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81.
82.
Responses of acutely isolated neurons from the rostral nucleus of the
solitary tract (rNST) to GABA receptor agonists and antagonists were
investigated using whole-cell recording in current clamp mode. The isolated
neurons retain their morphology and can be divided into multipolar,
elongate and ovoid cell types. Most rNST neurons (97%), including all three
cell types, respond to GABA with membrane hyperpolarization and a reduction
in input resistance. The GABA(A) receptor agonist muscimol reduces neuronal
input resistance in a concentration-dependent manner, whereas the GABA(B)
receptor agonist baclofen had no effect on any of the neurons tested. The
GABA and muscimol reversal potentials were both found to be -75 mV Both the
GABA competitive antagonist picrotoxin and the GABA(A) receptor antagonist
bicuculline block the effect of GABA in a concentration-dependent manner.
These results suggest that GABA activates all neurons in the rNST and that
inhibitory synaptic activity is important in brainstem processing of
gustatory and somatosensory information.
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83.
Replacement of receptor cells in the hamster vomeronasal epithelium after nerve transection 总被引:1,自引:1,他引:0
Chemoreceptor cells in the vomeronasal and olfactory epithelium are
replaced following experimentally induced degeneration. This study analyzes
quantitatively the time course and degree of vomeronasal receptor cell
replacement. Unilateral transection of the vomeronasal nerves in adult
hamster was used to induce a retrograde degeneration of receptor cells in
the vomeronasal organ. Histological measurement of both number of receptor
cells and epithelial thickness were made for recovery times from 0 to 60
days. After nerve transection, there was a gradual degeneration of receptor
cells, the number decreasing to 50% of control by day 2 and 16% by day 6.
During days 7-15 maximum receptor cell replacement was observed. Cell
number increased rapidly and reached a peak on day 15. At recovery times of
40-60 days, cell number returned to the control level. Epithelial
thickness, however, decreased to 60-70% during the degeneration period
(days 4-6) and did not return to control levels. After 40-60 days
epithelial thickness remained at 70% of control. These results demonstrate
that vomeronasal receptor cells are replaced following degeneration, but
epithelial thickness does not return to control levels. These findings
suggest that the number of replacement cells is not limited by the reduced
thickness of the epithelium, and that recovery mechanisms may function to
restore an optimum number of receptor cells.
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84.
85.
Charles K. Pallaghy Jeff Minchinton Gerald T. Kraft Richard Wetherbee 《Journal of phycology》1983,19(2):204-208
Electron-probe X-ray microanalysis of freeze dried sections of growing branch tips of Thysanocladia densa Sander shows high concentrations of bromine in the region of the medulla. Indirect evidence infers that the Br is associated with intercellular, granular deposits which accumulate within the mucilage of the medulla. The concentration of Br decreases in older regions of the thalli. 相似文献
86.
87.
Populations of the mangrove Avicennia marina in the Sydney region exist as stands of varying size, reflecting both natural and anthropogenic fragmentation. We hypothesised that, as observed in many terrestrial forests, small stands (<100 plants) would experience lower pollinator densities and altered pollinator behaviour and visitation and, in consequence, would display reduced pollen deposition as compared with large stands (>10,000 plants). Nevertheless, we recognise that such predictions may be overly simplistic because within this region A. marina attracts a diversity of flower visitors, but its only significant pollinator is the exotic honeybee Apis mellifera. Moreover, it is unclear how readily A. mellifera moves among groups of plants within different mangrove stands of varying sizes separated either by water or urban habitat matrix. Our detailed surveys within pairs of large and small stands in two locations support the predictions that pollinator density and pollen deposition are reduced or altered within small stands. Within small stands honeybee abundance and pollen deposition were on average reduced significantly by 84 and 61 %, respectively. Moreover, within small stands there was a non-significant 12 % increase in the mean time that honeybees spent foraging on individual plants and hence potentially depositing self pollen. Taken together, our data indicate that fragmentation affects the performance of A. mellifera as a pollinator of A. marina and reduce pollinator abundance, leading to pollen limitation in small as compared to large stands, which may negatively affect reproductive output. 相似文献