Use of a privacy panel in the home cage of female pair-housed rhesus monkeys has been reported to increase time spent in close proximity and time spent in affiliative behaviours. In the current study we measured these behaviours in more diverse populations; including male-male and male-female pairs of monkeys actively participating in cognitive experiments. We observed twenty-five pairs of rhesus macaques (Macaca mulatta) both with and without the presence of a privacy divider. Monkeys spent significantly more time in the same half of the pair-cage when the divider was in place. A significant increase in affiliative behaviour was not observed. The effects of privacy dividers previously reported for female monkeys partially extend to male pairs and mixed sex pairs under conditions typical of an active research setting.

Bodyweight is an important health and welfare indicator for captive non-human primates (NHPs). Bodyweight can be measured during routine handling procedures, which cause stress. Alternatively, animals can be trained to step onto a scale, but training success varies greatly between individuals. Being able to weigh animals regularly without having to handle or train them is thus desirable for monitoring animal health and welfare. This study investigates the utility, ie the participation, reliability and time investment, of voluntary weighing in captive NHPs living in large social groups. Subjects of the study were 92 rhesus macaques (Macaca mulatta) housed in four social groups at the Biomedical Primate Research Centre in Rijswijk, The Netherlands. A scale was placed in their home enclosure during several sessions. Individuals were unwilling to step onto an unbaited scale. When likeable food items were used to attract individuals to the scale, 68% of them stepped onto the scale. Age and dominance rank did not affect stepping onto the scale, whereas exploratory tendency and social group did. The level of agreement between bodyweight by voluntary weighing and bodyweight measured during sedation was very high. These results show that the majority of rhesus macaques in social groups can be weighed voluntarily and that voluntary weighing is reliable. When optimising and further developing the method, voluntary weighing can form a valuable tool in the captive management of NHPs.

Trichomonads, anaerobic microbial eukaryotes members of the phylum Parabasalia, are common obligate extracellular symbionts that can lead to pathological or asymptomatic colonization of various mucosal surfaces in a wide range of animal hosts. Results from previous in vitro studies have suggested a number of intriguing mucosal colonization strategies by Trichomonads, notably highlighting the importance of interactions with bacteria. However, in vivo validation is currently lacking. A previous metatranscriptomics study into the cause of idiopathic chronic diarrhoea in macaques reported the presence of an unidentified protozoan parasite related to Trichomonas vaginalis. In this work, we performed a reanalysis of the published data in order to identify the parasite species present in the macaque gut. We also leveraged the information-rich metatranscriptomics data to investigate the parasite behaviour in vivo. Our results indicated the presence of at least 3 genera of Trichomonad parasite; Tetratrichomonas, Pentatrichomonas and Trichomitus, 2 of which had not been previously reported in the macaque gut. In addition, we identified common in vivo expression profiles shared amongst the Trichomonads. In agreement with previous findings for other Trichomonads, our results highlighted a relationship between Trichomonads and mucosal bacterial diversity which could be influential in health and disease.

In recent years, a malaria infection of humans in South East Asia, originally diagnosed as a known human-infecting species, Plasmodium malariae, has been identified as a simian parasite, Plasmodium knowlesi. This species had been subject to considerable investigation in monkeys since the 1930s. With the development of continuous culture of the erythrocytic stages of the human malarial parasite, Plasmodium falciparum in 1976, the emphasis in research shifted away from knowlesi. However, its importance as a human pathogen has provoked a renewed interest in P. knowlesi, not least because it too can be maintained in continuous culture and thus provides an experimental model. In fact, this parasite species has a long history in malaria research, and the purpose of this chapter is to outline approximately the first 50 years of this history.

