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Long-term avoidance memory formation is associated with a transient increase in mushroom body synaptic complexes in leaf-cutting ants.

Falibene A, Roces F, Rössler W - Front Behav Neurosci (2015)

Bottom Line: Long-term avoidance memory formation was associated with a transient change in MG densities.At days 4 and 15 after learning-when ants still showed plant avoidance-MG densities had decreased to the initial state.Sensory exposure by the simultaneous collection of several, instead of one, non-harmful plant species resulted in a decrease in MG densities in the olfactory lip.

View Article: PubMed Central - PubMed

Affiliation: Department of Behavioral Physiology and Sociobiology, Biozentrum, University of Würzburg Würzburg, Germany.

ABSTRACT
Long-term behavioral changes related to learning and experience have been shown to be associated with structural remodeling in the brain. Leaf-cutting ants learn to avoid previously preferred plants after they have proved harmful for their symbiotic fungus, a process that involves long-term olfactory memory. We studied the dynamics of brain microarchitectural changes after long-term olfactory memory formation following avoidance learning in Acromyrmex ambiguus. After performing experiments to control for possible neuronal changes related to age and body size, we quantified synaptic complexes (microglomeruli, MG) in olfactory regions of the mushroom bodies (MBs) at different times after learning. Long-term avoidance memory formation was associated with a transient change in MG densities. Two days after learning, MG density was higher than before learning. At days 4 and 15 after learning-when ants still showed plant avoidance-MG densities had decreased to the initial state. The structural reorganization of MG triggered by long-term avoidance memory formation clearly differed from changes promoted by pure exposure to and collection of novel plants with distinct odors. Sensory exposure by the simultaneous collection of several, instead of one, non-harmful plant species resulted in a decrease in MG densities in the olfactory lip. We hypothesize that while sensory exposure leads to MG pruning in the MB olfactory lip, the formation of long-term avoidance memory involves an initial growth of new MG followed by subsequent pruning.

No MeSH data available.


Related in: MedlinePlus

Changes in the MB calyx synaptic organization promoted by odor sensory exposure by experiencing different kinds of leaves. (A) Density of synapsin-IR boutons in the ND lip region decreased in the brains of ants from the subcolony exposed to a higher variety of plant species. (B) Lip volume did not change with the experience. Dots represent the mean value and lines the S.D. ** p < 0.01. 1 plant species, N = 9; 10 plant species, N = 10.
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Figure 4: Changes in the MB calyx synaptic organization promoted by odor sensory exposure by experiencing different kinds of leaves. (A) Density of synapsin-IR boutons in the ND lip region decreased in the brains of ants from the subcolony exposed to a higher variety of plant species. (B) Lip volume did not change with the experience. Dots represent the mean value and lines the S.D. ** p < 0.01. 1 plant species, N = 9; 10 plant species, N = 10.

Mentions: We investigated whether simultaneous collection and incorporation of multiple plant species with distinct odors (as it often occurs under natural situations) leads to changes in MG organization in the olfactory MB calyces. We compared ants from subcolonies that had foraged on a single plant species with those that had experienced 10 different kinds of leaves over three consecutive days. Although ants showed preferences for some of the species, none of them was rejected during the 3-day experiment (data not shown). The simultaneous exposure to and collection of several plant species promoted after 3 days a significant reduction (~20%) of synapsin-IR bouton densities in the ND lip of the MB calyces compared to ants exposed to only one plant species (F1,17 = 9.08, p = 0.008; ANOVA; Figure 4A). As there were no changes in lip volume between groups (F1,17 = 2.82, p = 0.11; ANOVA; Figure 4B), this suggests that the decrease in bouton densities was due to a net reduction in MG numbers. No significant differences were found in collar volumes (F1,17 = 3.21, p = 0.09; ANOVA).


Long-term avoidance memory formation is associated with a transient increase in mushroom body synaptic complexes in leaf-cutting ants.

Falibene A, Roces F, Rössler W - Front Behav Neurosci (2015)

Changes in the MB calyx synaptic organization promoted by odor sensory exposure by experiencing different kinds of leaves. (A) Density of synapsin-IR boutons in the ND lip region decreased in the brains of ants from the subcolony exposed to a higher variety of plant species. (B) Lip volume did not change with the experience. Dots represent the mean value and lines the S.D. ** p < 0.01. 1 plant species, N = 9; 10 plant species, N = 10.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4389540&req=5

Figure 4: Changes in the MB calyx synaptic organization promoted by odor sensory exposure by experiencing different kinds of leaves. (A) Density of synapsin-IR boutons in the ND lip region decreased in the brains of ants from the subcolony exposed to a higher variety of plant species. (B) Lip volume did not change with the experience. Dots represent the mean value and lines the S.D. ** p < 0.01. 1 plant species, N = 9; 10 plant species, N = 10.
Mentions: We investigated whether simultaneous collection and incorporation of multiple plant species with distinct odors (as it often occurs under natural situations) leads to changes in MG organization in the olfactory MB calyces. We compared ants from subcolonies that had foraged on a single plant species with those that had experienced 10 different kinds of leaves over three consecutive days. Although ants showed preferences for some of the species, none of them was rejected during the 3-day experiment (data not shown). The simultaneous exposure to and collection of several plant species promoted after 3 days a significant reduction (~20%) of synapsin-IR bouton densities in the ND lip of the MB calyces compared to ants exposed to only one plant species (F1,17 = 9.08, p = 0.008; ANOVA; Figure 4A). As there were no changes in lip volume between groups (F1,17 = 2.82, p = 0.11; ANOVA; Figure 4B), this suggests that the decrease in bouton densities was due to a net reduction in MG numbers. No significant differences were found in collar volumes (F1,17 = 3.21, p = 0.09; ANOVA).

Bottom Line: Long-term avoidance memory formation was associated with a transient change in MG densities.At days 4 and 15 after learning-when ants still showed plant avoidance-MG densities had decreased to the initial state.Sensory exposure by the simultaneous collection of several, instead of one, non-harmful plant species resulted in a decrease in MG densities in the olfactory lip.

View Article: PubMed Central - PubMed

Affiliation: Department of Behavioral Physiology and Sociobiology, Biozentrum, University of Würzburg Würzburg, Germany.

ABSTRACT
Long-term behavioral changes related to learning and experience have been shown to be associated with structural remodeling in the brain. Leaf-cutting ants learn to avoid previously preferred plants after they have proved harmful for their symbiotic fungus, a process that involves long-term olfactory memory. We studied the dynamics of brain microarchitectural changes after long-term olfactory memory formation following avoidance learning in Acromyrmex ambiguus. After performing experiments to control for possible neuronal changes related to age and body size, we quantified synaptic complexes (microglomeruli, MG) in olfactory regions of the mushroom bodies (MBs) at different times after learning. Long-term avoidance memory formation was associated with a transient change in MG densities. Two days after learning, MG density was higher than before learning. At days 4 and 15 after learning-when ants still showed plant avoidance-MG densities had decreased to the initial state. The structural reorganization of MG triggered by long-term avoidance memory formation clearly differed from changes promoted by pure exposure to and collection of novel plants with distinct odors. Sensory exposure by the simultaneous collection of several, instead of one, non-harmful plant species resulted in a decrease in MG densities in the olfactory lip. We hypothesize that while sensory exposure leads to MG pruning in the MB olfactory lip, the formation of long-term avoidance memory involves an initial growth of new MG followed by subsequent pruning.

No MeSH data available.


Related in: MedlinePlus