ISSN:
1432-1351
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The parieto-visceral ganglion (PVG) control of the gill withdrawal reflex to tactile stimulation of the gill is absent in young animals, weighing 25 g or less. In older animals, weighing 160 g or more, the PVG control causes suppression of the reflex amplitude and a faster rate of habituation. 1) In youngAplysia the PVG did not suppress the reflex amplitude nor did it accelerate the rate of habituation (Fig. 2). The gill neural plexus, through which presumably, PVG control of the reflex is mediated, is as competent in young as in older animals to mediate habituation (Fig. 2). 2) PVG control was not evoked by increasing the intensity of the tactile stimulus 12 fold, from 0.15 g to 1.8 g, to the gill; in older animals the extent of control was dependent on stimulus intensity (Fig. 3). 3) In young animals the 0.15 g stimulus evoked spiking in L7, a gill motor neuron, and it evoked only an EPSP in L7 in olderAplysia (Figs. 4, 5). The decrement of evoked activity in L7 from both groups of animals was correlated with habituation of the reflex (Fig. 8). 4) Induced spiking of L7, in young and olderAplysia, resulted in dishabituation of the gill reflex (Fig. 8). These results and those in (3) show that the pathways between the gill and the PVG are functional in young animals. 5) No differences were found in membrane properties of L7 from young and older animals; L7's were only differentiated by cell size (Table 1, Figs. 6, 7). 6) In contrast R2, which is not involved in the reflex, was responsive to the weaker gill stimuli only in young animals (Figs. 4, 5). R2's greater responsiveness is attributed to small cell size which accounts for greater input resistance (Table 1, Fig. 7). 7) The absence of control of the gill withdrawal reflex and the greater synaptic efficacy in L7 to gill stimulation, we suggest, results from incompletely developed inhibitory mechanisms in the PVG of young animals (Fig. 9).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01380041
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