Genetics of Cerebellar and Neocortical Expansion in Anthropoid Primates: A Comparative Approach

What adaptive changes in brain structure and function underpin the evolution of increased cognitive performance in humans and our close relatives? Identifying the genetic basis of brain evolution has become a major tool in answering this question. Numerous cases of positive selection, altered gene expression or gene duplication have been identified that may contribute to the evolution of the neocortex, which is widely assumed to play a predominant role in cognitive evolution. However, the components of the neocortex co-evolve with other functionally interdependent regions of the brain, most notably in the cerebellum. The cerebellum is linked to a range of cognitive tasks and expanded rapidly during hominoid evolution. Here we present data that suggest that, across anthropoid primates, protein-coding genes with known roles in cerebellum development were just as likely to be targeted by selection as genes linked to cortical development. Indeed, based on currently available gene ontology data, protein-coding genes with known roles in cerebellum development are more likely to have evolved adaptively during hominoid evolution. This is consistent with phenotypic data suggesting an accelerated rate of cerebellar expansion in apes that is beyond that predicted from scaling with the neocortex in other primates. Finally, we present evidence that the strength of selection on specific genes is associated with variation in the volume of either the neocortex or the cerebellum, but not both. This result provides preliminary evidence that co-variation between these brain components during anthropoid evolution may be at least partly regulated by selection on independent loci, a conclusion that is consistent with recent intraspecific genetic analyses and a mosaic model of brain evolution that predicts adaptive evolution of brain structure.

Postnatal development of the monkey's visual system

The sudden increase of nervous activity after birth may influence the development of many parts of the brain. The visual system provides a particularly striking example of the crucial significance of birth itself in the maturation of the nervous system, for visual experience is obviously unlikely in utero. The role of the activity of afferent neurons in maintaining, even guiding, the formation of functional connections in the visual pathways has been extensively studied in a variety of species: such work in primates might give insight into the same process in man and into the aetiology of certain developmental disorders of vision. We have performed anatomical and physiological experiments on the monkey's lateral geniculate nucleus (LGN), which receives input from the optic nerves, and the primary visual cortex, to which the LGN sends its axons. In both structures there are enormous functional changes after birth, but those in the LGN seem not to depend on normal visual stimulation while those in the cortex seem crucially dependent on visual input.

Ontogeny of the nasolacrimal duct in primates: functional and phylogenetic implications

The ontogeny of the nasolacrimal ducts (NLD) and canals (NLC) are investigated in strepsirrhine and haplorhine primates. Developmental series of serially sectioned fetal, perinatal and adult specimens, in combination with juvenile and adult skulls subjected to high-resolution computed tomography, reveal that the vertical NLC and NLD of adult tarsiers and anthropoids are produced by the degeneration of a more horizontal anterior arm of the NLD that is present only transiently in haplorhines, but is maintained throughout life in strepsirrhines. This degeneration manifests as an 'unzipping' of the anterior arm by means of progressive enlargement (in a rostral direction) of a caudally placed opening of the NLD (at the base of the vertical NLC), followed by breakdown of the resulting epithelial groove. The similar mode by which the anterior arm of the membranous NLD degenerates in tarsiers and anthropoids strongly suggests that the conditions in these two taxa are homologous, and provides additional evidence for a monophyletic Haplorhini. The functional relationship between the nasolacrimal duct and the vomeronasal organ is reviewed in light of this evidence, and it is suggested that these changes in the haplorhine NLD were functionally linked to the development of anatomical haplorhinism of the oronasal complex.

Ontogenetic bases of canine dimorphism in anthropoid primates

This study tests hypotheses regarding the ontogeny of canine tooth size dimorphism in five anthropoid primate species (Saguinus fuscicollis, Macaca mulatta, Cercocebus atys, Papio hamadryas, and Mandrillus sphinx). Canine measurements and chronological age data are analyzed to determine if bimaturism, a sex difference in the age at which eruption ceases, accounts for canine tooth sexual dimorphism. Canine height measurements are evaluated through a variety of regression techniques. Results show a lack of sexual dimorphism in Saguinus. While size dimorphism is absent in the deciduous teeth of all species analyzed, the adult teeth in cercopithecines become increasingly dimorphic through ontogeny. Female adult tooth eruption regularly precedes male tooth eruption, and regression-based eruption trajectories for both sexes intersect at about the age at which the female tooth reaches adult size. Males erupt the tooth later and more rapidly than females. Males also reach a larger adult size than females by erupting the tooth for much longer periods of time. Bimaturism is primary in the production of dimorphism, but rates of eruption show modest variation. These results point to the scheduling of sexual selection through intermale competition as a primary factor determining male eruption timing, rates of eruption, and adult size. Life history factors may play a role in determining the relations between the scheduling of intrasexual competition and canine eruption. Female contributions to sexual dimorphism are apparent in these species, suggesting that similar levels of dimorphism can be attained through diverse ontogenetic pathways.

