Selective lesion of the hippocampus increases the differentiation of immature neurons in the monkey amygdala

A large population of immature neurons is present in the ventromedial portion of the adult primate amygdala, a region that receives substantial direct projections from the hippocampal formation. Here, we show the effects of neonatal (n = 8) and adult (n = 6) hippocampal lesions on the populations of mature and immature neurons in the paralaminar, lateral, and basal nuclei of the adult monkey amygdala. Compared with unoperated controls (n = 7), the number of mature neurons was about 70% higher in the paralaminar nucleus of neonate- and adult-lesioned monkeys, and 40% higher in the lateral and basal nuclei of neonate-lesioned monkeys. The number of immature neurons in the paralaminar nucleus was 40% higher in neonate-lesioned monkeys and 30% lower in adult-lesioned monkeys. Similar changes in neuron numbers were also found in two monkeys with nonexperimental, selective, bilateral hippocampal damage. These changes in neuron numbers following hippocampal lesions appear to reflect the differentiation of immature neurons present in the paralaminar nucleus. After adult lesions, the differentiation of immature neurons was essentially restricted to the paralaminar nucleus and was associated with a decrease in the population of immature neurons. In contrast, after neonatal lesions, the differentiation of immature neurons involved the paralaminar, lateral, and basal nuclei. It was associated with an increase in the population of immature neurons in the paralaminar nucleus. Such lesion-induced neuronal plasticity sheds new light on potential mechanisms that may facilitate functional recovery following focal brain injury

Stereological analysis of the rat and monkey amygdala

The amygdala is part of a neural network that contributes to the regulation of emotional behaviors. Rodents, especially rats, are used extensively as model organisms to decipher the functions of specific amygdala nuclei, in particular in relation to fear and emotional learning. Analysis of the role of the nonhuman primate amygdala in these functions has lagged work in the rodent but provides evidence for conservation of basic functions across species. Here we provide quantitative information regarding the morphological characteristics of the main amygdala nuclei in rats and monkeys, including neuron and glial cell numbers, neuronal soma size, and individual nuclei volumes. The volumes of the lateral, basal, and accessory basal nuclei were, respectively, 32, 39, and 39 times larger in monkeys than in rats. In contrast, the central and medial nuclei were only 8 and 4 times larger in monkeys than in rats. The numbers of neurons in the lateral, basal, and accessory basal nuclei were 14, 11, and 16 times greater in monkeys than in rats, whereas the numbers of neurons in the central and medial nuclei were only 2.3 and 1.5 times greater in monkeys than in rats. Neuron density was between 2.4 and 3.7 times lower in monkeys than in rats, whereas glial density was only between 1.1 and 1.7 times lower in monkeys than in rats. We compare our data in rats and monkeys with those previously published in humans and discuss the theoretical and functional implications that derive from our quantitative structural findings

Stereological analysis of the rat and monkey amygdala

The amygdala is part of a neural network that contributes to the regulation of emotional behaviors. Rodents, especially rats, are used extensively as model organisms to decipher the functions of specific amygdala nuclei, in particular in relation to fear and emotional learning. Analysis of the role of the nonhuman primate amygdala in these functions has lagged work in the rodent but provides evidence for conservation of basic functions across species. Here we provide quantitative information regarding the morphological characteristics of the main amygdala nuclei in rats and monkeys, including neuron and glial cell numbers, neuronal soma size, and individual nuclei volumes. The volumes of the lateral, basal, and accessory basal nuclei were, respectively, 32, 39, and 39 times larger in monkeys than in rats. In contrast, the central and medial nuclei were only 8 and 4 times larger in monkeys than in rats. The numbers of neurons in the lateral, basal, and accessory basal nuclei were 14, 11, and 16 times greater in monkeys than in rats, whereas the numbers of neurons in the central and medial nuclei were only 2.3 and 1.5 times greater in monkeys than in rats. Neuron density was between 2.4 and 3.7 times lower in monkeys than in rats, whereas glial density was only between 1.1 and 1.7 times lower in monkeys than in rats. We compare our data in rats and monkeys with those previously published in humans and discuss the theoretical and functional implications that derive from our quantitative structural findings

