Auditory-nerve activity in cats exposed to ototoxic drugs and high-intensity sounds

The response characteristics of auditory-nerve fibers in normal cats are compared with those in cats exposed to kanamycin and high-intensity sounds. The pathophysiology is characterized by an elevation of the tuning-curve "tips," which is sometimes associated with hypersensitivity of the "tails". Plots of unit thresholds are correlated with patterns of sensory-cell losses in the cochlea. There can be significant shifts in unit threshold without significant loss of hair cells; however, significant hair cell loss is always accompanied by highly abnormal unit thresholds. The presence of inner hair cells seems to be essential for the long-term survival of spiral ganglion cells. An incidental observation is that in the "normal" animal there is almost always a prominent "notch" at 3-4 kHz in the plots of threshold at characteristic frequency, which may have been produced by environmental noise.

Cyclic AMP in secretin choleresis. Evidence for a regulatory role in man and baboons but not in dogs

Cyclic AMP output in the bile in response to intravenous secretin was measured in 11 patients, 12 baboons, and 15 dogs. Secretin was given to patients with bile drainage tubes as an intravenous bolus (1 U per kg). In baboons and dogs both secretin infusion (4 U per kg per hr) and bolus injection (1 U per kg) were used. In baboons cyclic AMP was also determined in liver, extrahepatic duct tissue, and in perfusate from isolated segments of extrahepatic bile ducts. Secretin induced a marked choleresis in all three species. In humans, biliary cyclic AMP concentration increased an average (+/- 1 SE) of 68% +/- 12% and in baboons 4-fold, but no increase occurred in dogs. In baboons, cyclic AMP concentration increased in both bile duct tissue and perfusate from isolated bile ducts concomitant with secretin choleresis, but not in liver. In humans the choleretic effects of sodium dehydrocholate, aminophylline, and glucagon were compared to dibutyryl cyclic AMP (DBcyclic AMP). All agents increased bile flow 2- to 3-fold. Cyclic AMP concentration in bile markedly increased after glucagon and DBcyclic AMP but not after sodium dehydrocholate and aminophylline. We conclude that cyclic AMP is implicated in secretin choleresis in both humans and baboons, but not in dogs. The bile duct appears to be the site of cyclic AMP elaboration induced by secretin in baboons and probably is also in man.

Abnormal neuronal responses during evolution of a penicillin epileptic focus in cat visual cortex

After defining the receptive fields of single units in cortical area 17 of anesthetized cats, recurrent on-off stimulation with bars of light of optimal configuration win from a second micropipette; Progressively, three distinct alterations of neuronal activity developed. The most longlasting and usually the earliest abnormality was an increase in the number and frequency of spikes comprising a neuron's response to stimuli that were effective prior to iontophoresis. This enhanced physiologic response (EPR) could be elicited from a cell independently of the discharge activity of an induced focus, but only with stimuli appropriate for the cell's receptive field. With additional iontophoresis an entirely new response developed, which was consistent with an extracellular paroxysmal depolarization shift (PDS). This high-frequency burst of spikes appeared only in association with an ECoG interictal potential. It could be triggered, however, by stimuli which were previously effective or ineffective, as well as occur spontaneously. Characteristics which further distinguished the PDS from EPR included a longer and more-variable latency, a longer recovery period, and a different sensitivity to changes of stimulus intensity. A period of response inhibition also accompanied each interictal potential and persisted with a variable duration afterward. It was most noticeable as an interruption in the activity of tonically responding neurons and was often present before the cell began to generate PDSs. It was concluded that the EPR represents a direct effect of penicillin on the cell or its immediate synaptic connections, while the PDS appears dependent on the altered interactions within a population of such affected cells. The inhibitory phenomenon, in addition, seems a result of projected influences from cells more fully involved with the developing focus. A dynamic model of the EPR-PDS relationship is proposed.