Expression of BDNF and TrkB receptor subtypes in the postnatal developing Purkinje cells of monkey cerebellum

In the previous study, we have shown the complementary expression of TrkB subtypes (TK+ and T1) in the adult monkey cerebellar cortex. In this study, to clarify when that expression pattern appeared, we examined the expressions of TrkB subtypes and its ligand brain-derived neurotrophic factor (BDNF) by immunohistochemistry and Western blot analysis. At the newborn stage, both TK+ and T1 were expressed uniformly in the cerebellar cortex. At postnatal month 3.5, the uneven expression of TrkB subtypes was observed, while the BDNF immunoreactivity was strongly detected in all regions of the cerebellar cortex. The expression patterns of TrkB subtypes and BDNF at both postnatal month 6 and year 7 were the same as those at postnatal month 3.5. Western blot analysis demonstrated that TK+ and T1 were expressed at high levels in the synaptic membrane from newborn to adult stages. Furthermore, the dimerization of TrkB subtypes changed at postnatal month 3, which was similar to the adult pattern: at the newborn stage, the TK+ and TK- homodimers; after postnatal month 3.5, the TK+ and TK- homodimers, and the TK+/TK- heterodimer. These findings suggest that the localization of TrkB subtypes in each Purkinje would be changed at postnatal month 3.5, resulting in the uneven expression of TrkB subtypes and the change of TrkB dimerization.

Cellular mechanisms in retinal vascular development

Since the pioneering work of Ashton and others, the primate retina has been thought to vascularize by a vasculogenic linkage of endothelial precursor cells. Recent investigations using specific histologic and morphologic criteria question the contribution of vasculogenesis to retinal development. Instead, in primates and mice cells previously designated as retinal angioblasts have been identified as astrocytes that form a vascular-like plexus preceding vessel invasion. Further, in primates and mice retinal vascularization proceeds via angiogenic sprouting from pre-existing vessels in all regions and stages. However, the developing retinal vasculature may utilize novel sources of endothelial cells, such as recruitment of circulating stem cells and redeployment of mural cells from regressing vessel segments. These results provide a framework for study of retinal vascular development, validate the common use of perinatal retinal models in angiogenesis research, and clarify the cellular basis of retinopathy of prematurity.

Age-related changes in GluR2 and NMDAR1 glutamate receptor subunit protein immunoreactivity in corticocortically projecting neurons in macaque and patas monkeys

A distinct subpopulation of neurons forming long corticocortical projections in the association neocortex is highly vulnerable to the degenerative process in Alzheimer's disease. However, the degree to which age-related molecular and morphologic alterations of identifiable neuronal populations reflects early cellular degeneration leading to functional deficits has not yet been fully investigated in the aging brain. We performed an immunohistochemical analysis of neurons forming short and long corticocortical projections in young and old monkeys using antibodies to the GluR2 and NMDAR1 glutamate receptor subunit proteins. Projection neurons differed in their expression of these receptor subunits, as GluR2 was less prevalent than NMDAR1 among retrogradely labeled neurons. Long and short corticocortical pathways in old animals demonstrated a considerable decrease in the proportions of projection neurons containing GluR2 and NMDAR1, an observation that was particularly consistent in the case of GluR2. No age-related differences were observed in distribution of neurofilament protein in either type of projection neurons. These data suggest that cortical neurons furnishing long and short corticocortical projections display consistent neurochemical changes during aging and that a differential decrease in cellular expression of glutamate receptor subunit proteins occurs. The fact that in aging these neurons have lower levels of GluR2 than in young individuals, but comparatively higher levels of NMDAR1 than GluR2, may render them prone to calcium-mediated excitotoxicity, which in humans may be related to the selective vulnerability of such neurons during the course of Alzheimer's disease. Also, it is apparent that age-related neuronal changes are quite subtle and involve subcellular components of the cortical circuits rather than major morphologic alterations.