Stereological analysis of the rat and monkey amygdala

The amygdala is part of a neural network that contributes to the regulation of emotional behaviors. Rodents, especially rats, are used extensively as model organisms to decipher the functions of specific amygdala nuclei, in particular in relation to fear and emotional learning. Analysis of the role of the nonhuman primate amygdala in these functions has lagged work in the rodent but provides evidence for conservation of basic functions across species. Here we provide quantitative information regarding the morphological characteristics of the main amygdala nuclei in rats and monkeys, including neuron and glial cell numbers, neuronal soma size, and individual nuclei volumes. The volumes of the lateral, basal, and accessory basal nuclei were, respectively, 32, 39, and 39 times larger in monkeys than in rats. In contrast, the central and medial nuclei were only 8 and 4 times larger in monkeys than in rats. The numbers of neurons in the lateral, basal, and accessory basal nuclei were 14, 11, and 16 times greater in monkeys than in rats, whereas the numbers of neurons in the central and medial nuclei were only 2.3 and 1.5 times greater in monkeys than in rats. Neuron density was between 2.4 and 3.7 times lower in monkeys than in rats, whereas glial density was only between 1.1 and 1.7 times lower in monkeys than in rats. We compare our data in rats and monkeys with those previously published in humans and discuss the theoretical and functional implications that derive from our quantitative structural findings

Stereological analysis of the rat and monkey amygdala

The amygdala is part of a neural network that contributes to the regulation of emotional behaviors. Rodents, especially rats, are used extensively as model organisms to decipher the functions of specific amygdala nuclei, in particular in relation to fear and emotional learning. Analysis of the role of the nonhuman primate amygdala in these functions has lagged work in the rodent but provides evidence for conservation of basic functions across species. Here we provide quantitative information regarding the morphological characteristics of the main amygdala nuclei in rats and monkeys, including neuron and glial cell numbers, neuronal soma size, and individual nuclei volumes. The volumes of the lateral, basal, and accessory basal nuclei were, respectively, 32, 39, and 39 times larger in monkeys than in rats. In contrast, the central and medial nuclei were only 8 and 4 times larger in monkeys than in rats. The numbers of neurons in the lateral, basal, and accessory basal nuclei were 14, 11, and 16 times greater in monkeys than in rats, whereas the numbers of neurons in the central and medial nuclei were only 2.3 and 1.5 times greater in monkeys than in rats. Neuron density was between 2.4 and 3.7 times lower in monkeys than in rats, whereas glial density was only between 1.1 and 1.7 times lower in monkeys than in rats. We compare our data in rats and monkeys with those previously published in humans and discuss the theoretical and functional implications that derive from our quantitative structural findings

Stereological analysis of the rat and monkey amygdala

The amygdala is part of a neural network that contributes to the regulation of emotional behaviors. Rodents, especially rats, are used extensively as model organisms to decipher the functions of specific amygdala nuclei, in particular in relation to fear and emotional learning. Analysis of the role of the nonhuman primate amygdala in these functions has lagged work in the rodent but provides evidence for conservation of basic functions across species. Here we provide quantitative information regarding the morphological characteristics of the main amygdala nuclei in rats and monkeys, including neuron and glial cell numbers, neuronal soma size, and individual nuclei volumes. The volumes of the lateral, basal, and accessory basal nuclei were, respectively, 32, 39, and 39 times larger in monkeys than in rats. In contrast, the central and medial nuclei were only 8 and 4 times larger in monkeys than in rats. The numbers of neurons in the lateral, basal, and accessory basal nuclei were 14, 11, and 16 times greater in monkeys than in rats, whereas the numbers of neurons in the central and medial nuclei were only 2.3 and 1.5 times greater in monkeys than in rats. Neuron density was between 2.4 and 3.7 times lower in monkeys than in rats, whereas glial density was only between 1.1 and 1.7 times lower in monkeys than in rats. We compare our data in rats and monkeys with those previously published in humans and discuss the theoretical and functional implications that derive from our quantitative structural findings

Using recognition testing to support semantic learning in developmental amnesia

Patients with developmental amnesia (DA) have suffered hippocampal damage in infancy and subsequently shown poor episodic memory, but good semantic memory. It is not clear how patients with DA learn semantic information in the presence of episodic amnesia. However, patients with DA show good recognition memory and it is possible that semantic learning may be supported by recognition. Building on previous work, we compared two methods for supporting semantic learning in DA; recognition-learning and recall-learning. In each condition, a patient with DA (aged 8 years) was presented with semantic information in animated videos. After each presentation of a video, learning was supported by an immediate memory test. Two videos were paired with a cued recall test. Another two videos were paired with a multiple-choice test to enable recognition-based learning. The outcome measure was semantic recall performance after a short delay of 30 min and a long delay of one week. Results showed a benefit of recognition-learning compared to recall-learning on cued recall in the patient with DA (76% vs. 35%). This finding indicates that young people with severe hippocampal damage can utilize recognition to support semantic learning. This has implications for the support of school-aged children with episodic memory difficulties

