Visual input regulates circuit configuration in courtship conditioning of Drosophila melanogaster

Abstract

Courtship and courtship conditioning are behaviors that are regulated by multiple sensory inputs, including chemosensation and vision. Globally inhibiting CaMKII activity in Drosophila disrupts courtship plasticity while leaving visual and chemosensory perception intact. Light has been shown to modulate CaMKII-dependent memory formation in this paradigm and the circuitry for the nonvisual version of this behavior has been investigated. In this paradigm, volatile and tactile pheromones provide the primary driving force for courtship, and memory formation is dependent upon intact mushroom bodies and parts of the central complex. In the present study, we use the GAL4/UAS binary expression system to define areas of the brain that require CaMKII for modulation of courtship conditioning in the presence of visual, as well as chemosensory, information. Visual input suppressed the ability of mushroom body- and central complex-specific CaMKII inhibition to disrupt memory formation, indicating that the cellular circuitry underlying this behavior can be remodeled by changing the driving sensory modality. These findings suggest that the potential for plasticity in courtship behavior is distributed among multiple biochemically and anatomically distinct cellular circuits.

Figure 1

Inhibition of CaMKII in specific brain regions alters the response to the mated female during conditioning. Males heterozygous for the GAL4 lines indicated were trained by exposure to a female for 1 hr. A CI is measured for the first and last 10 min of the training period. Courtship decrement during training is shown by the ratio of CI_final/CI_initial, which for a wild-type male is ∼0.5 (Joiner and Griffith 1997). All manipulations were performed at 25°C, 75% humidity in normal room light. Statistical significance was assessed by Wilcoxon's signed-rank test. Data from GAL4/+;UAS–ala/+ males (gray bars) were compared to data from control males of the genotype GAL4/+ (white bars) for each line. Bars marked with an asterisk (*) are significantly different from the genotype control with level of significance as indicated: (*) P < 0.05; (**) P < 0.005; and (***) P < 0.0005. n ≥ 20 for each genotype.

Figure 2

Inhibition of CaMKII in specific brain areas does not alter associative memory formation. Males heterozygous for the GAL4 lines indicated were trained by exposure to a female for 1 hr and placed with an anesthetized virgin female. For sham training, flies of the same genotype were manipulated identically, except that no female was present in the chamber during training. Memory was tested by measuring the CI for the initial 10 min of exposure to the anesthetized virgin female after training with a mated female (CI_test) or after sham training (CI_sham). Data are expressed as the ratio of CI_test/mean CI_sham, which, for a wild type male, is ∼0.5 (Joiner and Griffith 1997). All manipulations were performed at 25°C, 75% humidity in normal room light. Statistical significance was assessed by Wilcoxon's signed-rank test. Data from GAL4/+;UAS–ala/+ males (gray bars) were compared to data from control males of the genotype GAL4/+ (white bars) for each line. Bars marked with an asterisk (*) are significantly different from the genotype control with level of significance as indicated: (*) P < 0.05, (**) P < 0.005, and (***) P < 0.0005. n ≥ 20 for each genotype.

Figure 3

Overexpression of CaMKII rescues both the response to the mated female and associative memory formation. CaMKII inhibitor was driven using MJ85b, a GAL4 line that expresses throughout the brain. The response to the mated female during conditioning and memory formation were measured as described in Materials and Methods and in Figures 1 and 2. All manipulations were performed at 25°C, 75% humidity in either dim red light (top two panels) or normal room light (bottom two panels). Statistical significance was assessed by Wilcoxon's signed-rank test. Data from MJ85b;UAS–ala/+ males (gray bars) were compared with data from MJ85b;UAS–ala/+; UAS–CaMKII males (black bars) and data from MJ85b controls (white bars). Bars marked with an asterisk (*) are significantly different from the genotype control with level of significance as indicated: (*) P < 0.05; (**) P < 0.005; and (***) P < 0.0005. n ≥ 20 for each genotype.

Figure 4

Multimodal behavioral circuits. Stimulatory connections between neural centers are indicated by (a T-bar) and inhibitory connections by (a solid circle). Stimulatory sensory inputs include vision (V) and positive chemosensory cues (+C). Inhibitory sensory inputs include aversive chemosensory cues (−C). Sensory inputs are integrated at one or more ICs to modulate behavior via the motor center. (A,B) Possible configurations of circuits that allow multiple sensory inputs to stimulate and modulate a behavior. In A, redundant sensory inputs feed into a single integration center that controls motor output. In B, redundant sensory inputs feed into IC 1 and IC 2, which can act independently. ICs are drawn to contain a subset of shared elements, although this need not be the case (see text). (C) A circuit with multiple integration centers operating under conditions where all sensory pathways are operative. In this case, both IC 1 and IC 2 are operative and redundant, that is, inactivation of one IC will not prevent modulation of behavior. Shading indicates neural centers that are active. (D) The circuit working in the absence of visual input. In this case, the only functional integration center is IC 2. Inactivation of this IC will prevent modulation of behavior.