The public health threat posed by zoonotic Plasmodium knowlesi appears to be growing: it is increasingly reported across South East Asia, and is the leading cause of malaria in Malaysian Borneo. Plasmodium knowlesi threatens progress towards malaria elimination as aspects of its transmission, such as spillover from wildlife reservoirs and reliance on outdoor-biting vectors, may limit the effectiveness of conventional methods of malaria control. The development of new quantitative approaches that address the ecological complexity of P. knowlesi, particularly through a focus on its primary reservoir hosts, will be required to control it. Here, we review what is known about P. knowlesi transmission, identify key knowledge gaps in the context of current approaches to transmission modelling, and discuss the integration of these approaches with clinical parasitology and geostatistical analysis. We highlight the need to incorporate the influences of fine-scale spatial variation, rapid changes to the landscape, and reservoir population and transmission dynamics. The proposed integrated approach would address the unique challenges posed by malaria as a zoonosis, aid the identification of transmission hotspots, provide insight into the mechanistic links between incidence and land use change and support the design of appropriate interventions.

The patches in primary visual cortex constitute hot spots of metabolic activity, manifested by enhanced levels of cytochrome oxidase (CO) activity. They are also labeled preferentially by immunostaining for glutamic acid decarboxylase (GAD), γ-aminobutyric acid (GABA), and parvalbumin. However, calbindin shows stronger immunoreactivity outside patches. In light of this discrepancy, the distribution of the vesicular GABA transporter (VGAT) was examined in striate cortex of two normal macaques. VGAT immunoreactivity was strongest in layers 4B, 4Cα, and 5. In tangential sections, the distribution of CO, GAD, and VGAT was compared in layer 2/3. There was a close match between all three labels. This finding indicates that GABA synthesis is enriched in patches, and that inhibitory synapses are more active in patches than interpatches.

Helminthes have the capacity to modulate host immunity, leading to positive interactions with coinfecting microparasites. This phenomenon has been primarily studied during coinfections with a narrow range of geo-helminthes and intracellular microparasites in human populations or under laboratory conditions. Far less is known regarding differences in coinfection dynamics between helminth types, the range of microparasites that might be affected or the overall community-level effects of helminth infections on microparasites in wild systems. Here, we analysed the presence/absence and abundance patterns of enteric parasites in long-tailed macaques (Macaca fascicularis) on the island of Bali, Indonesia, to assess whether naturally occurring helminth infections were associated with increased shedding of the most common intracellular (Cryptosporidium spp., Isospora spp.) and extracellular (Entamoeba spp., Giardia spp.) microparasites. We also comparatively assessed the statistical correlations of different helminth taxa with microparasite shedding to determine if there were consistent relationships between the specific helminth taxa and microparasites. Helminth infections were associated with increased shedding of both intracellular and extracellular microparasites. Platyhelminthes repeatedly displayed strong positive correlations with several microparasites; while nematodes did not. Our results indicate that helminthes can influence microparasite community shedding dynamics under wild conditions, but that trends may be driven by a narrow range of helminthes.

Explanations for color phenomena are often sought in the retina, lateral geniculate nucleus, and V1, yet it is becoming increasingly clear that a complete account will take us further along the visual-processing pathway. Working out which areas are involved is not trivial. Responses to S-cone activation are often assumed to indicate that an area or neuron is involved in color perception. However, work tracing S-cone signals into extrastriate cortex has challenged this assumption: S-cone responses have been found in brain regions, such as the middle temporal (MT) motion area, not thought to play a major role in color perception. Here, we review the processing of S-cone signals across cortex and present original data on S-cone responses measured with fMRI in alert macaque, focusing on one area in which S-cone signals seem likely to contribute to color (V4/posterior inferior temporal cortex) and on one area in which S signals are unlikely to play a role in color (MT). We advance a hypothesis that the S-cone signals in color-computing areas are required to achieve a balanced neural representation of perceptual color space, whereas those in noncolor-areas provide a cue to illumination (not luminance) and confer sensitivity to the chromatic contrast generated by natural daylight (shadows, illuminated by ambient sky, surrounded by direct sunlight). This sensitivity would facilitate the extraction of shape-from-shadow signals to benefit global scene analysis and motion perception.

