Saccular and utricular inputs to single vestibular neurons in cats

Saccular and utricular organs are essential for postural stability and gaze control. Although saccular and utricular inputs are known to terminate on vestibular neurons, few previous studies have precisely elucidated the orig in of these inputs. We investigated the saccular and utricular inputs to si ngle vestibular neurons in whole vestibular nuclei of decerebrated cats. Po stsynaptic potentials were recorded from vestibular neurons after electrica l stimulation of the saccular and utricular nerves. Ascending and descendin g axonal projections were examined by stimulating the oculomotor/trochlear nuclei and the cervical segment of the spinal cord, respectively. After eac h experiment, locations of recorded neurons were identified. The recorded n eurons (140) were classified into vestibule-spinal (79), vestibulo-oculo-sp inal (9), and vestibule-ocular (3) neurons based on antidromic responses; 4 9 other vestibular neurons were unidentified. The majority of recorded neur ons were mainly located in the lateral vestibular nucleus. Most of the otol ith-activated vestibular nuclei neurons seemed to participate in vestibulos pinal reflexes. Of the total 140 neurons recorded, approximately one third (51) received saccular and utricular inputs (convergent neurons). The prope rties of these 51 convergent neurons were further investigated. Most (33/51 ) received excitatory postsynaptic potentials (EPSPs) after saccular and ut ricular nerve stimulation. These results implied that most of the convergen t neurons in this study additively coded mixed information for vertical and horizontal linear acceleration. Based on the latencies of convergent neuro ns, we found that an early integration process for vertical and horizontal linear acceleration existed at the second-order level.