Electrodermal response in nonglabrous skin of freely moving rats: mediation by the sympathetic nervous system and evaluation in an animal model of depression.

Electrodermal responses in the facial region of freely moving rats were recorded bilaterally. After a nociceptive stimulus (ammonia vapor exposure), the response (a transient negative potential followed by a longer-lasting positive potential) attained a similar amplitude on both sides. Surgical sympathetic denervation of facial skin by ipsilateral superior cervical ganglionectomy (SCGx) significantly decreased the electrodermal response. When an inferior cervical ganglionectomy was performed in addition to SCGx, a further decrease in electrodermal response was observed. Pretreatment of unilaterally SCGx rats with atropine blunted the electrical response in the control side to levels similar to those found in the SCGx side. Treatment with phenoxybenzamine or propranolol was ineffective. Skin potential responses were measured in adult rats administered with clomipramine from the 8th to the 21st day of life and exhibiting a long-lasting syndrome resembling human depression. Clomipramine-injected rats developed larger skin potential responses to sound stimulation than controls while responses to ammonia vapor were similar in both groups, as well as the habituation rate after repetitive exposure to ammonia vapor. The results indicate that some of the altered electrodermal responses found in depressed patients are detectable in the clomipramine animal model of endogenous depression.

Diurnal variations in cyclic AMP and melatonin content of golden hamster retina.

The diurnal variations and photic regulation of cyclic AMP and melatonin content in golden hamster retina were studied. Both parameters showed significant diurnal variations with maximal values at night. Light exposure during the night inhibited retinal cyclic AMP and melatonin levels, whereas exposure to darkness during the day significantly increased cyclic AMP and melatonin content. Incubation with melatonin of retinas excised at different intervals indicated that the methoxyindole inhibited cyclic AMP accumulation in a time-dependent manner. The inhibitory effect of melatonin at 2400 h and at noon showed a threshold concentration of 1 and 10 pM, respectively. At 0400 h melatonin did not affect cyclic AMP accumulation. The results indicate a diurnal variability of retinal cyclic AMP and melatonin content in hamsters, mainly influenced by a photic stimulus. Cyclic AMP could be a putative second messenger for melatonin action in golden hamster retina.

Ca2+ role on the effect of phorbol esters on the spontaneous quantal release of neurotransmitter at the mouse neuromuscular junction.

The effect of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on the release process was studied in presence of different extracellular Ca2+ concentrations, in the mouse phrenic-diaphragm preparation. Hemidiaphragms were incubated for 2 h at room temperature in the presence or absence of TPA. TPA increased the basal frequency of miniature end plate potentials (mepp's) in a dose-dependent manner, resulting in a maximal increase of 280% at a concentration of 0.5 microM. An inverse relationship between extracellular Ca2+ concentration and TPA effect was observed: at high extracellular concentrations of Ca2+ the action of TPA decreased significatively, while at low Ca2+ concentrations the effect of TPA was remarkably augmented. The highest effect of TPA was obtained when tested in a calcium-free medium. TPA also increased mepp frequency stimulated by 10 mM K+. As at basal conditions, the effect of TPA was higher at lower concentrations of extracellular calcium. The results suggest that the effect of stimulation of PKC on neurotransmitter release at the mice neuromuscular junction is not exerted at the level of calcium influx to the nerve terminal. Moreover the action of calcium and TPA seems to be superimposed. The effect of K+ on neurotransmitter release could be explained not only by depolarization of the nerve terminal but by increasing the pool of activable PKC.

Electrical properties of normal, denervated and organ-cultured slow fibres of toad cruralis muscles.

Two types of fibres were characterized in the cruralis muscle of the toad using electrophysiological techniques: the slow and the fast fibres. Five to ten slow fibres were easily identified on the inner face of this muscle. The cruralis slow fibres developed the ability to produce action potentials 40 days after the sciatic nerve was transected at the hip level, while the slow fibres of the pyriformis muscle showed a latent period of 17 days after the same surgical treatment. However, when in addition to this procedure the nerve was transected at the point where it enters the muscle but without damaging the slow fibres, the latency was about 20 days. The slow fibres of the cruralis muscle maintained in organ culture developed the ability to produce action potentials in 24 days. During the winter the slow fibres of in vivo denervated cruralis and pyriformis muscles did not develop the ability to produce regenerative responses. More-over organ-cultured cruralis muscles taken from winter toads showed this same inability. These results further support the idea that the excitability of slow fibres is under the control of a neural factor rather than of activity. The seasonal dependence points to the fact that the metabolic state of the muscle is of crucial importance in determining the development of excitability of slow fibres.

Ca-dependent slow action potentials in human skeletal muscle.

Slow Ca-action potentials (CaAP) were studied in normal human skeletal muscle fibers obtained during surgery (fibers with both ends cut). Control studies also were carried out with intact as well as cut rat skeletal muscle fibers. Experiments were performed in hypertonic Cl-free saline with 10 or 84 mM Ca and K-channel blockers; muscles were preincubated in a saline containing Cs and tetraethylammonium. A current-clamp technique with two intracellular microelectrodes was used. In human muscle, 14.5% of the fibers showed fully developed CaAPs, 21% displayed nonregenerative Ca responses, and 64.5% showed only passive responses; CaAPs were never observed in 10 mM Ca. In rat muscle, nearly 90% of the fibers showed CaAPs, which were not affected by the cut-end condition. Human and rat muscle fibers had similar membrane potential and conductance in the resting state. In human muscle (22-32 degrees C, 84 mM Ca), the threshold and peak potential during a CaAP were +26 +/- 6 mV and +70 +/- 3 mV, respectively, and the duration measured at threshold level was 1.7 +/- 0.5 sec. In rat muscle, the duration was four times longer. During a CaAP, membrane conductance was assumed to be a leak conductance in parallel with a Ca and a K conductance. In human muscle (22-32 degrees C, 84 mM Ca, 40 micron fiber diameter), values were 0.4 +/- 0.1 microS, 1.1 +/- 0.7 microS, and 0.9 +/- 0.4 microS, respectively. Rat muscle (22-24 degrees C, 84 mM Ca) showed leak and K conductances similar to those found in human fibers. Ca-conductance in rat muscle was double the values obtained in human muscle fibers.

Effect of glycerol treatment on the calcium current of frog skeletal muscle.

1. Current and voltage clamp experiments were carried out on frog skeletal muscle fibres. For voltage clamp, the three micro-electrode technique near the fibre end was used. 2. Calcium spikes and currents were recorded in TEA sulphate saline. The addition of 400 mM-glycerol did not appreciably modify them. 3. Muscle fibers were detubulated with the glycerol method. They showed sodium propagating action potentials, with sodium and potassium currents of expected amplitudes. 4. Calcium spikes and currents were reduced or abolished in detubulated muscle fibres. 5. An analysis of fibre capacitance showed a linear correlation between the remaining ICa and the degree of electric discontinuity between the transverse tubular system and the surface membrane. 6. These results indicate that ICa is mainly located in the transverse tubular system. This localization is compatible with some role during mechanical activation.