Parallel processing of visual information begins at the first synapse in the retina between the photoreceptors and bipolar cells. Ten bipolar cell types have been previously described in the primate retina: one rod and nine cone bipolar types. In this paper, we describe an 11th type of bipolar cell identified in Golgi-stained macaque retinal whole mount and vertical section. Axonal stratification depth, in addition to dendritic and axonal morphology, distinguished the “giant” cell from all previously well-recognized bipolar cell types. The giant bipolar cell had a very large and sparsely branched dendritic tree and a relatively large axonal arbor that costratified with the DB4 bipolar cell near the center of the inner plexiform layer. The sparseness of the giant bipolar’s dendritic arbor indicates that, like the blue cone bipolar, it does not contact all the cones in its dendritic field. Giant cells contacting the same cones as midget bipolar cells, which are known to contact single long-wavelength (L) or medium-wavelength (M) cones, demonstrate that the giant cell does not exclusively contact short-wavelength (S) cones and, therefore, is not a variant of the previously described blue cone bipolar. This conclusion is further supported by measurement of the cone contact spacing for the giant bipolar. The giant cell contacts an average of about half the cones in its dendritic field (mean ± s.d. = 52 ± 17.6%; n = 6), with a range of 27–82%. The dendrites from single or neighboring giant cells that converge onto the same cones suggest that the giant cell may selectively target a subset of cones with a highly variable local density, such as the L or M cones.

If the relative phase of red and green modulated lights is changed, at low temporal frequencies the response of cells of the magnocellular (MC) pathway has been found to be minimal not to counterphase, chromatic modulation (as expected of a luminance mechanism) but shifted to some phase intermediate between luminance and chromatic modulation. The results could only be modeled by assuming interaction between achromatic and chromatic inputs to MC cells. The ‘phase shift’ resembled that seen with psychophysical threshold measurements using the same stimuli. Psychophysical results also showed that the phase shift is dependent on the chromaticity of a background. The results reported here show that the direction of the phase shift in MC cells is reversed by changing the background from long to short wavelengths and is consistent with psychophysical observations. Cell behavior was again modeled by assuming vector summation of achromatic and chromatic inputs. The reversal of phase-shift direction requires a reversal in polarity of the chromatic input. The underlying physiological mechanism may involve summation of chromatic signals of opposite polarity; if the relative size of these signals depends on the background, this may determine the direction of phase shift.

We recorded from single cells in area V2 of cynomolgus monkeys using standard acute recording techniques. After measuring each cell's spatial and temporal properties, we performed several tests of its chromatic properties using sine-wave gratings modulated around a mean gray background. Most cells behaved like neurons in area V1 and their responses were adequately described by a model that assumes a linear combination of cone signals. Unlike in V1, we found a subpopulation of cells whose activity was increased or inhibited by stimuli within a narrow range of color combinations. No particular color directions were preferentially represented. V2 cells showing color specificity, including cells showing narrow chromatic tuning, were present in any of the stripe compartments, as defined by cytochrome-oxidase (CO) staining. An addition of chromatic contrast facilitated the responses of most neurons to gratings with various luminance contrasts. Neurons in all three CO compartments gave significant responses to isoluminant gratings. Receptive-field properties of cells were generally similar for luminance and chromatically defined stimuli. We found only a small number of cells with a clearly identifiable double-opponent receptive-field organization.

To examine the role of visual area V4 in pattern vision, we tested two monkeys with lesions of V4 on tasks that required them to discriminate the orientation of contours defined by several different cues. The cues used to separate the contours from their background included luminance, color, motion, and texture, as well as phase-shifted abutting gratings that created an “illusory” contour. The monkeys were trained to maintain fixation on a fixation target while discriminating extrafoveal stimuli, which were located in either a normal control quadrant of the visual field or in a quadrant affected by a lesion of area V4 in one hemisphere. Comparing performance in the two quadrants, we found significant deficits for contours defined by texture and for the illusory contour, but smaller or no deficits for motion-, color-, and luminance-defined contours. The data suggest a specific role of V4 in the perception of illusory contours and contours defined by texture.

