Neural conduction time and steady-state evoked potentials.

Signal processing in neural networks will inevitably include delays due to the finite conduction velocity of the neurones and their interconnections. Diamond proposed a method for finding these delays in the case of (visual) steady-state responses. Alignment of response features, when represented in a time domain plot, would, allegedly, yield the delay. We show that filter action, by introducing frequency-dependent phase shifts, is bound to distort the time domain plot considerably, thereby aligning the response features in such a way that a wrong value for the delay is found. This makes that analysis method of doubtful significance.

Relation between meteorological factors and pain in rheumatoid arthritis in a marine climate.

Reports indicate that weather conditions may affect some symptoms of rheumatoid arthritis (RA) but not the disease itself. Eighty-eight patients living in the marine climate of the Dutch coastal provinces scored their pain symptoms daily during a full year. Correlation analyses of monthly patient averaged pain scores against each of 6 weather factors indicated that RA pain associates positively and quite significantly (p less than 0.01) with temperature and with vapour pressure, negatively and significantly (p less than 0.02) with relative humidity and not with any of the other factors. The fact that the relation between the temperature/vapour pressure complex and RA pain is stronger in summer than in winter is discussed.

Extracellular potassium controls responsiveness of the noradrenergic cAMP system in the rat retina to fluphenazine.

The effects of fluphenazine (FLU) on the noradrenaline (NA) induced cAMP-synthesis in intact rat retinae were studied as a function of extracellular K(+)- and Ca(2+)-ions. Thus NA-induced cAMP levels were measured after incubating intact rat retinae with 50 ?M NA in the presence or absence of FLU and in the presence of 1 or 10 mM theophylline. Results were: (1) Experimental condition a: standard NA-responses were measured after incubating retinae at 0.75 mM Ca(2+), at 10 mM theophylline, at 10 ?M FLU and at 2 and 0 mM K(+). FLU does not affect the NA-response at 2 mM K(+) significantly; however, it inhibits the NA-response at 0 mM K(+) in this condition. (2) Experimental condition b: NA-responses were measured after incubating retinae at 0.125 mM Ca(2+), 10 mM theophylline, 10 ?M FLU and at 2 and 0 mM K(+). At 2 mM K(+) FLU replaces a Ca(2+) function probably connected with the synthesis part of the NA-cAMP system and NA-responses in this low Ca(2+) condition are consequently enhanced by FLU; however, FLU inhibits the NA-response at 0 mM K(+) in this condition. (3) Experimental condition c: NA-responses were measured after incubating retinae at 0.75 mM Ca(2+), 1 mM theophylline, 10 ?M FLU and at 2 and 0 mM K(+). At 2 mM K(+) FLU enhances the NA-response by further inhibition of the degradation part of the NA-cAMP system; FLU inhibits the NA-response at 0 mM K(+) in this condition. (4) The inhibitions of the NA-responses by FLU at 0 mM K(+) in all three conditions a, b and c showed an apparent K(m) of 1 ?M. (5) Low concentrations of K(+) (0.4-0.8 mM) maintain the property of FLU to enhance the NA-responses at condition b (0.125 mM Ca(2+)) and at condition c (1 mM theophylline). Results suggest that the activation of NA-receptor coupled adenylate cyclases (NA-AC-ases) by NA, resulting in activation of phosphodiesterase activity by the NA-elevated cAMP-levels, is sustained by (a) membraneous factor(s) connected to the NA-receptor. This (these) factor(s) is (are) switched off in the absence of K(+). Evidence has been presented, that Ca(2+) and FLU do not have access to this intramembraneous factor-enzyme activating moiety of the NA-cAMP system at 0 mM K(+). Between 0.4 and 0.8 mM K(+) the factor-enzyme-NA-receptor complex is still intact.

Recording the visual electrically evoked potential (VEEP).

A system for recording cortical responses to electrical stimulation of the visual system (electrical phosphene) is described. The system included a rotatable electrode pair for stimulation, with which artifacts caused by the relatively large stimulating currents could be reduced to suitable levels. Optical isolation on both the stimulating and recording sides of the equipment provided safety for the subject and made precise application of the stimulating current possible.