Rod photoreceptor maturation does not vary with retinal eccentricity in mammalian retina

PURPOSE

Test the hypothesis that the development of mammalian rod outer segments (ROS) varies with retinal eccentricity.

METHODS

During the period of photoreceptor cell development, ROS lengths, opsin mRNA and (rhod)opsin were measured in central and peripheral retina of cows and pigmented rats. Published ROS length and/or rhodopsin data from albino rats, cows and monkeys were re-analyzed. Logistic growth curves were fitted to the newly obtained and published data. Within a species, growth in central and peripheral regions was compared.

RESULTS

The logistic growth curves fit all the data well and provide an excellent view of the developmental increases in ROS length, opsin mRNA and (rhod)opsin in each retinal region. Within a species, the growth curves for ROS length, opsin mRNA and (rhod)opsin concentration are superimposable. The age at which ROS length reaches 50% of its adult value is invariant with eccentricity. An exception to this pattern is the simian parafoveal ROS, which appears to have a delayed course of development.

CONCLUSIONS

The hypothesis is disproved. Unlike rod photoreceptor cell genesis, ROS development is invariant with retinal eccentricity. Primate parafoveal ROS appear to have a different pattern of development.

Active emmetropization--evidence for its existence and ramifications for clinical practice

There is increasing evidence from animal studies in support of the concept of an active emmetropization mechanism which has potentially important clinical ramifications for the management of refractive errors. Recent research into refractive development and emmetropization is reviewed, with emphasis given to work involving the chick, tree shrew and monkey, which represent the three most widely used animal models in this field. The findings of this research are reviewed in a clinical context. Compensatory eye growth responses to focusing errors imposed by lenses represent the most compelling evidence for active emmetropization. These observations are complemented by other evidence showing recovery from induced refractive errors such as form-deprivation myopia. Of the animals listed above, chicks show the most impressive emmetropization, being able to compensate fully (using choroidal and scleral mechanisms) to lens powers ranging from +15 D to -10 D. The range of lens powers eliciting appropriate compensatory responses is narrower in the tree shrew and monkey, and the response patterns generally are also more complex to interpret. These data relate to young animals and together indicate refractive plasticity during development. Extrapolation of these findings to humans predicts that natural emmetropization will be inhibited in neonates by early intervention with prescription lenses, and that refractive correction of myopia will lead to accelerated progression. This convincing evidence for active emmetropization warrants due consideration in developing clinical management strategies for refractive errors.

Activity and attention in zinc-deprived adolescent monkeys

Lethargy is characteristic of malnourished populations, but little is known about the biologic mechanism or consequences for cognitive performance. In the current experiment, 24-h activity patterns and performance of an attention task were studied in adolescent female monkeys (18-33 mo of age, n = 10/group) under conditions of moderate dietary zinc deprivation (2 micrograms Zn/g diet) and adequate dietary zinc (50 micrograms Zn/g). There were progressive decreases in daytime activity levels in the zinc-deprived group followed by slowing of growth around the time of the growth spurt. Attention performance was also impaired before the onset of growth retardation. Zinc-deprived monkeys failed to show the shift to later initiation of the rest phase of the diurnal cycle seen in controls in late adolescence. These data support previous findings that activity and attention can be affected during early stages of zinc deprivation before the onset of growth retardation.

Socioecology and the ontogeny of sexual size dimorphism in anthropoid primates

This study examines statistical correlations between socioecological variables (including measures of group composition, intermale competition, and habitat preference) and the ontogeny of body size sexual dimorphism in anthropoid primates. A regression-based multivariate measure of dimorphism in body weight ontogeny is derived from a sample of 37 species. Quantitative estimates of covariation between socioecological variables and this multivariate measure are evaluated. Statistically significant covariation between the ontogeny of dimorphism and socioecological variables, with the possible exception of habitat preference, is observed. Sex differences in ontogeny are lacking in species that exhibit low levels of intermale competition and are classifiable as species with monogamous/polyandrous mating systems. Among dimorphic species, two modes of dimorphic growth are apparent, which seem to be related to different kinds of group compositions. Multimale/multifemale species tend to become dimorphic through bimaturism (sex differences in duration of growth) with minimal sex differences in growth rate. Single-male/multifemale species tend to attain dimorphism through differences in rate of growth, often with limited bimaturism. Measures of intermale competition may also covary with these modes of dimorphic growth, but the relations among these variables are sometimes ambiguous. Correlations between dimorphic growth and behavioral variables may reflect alternative life history strategies in primates. Specifically, the ways in which risks faced by subadult males are distributed and the relations of these risks to growth rates seem to influence the evolution of size ontogenies. The absence of dimorphic ontogeny in some species can be tied to similar distributions of risk in each sex. In taxa that become dimorphic primarily through rate differences in growth, the lifetime distribution of risks for males may change rapidly. In contrast, males may face a pattern of uniformly changing or stable risk in species that become dimorphic through bimaturism. Finally, much variation recorded by this study remains unexplained, providing additional evidence of the need to specially examine female ontogeny before primate body size dimorphism can be satisfactorily explained.