lbotenic acid lesions were made in four macaque monkeys in a region of cortical area V4 that corresponds to the lower quadrant of one hemifield. For visual testing, fixation locus was monitoredwith scleral search coils and controlled behaviorally to place test stimuli either in the lesionedquadrant or in a control location in the opposite hemifield. Some basic visual capacities were slightly altered by the lesions; there was a two-fold reduction of luminance contrast sensitivity as well as red-green chromatic contrast sensitivity, both tested with stationary gratings. On the other hand, little or no loss was found when contrast sensitivity for detection or direction discrimination was tested with 10–Hz drifting gratings nor was there a reliable change in visual acuity. Hue and luminance matching were tested with a spatially more complex matching-to-sample task, but monkeys could not learn this task in the visual field locus of a V4 lesion. If previously trained at this locus, performance was not affected by the lesion. In contrast to the small effects on basic visual capabilities, performance on two form discrimination tasks was devastated by V4 lesions. The first involved discriminating the orientation of colinear groups of dots on a background of randomly placed dots. The second involved discriminating the orientation of a group of three line segments surrounded by differently oriented line segments. Some selectivity of the deficitsfor form discrimination was shown by the lack of an effect of the lesions on a global motion discrimination. These results show that while V4 lesions cause only slight disruptions of basic visual capacities, they profoundly disrupt form discriminations.

We investigated the representation of color in cortical area V2 of macaque monkeys, and the association of color with other stimulus attributes. We measured the selectivity of individual V2 neurons for color, motion, and form. Most neurons in V2 were orientation selective, about half of them were selective for color, and a minority of cells (about 20%) were selective for size or direction. We correlated these physiological measurements with the anatomical location of the cells with respect to the cytochrome oxidase (CO) compartments of area V2. There was a tendency for color-selective cells to be found more frequently in the thin stripes, but color-selective cells also occurred frequently in thick stripes and inter-stripes. We found no difference in the degree of color selectivity between the different CO compartments. Furthermore, there was no negative correlation between color selectivity and selectivity for other stimulus attributes. We found many cells capable of encoding information along more than one stimulus dimension, regardless of their location with respect to the CO compartments. We suggest that area V2 plays an important role in integrating information about color, motion, and form. By this integration of stimulus attributes a cue-invariant representation of the visual world might be achieved.

To study the relationship between ocular dominance columns (ODCs) and axonal projections of individual layer 6 pyramidal neurons in the primary visual cortex, neurons were intracellularly labeled with biocytin in live slices prepared from macaque monkeys that had received an intravitreal injection of tetrodotoxin (TTX). The TTX injection indirectly causes a decrease in cytochrome oxidase (CO) expression in the cortical ODCs corresponding to the treated eye (Wong-Riley & Carroll, 1984). Sections from slices with labeled layer 6 neurons were double stained for biocytin and CO, to allow visualization of neuronal processes as well as ODCs. Twenty-seven layer 6 pyramidal neurons in ODC-labeled slices were analyzed. These neurons were classified according to the criteria of Wiser and Callaway (1996). Eight of these are class I neurons, which have dense axonal projections to the monocular layer 4C. The remaining 19 are class II neurons which project primarily to the binocular layers outside 4C. Among class I neurons, two have dense axonal arbors in layer 4Cα (type Iα), one in layer 4Cβ (type Iβ), and two throughout the depth of layer 4C (type IC). None of these neurons have ODC-specific axonal arbors. The remaining three class I neurons have focused axonal projections in layers 4Cβ and 4A (type IβA). All three appear to have axonal arbors predominantly within their home ODC in layer 4C. The axonal arbors of class II neurons do not appear to relate to ODCs in any specific fashion.

