We studied the vertical vestibuloocular response (VVOR) in seven cynomolgus monkeys. Eye movements were measured by the search coil method. We tested the monkeys by rotating them about their interaural axis, which was colinear with gravity. Each monkey was tested by using a standard rotational paradigm that consisted of discrete sinusoidal oscillations at three frequencies (0.01, 0.1, and 1.0 Hz) and six peak velocities (5, 10, 30, 60, 100, and 150 degrees/S). The standard rotational paradigm was applied twice for each of two conditions. The first condition (EOD) consisted of rotations with the animal's vision occluded; the second condition (EOL) consisted of rotations during which the animal was allowed to view a well-lighted room. Using various statistics, we tested the linearity of the sinusoidal slow-phase velocity component of the VVOR. The largest nonlinearity found was a skewness of approximately 14% in the waveform of f = 0.01 Hz. We did not find an amplitude asymmetry between slow-phase eye velocity upward (SPVU) and slow-phase eye velocity downward (SPVD) greater than 6% for any oscillation. Nonlinearities present in the VVOR during testing with vision occluded (EOD condition) disappeared with the addition of vision (EOL condition). Intensity function plots [peak slow-phase eye velocity vs. peak rotator (head) velocity] revealed that at f = 0.01, 0.1, and 1.0 Hz over the intensity range from +/-30 degrees/s to +/-150 degrees/s, the VVOR is highly linear. The lowest correlation coefficient associated with linear regressions of the intensity function data at each frequency was 0.99. Analyses of frequency response functions for the bandwidth f = 0.01 to 1.0 Hz, revealed the following: 1) mean amplitude ratio (AR) and phase overlap for four different stimulus intensities (30, 60, 100, and 150 degrees/s); 2) no significant differences (Mann-Whitney U test, P greater than 0.05) between any AR or phase value for mean peak SPVU and mean peak SPVD re appropriately directed head velocity; 3) no significant differences (Mann-Whitney U test, P greater than 0.05) between AR and phase values for animals tested and then retested 1 mo later with five intervening standard rotational paradigms; 4) a large effect of vision in producing a VVOR with near-unity gain and near-perfect phase compensation.(ABSTRACT TRUNCATED AT 400 WORDS)

This report addresses two questions. First, what is the incidence and distribution of multiple type I hair cells within a single NC in the pigeon's anterior semicircular canal crista? Second, are the synaptic structures found in the avian anterior crista similar to those found in the mammalian crista and if so are they different for single and multiple hair cell calyxes? Three pigeon anterior cristae were studied using interference LM and one pigeon anterior crista was studied using TEM. The light microscope studies showed that about 28% of the NCs studied contained a single type I hair cell; 64% contained 2-5 type I hair cells; and about 8% contained 6-12 type I hair cells. It was noted that the largest number of type I hair cells/unit area was located on the lower slopes of the crista while the smallest number of type I hair cells/unit area was located on the upper slopes and apex of the crista. The TEM studies showed that of 51 hair cells studied, 35% were type II hair cells and 65% were type I hair cells. These studies also showed that synaptic structures described in mammals are also seen in the pigeon. So far, in our preliminary studies we have been unable to demonstrate any difference in synaptic structures associated with single calyxes and those associated with multiple calyxes.

A mixture of tritiated proline and fucose was injected into the endolymph of one of the membranous labyrinths of each of 5 white king pigeons (Columba livia). The membranous labyrinth was resealed and the animals were allowed to survive for 15 days. Brains and upper parts of the spinal cords were sectioned and processed by standard autoradiographic procedures. Clear labeling was noted in structures usually associated with both the ascending auditory pathways and the ascending and descending vestibular pathways. Vestibular structures ipsilateral to the injected labyrinth which contained heavy labeling were Scarpa's ganglion and all 6 vestibular nuclei. No labeling was noted in the contralateral Scarpa's ganglion and sparce, if any, labeling was noted in the contralateral vestibular nuclei. Contralateral structures associated with ascending vestibulo-ocular pathways which contained heavy labeling were the medial longitudinal fasciculus, abducens nucleus, trochlear nucleus, and two parts of the oculomotor nucleus--the dorsolateral part and the ventromedial part. Less heavily labeled ipsilateral vestibulo-ocular-related structures included the medial longitudinal fasciculus, abducens nucleus and the ventrolateral edge of the trochlear nucleus. The dorsomedial part of the oculomotor nucleus was heavily labeled on the side ipsilateral to the injected labyrinth. Slight, if any, labeling was noted in either the ipsilateral or contralateral brachium conjunctivum or regions corresponding to the mammalian ascending tract of Deiters. The medullary core of most folia but primarily the medullary core and granular areas of folia IX and X of the cerebellum were labeled.(ABSTRACT TRUNCATED AT 250 WORDS)

