Faculty Bibliography

Magnetic field variations from the human brain produced by visual stimulation have been observed in a normal laboratory setting with a superconducting quantum interference device and no magnetic shielding of the subject. Previously unknown temporal and spatial features of the field near the scalp are reported

The effects of changes in serum osmolarity on the rate and osmolarity of bulk flow of fluid into the cerebral ventricles and on cortical white and grey matter water content were studied in cats. Bulk flow rates and osmolarities were measured during ventriculocisternal perfusion both before and after intravenous infusion of glucose solutions. Infusions of glucose in concentrations greater than 6% decreased fluid bulk flow rate and its osmolarity. Glucose in concentrations less than 6 percent increased fluid bulk flow rate and decreased its osmolarity. Bulk flow rate and serum osmolarity were found to be linearly related with a coefficient of osmotic flow of minus 0.835 mul/min per mOsm/l. At the extremes of induced serum osmolarities, (290 and 360 mOsm/l) bulk flow rate was either increased by 120 percent or completely inhibited. Effluent osmolarity also increased proportionately to serum osmolarity (0.338 mOsm/l per mOsm/l). When compared to controls, cortical grey and white matter water content increased by 1.9 percent and 2.9 percent, respectively, when the infused glucose concentration was 2.5 percent or less, and decreased by 1.8 percent and 2.9 percent when the concentration was 10 percent or more. The results of these experiments suggest that the increased bulk flow comes from the brain, rather then directly from the blood.

1. The electrical activity of Cardiac Purkinje fibres was reconstructed using a mathematical model of the membrane current. The individual components of ionic curent were described by equations which wee based as closely as possible on previous experiments using the voltage clamp technique. 2. Membrane action potentials and pace-maker activity were calculated and compared with time course of underlying changes in two functionally distinct outeard currents, iX1 and iK2. 3. The repolarization of the theoretical action potential is triggered by the onset of iX1, which becomes activated over the plateau range of potentials. iK2 also activates during the plateau but does not play a controlling role in the repolarization. Hwever, iK2 does govern the slow pace-maker depolarization through its subsequent deactivation at negative potentials. 4. The individual phases of the calculated action potential and their 'experimental' modifications were compared with published records. The upstroke is generated by a Hodgkin-Huxley type sodium conductance (gNa), and rises with a maximum rate of 478 V/sec, somewhat less than experimentally observed values ( up to 800 V/sec). The discrepancy is discussed in relation to experimental attempts at measuring gNa. 5. The ole of the transient outward chloride current (called igr) was studied in calculations of the rapid phase of repolarization and 'notch' configuration..

Phylogenetic differences in acetylcholine receptors from skeletal neuromuscular synapses of various species of snakes and lizards have been investigated, using the snake venom alpha-neurotoxins alpha-atratoxin (cobrotoxin) and alpha-bungarotoxin. The acetylcholine receptors of the phylogenetically primitive lizards, like those from all other vertebrates previously tested, are blocked by these alpha-neurotoxins. In contrast, receptors from snakes and advanced lizards are insensitive to one or both of the toxins. It is suggested that toxin-resistant acetylcholine receptors appeared early in the evolution of Squamata and preceded the appearance of alpha-neurotoxins

With the Vibratome modification of the Falck-Hillarp technique, and with the indirect immunofluorescence technique for visualizing the first three enzymes in catecholamine synthesis, evidence has been obtained that in the rat olfactory bulb several periglomerular cells are dopaminergic. Both tyrosine hydroxylase and dopadecarboxylase, converting tyrosine to DOPA and DOPA to dopamine (DA), respectively, but not dopamine-beta-hydroxylase, converting DA to noradrenaline, are present in periglomerular cell bodies, as well as in their intraglomerular dendrites. These findings suggest that DA may be active at dendrodentritic synapses known to be present between periglomerular and mitral and/or tufted cells.