Localization and developmental expression of the NMDA receptor subunit NR2A in the mammalian retina

The localization of the N-methyl-D-aspartate receptor subunit NR2A was studied, by using light microscopic immunocytochemistry, in the retina of adult rat, rabbit, cat, and monkey. Strong, punctate immunolabeling was observed in the inner plexiform layer indicating a synaptic localization of the NR2A subunit. The punctate labeling was concentrated in two bands corresponding to the on- and off-sublaminae of the inner plexiform layer. The punctate character of immunofluorescence suggested a synaptic localization of the receptor. This was confirmed by electron microscopy of immunostained adult rat retina. The staining was localized postsynaptic to cone bipolar cells, and only one of the two postsynaptic elements of the dyad was labeled. Staining was not observed at extrasynaptic plasma membranes. In situ hybridization of adult rat retina showed expression of the NR2A subunit in virtually all ganglion cells and displaced amacrine cells in the ganglion cell layer and in a subset of amacrine cells in the inner nuclear layer. The postnatal developmental expression of the NR2A subunit was studied in rat retina by light microscopic immunocytochemistry. Punctate immunolabeling appeared prior to eye opening, and the developmental profile of NR2A could be compatible with a role in development of circuitry in the inner plexiform layer.

Development of inferior temporal cortex in the monkey

Inferior temporal (IT) cortex is critical for visual pattern recognition in adult primates. However, the functional development of IT cortex appears to be incomplete until late in the first year of life in monkeys and probably beyond. Responses of neurons in IT are substantially weaker, of longer latency, and more susceptible to anesthesia within at least the first half year of life. In addition, refinement of connections of IT, particularly those with regions in the opposite hemisphere and with regions related to memory and attention, continues for at least several months after birth. Moreover, many of the pattern recognition functions that IT supports in adulthood themselves show a very protracted period of development, and damage to IT cortex in infancy appears to have relatively little effect on pattern recognition abilities, despite the pronounced effects of comparable damage in adulthood. These findings all suggest that IT undergoes an extended period of postnatal development, during which both visual experience and the maturation of other brain structures may contribute to the emergence of mechanisms of pattern recognition within IT. In other respects, fundamental characteristics of IT emerge quite early. For example, despite their weaker responses, IT neurons have adult-like patterns of responsiveness--including pronounced form selectivity and large bilateral receptive fields--as early as we were able to test (approximately 6 weeks). Thus, IT cortex appears to be prewired with (or predisposed to develop rapidly) neural circuitry sufficient to produce basic properties remarkably similar to those found in the adult animal. Future studies of IT cortex will need to address the development of signals related to perceptual constancies and to formation and retrieval of visual object memories, the development of interactions with other regions involved in visual recognition (particularly frontal cortex), and the specific mechanisms underlying various types of plasticity present in IT cortex in both developing and mature primates.

Ontogenetic correlates of diet in anthropoid primates

This study assesses ontogenetic correlates of diet in anthropoid primates. Associations between body weight growth, adult size, and diet are evaluated for a sample of 42 primate species, of which 8 are classifiable as "folivores." The hypothesis that folivores show a pattern of growth that differs from "nonfolivores" is tested. Ontogenetic variation is summarized through use of parametric and nonparametric regression analysis. Several analytical techniques, including broad interspecific and detailed comparisons among species of similar adult size, are applied. This investigation indicates a clear association between body weight ontogeny and diet: folivorous species grow more rapidly over a shorter duration than comprably sized nonfolivorus species. A positive correlation between adult size and diet is not unambiguously established in this sample. A threshold (at around 1 kg) below which insectivory is very common may adequately characterize the association between adult size and diet in anthropoid primates. Above this threshold, adult size does not appear to covary predictably with diet. Evolutionary correlates of the ontogenetic pattern seen in folivores may include a variety of factors. The distinctive pattern of development in folivores may relate to the profile of ecological and social risks that these species face. Morphophysiological advantages to rapid growth may relate to a need for accelerated alimentary (dental and gut) development. The implications of ontogenetic variation in folivores are discussed.

