The Journal of neuroscience : the official journal of the Society for Neuroscience
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In numerous species of birds, individuals or species that sing larger numbers of song types have larger song control nuclei in their brains. The direction of the cause and effect relationship between the complexity of song behavior and brain space is unknown, however. The hypothesis that birds that learn large song repertoires develop large song nuclei was therefore tested with a songbird, the marsh wren (Cistothorus palustris). ⋯ When the birds were adults, the number of song types each male sang was first determined, and then the volume and certain cellular attributes of the song nuclei HVC and RA were measured. The two groups of wrens showed large behavioral differences in the size of their learned song repertoires, but did not differ in either the volumes of HVC and RA or in neuronal size, number, or density within these nuclei. These results suggest that the relationship between behavioral song complexity and brain space found in this and other species develops largely independently of early song learning experience and the later production of those songs.
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In animal models for retinitis pigmentosa (RP), rod photoreceptors show abnormal distribution of rhodopsin prior to undergoing cell death. To elucidate the steps in degeneration of human photoreceptors, immunocytochemistry was performed on donor retinas from 15 RP patients and five normal subjects. Rhodopsin immunolabeling in the normal retinas was restricted to the rod outer segments. ⋯ Neurite growth by surviving rods in the RP retinas may be a response to neurotrophic factor upregulation, loss of inhibitory factors, or changes in molecules associated with reactive Müller cells. Such changes in the retinal microenvironment may impede functional integration of transplanted photoreceptors. The contributions of the rhodopsin-positive rod neurites and abnormal cone axons to the functional abnormalities observed in RP are unknown.
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We have studied vertical synaptic pathways in two cytoarchitectonically distinct areas of rat neocortex--the granular primary somatosensory (SI) area and the agranular primary motor (MI) area--and tested their propensity to generate long-term potentiation (LTP), long-term depression (LTD), and related forms of synaptic plasticity. Extracellular and intracellular responses were recorded in layer II/III of slices in vitro while stimulating in middle cortical layers (in or around layer IV). Under control conditions, 5 Hz theta-burst stimulation produced LTP in the granular area, but not in the agranular area. ⋯ The results suggest that vertical pathways in primary somatosensory cortex and primary motor cortex express several forms of synaptic plasticity. They were equally capable of generating LTD, but the pathways in somatosensory cortex much more reliably generated LTP, unless inhibition was reduced. LTP may be more easily produced in sensory cortex because of the pronounced synaptic facilitation that occurs there during repetitive stimulation of the induction phase.(ABSTRACT TRUNCATED AT 400 WORDS)
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Comparative Study
Elements in the 5' flanking sequences of the mouse low-affinity NGF receptor gene direct appropriate CNS, but not PNS, expression in transgenic mice.
We have initiated a characterization of the cis-acting regulatory elements of the murine low-affinity NGF receptor (p75NGFR) gene. Despite studies in cultured cells that suggest the p75NGFR promoter is constitutive, a detailed analysis of this promoter in five lines of transgenic mice demonstrated a high degree of cell-type specificity: 8.4 kb of 5' flanking sequence directs expression of a lacZ reporter to retinal and CNS neurons normally expressing p75NGFR. A transgene with 470 bp of 5' flanking sequence is also expressed in the CNS, but its regulation is aberrant, with a loss of basal forebrain expression. ⋯ Further regulatory elements are possibly required for expression in at least some sensory and sympathetic neurons in the PNS and in Schwann cells. To identify potential regulatory elements in the 470 bp of 5' flanking sequence from the smaller transgene, we compared the sequences of equivalent regions from the mouse, rat, and human p75NGFR genes. This "phylogenetic footprint" identified conserved motifs potentially important for the regulation of this gene in the CNS.
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Comparative Study
A dominant role of acid pH in inflammatory excitation and sensitization of nociceptors in rat skin, in vitro.
A major role of local acidosis in long lasting excitation and sensitization of cutaneous nociceptors has recently been demonstrated. In inflamed tissue, acid pH meets with a mixture of inflammatory mediators which, by themselves, stimulate nociceptors though being subject to profound tachyphylaxis. We have mimicked this condition in a rat skin-saphenous nerve preparation in vitro which allows direct application of chemicals to the isolated receptive fields at the corium side. ⋯ Identified mechano-heat sensitive ("polymodal") C-fiber terminals (n = 36) were treated with these solutions for 5 min at 10 min intervals or for 30 min of sustained stimulation: 20 units responded to CO2-SIF, 12 to IS, whereas 27 units (75%) were excited by CO2-IS. Thus, 6 out of 15 units insensitive to either of the two basic solutions were stimulated by their combination. This enhanced effect of CO2-IS was also expressed in shorter latencies (than with CO2-SIF) and in a significantly larger mean response magnitude of the fiber population: 152 spikes with the combination versus 45 spikes evoked by IS and 93 spikes by CO2-SIF (n = 25; p < 0.002 and < 0.02, respectively, Wilcoxon test).(ABSTRACT TRUNCATED AT 250 WORDS)