by Nilupaer Abudukeyoumu, Marianela Garcia-Munoz, Yoko Nakano, Gordon W. Arbuthnott.
Brain Mechanism for Behavior Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan
Cholinergic interneurons (ChIs) are sparsely distributed within the striatum, a nucleus that plays important roles in voluntary motor control, associated learning, procedural memory, execution of movement, action selection, and planning.
ChIs comprise 1-3% of all striatal neurons, are the main source of striatal acetylcholine, and have long been associated with deficits in Parkinson’s disease. A striatal imbalance between dopamine and acetylcholine has been suggested as one of the causes of parkinsonism.
To selectively deplete ChIs in the dorsolateral striatum of 21-day-old male mice (C57BL/6J), we used the saporin immunotoxin that targets choline acetyltransferase (Anti-ChAT-SAP, Cat. #IT-42). Experimental animals received a stereotaxic unilateral infusion of the targeted toxin (0.3μl/3min) and sham controls received the same volume of sterile saline (sham control). Our histological analysis encompassed Weeks 2-6 postsurgery performed at 2-week intervals (Fig. 1). The loss of cells reached a stable ~70% level by 4 to 6 weeks with the additional surprising finding that axon terminals stained with a vesicular acetylcholine transporter antibody were more numerous two weeks after the injection, returning to control levels by six weeks.
From a functional point of view, it will be important to find out if despite the cell loss, axon terminals sprout to invade the Anti-ChAT-SAP injected area from ~30% surviving ChIs or from ChIs in the surrounding tissue. To begin the study of dorsolateral striatal function following Anti-ChAT-SAP-induced ChI loss, we followed the same procedures as before and observed the animal’s perfomance in a reach-to-grasp task (Fig. 2). Mice were divided in two control groups (intact and sham) and one experimental Anti-ChAT-SAP-injected group. Training started one week postsurgery during the animal’s active circadian cycle and following 12 hours of food deprivation.
Once the animals passed the initial acquisition phase, the successful performance in the reach-to-grasp task — expressed as mean ± SD percentage is shown in Fig. 3.
Controls: 51.11 ± 3.83; n = 25 [intact], 48.79 ± 4.6; n = 9 [sham]
Treated: 26.28 ± 3.74; n = 13
The significantly-impaired performance of the experimental group compared to controls was present even when the animals were pretrained. The loss of ChIs impairs the performance of striatally-mediated motor tasks, which suggests that cholinergic synaptic function is more important than non-synaptic communication in this situation. A non-synaptic cholinergic tone may be important for setting functional striatal states in other circumstances, however, these specific lesions of ChI cells suggest that performance of a learned forelimb task requires that the cholinergic synaptic circuits of the striatum are intact.
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Other References Using Anti-ChAT-SAP
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