Edridge-Green Lecture. Competition and cooperation in visual development

Studies of the effect of visual deprivation on cells in the lateral geniculate nucleus (LGN) show that there are two distinct sensitive periods in the monkey during which different reactions between the visual pathways related to the two eyes predominate and requirements for recovery from deprivation differ. The first extends from birth to about 8 weeks of age. The main interaction between the pathways from the two eyes is competitive, segregation of cortical ocular dominance columns occurs during this early period and monocular deprivation results initially in hypertrophy of undeprived LGN cells, with later parallel shrinkage of both deprived and undeprived parvocellular cells. Simply reopening the closed eye produces no recovery but reverse suture is effective in reversing some of the changes. The second sensitive period starts from about 8 weeks of age, although the peak of the later sensitivity appears to be at 7-9 months of age and some effect is still present at 12-18 months. During this later phase a cooperative interaction between the pathways related to the two eyes is necessary for normal development and in the absence of this selective shrinkage of both deprived and undeprived parvocellular LGN cells occurs. Simply reopening an eye during this late sensitive period allows recovery of these cells to normal size.

Ontogenetic development of habit and memory formation in primates

Lesion studies in adult monkeys have suggested that an experience can enter into memory in two ways: as cognitive information stored in a cortico-limbo-thalamocortical system (involving the higher order sensory areas of cortex, the amygdala, hippocampus, and entorhinal cortex, the medial thalamic nuclei, or ventromedial prefrontal cortex, and the basal forebrain) and as a habit stored perhaps in a cortico-striatal system (involving the sensory cortical areas and the caudate and putamen). Our studies of behavioral development in infant monkeys as well as those in human infants provide complementary evidence by suggesting that these two systems are developmentally dissociable, in that the cognitive memory system, assessed by the delayed non-matching to sample task, appears to mature considerably more slowly than the habit system, assessed by the concurrent visual discrimination task, a notion that has also been discussed recently by others (Nadel & Zola-Morgan, 1984; Rose, 1980). Furthermore, despite the late development of the cortico-limbo-diencephalic memory system, this chapter has presented evidence that some limbic-dependent memory processes, such as those required for success on the visual paired comparison task, develop extremely early. The notion that at least one type of recognition process mediated by the limbic system is present neonatally provides new insight into the normal development of memory processes and indicates the need to identify further the memory processes and substrates that become available to an infant at different time points during maturation. Such studies will help one day to determine the immaturity of structure or function that is responsible for the intriguing phenomenon of infantile amnesia, that is, the inability to recall the stimuli or events experienced in the first few years of life.

Neuron numbers and sizes in aging brain: comparisons of human, monkey, and rodent data

One of the several sources of interest in aging animal brains is their potential as models of the aging human brain. In this review we examine whether neuron numbers and sizes change similarly in aging human, monkey and rodent brain regions which data are available from more than one species. The number of brain regions studied in more than one species is surprisingly limited. Some regions show correspondence in age-related changes between humans and selected animal models (primary visual cortex, CA1 of hippocampus). For the majority of regions the data are conflicting, even within one species (e.g., somatosensory cortex, frontal cortex, cerebellum, cholinergic forebrain areas, locus coeruleus). Although some of the conflicting data may be attributed to procedural differences, particularly when data are expressed as density changes, much must be attributed to real species and/or strain differences in rodents. We conclude that neuron numbers and sizes may show similar age-related changes in human and animal brains only for sharply defined brain regions, animal species and/or strains, and age ranges.

Patterns and rates of enamel growth in the molar teeth of early hominids

A recent study of the surface manifestation of incremental lines associated with enamel formation suggested that the crowns of early hominid incisor teeth were formed more rapidly than those of modern humans. In the absence of comparative data, the authors were forced to assume that enamel increments in fossil teeth were similar to those in modern humans. We have used evidence from the fractured surfaces of molar teeth to deduce estimates for both long- and short-period incremental growth markers within enamel in east African 'robust' australopithecine and early Homo teeth. We conclude that in these early hominids, crown formation times in posterior teeth, particularly in the large thick enamelled molar teeth of the east African 'robust' australopithecines, were shorter than those of modern humans. This evidence, considered together with data on crown and root formation times in modern apes, suggests that the posterior teeth in these hominids both formed and erupted more rapidly than those of modern man. These results have implications for attempts to assess dental and skeletal maturity in hominids.

