Time structure, temporal correlation and coherence of chemosensory impulses propagated through both carotid nerves in cats

In spontaneously breathing, pentobarbitone anesthetized cats, we recorded simultaneously the impulses in the chemosensory fibers of both carotid (sinus) nerves, to analyze the correlations between the frequencies of chemosensory discharges (f chi) and their activation ({df chi/dt}a) and deactivation ({df chi/dt}d) rates. We studied the chemosensory responses to brief exposures to hypoxia (100 percent N2; 5-s and 10-s) and hyperoxia (100 percent O2; 30-s), and intravenous injections of excitatory (NaCN 0.2-100 micrograms/kg) and inhibitory (dopamine hydrochloride 0.02-20 micrograms/kg) chemoreceptor agents. Hypoxia increased f chi, with a high temporal correlation between frequency levels in both nerves. Prolonging hypoxic stimulation increased {df chi/dt}d, with preservation of {df chi/dt}a. Hyperoxic exposure produced highly correlated decreases in f chi in both nerves, but reduced correlation in df chi/dt. Increasing doses of NaCN produced analogous increments in f chi, df chi/dt and their correlations, the {df chi/dt}a/{df chi/dt}d ratio remaining constant along all the experimental range, except in one animal in which the ratio increased in both nerves alike. Dopamine reduced f chi bilaterally, with chemosensory silencing being reached with doses of about 0.2-0.5 microgram/kg, the correlations between f chi's of both nerves remaining constant within the range analyzed. Maximal {df chi/dt}d was not affected along the range of dopamine doses, except in one animal in which it increased in both nerves. It is concluded that both carotid nerves convey similar quantitative information to the brain stem. Thus, the carotid nerves constitute either cooperative inputs or redundant afferences contributing to a high safety factor

The petrosal ganglion of the adult cat: neuronal count, sectional area, and their respective distributions

The petrosal ganglion contains most of the perikarya of sensory neurons of the glossopharyngeal nerve. We studied the number and size of neuronal somata in 4 petrosal ganglia from adult cats. Ganglia were serially sectioned in length at 8 microns, sections drawn through a projection microscope, and those neuronal profiles presenting nuclei and nucleoli on each section were counted and their areas measured. The number of neurons ranged from 2311 to 3429 (2908 +/- 271; mean +/- SEM). Neurons were symmetrically distributed around the longitudinal axes of most ganglia, with a skewed distribution in only one ganglion. The sectional area of most neurons (> 98 percent) ranged between 250 and 1725 microns 2, with median values of 667-963 microns 2. Area distributions were significantly different, but differences never exceeded 8.2 percent in related area bins. The ganglion presenting a skewed count distribution and the highest median area departed from the rest, with differences surpassing 25 percent. We conclude that the neuronal population of the petrosal ganglion of the cat is regular both with respect to the number and the size of its constituents, with departures from this pattern probably reflecting individual variations