Effect of varying the intensity and train frequency of forelimb and cerebellar mossy fiber conditioned stimuli on the latency of conditioned eye-blink responses in decerebrate ferrets.
(25/1624)
To study the role of the mossy fiber afferents to the cerebellum in classical eye-blink conditioning, in particular the timing of the conditioned responses, we compared the effects of varying a peripheral conditioned stimulus with the effects of corresponding variations of direct stimulation of the mossy fibers. In one set of experiments, decerebrate ferrets were trained in a Pavlovian eye-blink conditioning paradigm with electrical forelimb train stimulation as conditioned stimulus and electrical periorbital stimulation as the unconditioned stimulus. When stable conditioning had been achieved, the effect of increasing the intensity or frequency of the forelimb stimulation was tested. By increasing the intensity from 1 to 2 mA, or the train frequency from 50 to 100 Hz, an immediate decrease was induced in both the onset latency and the latency to peak of the conditioned response. If the conditioned stimulus intensity/frequency was maintained at the higher level, the response latencies gradually returned to preshift values. In a second set of experiments, the forelimb stimulation was replaced by direct train stimulation of the middle cerebellar peduncle as conditioned stimulus. Varying the frequency of the stimulus train between 50 and 100 Hz had effects that were almost identical to those obtained when using a forelimb conditioned stimulus. The functional meaning of the latency effect is discussed. It is also suggested that the results support the view that the conditioned stimulus is transmitted through the mossy fibers and that the mechanism for timing the conditioned response is situated in the cerebellum. (+info)
Human serum-resistant retroviral vector particles from galactosyl (alpha1-3) galactosyl containing nonprimate cell lines.
(26/1624)
Retroviral vector particles (RVP) which are resistant to inactivation by human serum will be needed for many in vivo gene therapy applications. Murine-based producer cell lines generate RVP which are inactivated by human serum, reportedly due to the presence of the galactosyl (alpha1-3) galactosyl carbohydrate moiety (alphaGal) on these and other nonprimate producer cells and RVP. Consequently, human cells (which lack the alphaGal moiety) have been developed as producer cell lines for generation of human serum-resistant RVP. In this study, we report that contrary to earlier reports, the presence of the alphaGal moiety on producer cells and RVP does not necessarily correlate with cell killing or RVP inactivation by human serum. We show that the alphaGal-positive ferret brain cell line, Mpf, is an excellent basal cell line for generation of RVP which have titers and serum resistance levels equal to or greater than RVP produced in human cell lines such as HT1080. Therefore, packaging cell lines need not be limited to those of human or primate origin for production of human serum-resistant RVP. (+info)
Survival of axotomized retinal ganglion cells in peripheral nerve-grafted ferrets.
(27/1624)
PURPOSE: Peripheral nerve (PN) grafting to the optic nerve stump stimulates not only axonal regeneration of the axotomized retinal ganglion cells (RGCs) into the grafted PN but also their survival. The purpose of the present study was to determine the number, distribution, and soma diameter of only surviving RGCs without regenerated axons and surviving RGCs with regenerated axons in PN-grafted mammals. METHODS: A segment of PN was grafted to the optic nerve stump of adult ferrets. Two months after the PN grafting, surviving RGCs with regenerated axons were retrogradely labeled with granular blue (GB) and stained with RGC-specific antibody C38. Surviving RGCs without regenerated axons were identified as C38-positive cells without GB labeling. RESULTS: Twenty-one percent of RGCs survived axotomy after PN grafting in the area centralis (AC), whereas 47% survived in the peripheral retina. Twenty-six percent of surviving RGCs in the AC exhibited axonal regeneration, which was higher than that in the peripheral retina. Soma diameter histograms revealed that RGCs with regenerated axons showing both GB and C38 positivity were in the large soma diameter ranges. In contrast, the soma diameter distribution of surviving RGCs that did not have regenerated axons showed a peak in the smaller soma diameter ranges. CONCLUSIONS: The present data suggest that PN grafting promotes survival of axotomized RGCs more effectively in the peripheral retina than in the AC. Among surviving RGCs, the larger cells exhibited axonal regeneration into the grafted PN, whereas the axons of smaller cells did not to regenerate in either the AC or the peripheral retina. (+info)
Cross-modal reorganization of horizontal connectivity in auditory cortex without altering thalamocortical projections.
(28/1624)
The development of the different, highly specialized regions of the mammalian cerebral cortex depends in part on neural activity, either intrinsic spontaneous activity or externally driven sensory activity. To determine whether patterned sensory activity instructs the development of intrinsic cortical circuitry, we have experimentally altered the modality of sensory inputs to cerebral cortex. Neonatal diversion of retinal axons to the auditory thalamus (cross-modal rewiring) results in a primary auditory cortex (AI) that resembles visual cortex in its response properties and topography (Roe et al., 1990, 1992). To test the hypothesis that the visual response properties are created by a visually driven reorganization of auditory cortical circuitry, we investigated the effect of early visual experience on the development of intrinsic, horizontal connections within AI. Horizontal connections are likely to play an important role in the construction of visual response properties in AI as they do in visual cortex. Here we show that early visual inputs to auditory thalamus can reorganize horizontal connections in AI, causing both an increase in their extent and a change in pattern, so that projections are not restricted to the isofrequency axis, but extend in a more isotropic pattern around the injection site. Thus, changing afferent modality, without altering the source of the thalamocortical axons, can profoundly alter cortical circuitry. Similar changes may underlie cortical compensatory processes in deaf or blind humans and may also have played a role in the parcellation of neocortex during mammalian evolution. (+info)
GABA(B) receptors inhibit mechanosensitivity of primary afferent endings.
