Whole-Body Prepulse Inhibition Protocol to Test Sensorymotor Gating Mechanisms in Monkeys

<div><p>Prepulse inhibition (PPI) is the decrease of startle reflex amplitude when a slight stimulus is previously generated. This paradigm may provide valuable information about sensorimotor gating functionality. Here we aimed at determining the inhibited and uninhibited startle response of capuchin monkeys (<i>Sapajus spp</i>.), and to evaluate the role of the superior colliculus in PPI. Capuchin monkeys were tested in a whole-body protocol, to determine the best startle amplitude and interstimuli interval. Additionally we tested two subjects with bilateral superior colliculus damage in this protocol. Results show that 115 dB auditory pulse has induced the best startle response. In contrast to reports in other species, no habituation to the auditory stimuli was observed here in capuchins. Also, startle reflex inhibition was optimal after 120 msec interstimuli interval. Finally, there was a downward tendency of percentage inhibition in superior colliculus-lesioned monkeys. Our data provides the possibility of further studies with whole-body protocol in capuchin monkeys and reinforces the importance of the superior colliculus in PPI.</p></div

Monkeys startle response amplitude.

<p>A – Mean relative startle responses, collapsed across stimulus intensities, across repeated blocks of test trials. B - Mean relative startle responses across repeated blocks. * basal activity vs. all acoustic intensities (90–120 dB); # no statistical difference. (n = 6).</p

Monkeys startle response with and without prepulse stimuli.

<p>A - Mean relative startle responses, collapsed across interstimulus intervals, across 7 blocks of test trials. B - Mean relative startle responses in each test situation. * difference of pulse-alone response (p<0.05). C – Mean relative percent of startle inhibition provoked by each interval between prepulse and pulse stimuli. (n = 8).</p

A Markerless 3D Computerized Motion Capture System Incorporating a Skeleton Model for Monkeys

<div><p>In this study, we propose a novel markerless motion capture system (MCS) for monkeys, in which 3D surface images of monkeys were reconstructed by integrating data from four depth cameras, and a skeleton model of the monkey was fitted onto 3D images of monkeys in each frame of the video. To validate the MCS, first, estimated 3D positions of body parts were compared between the 3D MCS-assisted estimation and manual estimation based on visual inspection when a monkey performed a shuttling behavior in which it had to avoid obstacles in various positions. The mean estimation error of the positions of body parts (3–14 cm) and of head rotation (35–43°) between the 3D MCS-assisted and manual estimation were comparable to the errors between two different experimenters performing manual estimation. Furthermore, the MCS could identify specific monkey actions, and there was no false positive nor false negative detection of actions compared with those in manual estimation. Second, to check the reproducibility of MCS-assisted estimation, the same analyses of the above experiments were repeated by a different user. The estimation errors of positions of most body parts between the two experimenters were significantly smaller in the MCS-assisted estimation than in the manual estimation. Third, effects of methamphetamine (MAP) administration on the spontaneous behaviors of four monkeys were analyzed using the MCS. MAP significantly increased head movements, tended to decrease locomotion speed, and had no significant effect on total path length. The results were comparable to previous human clinical data. Furthermore, estimated data following MAP injection (total path length, walking speed, and speed of head rotation) correlated significantly between the two experimenters in the MCS-assisted estimation (r = 0.863 to 0.999). The results suggest that the presented MCS in monkeys is useful in investigating neural mechanisms underlying various psychiatric disorders and developing pharmacological interventions.</p></div

Primate test chamber.

<p>Monkeys were positioned with the neck at the neck-hole in a standing position on the accelerometer platform.</p

Selection of partial 3D hulls with normal for the reconstruction of a full 3D hull.

<p>C: camera, R: reference camera. Example frames with partial 3D hulls constructed from 4 cameras (C1 to C4), and frames with full 3D hulls reconstructions (top) are shown. Thick vertical lines indicate times when the frames were captured. Dotted lines connect selected frames for reconstruction of a full 3D hull. The frames were captured while a male was chasing a female.</p

Markerless MCS for monkeys.

<p>A: Experimental setup consisting of a monkey cage with four depth cameras. B: Schematic illustration of processing steps of the present MCS. A monkey was captured by four depth cameras (Cam1-4) (a, b), and the images were merged to make a 3D image of the monkey represented by 3D points on the entire surface of the monkey (b). Simultaneously captured color images were mapped onto the 3D points (c). Finally, a skeleton model of the monkey was fitted onto the 3D image (d). C: A skeletal model of a monkey used in the present study. The model consisted of spheres connected by joints. Centers of the spheres, where lines are connected, indicates joints. Number of degrees of freedom (DOF) in each joint is shown by color. D: Attraction force from the points. Small squares represent captured 3D points. Gray spheres represent spheres in the model. The red points attract the sphere <i>i</i>. E: Repulsive force from the points. Arrows indicate the surface normal at the points. The blue points push the sphere <i>i</i> away. Other descriptions are same as D.</p

Basic concept of the position estimation algorithm.

<p>A. The strategy of the position estimation. To estimate the positions of body parts (shown as cross marks), the skeleton model of a rat (shown in red) is physically fitted into the 3D hull of a rat (shown as gray squares). B: Schematics explaining the physical forces that were assumed to converge the skeleton model into the 3D hull. Left: before converge; right: after converge. Red lines: the attraction forces; blue lines: the repulsive forces.</p

Examples of analysis of behavioral events.

<p>A: An example of a chronogram of the occurrence of behavioral events (a test session of AM-251). In the chronogram, each line represents the time at which each event occurred. M: male; F: female. The first red vertical line indicates the time at which the female was introduced, while the second red vertical line indicates the timing of ejaculation. B: Mean transitional behavioral graphs for all of the test sessions. The colored edges (arrows) indicate significant differences in probability of transitions between the 2 groups (unpaired t-test, p<0.05); blue and red arrows indicate that probability was higher in the vehicle AM-251 groups, respectively. Black arrows indicate that probability was not significantly different between the 2 groups. The thickness of the edge (arrow) is proportional to the corresponding probability of transition. Only the edges with a probability of transition >3% are shown. C: Comparison between the 2 groups for durations of head-head contact events during copulatory period, * p<0.05. D: Comparison between the 2 groups for frequency of transition from stop without contact to head-head contact (left), and the transition from follow to head-head contact (right),*p<0.05.</p

Examples of captured motion in the shuttling task.

<p>A: Snapshots of the video captured in the task without obstacles (session 1), the task with obstructing bars at a low height in the middle of the cage (session 2), and the task with obstructing bars at a medium height in the middle of the cage (session 3). White solid lines indicate inner skeletons in the trunk and right limbs, dotted lines indicate inner skeletons in the left limbs. B and C: Traces of the estimated posture from the side view (B) and top view (C) based on the snapshots shown in A. Black bars and points represent the obstacle bars. Green lines, trunk; black lines, head; red lines, forelimbs; blue lines, hind limbs. The solid and dotted lines represent right and left limbs, respectively.</p