On the eruption pattern of the permanent incisors and first permanent molars in Paranthropus

It has been claimed recently that Australopithecus exhibited a pattern of permanent tooth eruption like that of extant great apes, whereas a significantly different pattern was shared by Paranthropus and Homo (Dean, 1985). More particularly, each of the four Paranthropus specimens examined in that study was held to show advanced development and eruption of the permanent incisors relative to the first molar. It is demonstrated here that the eruption sequence that was posited for at least one of these four Paranthropus specimens (SK 61) is clearly erroneous, while the developmental/eruption sequences manifested by the other three specimens would appear to be more ambiguous than was claimed. Another juvenile specimen of Paranthropus (KNM-ER 1820) that was not included in Dean's study also does not necessarily support the eruption pattern that was said to characterize that taxon.

Evolution of the lumbosacral angle

The lumbosacral angle (LSA) was studied in 131 children ranging in age from birth to 5 years. This angle increases from an average of 20 degrees at birth to an average of 70 degrees at the age of 5 years; it remains at that level thereafter. This study demonstrates that the formation of the LSA is not related to increasing age, height, or weight. Nor do obstetrical requirements seems to play any major role in the formation of the lumbosacral angle. Rather, it appears that the development of the LSA is related to the progressive acquisition of erect posture and the ontogeny of bipedal locomotion. This angle is almost nil in the nonprimate mammals (who only infrequently stand erect). It is minimal in monkeys who occasionally assume bipedal postures and increases somewhat in living apes who engage in facultative bipedal positional behavior. In the early australopithecines, the LSA is increased over that in apes, and it reaches its maximum in Homo sapiens. Deviations from normal and healthy erect posture in Homo sapiens result in corresponding changes in the lumbosacral angle. Lumbar and sacral angles (both forming the lumbosacral angle) are almost equal in all mammalian species. Since the sacral angle of Australopithecus afarensis is approximately 15 degrees, it can be implied that its lumbosacral angle was small, thus attesting to its "imperfect" erect posture and "primitive" form of bipedal locomotion.

Femoral diaphyseal histomorphometric age determinations for the Shanidar 3, 4, 5, and 6 Neandertals and Neandertal longevity

Histomorphometric analysis of femoral diaphyseal fragments from the Shanidar 3, 4, 5, and 6 Neandertals provide age at death estimates of 41 (+/- 6.7), 36 (+/- 6.7), 40 (+/- 6.7), and 24 (+/- 6.7) years. These determinations are in agreement with previous macroscopic age assessments. Since the Shanidar 3, 4, and 5 (and slightly younger Shanidar 1) individuals are among the oldest known Neandertals, these age determinations suggest that significant postreproductive survival was rare among the Neandertals and a phenomenon primarily of anatomically modern humans.

[Comparative analysis of the neocortex during the ontogenesis of cetaceae and primates]

Comparative ontogenetic investigation of cytoarchitectonics of the cerebral neocortex has been performed in Cetacea and Primates using paraffin frontal and sagittal cerebral sections stained after Nissl. Cerebral hemispheres of dolphins, whales, monkeys and human being have been studied at various periods of prenatal development and in mature individuals. The comparison has been made at similar stages of cytoarchitectonical differentiation of the cortical plate. At two first stages of the prenatal ontogenesis (formation of the cortical plate and its differentiation into layers) there is not any principle differences between the Cetacea and Primates. Peculiarities of the cerebral cortical plate differentiation in the Cetacea (absence of the internal granular layer IV) is determined at the stage of stratification. Similar agranular character of the cerebral cortex differentiation is maintained during the whole subsequent ontogenesis in the Cetacea (heterogenetic type of the neocortex after Brodman). Absence of the layer IV in the cerebral neocortex determines some other principles in the spatial organization of the cortical-subcortical and in the intracortical connections in the Cetacea brain. This is confirmed by modern data of morphological and electrophysiological investigations. Perhaps, a comparatively more simple initial architectonics of the Cetacea brain limited the level of their functional possibilities, the latter is comparable only with anthropoid apes.

