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França TFA. Plasticity and redundancy in the integration of adult born neurons in the hippocampus. Neurobiol Learn Mem 2018; 155:136-142. [PMID: 30031119 DOI: 10.1016/j.nlm.2018.07.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 07/05/2018] [Accepted: 07/17/2018] [Indexed: 01/05/2023]
Abstract
Hippocampal neurogenesis (HN) is an extreme form of plasticity that inevitably rewires the hippocampal circuit and this rewiring was put forward as a possible mechanism for neurogenesis' behavioral effects. Here, I critically evaluate multiple lines of evidence to argue that structural plasticity induced by HN is, to a large extent, functionally redundant and thus has limited impact on behavior. The associative plasticity rules along with properties of immature neurons should only allow the survival of new neurons whose pre and postsynaptic partners have correlated activity, leading to functional redundancy. Moreover, non-redundant rewiring, even with its computational benefits, would impair meaningful communication between the hippocampus and other brain regions. This implies that associative plasticity rules constrain structural plasticity induced by neurogenesis, allowing the brain to balance plasticity and stability to maintain proper functioning. It also implies that behavioral effects of HN are mediated by other mechanisms apart from circuit rewiring.
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Affiliation(s)
- Thiago F A França
- Programa de Pós-graduação em Ciências Fisiológicas, Universidade Federal do Rio Grande - FURG, Rio Grande, RS, Brazil; Curso de graduação em Ciências Biológicas, Universidade Federal do Rio Grande -FURG, Rio Grande, RS, Brazil; Instituto de Ciências Biológicas, Universidade Federal do Rio Grande (FURG), Rio Grande, RS, Brazil.
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Herczeg G, Gonda A, Balázs G, Noreikiene K, Merilä J. Experimental evidence for sex-specific plasticity in adult brain. Front Zool 2015; 12:38. [PMID: 26705404 PMCID: PMC4690261 DOI: 10.1186/s12983-015-0130-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 12/15/2015] [Indexed: 01/22/2023] Open
Abstract
Background Plasticity in brain size and the size of different brain regions during early ontogeny is known from many vertebrate taxa, but less is known about plasticity in the brains of adults. In contrast to mammals and birds, most parts of a fish’s brain continue to undergo neurogenesis throughout adulthood, making lifelong plasticity in brain size possible. We tested whether maturing adult three-spined sticklebacks (Gasterosteus aculeatus) reared in a stimulus-poor environment exhibited brain plasticity in response to environmental enrichment, and whether these responses were sex-specific, thus altering the degree of sexual size dimorphism in the brain. Results Relative sizes of total brain and bulbus olfactorius showed sex-specific responses to treatment: males developed larger brains but smaller bulbi olfactorii than females in the enriched treatment. Hence, the degree of sexual size dimorphism (SSD) in relative brain size and the relative size of the bulbus olfactorius was found to be environment-dependent. Furthermore, the enriched treatment induced development of smaller tecta optica in both sexes. Conclusions These results demonstrate that adult fish can alter the size of their brain (or brain regions) in response to environmental stimuli, and these responses can be sex-specific. Hence, the degree of SSD in brain size can be environment-dependent, and our results hint at the possibility of a large plastic component to SSD in stickleback brains. Apart from contributing to our understanding of the processes shaping and explaining variation in brain size and the size of different brain regions in the wild, the results show that provision of structural complexity in captive environments can influence brain development. Assuming that the observed plasticity influences fish behaviour, these findings may also have relevance for fish stocking, both for economical and conservational purposes. Electronic supplementary material The online version of this article (doi:10.1186/s12983-015-0130-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Gábor Herczeg
- Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány Péter sétány1/C, 1117 Budapest, Hungary ; Ecological Genetics Research Unit, Department of Biosciences, FI-00014 University of Helsinki, Helsinki, Finland
| | - Abigél Gonda
- Ecological Genetics Research Unit, Department of Biosciences, FI-00014 University of Helsinki, Helsinki, Finland
| | - Gergely Balázs
- Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány Péter sétány1/C, 1117 Budapest, Hungary
| | - Kristina Noreikiene
- Ecological Genetics Research Unit, Department of Biosciences, FI-00014 University of Helsinki, Helsinki, Finland
| | - Juha Merilä
- Ecological Genetics Research Unit, Department of Biosciences, FI-00014 University of Helsinki, Helsinki, Finland
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Gonda A, Herczeg G, Merilä J. Habitat-dependent and -independent plastic responses to social environment in the nine-spined stickleback (Pungitius pungitius) brain. Proc Biol Sci 2009; 276:2085-92. [PMID: 19324759 DOI: 10.1098/rspb.2009.0026] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The influence of environmental complexity on brain development has been demonstrated in a number of taxa, but the potential influence of social environment on neural architecture remains largely unexplored. We investigated experimentally the influence of social environment on the development of different brain parts in geographically and genetically isolated and ecologically divergent populations of nine-spined sticklebacks (Pungitius pungitius). Fish from two marine and two pond populations were reared in the laboratory from eggs to adulthood either individually or in groups. Group-reared pond fish developed relatively smaller brains than those reared individually, but no such difference was found in marine fish. Group-reared fish from both pond and marine populations developed larger tecta optica and smaller bulbi olfactorii than individually reared fish. The fact that the social environment effect on brain size differed between marine and pond origin fish is in agreement with the previous research, showing that pond fish pay a high developmental cost from grouping while marine fish do not. Our results demonstrate that social environment has strong effects on the development of the stickleback brain, and on the brain's sensory neural centres in particular. The potential adaptive significance of the observed brain-size plasticity is discussed.
