hyperpolarizing IPSP with a reversal potential 15-20 mV negative to the resting level. 6. Neocortical neurons in vitro retain the basic membrane and synaptic properties ascribed to them in situ. However, the array of passive and active membrane behavior observed in the slice suggests that cortical neurons may be differentiated by specific functional properties as well as by their extensive morphological diversity.

Electrophysiological properties of neocortical neurons in vitro

The thalamus as a neuronal oscillator.

Control of postsynaptic Ca2+ influx in developing neocortex by excitatory and inhibitory neurotransmitters

Properties of synaptic activities and spike potentials of neurons in immature neocortex

Cortical intracellular potentials during augmenting and recruiting responses. ii. patterns of synaptic activities in pyramidal and nonpyramidal tract neurons.

Cortical intracellular potentials during augmenting and recruiting responses. i. effects of injected hyperpolarizing currents on evoked membrane potential changes.

Intracellular recording from thalamic neurons during reticulocortical activation.

THE extent to which dendrites of neurones in the central nervous system are capable of supporting conductile activity has been a matter of considerable controversy1. Impulse initiation in the vast majority of neurones occurs in the initial axonal segment or cell body and this is followed by a variable degree of dendritic invasion by the spike potential2–5. Partial spikes in dendrites, which electrotonically influence low-threshold trigger zones in the initial axonal segment, have been observed in a small proportion of hippocampal neurones6 but only rarely in neocortical neurones7,8. Spike-generation in dendrites with conduction into the soma has not been demonstrated with intracellular recording in the mammalian brain although such a mode of impulse initiation has recently been shown for crustacean pit receptor neurones9. In contrast to the stereotyped pattern of impulse initiation in neurones of adult animals, we have observed a remarkable lability in respect to spike-generation in neurones of immature cerebral cortex.

Robert J. Shofer

Papers

Properties of synaptic activities and spike potentials of neurons in immature neocortex

Cortical intracellular potentials during augmenting and recruiting responses. ii. patterns of synaptic activities in pyramidal and nonpyramidal tract neurons.

Cortical intracellular potentials during augmenting and recruiting responses. i. effects of injected hyperpolarizing currents on evoked membrane potential changes.

Intracellular recording from thalamic neurons during reticulocortical activation.

Spike-generation in dendrites and synaptic inhibition in immature cerebral cortex.