(29/1624)
The modulatory effects of baclofen on the sensitivity of peripheral afferent endings to mechanical stimulation were investigated using an in vitro ferret gastroesophageal vagal afferent preparation. Changes in sensitivity of three types of gastroesophageal vagal afferent endings previously categorized as mucosal, tension, and tension-mucosal (TM) receptors according to their mechanoreceptive field characteristics were investigated. Baclofen (30-200 microM) dose dependently reduced responses of mucosal afferents to mucosal stroking with calibrated von Frey hairs (10-1000 mg). This was reversed by the GABA(B) receptor antagonist SCH50911 (1 microM). TM afferent responses to mucosal stroking (10-1000 mg) were unaffected by baclofen (30-200 microM). However, baclofen (30-200 microM) significantly inhibited the response of 11 of 18 TM afferents to circumferential tension. This was reversed by SCH50911 (1 microM). Baclofen (100 and 200 microM) significantly inhibited the response of all tension receptor afferents to circumferential tension in the lower range (1-3 gm) but not in the higher range (4-7 gm). This inhibition was reversed by SCH50911 (1 microM; n = 3). This study provides the first direct evidence for the inhibitory modulation of peripheral mechanosensory endings by the G-protein-coupled GABA(B) receptor. Inhibition was dose-dependent, pharmacologically reversible, and selective to certain aspects of mechanosensitivity. These findings have important relevance to strategies for selective reduction of sensory input to the CNS at a peripheral site. (+info)
Conductive hearing loss produces a reversible binaural hearing impairment.
(30/1624)
Conductive hearing loss, produced by otitis media with effusion, is widespread in young children. However, little is known about its short- or long-term effects on hearing or the brain. To study the consequences of a conductive loss for the perception and processing of sounds, we plugged the left ear canal of ferrets for 7-15 months during either infancy or adulthood. Before or during plugging, the ferrets were trained to perform a binaural task requiring the detection of a 500 Hz tone, positioned 90 degrees to the right, that was masked by two sources of broad-band noise. In one condition ("control"), both noise sources were 90 degrees right and, in the second condition ("bilateral"), one noise source was moved to 90 degrees left. Normal ferrets showed binaural unmasking: tone detection thresholds were lower (mean 10.1 dB) for the bilateral condition than for the control condition. Both groups of ear-plugged ferrets had reduced unmasking; the mean residual unmasking was 2.3 dB for the infant and 0.7 dB for the adult ear-plugged animals. After unplugging, unmasking increased in both groups (infant, 7.1 dB; adult, 6.9 dB) but not to normal levels. Repeated testing during the 22 months after unplugging revealed a gradual return to normal levels of unmasking. These results show that a unilateral conductive hearing loss, in either infancy or adulthood, impairs binaural hearing both during and after the hearing loss. They show scant evidence for adaptation to the plug and demonstrate a recovery from the impairment that occurs over a period of several months after restoration of normal peripheral function. (+info)
Coexistence of widespread clones and large radial clones in early embryonic ferret cortex.
(31/1624)
Cell lineage analysis in rodents has shown that the cerebral cortex is formed from both widespread and large radial clustered clones representing partly distinct lineages and producing differing cell types. Since previous cell lineage analysis of the ferret cortex using retroviral libraries showed that most neurons labeled at E33-E35 formed widespread clones, we determined whether clones labeled earlier in neurogenesis showed a greater tendency to form coherent radial clones. Clones labeled at E27-E29 occasionally consisted of widespread multineuron clones (13% of PCR-defined clones), but commonly consisted of small clusters of two to four neurons (65%). Moreover, 6/21 hemispheres contained a single, much larger (6-150 cells) radial cluster. Although large clusters were observed in 28% of experiments, they contained many neurons, accounting for 38% of retrovirally labeled cells. The large clusters showed at most few widely scattered sibling cells, either by histological analysis or by PCR analysis, suggesting that radial and widespread clones coexist but are lineally separate at early stages of corticogenesis. Coexistence of large radial and widespread neuronal clones appears to be an evolutionarily conserved mechanism for cortical neurogenesis. (+info)
Submucosal gland development in the airway is controlled by lymphoid enhancer binding factor 1 (LEF1).
(32/1624)
Previous studies have demonstrated that transcription of the lymphoid enhancer binding factor 1 (Lef1) gene is upregulated in submucosal gland progenitor cells just prior to gland bud formation in the developing ferret trachea. In the current report, several animal models were utilized to functionally investigate the role of LEF1 in initiating and supporting gland development in the airway. Studies on Lef1-deficient mice and antisense oligonucleotides in a ferret xenograft model demonstrate that LEF1 is functionally required for submucosal gland formation in the nasal and tracheal mucosa. To determine whether LEF1 expression was sufficient for the induction of airway submucosal glands, two additional model systems were utilized. In the first, recombinant adeno-associated virus was used to overexpress the human LEF1 gene in a human bronchial xenograft model of regenerative gland development in the adult airway. In a second model, the LEF1 gene was ectopically overexpressed under the direction of the proximal airway-specific CC10 promoter in transgenic mice. In both of these models, morphometric analyses revealed no increase in the number or size of airway submucosal glands, indicating that ectopic LEF1 expression alone is insufficient to induce submucosal gland development. In summary, these studies demonstrate that LEF1 expression is required, but in and of itself is insufficient, for the initiation and continued morphogenesis of submucosal glands in the airway. (+info)