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Affiliation(s)
- Abigél Gonda
- Ecological Genetic Research Unit, Department of Biological and Environmental Sciences, University of Helsinki, PO Box 65, 00014 Helsinki, Finland.
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YANAI SHUICHI, OKAICHI HIROSHIGE, SUGIOKA KOZO. Dietary restriction inhibits spatial learning ability and hippocampal cell proliferation in rats. JAPANESE PSYCHOLOGICAL RESEARCH 2008. [DOI: 10.1111/j.1468-5884.2007.00360.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Pytte CL, Gerson M, Miller J, Kirn JR. Increasing stereotypy in adult zebra finch song correlates with a declining rate of adult neurogenesis. Dev Neurobiol 2007; 67:1699-720. [PMID: 17595004 DOI: 10.1002/dneu.20520] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Adult neurogenesis is often correlated with learning new tasks, suggesting that a function of incorporating new neurons is to permit new memory formation. However, in the zebra finch, neurons are added to the song motor pathway throughout life, long after the initial song motor pattern is acquired by about 3 months of age. To explore this paradox, we examined the relationship between adult song structure and neuron addition using sensitive measures of song acoustic structure. We report that between 4 and 15 months of age there was an increase in the stereotypy of fine-grained spectral and temporal features of syllable acoustic structure. These results indicate that the zebra finch continues to refine motor output, perhaps by practice, over a protracted period beyond the time when song is first learned. Over the same age range, there was a decrease in the addition of new neurons to HVC, a region necessary for song production, but not to Area X or the hippocampus, regions not essential for singing. We propose that age-related changes in the stereotypy of syllable acoustic structure and HVC neuron addition are functionally related.
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Affiliation(s)
- Carolyn L Pytte
- Department of Psychology, Queens College, Flushing, New York 11367, USA.
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Ueda S, Sakakibara S, Yoshimoto K. Effect of long-lasting serotonin depletion on environmental enrichment-induced neurogenesis in adult rat hippocampus and spatial learning. Neuroscience 2006; 135:395-402. [PMID: 16125851 DOI: 10.1016/j.neuroscience.2005.06.065] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2004] [Revised: 04/30/2005] [Accepted: 06/17/2005] [Indexed: 11/26/2022]
Abstract
The dentate gyrus of the hippocampal formation produces new neurons throughout adulthood in mammalian species. Several experimental statuses and factors regulating to neurogenesis have been identified in the adult dentate gyrus. For example, exposure to an enriched environment enhances neurogenesis in the dentate gyrus and improves hippocampus-dependent spatial learning. Furthermore, serotonin is known to influence adult neurogenesis, and learning and memory. However, the effects of long-lasting depletion of serotonin over the developing period on neurogenesis have not been investigated. Thus, we examined the influence of long-lasting serotonin depletion on environmental enrichment-induced neurogenesis and spatial memory performance. As reported previously, environmental enrichment significantly increased new neurons in the dentate gyrus. However, there was no improvement of the spatial learning test in adult rats in standard and in environmental enrichment housings. Intracisternal administration of the serotonergic neurotoxin, 5,7-dihydroxytryptamine, on postnatal day 3 apparently reduced serotonin content in the adult hippocampus without regeneration. This experimental depletion of serotonin in the hippocampus of rats housed in an enriched environment had no effect on spatial memory performance, but produced significant decreases in the number of bromodeoxyuridine-labeled new cells in the dentate gyrus. These findings indicate that newly generated cells stimulated by environmental enrichment are not critical for improvements in hippocampus-dependent learning. Furthermore, numbers of bromodeoxyuridine-labeled cells in the dentate gyrus of 5,7-dihydroxytryptamine-injected rats did not differ between 1 day and 4 weeks after bromodeoxyuridine injection. These data suggest that survival of newly generated dentate gyrus cells remains relatively constant under long-lasting serotonin depletion.
