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Aging in Sensory and Motor Neurons Results in Learning Failure in Aplysia californica.

Kempsell AT, Fieber LA - PLoS ONE (2015)

Bottom Line: The physiological and molecular mechanisms of age-related memory loss are complicated by the complexity of vertebrate nervous systems.This implied that the neuronal machinery governing nonassociative learning was compromised during aging.Synaptic plasticity in the form of short-term facilitation between tail sensory and motor neurons decreased during aging whether the sensitizing stimulus was tail shock or the heterosynaptic modulator serotonin (5-HT).

View Article: PubMed Central - PubMed

Affiliation: University of Miami, Rosenstiel School of Marine and Atmospheric Science, Department of Marine Biology and Ecology, Miami, Florida, United States of America.

ABSTRACT
The physiological and molecular mechanisms of age-related memory loss are complicated by the complexity of vertebrate nervous systems. This study takes advantage of a simple neural model to investigate nervous system aging, focusing on changes in learning and memory in the form of behavioral sensitization in vivo and synaptic facilitation in vitro. The effect of aging on the tail withdrawal reflex (TWR) was studied in Aplysia californica at maturity and late in the annual lifecycle. We found that short-term sensitization in TWR was absent in aged Aplysia. This implied that the neuronal machinery governing nonassociative learning was compromised during aging. Synaptic plasticity in the form of short-term facilitation between tail sensory and motor neurons decreased during aging whether the sensitizing stimulus was tail shock or the heterosynaptic modulator serotonin (5-HT). Together, these results suggest that the cellular mechanisms governing behavioral sensitization are compromised during aging, thereby nearly eliminating sensitization in aged Aplysia.

No MeSH data available.


Related in: MedlinePlus

5-HT caused increased excitability in SNs of mature but not aged II Aplysia.A) Membrane potential in SNs in response to 5-HT (20 μM) perfusion onto the pleural-pedal ganglion. B) 3 min of 5-HT significantly depolarized mature but not aged II tail SNs. * denotes significant difference from ASW control at p≤0.05 via paired t-test. C) Injection of 3 ms depolarizing current evoked a single AP in tail SNs that was compared before (ASW) and after 5-HT treatment. D) AP duration increased significantly in mature but not aged II tail SNs after 3 min 5-HT. * denotes significant difference from ASW control at p≤0.05, paired t-test (n = 25 for mature, n = 23 for aged II).
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pone.0127056.g006: 5-HT caused increased excitability in SNs of mature but not aged II Aplysia.A) Membrane potential in SNs in response to 5-HT (20 μM) perfusion onto the pleural-pedal ganglion. B) 3 min of 5-HT significantly depolarized mature but not aged II tail SNs. * denotes significant difference from ASW control at p≤0.05 via paired t-test. C) Injection of 3 ms depolarizing current evoked a single AP in tail SNs that was compared before (ASW) and after 5-HT treatment. D) AP duration increased significantly in mature but not aged II tail SNs after 3 min 5-HT. * denotes significant difference from ASW control at p≤0.05, paired t-test (n = 25 for mature, n = 23 for aged II).

Mentions: 5-HT is an important neuromodulator implicated in forms of learning and memory including behavioral sensitization in TWR. Previous studies showed that 5-HT treatment induces changes in biophysical properties of tail SNs that enhance excitability, including resting membrane potential and duration of evoked AP [34, 38]. In mature tail SNs, 5-HT treatment resulted in a slow and maintained depolarization of resting membrane potential, significantly different at 3 min in 5-HT from the initial measurement (Fig 6A and 6B; p≤0.05; paired t-test). In aged II tail SNs, the effects of 5-HT treatment were much more variable. No significant changes in resting membrane potential were observed in aged II tail SNs after 5-HT (Fig 6A and 6B).


Aging in Sensory and Motor Neurons Results in Learning Failure in Aplysia californica.

Kempsell AT, Fieber LA - PLoS ONE (2015)

5-HT caused increased excitability in SNs of mature but not aged II Aplysia.A) Membrane potential in SNs in response to 5-HT (20 μM) perfusion onto the pleural-pedal ganglion. B) 3 min of 5-HT significantly depolarized mature but not aged II tail SNs. * denotes significant difference from ASW control at p≤0.05 via paired t-test. C) Injection of 3 ms depolarizing current evoked a single AP in tail SNs that was compared before (ASW) and after 5-HT treatment. D) AP duration increased significantly in mature but not aged II tail SNs after 3 min 5-HT. * denotes significant difference from ASW control at p≤0.05, paired t-test (n = 25 for mature, n = 23 for aged II).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4430239&req=5

pone.0127056.g006: 5-HT caused increased excitability in SNs of mature but not aged II Aplysia.A) Membrane potential in SNs in response to 5-HT (20 μM) perfusion onto the pleural-pedal ganglion. B) 3 min of 5-HT significantly depolarized mature but not aged II tail SNs. * denotes significant difference from ASW control at p≤0.05 via paired t-test. C) Injection of 3 ms depolarizing current evoked a single AP in tail SNs that was compared before (ASW) and after 5-HT treatment. D) AP duration increased significantly in mature but not aged II tail SNs after 3 min 5-HT. * denotes significant difference from ASW control at p≤0.05, paired t-test (n = 25 for mature, n = 23 for aged II).
Mentions: 5-HT is an important neuromodulator implicated in forms of learning and memory including behavioral sensitization in TWR. Previous studies showed that 5-HT treatment induces changes in biophysical properties of tail SNs that enhance excitability, including resting membrane potential and duration of evoked AP [34, 38]. In mature tail SNs, 5-HT treatment resulted in a slow and maintained depolarization of resting membrane potential, significantly different at 3 min in 5-HT from the initial measurement (Fig 6A and 6B; p≤0.05; paired t-test). In aged II tail SNs, the effects of 5-HT treatment were much more variable. No significant changes in resting membrane potential were observed in aged II tail SNs after 5-HT (Fig 6A and 6B).

Bottom Line: The physiological and molecular mechanisms of age-related memory loss are complicated by the complexity of vertebrate nervous systems.This implied that the neuronal machinery governing nonassociative learning was compromised during aging.Synaptic plasticity in the form of short-term facilitation between tail sensory and motor neurons decreased during aging whether the sensitizing stimulus was tail shock or the heterosynaptic modulator serotonin (5-HT).

View Article: PubMed Central - PubMed

Affiliation: University of Miami, Rosenstiel School of Marine and Atmospheric Science, Department of Marine Biology and Ecology, Miami, Florida, United States of America.

ABSTRACT
The physiological and molecular mechanisms of age-related memory loss are complicated by the complexity of vertebrate nervous systems. This study takes advantage of a simple neural model to investigate nervous system aging, focusing on changes in learning and memory in the form of behavioral sensitization in vivo and synaptic facilitation in vitro. The effect of aging on the tail withdrawal reflex (TWR) was studied in Aplysia californica at maturity and late in the annual lifecycle. We found that short-term sensitization in TWR was absent in aged Aplysia. This implied that the neuronal machinery governing nonassociative learning was compromised during aging. Synaptic plasticity in the form of short-term facilitation between tail sensory and motor neurons decreased during aging whether the sensitizing stimulus was tail shock or the heterosynaptic modulator serotonin (5-HT). Together, these results suggest that the cellular mechanisms governing behavioral sensitization are compromised during aging, thereby nearly eliminating sensitization in aged Aplysia.

No MeSH data available.


Related in: MedlinePlus