The effects of bath-applied 4-aminopyridine on neurones and extracellular potassium and calcium concentrations were recorded in slices of guinea-pig olfactory cortex. Neurones were orthodromically activated by stimulating the lateral olfactory tract. 4-Aminopyridine (3–10 μM) had the following effects: (1) an increase in the frequency and amplitude of spontaneous postsynaptic potentials: (2) a prolongation and oscillatory behaviour or orthodromically evoked postsynaptic potentials; (3) induction of spontaneous or stimulus-evoked seizure-type discharges which were accompanied by large rises in extracellular potassium and falls in calcium concentration; (4) a prolongation of the lateral olfactory tract population fibre spike. Prior to paroxysmal depolarization, membrane potential, input resistance and soma spike duration were unaffected. In the seconds before seizure discharges, a late hyperpolarizing potential (evoked by orthodromic stimulation) was reduced in amplitude or abolished. Diphenylhydantoin (50 μM) or magnesium ions (5 mM) prevented paroxysmal activity. Our results whow that 4-aminopyridine can produce seizure-type discharges in a brain slice preparation. The role of increased spontaneous potentials and possible loss of synaptic inhibition as causal factors for such discharges is discussed.

A post-tetanic membrane hyperpolarization following repetitive neuronal activity is a commonly observed phenomenon in the isolated frog spinal cord as well as in neurons of other nervous tissues. We have now used double-barrelled Na+- and K+-ion-sensitive microelectrodes to measure the intracellular Na+- and K+-concentrations and also the extracellular K+-concentration of lumbar spinal motoneurons during and after repetitive stimulation of a dorsal root. The results show that the posttetanic membrane hyperpolarization occurred at a time when the intracellular [Na+] reached its maximal value, intracellular [K+] had its lowest level and extracellular [K+] was still elevated. The hyperpolarization was blocked by ouabain and reduced by Li+.

These data support the previous suggestion that an electrogenic Na+/K+ pump mode may be the mechanism underlying the post-tetanic membrane hyperpolarization.

Lithium sensitive microelectrodes were used to investigate the transmembrane distribution of lithium ions (Li+) in motoneurons of the isolated frog spinal cord. After addition of 5 mmol·l–1 LiCl to the bathing solution the extracellular diffusion of Li+ was measured. At a depth of 500 m, about 60 min elapsed before the extracellular Li+ concentration approached that of the bathing solution. Intracellular measurements revealed that Li+ started to enter the cells soon after reaching the motoneuron pool and after up to 120 min superfusion, an intra — to extracellular concentration ratio of about 0.7 was obtained. The resting membrane potential and height of antidromically evoked action potentials were not altered by 5 mmol·l–1 Li+.

It is becoming increasingly clear that nerve cells in the mammalian central nervous system (CNS) have a very complex electroresponsiveness. They exhibit not only time- and voltage-dependent Na+ and K+ conductances, analogous to those in the squid giant axon1, but also a variety of other conductances that have a significant role in the control of cell excitability. Of the outward currents, there are, in addition to the delayed rectifier, the Ca2+-activated K+ current2,3 which underlies the long-lasting spike afterhyperpolarization, and the M current4, a non-inactivating K+ current evoked by membrane depolarization and blocked by muscarinic, cholinergic agonists. We demonstrate here the existence in a mammalian central neurone (hip-pocampal CA3 pyramidal cells) of yet another outward current, which is transient and may be carried by K+ ions. Further, the experiments show that this current is substantially reduced by the convulsant 4-aminopyridine (4-AP)5, resulting in a marked increase in cell excitability.

Four porous synthetics were tested for their applicability as cartilage replacement in the reconstruction of the auricle: teflon velour, filamentous dacron, porous polyethylene and proplast II. After formation of a fold, the implants were sutured into subcutaneous cavities of the abdominal skin of rats or fixed with fibrin adhesive. Histological and scanning-electron-microscopic examinations have so far been performed after 1 and 3 months. Form stability with persistence of the desired skin fold was good when the material was not too thin or too thick. The infection rate was surprisingly low; skin necroses occurred largely in the area of transfixion sutures. The porosity appears to promote adaptation of the skin to the material and to thus counteract an effacement of the skin fold. The best form stability was evidenced by thermoplastic polyethylene, which was thus also chosen for first clinical applications.