Variation in the developing root cone angle of the permanent mandibular teeth of modern man and certain fossil hominids

The radiographic appearance of the developing root apex of 461 mandibular teeth was studied using ellipsopantomographs of 77 individuals. The angle formed by the mesial and distal aspects of the developing root cone was measured for each quarter of root development in the permanent mandibular teeth of each subject. Large values for this angle in the more coronal part of the root gradually decreased towards the root apex where values were small in all teeth studied. This gradual decrease in the angle of the developing root cone is concordant with the faster increase in root length but slower rates of dentinogenesis reported for the apical region of human teeth in the literature, as the decrease is likely to reflect the increasing numbers of odontoblasts that become involved in root formation as it proceeds apically. The developing root cone angles of one of the five fossil hominid specimens studied (KMN-ER 820) fall outside the range for the developing root cone angle of the developing premolar and permanent second molar roots in modern Homo sapiens and is evidence of a faster rate of root elongation than is typical for modern man.

Surgical approaches in fetal radiography and the study of skeletal age in Macaca mulatta

The fetal surgery and fetal radiography utilized in longitudinal radiographic study of bone maturation in Macaca mulatta and their implications for fetal surgery are discussed. The novel technique of serial uterotomies and multiple exposure of the same fetus (two-week intervals) starting on 120 days of gestation as well as anesthesia and surgical procedures are presented.

The growth and development of the squirrel monkey (Saimiri Sciureus)

Squirrel monkeys of 2 subspecies, Bolivian and Colombian, were removed from their mothers on the day of birth and nursery reared for up to 2 years of age. Infants were tested weekly for 12 weeks, then monthly for 1 year, and at 2 years of age. Tests included morphology (body weight, crown-rump length, and head measurements), behavior (reflexes, activity, reaction to the surrogate), and physiology (heart rate, respiratory rate, temperature and optokinetic nystagmus). Data show some likenesses and some differences between the 2 subspecies.

Physical growth and brain development of captive-bred male and female squirrel monkeys, Saimiri sciureus

The physical growth and brain development of the captive bred male and female squirrel monkeys have shown that the male grows at a significantly faster rate with respect to these parameters in the postnatal life, starting from preweaning stage as compared to the female infant. During the prenatal life the male and the female fetuses grow at similar rates and show comparable brain development as indicated by its weight.

Implantation of cranial base metallic markers in nonhuman primates

Cranial base metallic markers are useful in growth and developmental research on the nonhuman primate model. Metallic implants aid in superimposing serial cephalometric roentgenograms in the study of craniofacial changes. They also enable measurement of linear and angular changes in the cranial base. The design of a special implant gun is described in detail. A suggested technique for placement of tantalum markers in the cranial base of nonhuman primates is discussed.

Protein and calorie malnutrition in infant cebus monkeys: growth and behavioral development during deprivation and rehabilitation

The growth and development of 32 cebus monkeys were studied during a period of insult in nutritional or rearing conditions and after rehabilitation. Eight experimental groups of four animals each were subjected to one of four diets--control, protein restricted, calorie restricted, and protein-calorie restricted, and one of two rearing conditions-partial isolation or a comparatively enriched condition-in a 4 x 2 factorial design. The period of insult from 2 to 6 months of age was followed by 6 months of rehabilitation in both diet and rearing conditions. It was found that only diet affected physical growth, but both diet and rearing affected behavioral development and exploratory behavior. Whereas calorie deficiency produced a direct effect on behavior independent of rearing conditions, protein deficiency produced an effect only in combination with rearing restriction. The effect of protein-calorie deficiency had some characteristics in common with each of the other deficiencies. Retardation in rate of behavioral development was less severe than retardation in growth, most notably in the protein-restricted, enriched-rearing group, producing animals who were behaviorally mature for their size. All groups caught up in physical growth during rehabilitation but the protein-calorie restricted groups failed to recuperate completely in exploratory behavior.

Sequence of eruption of permanent teeth and epiphyseal union in three species of African monkeys

Sequences of eruption of teeth and union of epiphyses determined for three species of African Cercopithecinae. These sequences are highly scalable and are highly comparable between among the species. Some sex differences in sequence were found within each species. The sequences of epiphyseal union in these species of Old World monkeys are very similar to published sequences in New World monkeys and other groups of higher primates. It appears that there is a single pattern common to the Anthropoidea as a whole.

Variation in age at puberty in monkeys

5 female and 3 male patas monkeys and 6 female and 3 male talapoin monkeys matured in a captive breeding colony. Age at puberty is given, and some variation discussed. The talapoin, a very small monkey, becomes adult at 4 1/2 years for females, 1 or 2 years later for males. The patas, a rather large monkey, becomes adult at 2 1/2 years, for females, and 1 or 2 years later for males. Both these ages for puberty differ from data for the rhesus monkey which has been accepted as generalizable to all Old World monkeys. Possible causes of differences between species in average age at puberty are discussed, including nutrition, environmental inconstancy, and relative size of infant and mother. It is suggested that age at first conception, a biologically more relevant index than menarche, should be considered as a potentially important adaptive variable when describing primate species.

