The activity of neurons in the dorsolateral pontine nucleus (dlpn) was studied in two awake rhesus monkeys trained to participate in a variety of visual and oculomotor tests. The visual and eye movement related responses of 73 neurons encountered in the more caudal part of the dlpn were analyzed. Thirty eight of these could be assigned to one of the three following groups. Visual-only neurons (Type 1, n = 10) responded to movement of a broad range of visual stimuli in certain preferred directions. Their receptive fields were usually large, not restricted to the contralateral visual field and always included the fovea. Visual-tracking (VT) neurons (n = 28) discharged in relation to smooth pursuit of a small target in particular preferred directions. Nine of these (Type 2) did not respond to visual stimulation during stationary fixation. Nineteen VT-cells (Type 3) discharged in relation to both visual tracking and visual stimulation. In 9 of the Type 3 neurons, the preferred directions for visual stimulation and tracking were opposite, whereas they were the same in the other 10. Visual responses of Type 3 neurons were indistinguishable from those of Type 1 neurons. Testing of an additional 9 neurons driven by either visual-tracking or pattern movement was not sufficient to allow a definite assignment to one of the groups 1, 2 or 3. The distribution of preferred directions for both visual stimulation and visual tracking was widely scattered between 0 and 360 deg. Our results suggest that the dlpn is a constituent in a cerebro-cerebellar loop important for the generation of smooth pursuit eye movements.

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SUMMARY1. In high spinal paralysed cats electromyograms were recorded from nerves supplying lumbar back muscles (longissimus dorsi) and abdominal muscles (obliquus abdominis externus) during fictive locomotion induced by I.v. injection of nialamide and L-DOPA. Activity in nerves to hind-limb muscles was also recorded.2. During periods of stable 'locomotor' activity in the hind-limb nerves the efferents to the back and abdominal trunk muscles were generally also rhythmically active. Three different patterns of activity were observed.3. The predominant rhythmic pattern showed a synchronous activation of the efferents to the back and abdominal muscles of one side together with an activation of the hind-limb flexors of that side, alternating with activation of the efferents to the corresponding contralateral muscles. This pattern was very stable and could last for about 3 h. Such a pattern of activity would be expected during the alternate stepping characteristic of walking and trotting.4. The second type of rhythmic locomotor activity was characterized by a synchronous bilateral activation ofthe efferents to the back muscles, alternating with activation of the abdominal muscles on both sides. This pattern occurred only for short periods and appears to correspond to the activity during in-phase stepping such as occurs during a gallop.5. Beside these well co-ordinated patterns less well co-ordinated rhythmic activities were also observed. These included regular rhythmic activity which occurred independently in different muscle groups as well as irregular rhythmic activity with unstable phase relations between different muscle groups.6. The rhythmic locomotor activity in efferents to trunk and limb muscles could be modulated by afferent nerve stimulation and by hypoxia.7. The results reveal that the spinal cord deprived of its supraspinal and peripheral control may generate a variety of different locomotor patterns, which incorporate the trunk muscles in an apparently meaningful way.

Vasoactive intestinal peptide (VIP) is a 28-amino acid peptide that has been demonstrated to reside in cells ( = VIP+ cells) of the retinae of various vertebrate species. In an attempt to study the morphology and distribution of VIP+ cells in the retina of the rhesus monkey in more detail, we subjected VIP+ cells observed in cryostat sections or wholemounts rhesus monkey retinae to a quantitative analysis. VIP+ cells were found to reside in the innermost row of the inner nuclear layer (INL) and in the ganglion cell layer (GCL) in similar numbers (estimate: 50 cells/mm2 at 6-10 mm eccentricity each) and only on rare occasions (12% of all VIP+ cells) in varying positions within the inner plexiform layer (IPL). Somata of VIP+ cells were circular and had a mean diameter of 9.1 microns. They gave rise to 1-3 main dendrites, which were usually oriented toward the IPL. Main dendrites ramified widely into thin fibers (dendritic field diameter less than = 1 mm), carrying varicose swellings. The fibers that contributed to one and the same plexus of VIP+ fibers preferred the middle third of the IPL, independent of the positions of the parent somata. A quantitative analysis of nearest-neighbour distances in the retinal wholemount preparation suggested that VIP+ cells in the GCL and in the INL might be distributed according to 2 independent mosaics. A comparison with Golgi-stained material leads to the tentative equation of VIP+ cells with the "spiny" A12 amacrine cell of Mariani ('90). Whereas the low density and large dendritic field size of VIP+ cells might suggest a more widespread function, the varicose dendritic morphology seems to be more compatible with functionally independent dendritic subunits mediating localized effects.