Neuroscience
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The acquisition, production and maintenance of song by oscine birds is a form of audition-dependent learning that, in many ways, resembles the process by which humans learn to speak. In songbirds, the generation of structured song is determined by the activity of two interconnected neuronal pathways (the anterior forebrain pathway and the vocal motor pathway), each of which contains a number of discrete nuclei that together form the song system. It is becoming increasingly evident that inhibitory GABAergic mechanisms are indispensable in counterbalancing the excitatory actions of glutamate and, thus, likely shape the neuronal firing patterns of neurons within this network. ⋯ Our findings show, remarkably, that the gamma4-subunit transcript is highly enriched in the major nuclei of the song system, including the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the medial magnocellular nucleus of the anterior nidopallium (MMAN), Area X, the robust nucleus of the arcopallium (RA) and the HVC (used as the proper name), as well as Field L, which innervates the area surrounding HVC. In summary, we have demonstrated the presence of the mRNA for the gamma4 subunit of the GABA(A) receptor, the major inhibitory receptor in brain, in most of the nuclei of the two neural circuits that mediate song production in the zebra finch. This not only marks the beginning of the characterization of the GABA(A) receptor subtype(s) that mediates the actions of GABA in the song system but it also provides a robust molecular marker with which to distinguish song system-specific brain structures.
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Mole-rat species within the family Bathyergidae exhibit a wide range of reproductive strategies and social systems. Various forms of reproductive suppression are displayed within this family: in the solitary species, breeding is suspended for part of the year and in the social species, reproduction is suppressed in subordinate animals. This study investigated the gonadotrophin-releasing hormone 1 (GnHR-1) systems of breeding and non-breeding solitary Cape mole-rats and social Natal mole-rats for possible inter- and/or intra-species differences. ⋯ In female and male Natal mole-rats, GnRH-1-immunoreactivity in the median eminence is less dense in the reproductive animals; no such difference was found in Cape mole-rats between the breeding and non-breeding seasons. These immunohistochemical results are discussed in the light of earlier studies which identified no functional neuroendocrine impediments underlying regulated reproduction in either Cape or Natal mole-rats. The cumulative findings suggest that the principal factors determining seasonal or socially induced suppression of reproduction in these species are behavioral rather than neuroendocrine.
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In humans and nonhuman primates, the structure and function of frontal cortical regions of the brain are not completely developed until early adulthood. How this cortical development affects cognitive function continues to be elucidated. To that end, this experiment tested the ability of juvenile and adult rhesus monkeys to perform a cognitive task that is dependent upon intact frontal cortical function for optimal performance. ⋯ These results indicate juveniles committed more perseverative errors and more errors on the set-formation and set-shifting components of the ID/ED task. The developmental stage of the juvenile monkeys corresponds to roughly 5 to 6-year-old children, and these results are consistent with performance of human children and adults on similar ID/ED tests and on several other tests of attentional set-shifting or attentional flexibility. Furthermore, these results are consistent with the ongoing development of frontal cortical structures relating to ongoing cognitive development in nonhuman primates.
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The relative distribution of the excitatory amino acid transporter 2 (EAAT2) between synaptic terminals and astroglia, and the importance of EAAT2 for the uptake into terminals is still unresolved. Here we have used antibodies to glutaraldehyde-fixed d-aspartate to identify electron microscopically the sites of d-aspartate accumulation in hippocampal slices. About 3/4 of all terminals in the stratum radiatum CA1 accumulated d-aspartate-immunoreactivity by an active dihydrokainate-sensitive mechanism which was absent in EAAT2 glutamate transporter knockout mice. ⋯ Most of the remaining immunoreactivity (8%) was found in axons where it was distributed in a plasma membrane surface area several times larger than that of astroglia. This explains why the densities of neuronal EAAT2 are low despite high levels of mRNA in CA3 pyramidal cell bodies, but not why EAAT2 in terminals account for more than half of the uptake of exogenous substrate by hippocampal slice preparations. This and the relative amount of terminal versus glial uptake in the intact brain remain to be discovered.