The Radish Gene Reveals a Memory Component with Variable Temporal Properties

Memory phases, dependent on different neural and molecular mechanisms, strongly influence memory performance. Our understanding, however, of how memory phases interact is far from complete. In Drosophila, aversive olfactory learning is thought to progress from short-term through long-term memory phases. Another memory phase termed anesthesia resistant memory, dependent on the radish gene, influences memory hours after aversive olfactory learning. How does the radish-dependent phase influence memory performance in different tasks? It is found that the radish memory component does not scale with the stability of several memory traces, indicating a specific recruitment of this component to influence different memories, even within minutes of learning

Mutation of the <i>rsh</i> gene does not influence conditioning or place memory tested directly after training.

<p>Following a 30 s pre-test period (black bars), wild-type CS and <i>rsh¹</i> mutant flies were trained in two equal length periods for a total of either 6 or 20 min with 41°C (light gray bars). A 3 min memory was tested directly following in the post-test period (dark gray bars). The training, retention intervals, and testing patterns (both pre and post) are diagrammed for each panel, the time axis is not to scale. (<i>A</i>), Conditioning and memory tests were similar between the genotypes with 6 min of training (N = 331; pre-test: U = 12753.5, z = 1.07, P = 0.28; 1^st training period: U = 11877.0, z = 2.08, P = 0.04; 2^nd training period: U = 12888.5, z = 0.92, P = 0.36; post-test: U = 13237.0, z = 0.51, P = 0.61). (<i>B</i>) Conditioning and memory tests were also similar between the genotypes with 20 min of training (N = 232; pre-test: U = 6106.5, z = 1.22, P = 0.22; 1^st training period: U = 5740.5, z = 1.93, P = 0.06; 2^nd training period: U = 5802.0, z = −1.81,  = 0.07; post-test: U = 6463.0, z = −0.52, P = 0.60). (<i>C</i>) The <i>rsh</i> gene is necessary for normal short-term place memory. Flies were trained with intermittent training and then held for varying times (1 – 40 min) before being tested for memory with a short reminder training. The <i>rsh¹</i> flies had memory performance similar to wild-type CS levels with a 1 min delay between training and the memory test (N = 447, U = 24641.5, z = 0.24, P = 0.8). Significant differences were found at several time points following training (10 min: N = 295, U = 8637.0, z = .02, **  =  P<0.01; 20 min: N = 330, U = 10074.5, z = 3.95, ***  =  P<0.001; 30 min: N = 311, U = 10926.0, z = 1.45, P = 0.1; 40 min: N = 351, U = 12941.5, z = 2.48, **  =  P<0.01). The values are means and error bars represent s.e.m.</p

Mutation of the <i>rsh</i> gene reveals a major role in aversive olfactory memory (ARM) and is necessary for appetitive olfactory memory shortly after conditioning.

<p>Flies were either trained with odorants paired with electric shock or sugar reward. The training, cold-shock, retention intervals, and testing patterns (both pre and post) are diagrammed for each panel, the time axis is not to scale. (<i>A</i>) Olfactory memory tested three min after training is reduced in <i>rsh¹</i> flies compared to CS flies, although levels do not reach statistical significance (F(1,12)  = 3.5, P = 0.09). To reveal the <i>rsh</i> function in aversive olfactory memory, wild-type CS and <i>rsh¹</i> flies were trained with odorant / shock pairings, then after 2 hrs were given a cold-shock, memory was tested 1 hr later. Memory performance of <i>rsh¹</i> flies was significantly lower than wild-type CS flies with this procedure (F(1,10)  = 5.0, *  =  P = 0.04). (<i>B</i>) Appetitive olfactory short-term memory was tested at 3, 30, and 60 min after the odorant / sucrose training session. A <i>rsh¹</i> phenotype was evident at all tested time points after training (3 min: F(1,16)  = 29.2, ***  =  P<0.001; 30 min: F(1,14)  = 12.3, **  =  P<0.01; 60 min: F(1,14)  = 12.1, **  =  P<0.01). (<i>C</i>) The <i>rsh¹</i> appetitive short term olfactory memory phenotype is rescued with a transgenic copy of the wild-type version of the <i>rsh</i> gene (F(3,32)  = 13.0, P<0.0001; post-hoc tests: CS vs <i>rsh¹</i> ***  = P<0.001, <i>rsh¹</i> vs. <i>rsh¹</i>; hs-<i>rsh-1</i> *  = P<0.05, CS vs. <i>rsh¹</i>; hs-<i>rsh-1</i>, *  = P<0.05; <i>rsh¹</i> vs. CS; hs-<i>rsh-1</i> *  = P<0.05; CS vs. CS; hs-<i>rsh-1</i> *  = P<0.05). The values are means and error bars represent s.e.m.</p

Control behaviors of wild-type CS and <i>rsh¹</i> mutant flies.

<p>MCH avoidance: ANOVA F(3,32)  = 1.07, P = 0.4; Oct avoidance: F(3,20)  = 1.3, P = 0.3; Sugar attractiveness: ANOVA F(3,44) = 0.75, P = 0.53; Activity: F(1,561) = 3.3, P = 0.07.</p