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Affiliation(s)
- S Ueda
- Department of Histology and Neurobiology, Dokkyo University School of Medicine, Mibu Tochigi 321-0293, Japan.
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Abstract
It now appears that new neurons are produced not only in the healthy adult brain but also in the brains of patients with Alzheimer's disease (AD). Although the function of new neurons in the healthy brain is unknown, there is evidence that they are involved in certain types of memory formation and that their survival is enhanced dramatically and persistently by learning experiences. The evidence that neurogenesis, or at least the expression of proteins unique to immature neurons, occurs during the late stages of AD raises the possibility that their production could be enhanced earlier in the disease process before so many neurons and memories are lost.
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Affiliation(s)
- Tracey J Shors
- Department of Psychology, Rutgers University, Piscataway, NJ 08854, USA.
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Turlejski K, Djavadian R. Life-long stability of neurons: a century of research on neurogenesis, neuronal death and neuron quantification in adult CNS. PROGRESS IN BRAIN RESEARCH 2002; 136:39-65. [PMID: 12143397 DOI: 10.1016/s0079-6123(02)36006-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In this chapter we provide an extensive review of 100 years of research on the stability of neurons in the mammalian brain, with special emphasis on humans. Although Cajal formulated the Neuronal Doctrine, he was wrong in his beliefs that adult neurogenesis did not occur and adult neurons are dying throughout life. These two beliefs became accepted "common knowledge" and have shaped much of neuroscience research and provided much of the basis for clinical treatment of age-related brain diseases. In this review, we consider adult neurogenesis from a historical and evolutionary perspective. It is concluded, that while adult neurogenesis is a factor in the dynamics of the dentate gyrus and olfactory bulb, it is probably not a major factor during the life-span in most brain areas. Likewise, the acceptance of neuronal death as an explanation for normal age-related senility is challenged with evidence collected over the last fifty years. Much of the problem in changing this common belief of dying neurons was the inadequacies of neuronal counting methods. In this review we discuss in detail implications of recent improvements in neuronal quantification. We conclude: First, age-related neuronal atrophy is the major factor in functional deterioration of existing neurons and could be slowed down, or even reversed by various pharmacological interventions. Second, in most cases neuronal degeneration during aging is a pathology that in principle may be avoided. Third, loss of myelin and of the white matter is more frequent and important than the limited neuronal death in normal aging.
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Affiliation(s)
- Kris Turlejski
- Department of Neurophysiology, Nencki Institute of Experimental Biology, 3 Pasteur Street, 02-093 Warsaw, Poland.
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Shors TJ, Townsend DA, Zhao M, Kozorovitskiy Y, Gould E. Neurogenesis may relate to some but not all types of hippocampal-dependent learning. Hippocampus 2002; 12:578-84. [PMID: 12440573 PMCID: PMC3289536 DOI: 10.1002/hipo.10103] [Citation(s) in RCA: 679] [Impact Index Per Article: 30.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The hippocampal formation generates new neurons throughout adulthood. Recent studies indicate that these cells possess the morphology and physiological properties of more established neurons. However, the function of adult generated neurons is still a matter of debate. We previously demonstrated that certain forms of associative learning can enhance the survival of new neurons and a reduction in neurogenesis coincides with impaired learning of the hippocampal-dependent task of trace eyeblink conditioning. Using the toxin methylazoxymethanol acetate (MAM) for proliferating cells, we tested whether reduction of neurogenesis affected learning and performance associated with different hippocampal dependent tasks: spatial navigation learning in a Morris water maze, fear responses to context and an explicit cue after training with a trace fear paradigm. We also examined exploratory behavior in an elevated plus maze. Rats were injected with MAM (7 mg/kg) or saline for 14 days, concurrent with BrdU, to label new neurons on days 10, 12, and 14. After treatment, groups of rats were tested in the various tasks. A significant reduction in new neurons in the adult hippocampus was associated with impaired performance in some tasks, but not with others. Specifically, treatment with the antimitotic agent reduced the amount of fear acquired after exposure to a trace fear conditioning paradigm but did not affect contextual fear conditioning or spatial navigation learning in the Morris water maze. Nor did MAM treatment affect exploration in the elevated plus maze. These results combined with previous ones suggest that neurogenesis may be associated with the formation of some but not all types of hippocampal-dependent memories.
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Affiliation(s)
- Tracey J Shors
- Department of Psychology and Center for Collaborative Neuroscience, Rutgers University, Piscataway, New Jersey 08854-8020, USA.
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Kaplan MS. Environment complexity stimulates visual cortex neurogenesis: death of a dogma and a research career. Trends Neurosci 2001; 24:617-20. [PMID: 11576677 DOI: 10.1016/s0166-2236(00)01967-6] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Over the past few years, the classic idea that no new nerve cells are born in the adult mammalian brain has finally and conclusively been refuted by the scientific community. Yet, the first indications that neurogenesis occurs in the brain of adult mammals were obtained using light and electron microscopy over two decades ago. Why this went unrecognized is described in a personal account by the researcher who pioneered those studies: Michael Kaplan.
