Juri Suzuki

Descent of the larynx in chimpanzee infants

The human larynx descends during infancy and the early juvenile periods, and this greatly contributes to the morphological foundations of speech development. This developmental phenomenon is believed to be unique to humans. This concept has formed a basis for paleoanthropological studies on the origin and evolution of human speech. We used magnetic resonance imaging to study the development of three living chimpanzees and found that their larynges also descend during infancy, as in human infants. This descent was completed primarily through the rapid descent of the laryngeal skeleton relative to the hyoid, but it was not accompanied by the descent of the hyoid itself. The descent is possibly associated with developmental changes of the swallowing mechanism. Moreover, it contributes physically to an increased independence between the processes of phonation and articulation for vocalization. Thus, the descent of the larynx and the morphological foundations for speech production must have evolved in part during hominoid evolution, and not in a single shift during hominid evolution.

Differential Prefrontal White Matter Development in Chimpanzees and Humans

A comparison of developmental patterns of white matter (WM) within the prefrontal region between humans and nonhuman primates is key to understanding human brain evolution. WM mediates complex cognitive processes and has reciprocal connections with posterior processing regions [1, 2]. Although the developmental pattern of prefrontal WM in macaques differs markedly from that in humans [3], this has not been explored in our closest evolutionary relative, the chimpanzee. The present longitudinal study of magnetic resonance imaging scans demonstrated that the prefrontal WM volume in chimpanzees was immature and had not reached the adult value during prepuberty, as observed in humans but not in macaques. However, the rate of prefrontal WM volume increase during infancy was slower in chimpanzees than in humans. These results suggest that a less mature and more protracted elaboration of neuronal connections in the prefrontal portion of the developing brain existed in the last common ancestor of chimpanzees and humans, and that this served to enhance the impact of postnatal experiences on neuronal connectivity. Furthermore, the rapid development of the human prefrontal WM during infancy may help the development of complex social interactions, as well as the acquisition of experience-dependent knowledge and skills to shape neuronal connectivity.

Lactation in the Japanese monkey (Macaca fuscata): Yield and composition of milk and nipple preference of young

Changes in the yield and chemical composition of milk, together with those in the nipple preferences and suckling behavior of infants, were followed in three lactating Japanese monkeys rearing single infants under laboratory conditions at monthly intervals for six months after their paturition. Milk accumulating in the mammary glands during a 4-hr separation of the infant was collected by milking under anesthesia with the aid of a physiological dose of oxytocin.The stage of full lactation appeared to last for about two or three months after parturition. The milk at this stage contained 14.0% of total solids, 4.2% of lipids, 1.6% of proteins, and 6.2% of lactose, and the concentrations of Na, Cl, and K in the milk water were 7.4, 15.1, and 5.9 mM, respectively. From the 9th or 13th week of lactation onwards, according to the individual, the milk composition changed appreciably and the time during which the young left hold of the mothers nipple also increased. The weaning of young in the Japanese monkey appears to begin during the 3rd or 4th month of age. The milk production then wanes and almost ceases by the end of the 6th month. The nipple preference of the young was generally established completely by the 3rd, or the 8th at latest, week of age. However, no difference in either the yield or composition of the milk secreted was found between the mammary glands of the preferred and non-preferred sides. Without regard to the apparent nipple preference, infants seem to ingest milk from the mothers breasts of both sides.Accurate estimation of the rate of milk production could not be achieved, but the rate was expected to be 150–200 g/day at the height of lactation based on the relation between the mothers body weight and the milk production rates of other primate species. A disparity was noted between the observed and estimated values for the milk yield, and a diurnal fluctuation in the milk secretion of the Japanese monkey was inferred.

Cortisol analysis of hair of captive chimpanzees (Pan troglodytes).

In addition to behavioral evaluations, stress assessments are also important for measuring animal welfare. Assessments of long-term stress are particularly important given that prolonged stress can affect physical health and reproduction. The use of hair cortisol as a marker of long-term stress has been increasing, but there has not yet been any report on the use of such methods with chimpanzees. Therefore, the purpose of this study was to establish and validate a methodology for analyzing hair cortisol in captive chimpanzees. In the first experiment, hair was removed from the arms of nine chimpanzees living in the Kumamoto Sanctuary (KS) and the regrown hair was sampled 3 months later. Fecal samples were collected periodically during the hair-growth period. The results showed that hair cortisol level was positively correlated with the rate of receiving aggression. Although the correlation between hair and fecal cortisol levels was not significant, the individual with the highest hair cortisol concentration also had the highest fecal cortisol concentration. These results suggest that hair cortisol may reflect long-term stress in chimpanzees. In the second experiment, we investigated the physiological factors affecting hair cortisol concentrations. We cut hair from the arms, sides, and backs of 25 chimpanzees living at the KS and the Primate Research Institute. The results revealed that cortisol varied based on source body part and hair whiteness. Therefore, we recommend that hair should always be collected from the same body part and that white hair should be avoided as much as possible.

