Age-dependent CNS control of the habituating gill withdrawal reflex and of correlated activity in identified neurons inAplysia

Abstract

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 young Aplysia 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 L~, a gill motor neuron, and it evoked only an EPSP in L~ in older Aplysia (Figs. 4, 5). The decrement of evoked activity in L~ from both groups of animals was correlated with habituation of the reflex (Fig. 8).4) Induced spiking of L~, in young and older Aplysia, 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 L~ from young and older animals; L~'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). Re'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 L~ to gill stimulation, we suggest, results from incompletely developed inhibitory mechanisms in the PVG of young animals (Fig. 9).

JuvenileLymnaeaventilate,learn and remember differently than do adultLymnaea

“…Our data concerning the acquisition of learning and its lack of consolidation into LTM are consistent with previous data from juveniles that typically perseverate on tasks where they have to withhold a response, including habituation (Peretz and Lukowiak, 1975;Lukowiak, 1980), suppression of attack responses (Wells, 1962;Dickel et al, 1997), passive avoidance (Blozovski and Cudennec, 1980;Mattingly and Zolman, 1980), spatial discrimination (Bronstein and Spear, 1972) and the classical conditioning of Lymnaea's whole-body withdrawal response (Ono et al, 2002). We now have the possibility of determining whether the inability to form LTM for associative learning is dependent partly or completely on differences in a single neuron.…”

“…Typically, younger animals (vertebrate and invertebrate) 'perseverate' (the inappropriate or unintentional repetition of a response or behaviour) (Cider, 1997) on learning tasks where they are required to withhold a behavioural response (Denenberg and Kine, 1958;Peretz and Lukowiak, 1975;Blozovski and Cudennec, 1980;Mattingly and Zolman, 1980;Dickel et al, 1997Dickel et al, , 2000. The neuronal basis of behavioural perseveration is not known.…”

Development of sensitization in the escape locomotion system in Aplysia

“…The development of learning and memory has been analyzed in considerable detail in defensive reflexes of Aplysia (Peretz and Lukowiak, 1975;Rayport and Camardo, 1984;Carew, 1987, 1988;Carew, 1987a, 1988;Rankin et al, 1987). The gill and siphon withdrawal reflex in particular has been examined both because it exhibits a variety of forms of learning and memory (Pinsker et al, 1970(Pinsker et al, , 1973Carew, et al, 1981aCarew, et al, , 1983Hawkins, et al, 1985) and because its neural circuitry is very well understood (Kupfermann and Kandel, 1969;Kupfermann et al, 1974;Byrne, et al, 1978;Hawkins et al, 198 1).…”

Juveniles ofLymnaeasmart snails do not perseverate and have the capacity to form LTM

“…This appears to be a recurring theme in the literature across species. Such behaviours included habituation (Peretz and Lukowiak, 1975;Lukowiak, 1980), suppression of attack responses (Dickel et al, 1997), passive avoidance (Blozovski and Cudennec, 1980;Mattingly and Zolman, 1980), spatial discrimination (Bronstein and Spear, 1972) and the classical conditioning of Lymnaea's whole-body withdrawal response (Ono et al, 2002). However, this does not mean that the nervous system in each of the three juvenile strains (TC2, TC3 and Dutch) is incapable of mediating LTM formation.…”

“…These snails were said to perseverate (defined as an inappropriate repetition of a behaviour). Typically, younger animals perseverate in situations where they are required to withhold a behavioural response (Peretz and Lukowiak, 1975;Peretz et al, 1976). However, Dutch juveniles are capable of both associative learning and LTM for tasks where withholding a behaviour is not required.…”