Olanzapine causes a leptin-dependent increase in acetylcholine release in mouse prefrontal cortex

Abstract

Study objectives: The atypical antipsychotic olanzapine is used effectively for treating symptoms of schizophrenia and bipolar disorder. Unwanted effects of olanzapine include slowing of the electroencephalogram (EEG) during wakefulness and increased circulating levels of leptin. The mechanisms underlying the desired and undesired effects of olanzapine are poorly understood. Sleep and wakefulness are modulated by acetylcholine (ACh) in the prefrontal cortex, and leptin alters cholinergic transmission. This study tested the hypothesis that olanzapine interacts with leptin to regulate ACh release in the prefrontal cortex.

Design: Within/between subjects.

Setting: University of Michigan.

Patients or participants: Adult male C57BL/6J (B6) mice (n = 33) and B6.V-Lep(ob) (leptin-deficient) mice (n = 31).

Interventions: Olanzapine was delivered to the prefrontal cortex by microdialysis. Leptin-replacement in leptin-deficient mice was achieved using subcutaneous micro-osmotic pumps.

Measurements and results: Olanzapine caused a concentration-dependent increase in ACh release in B6 and leptin-deficient mice. Olanzapine was 230-fold more potent in leptin-deficient than in B6 mice for increasing ACh release, yet olanzapine caused a 51% greater ACh increase in B6 than in leptin-deficient mice. Olanzapine had no effect on recovery time from general anesthesia. Olanzapine increased EEG power in the delta (0.5-4 Hz) range. Thus, olanzapine dissociated the normal coupling between increased cortical ACh release, increased behavioral arousal, and EEG activation. Leptin replacement significantly enhanced (75%) the olanzapine-induced increase in ACh release.

Conclusion: Replacing leptin by systemic administration restored the olanzapine-induced enhancement of ACh release in the prefrontal cortex of leptin-deficient mouse.

Keywords: Atypical antipsychotics; B6.V-Lepob mouse; C57BL/6J mouse.

Figure 1

Histological analysis confirmed that all microdialysis sites were localized to the prefrontal cortex. (A) Vertical lines on the sagittal diagram of the mouse brain delineate the rostral-to-caudal extent of the microdialysis sites in the prefrontal cortex. Numbers at top and right of schematic indicate stereotaxic coordinates in mm, with bregma at 0, 0. (B) A digitized image of a coronal section from the brain of a C57BL/6J (B6) mouse shows a typical microdialysis site (arrow), located approximately 2.7 mm anterior to bregma. (C and D) The coronal diagrams were modified from a mouse brain atlas to show the locations of microdialysis sites for 24 B6 (C) and 24 leptin-deficient (D) mice. The prefrontal cortex is labeled as the frontal association area (FrA). Cylinders represent microdialysis membranes and are drawn to scale. Numbers at the lower right of each coronal diagram indicate mm anterior to bregma.

Figure 2

Time course of ACh release in the prefrontal cortex of C57BL/6J mouse shows stability and the olanzapine-induced increase. (A) Sequential measures of ACh release during dialysis with Ringer's solution (control). Each bar shows average ACh release from 3 mice. (B) Sequential measures of ACh release during dialysis with Ringer's solution (control) followed by dialysis with olanzapine. Each bar shows data from 3 mice, averaged for each time point.

Figure 3

Olanzapine delivered to the prefrontal cortex increased local ACh release and uncoupled the normal correlation of increased ACh release with behavioral and EEG activation. (A) Olanzapine caused a concentration-dependent increase in ACh release in the prefrontal cortex of C57BL/6J (B6) and leptin-deficient mice. Data are from 3 mice per concentration. Olanzapine (100 μM) caused a significantly smaller increase in ACh release in leptin-deficient mice than in B6 mice (*P < 0.01). (B) Olanzapine administered to the prefrontal cortex did not alter recovery time from isoflurane anesthesia. Average anesthesia recovery time for B6 and leptin-deficient mice is plotted as a function of the concentration of olanzapine used for dialysis. Each concentration was tested in 3 mice. (C) Olanzapine increased EEG power in the delta (0.5-4 Hz) range. Average power spectral densities for B6 mice (n = 7) are plotted from data recorded during dialysis with Ringer's solution (control) and with Ringer's solution containing olanzapine (30 μM). Olanzapine significantly (*P < 0.0001) increased EEG power at 1 Hz. Inset shows 10-s recordings of the cortical EEG obtained from the same mouse during dialysis with Ringer's solution and Ringer's solution containing olanzapine.

Figure 4

Leptin replacement in leptin-deficient mice enhanced the olanzapine-induced increase in ACh release within the prefrontal cortex. Each bar illustrates the average increase in ACh release from 5 mice during dialysis with olanzapine (100 μM). (Data for 3 of the 5 B6 mice and 3 of the 5 leptin-deficient mice are from Figure 3A.) Leptin-deficient mice showed a significantly (*P < 0.05) smaller olanzapine-induced increase in ACh release compared to B6 mice. The olanzapine-induced increase in ACh release in leptin-replaced mice was not significantly different from the olanzapine-induced increase measured from B6 mice.