Birth of Projection Neurons in Adult Avian Brain May Be Related to Perceptual or Motor Learning

Avian song learning involves memorizing and reproducing song material produced by conspecifics. In several species song repertoire size correlates with the overall volume of two song-related brain regions, the HVc (acronym used as the proper name) and the robust nucleus of the archistriatum (RA). We raised male zebra finches with two adult tutors and found that individual differences in HVc volume and neuron number correlated positively with differences in the number of tutor syllables accurately copied. These results were replicated in a second study. The relationship between RA volume and song learning was similar, but less robust. Importantly, total repertoire size (number of song syllables) did not correlate significantly with anatomical measures of either the HVc or RA. Because previous work suggests that the volume and neuron number of these regions are not regulated by song learning, it is possible that naturally occurring variation in neuron number constrains how much song material can be copied or reproduced.Comparative analyses of neuroanatomical organization imply that an expansion of neural network space permits the development of more complex behavior. However, within species there is little evidence that individual differences in learning capacity relate to differences in brain space. Perhaps such relationships are elusive because the neural circuitry involved in learning a specific skill often participates in many different behaviors. However, in oscine songbirds a network of brain regions appears to be dedicated to the learning, production, and perception of song, and there are several indications that the sizes of these regions correlate with the capacity for song learning and production. Song is a male-typical behavior, and across species, sexual dimorphisms in the anatomy of songrelated brain nuclei relate to the degree of sex difference in vocal behavior (1-3). Also, the volume of one song region, the HVc, tends to be larger in males of those species with larger song repertoires than in those that produce simpler songs (4-6). This relationship seems not to reflect species differences in perceptual demands because population differences in repertoire size of marsh wrens correlate significantly with the size of the HVc in males (who produce the songs) but not in females (7). Finally, in at least two species individual differences in HVc size correlate with individual differences in song complexity. Male canaries that produce a large number of song syllables have a larger HVc than do those that have a smaller repertoire (8), and a similar relationship is evident within two different populations of marsh wrens (4). Despite these strong brain-behavior relationships, a causal relationship between the size of individual song regions and song learning has not been established.If such correlations between brain space and song complexity reflect a causal relationship, it could be that HVc growth is influenced by how much song material is learned. Song learning is tightly coupled with the additi...

Section: Discussionmentioning

confidence: 66%

“…Song learning is tightly coupled with the addition, growth, and loss of songrelated neurons (9)(10)(11)(12)(13)(14)(15)(16), and these cellular events could be affected by the complexity of song material processed and acquired. In fact, such experience-dependent neural growth does occur in the hippocampus of food-storing passerine birds (17).…”

mentioning

confidence: 99%

Individual variation in neuron number predicts differences in the propensity for avian vocal imitation

Ward

Nordeen²,

Nordeen³

1998

“…1b. Only the RA-projecting neurons are replaced in adult birds (22), even when neuron death is induced (3). No differences were seen between presurgery and postsurgery song recordings (data not shown), indicating that neuron function was unaffected.…”

Section: Methodsmentioning

confidence: 92%

Replaceable neurons and neurodegenerative disease share depressed UCHL1 levels

Lombardino

Hertel

et al. 2005

Self Cite

Might there be systematic differences in gene expression between neurons that undergo spontaneous replacement in the adult brain and those that do not? We first explored this possibility in the high vocal center (HVC) of male zebra finches by using a combination of neuronal tracers, laser capture microdissection, and RNA profiling. HVC has two kinds of projection neurons, one of which continues to be produced and replaced in adulthood. HVC neurons of the replaceable kind showed a consistent and robust underexpression of the deubiquitination gene ubiquitin carboxyl-terminal hydrolase (UCHL1) that is involved with protein degradation. Singing behavior, known to increase the survival of adult-born HVC neurons in birds, significantly up-regulated the levels of UCHL1 in the replaceable neurons but not in their equally active nonreplaceable counterparts. We then looked in the mouse brain and found relatively low UCHL1 expression in granule neurons of the hippocampus and olfactory bulb, two well characterized types of replaceable neurons in mammals. UCHL1 dysfunction has been associated with neurodegeneration in Parkinson's, Alzheimer's, and Huntington's disease patients. In all these instances, reduced UCHL1 function may jeopardize the survival of CNS neurons.adult neurogenesis ͉ gene expression ͉ laser capture microdissection ͉ neurodegeneration

“…Although the importance of identifying factors that regulate adult neurogenesis is clear, there is still significant debate about the functional implications of this phenomenon. It has been proposed that neurogenesis plays a role in cognitive aspects of hippocampal functioning (6,7,55,56). For example, evidence suggests that the survival of newly born cells in the adult dentate gyrus is positively influenced by hippocampal-dependent learning (7,55).…”

Section: Discussionmentioning

confidence: 99%

Opiates inhibit neurogenesis in the adult rat hippocampus

Eisch

Barrot

Schad

et al. 2000

539

384

Recent work implicates regulation of neurogenesis as a form of plasticity in the adult rat hippocampus. Given the known effects of opiates such as morphine and heroin on hippocampal function, we examined opiate regulation of neurogenesis in this brain region. Chronic administration of morphine decreased neurogenesis by 42% in the adult rat hippocampal granule cell layer. A similar effect was seen in rats after chronic self-administration of heroin. Opiate regulation of neurogenesis was not mediated by changes in circulating levels of glucocorticoids, because similar effects were seen in rats that received adrenalectomy and corticosterone replacement. These findings suggest that opiate regulation of neurogenesis in the adult rat hippocampus may be one mechanism by which drug exposure influences hippocampal function. Opiates are among the most commonly abused illegal drugs in the United States (1, 2). Several reports suggest that chronic exposure to opiates, such as morphine and heroin, can result in cognitive deficits (3-5). For example, heroin users have poorer performance on attention, verbal fluency, and memory tasks than controls (3), and rats chronically exposed to morphine show impaired acquisition of reference memory (5). Such findings suggest that long-term opiate use may produce maladaptive plasticity in brain structures involved in learning and memory, such as the hippocampus.One aspect of the mammalian hippocampus that recently has received considerable attention is the birth of new neurons that occurs in the dentate gyrus throughout the lifetime of the animal (6-8). This phenomenon has been described in rodents, nonhuman primates, and, most recently, humans (9-12). Research suggests that cells are born in the subgranular zone of the dentate gyrus, migrate into the granule cell layer and express neuronal markers (8,13,14), extend processes to CA3 pyramidal neurons (15, 16), receive synaptic connections (10, 13, 16), and demonstrate long-term potentiation (17). Although a growing number of pharmacological and environmental manipulations have been shown to influence adult neurogenesis, the functional implication of the newly born neurons remains poorly understood (see Discussion). It has been proposed that the thousands of new neurons born each day in the adult rodent hippocampus may contribute to a variety of hippocampal-related functions, including learning and memory (6, 7).Drugs of abuse, including opiates, can significantly alter the birth of neural progenitors during early stages of development (18)(19)(20), yet it remains unclear what effect drug exposure has on the birth of neural progenitors in the mature brain. Here we examine the consequence of long-term opiate exposure on the birth of new neurons in the adult rat hippocampus. Materials and MethodsAnimals and Drug Treatment. Adult, male Sprague-Dawley rats (initial weight 275-300 g; Charles River Breeding Laboratories) were used for all experiments. For chronic morphine treatment, rats were given sham surgery (n ϭ 10) or a morphine pellet (75 ...