The development and maturation of the supracrestal fibers in nonhuman primates

The transseptal fibers appear to develop independently in adjacent teeth and course toward each other meeting at the midline. Correction of rotations should be accomplished if possible before the teeth are in clinical occlusion. The thickness of the band of transeptal fibers depends on the anatomy of the interproximal space. The fibers are not continuous but interlace at the midline. In disease the transseptal fibers are destroyed first at the midline and appear to reorganize at that point. A thick fiber bundle was demonstrated to run buccolingually in the interdental space which served to connect the buccal and lingual gingiva. It was independent of the dentogingival fibersfibers. Circumferential fibers which extend from the interproximal to the labial and lingual gingiva were also noted. Poor hygiene which contributes to the formation of gingivitis and in extreme cases periodontitis causes the lysing of the gingival fibers. This study does not answer the problem of why certain rotations reoccur even after surgical transsection of the fibers. Further morphologic studies in a time sequence during rotation correction and retention are needed to determine which fibers play an exact role in the rotational relapse phenomenon.

Newborn: adult brain ratios in hominid evolution

The ratio of newborn to adult brain size varies widely in primates. These variations provide an index of the different degrees of postnatal brain growth in the different members of the primate order. The uniquely low figure for Homo sapiens indicates a greater degree of postnatal brain growth and therefore postnatal dependence and also a greater need and opportunity for social organisation. An attempt is made to determine the newborn adult brain ratio in a proto-human population, Australopithecus africanus. Two possible causes of the reduction of the ratio in hominid evolution are discussed. The first is the limiting confines of the maternal pelvis adapted primarily for orthograde progression rather than parturition. The second concerns the resultant of a set of three paired variables between the members of each pair of which there exists an allometric relationship. These are the relation between brain and body size in the adult, feto-maternal weight allometry and the relation between newborn brain-size and birth weight.

Effects of modification of the social environment on young monkey development

Experiments and observations of the effects of modifications of the social environment on the young primate's relationship with its mother and its social-sexual development have begun to delineate the large number of variables that determine and affect the attachment relationship and that are contingent upon it. Attachment can occur to a number of mother substitutes, including a dog. Early experience has special importance but young monkeys are surprisingly responsive and adaptable to substitute maternal stimuli. The quality of developing social behavior is dependent on both the quantity and quality of an attachment. We have yet to learn what are the critical component stimuli which make up an adequate early social environment for young monkeys and apes.

Physical growth of cebus monkeys (Cebus albifrons) during the first year of life

Infannt cebus monkeys, removed from their mothers shortly after birth, were reared in a primate nursery on diets of controlled nutritional quality. At regular intervals between birth and one year of age, each monkey was anesthetized, measured, and radiographed. Measurements were fitted to functions of the animal's age in days; a linear function for the first 6 to 8 weeks and a logarithmic function for the remainder of the first year. Mean constant curves have been calculated for each measure and estimates of animal variability have been obtained by interpolating sizes at given ages from regression lines fitted to the data for each animal. The maximum rate of growth was attained soon after birth. Cranial-caudal and distal-proximal maturity gradients in size attainment were observed.

Ontogeny of squirrel monkey calls under normal conditions and under acoustic isolation

Abstract

Five mothers of squirrel monkey infants isolated from other species members were muted by severence of their vocal cords during pregnancy. After delivery, mother infant pairs were brought up in an environment free of any species-specific auditory input. One of these infants underwent a deafening operation five days after birth. In addition, two infants grew up under normal conditions, i.e., exposed to species-specific vocalization. Supplemental data were acquired from six other infants, four of them normally raised and two handraised. Soundspectrograms were taken over a period up to six months in the case of the isolates and up to 17 months for the normal animals. Samples of this spectrographical material were analyzed with respect to the form of calls and to quantitative criteria, such as duration, starting frequency, mid-frequency, and end frequency of peep and cackle calls. Clear evidence is presented that the vocal repertoire of squirrel monkey infants raised under normal conditions and those raised in the absence of species-specific auditory input are virtually identical. Furthermore, comparison of the infants' vocalization with those of adult animals shows no significant differences.