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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

Examples of synapsin-IR bouton quantification in the ND lip (A,B) before and (C,D) 2 days after learning. (A,C) Three-dimensional reconstruction of the position of the boutons visualized by AMIRA in a 1000 μm3-volume (86 × 86 voxel). Each yellow sphere marks the center of a bouton. (B,D) Single confocal image of a 10 × 10 μm2 (86 × 86 voxel) synapsin-stained area in the ND lip.
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Figure 6: Examples of synapsin-IR bouton quantification in the ND lip (A,B) before and (C,D) 2 days after learning. (A,C) Three-dimensional reconstruction of the position of the boutons visualized by AMIRA in a 1000 μm3-volume (86 × 86 voxel). Each yellow sphere marks the center of a bouton. (B,D) Single confocal image of a 10 × 10 μm2 (86 × 86 voxel) synapsin-stained area in the ND lip.

Mentions: Figure 5 further shows the analysis of the MG organization in the MB calyx lip before and at different times after long-term avoidance memory formation. Examples of synapsin-IR bouton quantifications before and 2 days after learning are shown in Figure 6. Two days after learning, the number of synapsin-IR boutons per volume in the ND lip was significantly higher compared to the initial number (25% increase compared to day 0; F2,16 = 4.44, p = 0.029; ANOVA; Figure 5C). Interestingly, synapsin-IR bouton densities in the lip region decreased on day 4, averaging intermediate values between days 0 and 2, yet not different from those of day 0. We then analyzed whether changes in synapsin-IR bouton densities were caused by a reduction in lip volume and found no significant volumetric changes in the lip (F2,18 = 3.41, p = 0.06; ANOVA; Figure 5D), nor in the collar (H2, N = 21 = 3.73, p = 0.15; Kruskal–Wallis). This suggests that the changes in synapsin-IR bouton densities were due to an increase in the number of synapsin-IR boutons in the ND lip.


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)

Examples of synapsin-IR bouton quantification in the ND lip (A,B) before and (C,D) 2 days after learning. (A,C) Three-dimensional reconstruction of the position of the boutons visualized by AMIRA in a 1000 μm3-volume (86 × 86 voxel). Each yellow sphere marks the center of a bouton. (B,D) Single confocal image of a 10 × 10 μm2 (86 × 86 voxel) synapsin-stained area in the ND lip.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Examples of synapsin-IR bouton quantification in the ND lip (A,B) before and (C,D) 2 days after learning. (A,C) Three-dimensional reconstruction of the position of the boutons visualized by AMIRA in a 1000 μm3-volume (86 × 86 voxel). Each yellow sphere marks the center of a bouton. (B,D) Single confocal image of a 10 × 10 μm2 (86 × 86 voxel) synapsin-stained area in the ND lip.
Mentions: Figure 5 further shows the analysis of the MG organization in the MB calyx lip before and at different times after long-term avoidance memory formation. Examples of synapsin-IR bouton quantifications before and 2 days after learning are shown in Figure 6. Two days after learning, the number of synapsin-IR boutons per volume in the ND lip was significantly higher compared to the initial number (25% increase compared to day 0; F2,16 = 4.44, p = 0.029; ANOVA; Figure 5C). Interestingly, synapsin-IR bouton densities in the lip region decreased on day 4, averaging intermediate values between days 0 and 2, yet not different from those of day 0. We then analyzed whether changes in synapsin-IR bouton densities were caused by a reduction in lip volume and found no significant volumetric changes in the lip (F2,18 = 3.41, p = 0.06; ANOVA; Figure 5D), nor in the collar (H2, N = 21 = 3.73, p = 0.15; Kruskal–Wallis). This suggests that the changes in synapsin-IR bouton densities were due to an increase in the number of synapsin-IR boutons in the ND lip.

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