Donald T. Frazier

Sodium and Chloride Movement into the Central Canal of Cat Spinal Cord.

Summary Net fluxes of sodium, chloride and water across the ependymal lining of tral canal and that a sodium transport system is involved in this process. We are indebted to Dr. Leonard Napolitano of the Department of Anatomy for his help with the micrographs.

Hemicholinium-3: Noncholinergic Effects on Squid Axons

Hemicholinium-3, when applied to the inside of a squid axon, is effective in blocking the action potential. This action is not antagonized by the addition of choline or acetylcholine to the perfusate. Voltage-clamp experiments show that hemicholinium-3 depresses both the early transient and late steady-state components of membrane ionic conductances, with a greater effect on the peak transient component.

Hypothalamic Unit Activity in the Cat: Effects of Estrogen and Vaginal Stimulation

Summary Unit activity in the anterior and posterior hypothalamus was studied during stimulation of the vaginal cervix in anestrus, ovariectomized, and estrogen-treated ovariectomized cats. The results were as follows: (i) cells in the anterior and posterior hypothalamus were influenced by stimulation of the vaginal cervix; (ii) there was a greater tendency for increased firing rates in the anterior as compared to the posterior hypothalamus; (iii) estrogen treatment did not change the responsiveness of cells in the anterior hypothalamus; (iv) estrogen treatment was associated with a general depression of unit activity in the posterior hypothalamus. These findings suggest that the posterior hypothalamus may play a role in the regulation of ovulation and expression of sexual behavior in the cat.

Light Sensitive Neurons in the Pulvinar Nucleus of the Cat

Summary The effects of light stimulation to the retina on the activity of neurons in the pulvinar nucleus were studied in anesthetized cats. Observations were made on a total of 69 samples on ongoing pulvinar activity in the following sequence: a period of spontaneous activity; a period of light stimulation; and a period of recovery. Intermittent light flashes changed both the pattern and rate of firing of 77% of the 62 areas studied with this type of stimulus. The evoked response was usually a burst of activity from 3–4 units following the onset of stimulation. At no time was there a decrease in ongoing activity observed with intermittent stimulation. With steady light, an inhibition of ongoing activity was observed in 2 experiments. The data indicate that a large portion of the nucleus contains cells which respond to light stimulation of the retina.

Effect of hemicholinium no. 3 on amphibian nerve.

Abstract The effect of hemicholinium No. 3 (HC-3) on the amplitude of action potentials recorded from partially stripped frog sciatic nerves has been studied. Stimulation and recordings were carried out in nerve chambers to which various concentrations of HC-3 could be added (10 −3 –10 −5 m ). The stimulating pulse was a square wave, supermaximal for all fibers and delivered to the nerve at various frequencies (0,10,30 cycle/sec). When compared to a control Ringers solution, HC-3 was found to markedly depress the amplitude of the action potential with the effect being both concentration and frequency dependent. Choline, when added in varying concentrations (10 −3 –10 −5 m ) to the HC-3 solution, reduced the effect of HC-3 in a manner suggestive of competitive interactions. Choline at ten times the HC-3 concentration maintained the response of the nerve within control limits. Based on the concept that HC-3 interferes with cholinergic transmission, these data could be interpreted as indicating the involvement of acetylcholine in nerve conduction. If, however, as the current hypothesis suggests, HC-3 exerts its effect by competing with the transport of choline, one cannot exclude the possibility that cations other than choline are similarly affected.

Organic acid movement out of the central canal.

Summary A method for perfusing the central canal of cats and rabbits is described. The reduction of concentration of PAH or CPR added to the perfusate is about the same as the reduction in concentration of added radio inulin. Reduction of CPR concentration is not influenced by probenecid or by the presence of another organic acid (PAH). The data are interpreted to indicate that the ependymal cells lining the central canal do not transport organic acids. It is suggested that the parallel reduction in concentration of inulin and added organic acid results from dilution of the perfusate.