The size, pattern of terminal arborizations, and laminar specificity of individual retinogeniculate axons were studied in the macaque following injections of HRP into the optic tract. Axons that terminated in the magnocellular layers had significantly larger fiber diameters and wider terminal fields than those that terminated in the parvocellular layers. Terminal fields of magnocellular fibers spanned most of the width of their target layer, whereas those of parvocellular fibers were restricted to approximately one-half the width of their target layers; almost all terminal fields were oriented along lines of projection. All of the optic tract fibers that we examined terminated in only one layer of the lateral geniculate nucleus (GL), including a population of fine caliber fibers that project to the intercalated layers, and none had collateral projections outside the GL. The results suggest that each layer – magnocellular, parvocellular, and intercalated – receives projections from a morphologically distinct population of optic tract fibers.

As a step toward understanding the mechanism by which targets are selected for smooth-pursuit eye movements, we examined the behavior of the pursuit system when monkeys were presented with two discrete moving visual targets. Two rhesus monkeys were trained to select a small moving target identified by its color in the presence of a moving distractor of another color. Smooth-pursuit eye movements were quantified in terms of the latency of the eye movement and the initial eye acceleration profile. We have previously shown that the latency of smooth pursuit, which is normally around 100 ms, can be extended to 150 ms or shortened to 85 ms depending on whether there is a distractor moving in the opposite or same direction, respectively, relative to the direction of the target. We have now measured this effect for a 360 deg range of distractor directions, and distractor speeds of 5–45 deg/s. We have also examined the effect of varying the spatial separation and temporal asynchrony between target and distractor. The results indicate that the effect of the distractor on the latency of pursuit depends on its direction of motion, and its spatial and temporal proximity to the target, but depends very little on the speed of the distractor. Furthermore, under the conditions of these experiments, the direction of the eye movement that is emitted in response to two competing moving stimuli is not a vectorial combination of the stimulus motions, but is solely determined by the direction of the target. The results are consistent with a competitive model for smooth-pursuit target selection and suggest that the competition takes place at a stage of the pursuit pathway that is between visual-motion processing and motor-response preparation.

Several neurophysiological studies have shown that the visual cerebral cortex of macaque monkeys performing delayed match-to-sample tasks contains individual neurons whose levels of activity depend on the sample the animal is required to remember. Haenny et al. (1988) reported that the activity of neurons in area V4 of monkeys performing an orientation matching task depends on the orientation for which the animal is searching. It was proposed that these neurons contribute to a representation of the orientation being sought.

We have further characterized these neurons by recording visual responses from individual neurons during multiple behavioral tasks. Animals were trained to perform an orientation match-to-sample task using either a visual or a tactile orientation sample. In a set of 89 neurons examined using both types of sample, 25% showed statistically significant effects of sample orientation regardless of whether the sample was visual or tactile. Most of these preferred the same sample orientation in both conditions. These results allow us to specify the nature of the information signaled by these neurons more precisely than has previously been possible.

For 193 units tested using one of the matching tasks, responses were also recorded while the animal performed a simple fixation task. In this task the animal was not required to attend to the visual stimuli that were presented. A few neurons that were responsive during the matching task were silent during fixation, but a comparable number was much more responsive during fixation. Across the whole population there was no systematic change in either responsivity or selectivity for orientation under the two conditions.

We have studied the responses of MT neurons to moving gratings, spatially modulated in luminance and chromaticity. Most MT neurons responded briskly and with high contrast sensitivity to targets whose luminance was modulated, with or without added chromatic contrast. When luminance modulation was removed and only chromatic stimulation was used, the responses of all MT neurons were attenuated. Most were completely unresponsive to stimulation with targets whose modulation fell within a “null” plane in color space; these null planes varied from neuron to neuron, but all lay close to the plane of constant photometric luminance. For about a third of the neurons, there was no color direction in which responses were completely abolished; almost all of these neurons had a definite minimum response for chromatic modulation near the isoluminant plane. MT neurons that responded to isoluminant targets did so inconsistently and with poor contrast sensitivity, so that only intensely modulated targets were effective. Whereas the best thresholds of MT neurons for luminance targets are close to behavioral contrast threshold, the thresholds for isoluminant targets lie considerably above behavioral contrast threshold. Therefore, although some MT neurons do give responses to isoluminant targets, they are unlikely to be the source of the chromatic motion signals revealed behaviorally.