Developmental patterns of chimpanzee cerebral tissues provide important clues for understanding the remarkable enlargement of the human brain.

Developmental prolongation is thought to contribute to the remarkable brain enlargement observed in modern humans (Homo sapiens). However, the developmental trajectories of cerebral tissues have not been explored in chimpanzees (Pan troglodytes), even though they are our closest living relatives. To address this lack of information, the development of cerebral tissues was tracked in growing chimpanzees during infancy and the juvenile stage, using three-dimensional magnetic resonance imaging and compared with that of humans and rhesus macaques (Macaca mulatta). Overall, cerebral development in chimpanzees demonstrated less maturity and a more protracted course during prepuberty, as observed in humans but not in macaques. However, the rapid increase in cerebral total volume and proportional dynamic change in the cerebral tissue in humans during early infancy, when white matter volume increases dramatically, did not occur in chimpanzees. A dynamic reorganization of cerebral tissues of the brain during early infancy, driven mainly by enhancement of neuronal connectivity, is likely to have emerged in the human lineage after the split between humans and chimpanzees and to have promoted the increase in brain volume in humans. Our findings may lead to powerful insights into the ontogenetic mechanism underlying human brain enlargement.

Hepatitis E Virus Outbreak in Monkey Facility, Japan

An outbreak of hepatitis E virus occurred in an outdoor monkey breeding facility in Japan during 2004–2006. Phylogenetic analysis indicated that this virus was genotype 3. This virus was experimentally transmitted to a cynomolgus monkey. Precautions should be taken by facility personnel who work with monkeys to prevent infection.

Adolescent Growth and Development in Japanese Macaques (Macaca fuscata) : Punctuated Adolescent Growth Spurt by Season

Adolescent growth of Japanese macaques (Macaca fuscata) was studied. Their growth is composed both of a seasonal cycle of acceleration and deceleration and of linear increases. There is a major growth spurt in linear dimension and body weight at the beginning of the breeding season of the third and fourth year of life in females and males respectively, when they mature reproductively. They show additional accelerated growth in the following year(s). These growth spurts, in total, are considered to correspond with the adolescent growth spurt in humans. Adolescent growth of Japanese macaques is characterized by a punctuation by slower growth and a later start, which is considered to be the product of adaptation to a strongly seasonal environment.

Oestrogen‐Induced Activation of Preoptic Kisspeptin Neurones May be Involved in the Luteinising Hormone Surge in Male and Female Japanese Monkeys

The oestrogen‐induced luteinising hormone (LH) surge is evident in male primates, including humans, whereas male rodents never show the LH surge, even when treated with a preovulatory level of oestrogen. This suggests that the central mechanism governing reproductive hormones in primates is different from that in rodents. The present study aimed to investigate whether male Japanese monkeys conserve a brain mechanism mediating the oestrogen‐induced LH surge via activation of kisspeptin neurones. Adult male and female Japanese monkeys were gonadectomised and then were treated with oestradiol‐17β for 2 weeks followed by a bolus injection of oestradiol benzoate. Both male and female monkeys showed an oestrogen‐induced LH surge. In gonadectomised monkeys sacrificed just before the anticipated time of the LH surge, oestrogen treatment significantly increased the number of KISS1‐expressing cells in the preoptic area (POA) and enhanced the expression of c‐fos in POA KISS1‐positive cells of males and females. The oestrogen treatment failed to induce c‐fos expression in the arcuate nucleus (ARC) kisspeptin neurones in both sexes just prior to LH surge onset. Thus, kisspeptin neurones in the POA but not in the ARC might be involved in the positive‐feedback action of oestrogen that induces LH surge in male Japanese monkeys, as well as female monkeys. The present results indicate that oestrogen‐induced activation of POA kisspeptin neurones may contribute to the LH surge generation in both sexes. The conservation of the LH surge generating system found in adult male primates, unlike rodents, could be a result of the capability of oestrogen to induce POA kisspeptin expression and activation.

Tetraparesis resembling acute transverse myelitis in a captive chimpanzee (Pan troglodytes): long-term care and recovery.

Background  A 24‐year‐old, male chimpanzee (Pan troglodytes) developed acute tetraparesis. Magnetic resonance imaging showed a diffuse T2‐weighted hyperintensive lesion, indicating inflammation at the C1–2 level. All infective, autoimmune, and vascular investigations were unremarkable.

Analysis of hair cortisol levels in captive chimpanzees: Effect of various methods on cortisol stability and variability

Graphical abstract Summary of the experimental process. The items colored blue affected the results of the hair cortisol analysis in the present study. The stippled items were found to affect the results obtained in our previous study [1].