Postnatal development of the entorhinal cortex: a stereological study in macaque monkeys

The entorhinal cortex is the main gateway for interactions between the neocortex and the hippocampus. Distinct regions, layers, and cells of the hippocampal formation exhibit different profiles of structural and molecular maturation during postnatal development. Here, we provide estimates of neuron number, neuronal soma size, and volume of the different layers and subdivisions of the monkey entorhinal cortex (Eo, Er, Elr, Ei, Elc, Ec, Ecl) during postnatal development. We found different developmental changes in neuronal soma size and volume of distinct layers in different subdivisions, but no changes in neuron number. Layers I and II developed early in most subdivisions. Layer III exhibited early maturation in Ec and Ecl, a two‐ step/early maturation in Ei and a late maturation in Er. Layers V and VI exhibited an early maturation in Ec and Ecl, a two‐step and early maturation in Ei, and a late maturation in Er. Neuronal soma size increased transiently at 6 months of age and decreased thereafter to reach adult size, except in Layer II of Ei, and Layers II and III of Ec and Ecl. These findings support the theory that different hippocampal circuits exhibit distinct developmental profiles, which may subserve the emergence of different hippocampus‐dependent memory processes. We discuss how the early maturation of the caudal entorhinal cortex may contribute to path integration and basic allocentric spatial processing, whereas the late maturation of the rostral entorhinal cortex may contribute to the increased precision of allocentric spatial representations and the temporal integration of individual items into episodic memories

Postnatal development of the amygdala: a stereological study in rats

The amygdala is the central component of a functional brain system regulating fear and emotional behaviors. Studies of the ontogeny of fear behaviors reveal the emergence of distinct fear responses at different postnatal ages. Here, we performed a stereological analysis of the rat amygdala to characterize the cellular changes underlying its normal structural development. Distinct amygdala nuclei exhibited different patterns of postnatal development, which were largely similar to those we have previously shown in monkeys. The combined volume of the lateral, basal, and accessory basal nuclei increased by 113% from 1 to 3 weeks of age and by an additional 33% by 7 months of age. The volume of the central nucleus increased only 37% from 1 to 2 weeks of age and 38% from 2 weeks to 7 months. At 1 week of age, the medial nucleus was 77% of the 7-month-old's volume and exhibited a constant, marginal increase until 7 months. Neuron number did not differ in the amygdala from 1 week to 7 months of age. In contrast, astrocyte number decreased from 3 weeks to 2 months of age in the whole amygdala. Oligodendrocyte number increased in all amygdala nuclei from 3 weeks to 7 months of age. Our findings revealed that distinct amygdala nuclei exhibit different developmental profiles and that the rat amygdala is not fully mature for an extended period postnatally. We identified different periods of postnatal development of distinct amygdala nuclei and cellular components, which are concomitant with the ontogeny of different fear and emotional behaviors

Postnatal development of the amygdala: A stereological study in macaque monkeys

Abnormal development of the amygdala has been linked to several neurodevelopmental disorders, including schizophrenia and autism. However, the postnatal development of the amygdala is not easily explored at the cellular level in humans. Here, we performed a stereological analysis of the macaque monkey amygdala in order to characterize the cellular changes underlying its normal structural development in primates. The lateral, basal and accessory basal nuclei exhibited the same developmental pattern, with a large increase in volume between birth and three months of age, followed by slower growth continuing beyond one year of age. In contrast, the medial nucleus was near adult size at birth. At birth, the volume of the central nucleus was half of the adult value; this nucleus exhibited significant growth even after one year of age. Neither neuronal soma size, nor neuron or astrocyte numbers changed during postnatal development. In contrast, oligodendrocyte numbers increased substantially, in parallel with an increase in amygdala volume, after three months of age. At birth, the paralaminar nucleus contained a large pool of immature neurons that gradually developed into mature neurons, leading to a late increase in the volume of this nucleus. Our findings revealed that distinct amygdala nuclei exhibit different developmental profiles and that the amygdala is not fully mature for some time postnatally. We identified different periods during which pathogenic factors might lead to the abnormal development of distinct amygdala circuits, which may contribute to different human neurodevelopmental disorders associated with alterations of amygdala structure and functions