AbstractThis study examines the connections underlying the vestibulocollic system in the adult pigeon by using retrogradely transported horseradish peroxidase (HRP) to identify neck muscle motoneurons in one set of animals, and transneural anterograde transport of tritiated proline‐fucose to delineate the descending medial (MVST) and lateral (LVST) vestibulospinal tracts in a second set of animals. Correlations of location and distribution of HRP‐labeled motoneurons and autoradiographically labeled fiber tracts and terminal fields were performed between the two sets of experiments.The right biventer cervicis and complexus neck muscles were subdivided into rostral and caudal halves in ten animals and HRP injected into only half of one of the two muscles in each experiment. Following a 16–48‐hour survival, the brain was fixed by intracarotid catheterization and perfusion and the HRP in the brain sections reacted with the tetramethylbenzidine (TMB) blue reaction process. Three groups of HRP‐labeled motoneurons were identified in the ipilateral ventral horn of the upper cervical spinal cord: a ventromedial and ventrolateral group within lamina VIII innervating the biventer cervicis and the more rostral part of the complexus muscle, and a dorsolateral group of motoneurons within lamina VII innervating the caudal part of the complexus muscle. The dorsolateral motoneurons with their HRP‐labeled axons leaving the cord through the dorsal root are homologous to the spinal accessory nucleus of mammals. Labeled motoneurons were also noted in the ipsilateral medulla adjacent to the medial longitudinal fasiculus (ELM) in a location previously identified as the hy‐poglossal nucleus. Additional experiments were performed in which HRP was injected directly into the base of the tongue. The resultant HRP‐labeled hypoglossal motoneurons were separate and dorsolateral to the collic motoneurons.Descending vestibulospinal projections from one vestibular labyrinth were identified autoradiographicalry (ARG) by transneural anterograde transport of 3H‐proline‐fucose injected into the left labyrinthine endolytine endolymph in five animals. Heavily labeled MVST fibers were observed crossing the midline of the brain to enter and descend in the contralateral ELM. Labeled MVST fibers were noted to leave the contralateral FLM and surround the previously identified collie motoneurons in the medulla with intense terminal fields suggestive of synaptic contact. Labeled MVST fibers in the contralateral ventral funiculus of the cord were also noted to innervate the HRP‐identified ventromedial and ventrolateral cervical motoneurons, but not the dorsolateral motoneurons in lamina VII. Ipsilateral (left) descending MVST and LVST fibers were less heavily labeled at all levels in the medulla and upper cervical cord. Labeled ipsilateral (left) vestibulospinal fibers were also observed to leave the lateralmost aspect of the left ventrolateral funiculus in the upper cervical cord to terminate among left ventrolateral motoneurons. Our findings are compared and contrasted with previous studies of vestibulocollic pathways.

This study was designed to investigate the efferent innervation of the pigeon labyrinth. Horseradish peroxidase (HRP) was injected and confined within the endolymphatic space of one labyrinth in 9 adult pigeons. The brain was perfused by transcardiac carotid catheterization and the HRP reacted by the tetramethylbenzidine (TMB) blue reaction process. Five different groups of HRP-labeled vestibular efferent neurons were identified. Three groups were located within the confines of the ipsilateral vestibular nuclear complex (in the lateral, tangential and descending nucleus) and two additional groups, each bilateral, were located in the reticular formation. In 9 additional pigeons, 4,6-diamidino-2-phenylindole (DAPI) was also injected and confined within the endolymphatic space of one labyrinth. DAPI-labeled cells were noted in 3 of the 5 locations (tangential nucleus, and both reticular groups) which in the other animals contained HRP-labeled cells. These findings raise the possibility of different physiological roles for the efferent vestibular groups in the ipsilateral vestibular nuclear complex and bilateral reticular formation.

A mixture of tritiated proline and fucose was injected into the labyrinthine endolymphatic space of 5 white king pigeons (Columba livia). Using standard autoradiographic techniques, we observed transsynaptic labeling in ascending auditory pathways to the level of the mesencephalon. Auditory system structures, ipsilateral to the injection site, which labeled heavily were the cochlear nerve, the magnocellular and angular nuclei, and the superior olive. Those ipsilateral structures which were slightly labeled were the lateral leminscus and the dorsal part of the lateral mesencephalic nucleus. Contralateral structures which labeled were the superior olive, lateral lemniscus, and dorsal part of the lateral mesencephalic nucleus. The results of this study suggest that ascending auditory pathways (to the level of the mesencephalon) in the pigeon are more similar to those described for mammals in general than previously thought.

Three to five microliters of 50% HRP in saline was injected along a central axis into one of the 6 extraocular muscles in each of 18 adult pigeons. The brain was fixed and serially sectioned 16-20 h postinjection and the HRP reacted with tetramethylbenzidine (TMB). HRP-labeled proprioceptive neurons were located in the ipsilateral nucleus descendens nervi trigemini (TTD) for all muscle injections. The labeled neurons were further subdivided into two groups based on size and shape. In each experiment the number of labeled proprioceptive cells relative to the number of labeled motoneurons ranged between 4.9 and 15.5%. There were no labeled cells in the trigeminal mesencephalic nucleus or contralateral TTD. The study suggests that at least partial afferent (proprioceptive) innervation of the extraocular muscles in the pigeon derived from neurons in the ipsilateral TTD.

We describe a technique of selective and controlled fixation of the brain and upper spinal cord in the adult pigeon by in vivo transcardiac bilateral carotid catheterization and pump perfusion. We were unable to achieve adequate and repeated fixation of these structures for histochemical techniques in the pigeon using the conventional intracardiac perfusion techniques described for mammals. Our intracarotid technique yields a blood-free and well fixed brain and upper spinal cord. A series of intracarotid pump perfusions (saline, fixative, and sucrose buffer) has significantly reduced histochemical processing time by allowing immediate cryosectioning of the dissected brain.

This study was designed to investigate the relationship between vestibular efferent neurons and catecholamine cell groups within the reticular formation of the pigeon. Horseradish peroxidase (HRP) was injected into the endolymphatic space of one labyrinth. The brain was perfused with glyoxylic acid and serial sections were examined with a fluorescence microscope. After documentation of the location of fluorescent cells the sections were reacted for HRP with tetramethylbenzidine. Fluorescent cells were noted intermingled among the HRP-labeled vestibular efferent neurons in the nucleus reticularis pontis caudalis. No neurons were both fluorescent and HRP-positive. Fluorescent cells were also noted bilaterally in locus ceruleus, raphe nucleus, and in close proximity to the abducent, facial, hypoglossal and ambiguus nuclei.