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Gould E, Vail N, Wagers M, Gross CG. Adult-generated hippocampal and neocortical neurons in macaques have a transient existence. Proc Natl Acad Sci U S A 2001; 98:10910-7. [PMID: 11526209 PMCID: PMC58573 DOI: 10.1073/pnas.181354698] [Citation(s) in RCA: 295] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/11/2001] [Indexed: 01/12/2023] Open
Abstract
Previously we reported that new neurons are added to the hippocampus and neocortex of adult macaque monkeys. Here we compare the production and survival of adult-generated neurons and glia in the dentate gyrus, prefrontal cortex, and inferior temporal cortex. Twelve adult macaques were injected with the thymidine analogue BrdUrd, and the phenotypes of labeled cells were examined after 2 h, 24 h, 2 wk, 5 wk, 9 wk, and 12 wk by using the following immunocytochemical markers: for immature and mature neurons, class III beta-tubulin (TuJ1); for mature neurons, neuronal nuclei; for astrocytes, glial fibrillary acidic protein; and for oligodendrocytes, 2',3'-cyclic nucleotide 3' phosphodiesterase. We found that the dentate gyrus had many more BrdUrd-labeled cells than either neocortical area. Furthermore, a greater percentage of BrdUrd-labeled cells expressed a neuronal marker in the dentate gyrus than in either neocortical area. The number of new cells in all three areas declined by 9 wk after BrdUrd labeling, suggesting that some of the new cells have a transient existence. BrdUrd-labeled cells also were found in the subventricular zone and in the white matter between the lateral ventricle and neocortex; some of the latter cells were double-labeled for BrdUrd and TuJ1. Adult neocortical neurogenesis is not restricted to primates. Five adult rats were injected with BrdUrd, and after a 3-wk survival time, there were cells double-labeled for BrdUrd and either TuJ1 or neuronal nuclei in the anterior neocortex as well as the dentate gyrus.
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Affiliation(s)
- E Gould
- Department of Psychology, Princeton University, Princeton, NJ 08544, USA
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Tanapat P, Hastings NB, Rydel TA, Galea LA, Gould E. Exposure to fox odor inhibits cell proliferation in the hippocampus of adult rats via an adrenal hormone-dependent mechanism. J Comp Neurol 2001; 437:496-504. [PMID: 11503148 DOI: 10.1002/cne.1297] [Citation(s) in RCA: 282] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
To determine whether exposure to fox odor alters granule neuron production, we examined proliferating cells and their progeny in the dentate gyrus of adult male rats exposed to trimethyl thiazoline, a component of fox feces. Additionally, to determine whether this effect is adrenal hormone-mediated, we examined animals exposed to fox odor after bilateral adrenalectomy and replacement with low levels of the endogenous glucocorticoid corticosterone. Stereologic analyses of the number of 5-bromo-2'deoxyuridine (BrdU) -labeled cells revealed that exposure to fox odor but not other, nonthreatening, odors (mint or orange) rapidly decreased the number of proliferating cells in the dentate gyrus. This effect is dependent on a stress-induced rise in adrenal hormones; exposure to fox odor resulted in an increase in circulating corticosterone levels and prevention of this increase (by means of adrenalectomy plus low-dose corticosterone replacement) eliminated the suppression of cell proliferation. Examination at longer survival times revealed that the decrease in the number of new granule cells in fox odor-exposed animals was transient; a difference was still detectable at 1 week after BrdU labeling but not at 3 weeks. In both fox and sham odor-exposed animals, many new cells acquired morphologic and biochemical characteristics of mature granule neurons. The majority of these cells expressed a marker of immature granule neurons (TuJ1) by 1 week after BrdU labeling and markers of mature granule neurons (calbindin, NeuN) by 3 weeks after labeling. These findings suggest that stressful experiences rapidly diminish cell proliferation by increasing adrenal hormone levels, resulting in a transient decrease in the number of adult-generated immature granule neurons.
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Affiliation(s)
- P Tanapat
- Department of Psychology, Princeton University, Princeton, New Jersey 08544, USA.
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Abstract
For over 100 years a central assumption in the field of neuroscience has been that new neurons are not added to the adult mammalian brain. This perspective examines the origins of this dogma, its perseverance in the face of contradictory evidence, and its final collapse. The acceptance of adult neurogenesis may be part of a contemporary paradigm shift in our view of the plasticity and stability of the adult brain.
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Affiliation(s)
- C G Gross
- Department of Psychology, Green Hall, Princeton University, Princeton, New Jersey 08544, USA.
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