Article

Association learning-dependent increases in acetylcholine release in the rat auditory cortex during auditory classical conditioning

Department of Psychology, California State University San Bernardino, San Bernardino, CA 92399, USA.
Neurobiology of Learning and Memory (Impact Factor: 4.04). 06/2009; 92(3):400-9. DOI: 10.1016/j.nlm.2009.05.006
Source: PubMed

ABSTRACT The cholinergic system has been implicated in sensory cortical plasticity, learning and memory. This experiment determined the relationship between the acquisition of a Pavlovian conditioned approach response (CR) to an auditory conditioned stimulus (CS) and the release of acetylcholine (ACh) in the primary auditory cortex in rats. Samples of ACh were collected via microdialysis during behavioral training in either an auditory classical conditioning task or in a non-associative control task. The conditioning group received daily pairings of a white noise CS with a sucrose pellet unconditioned stimulus (US), while the control group received an equal number of CS and US presentations, but with these stimuli being presented randomly. Training was conducted on three consecutive days, with microdialysis samples being collected on Days 1 and 3 in separate sub-groups. The level of ACh released in the auditory cortex during conditioning trials increased from the first to the third day of training in the conditioning group as rats acquired the CR, but did not change in the control group, which did not acquire a CR. These data provide direct evidence for the hypothesis that ACh release increases in the primary auditory cortex during natural memory formation, where cholinergic activation is known to contribute to the formation of specific associative representational plasticity in conjunction with specific memory formation.

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    • "The apparent " return " to normality of memory at 4 days for VAChT KD HET mice may simply reflect a much slower build-up of memory to regular LTM levels in the animals with decreased ACh tone, so that it would take 4 days instead of one to encode the trace. Such an explanation would be in line with recent observations of a very protracted ACh intervention in other forms of memory [28]. Unfortunately, we were not able to see if the VAChT KD HOM mice would be able to remember the object after a longer delay (8 days) because this memory is absent even in the WT mice. "
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    • "However, recent imaging data in humans (Powers et al. 2012) suggests that these physiological integration windows may become more dynamic when tested across a range of stimulus types or when measured in behaving animals. Neuromodulators such as acetylcholine, noradrenaline, and serotonin can modulate the excitability of auditory cortical neurons (Foote et al. 1975; Hurley and Hall 2011) and are released during behavioral tasks (Stark and Scheich 1997; Butt et al. 2009). Acetylcholine release from the basal forebrain has been shown to alter the reliability of spike firing and synchrony among neurons in the visual cortex (Goard and Dan 2009), which will presumably influence the way cortical neurons multiplex sensory signals. "
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    • "Here we report the development of a single-cell analog for classical conditioning, using ACh as the CS and DA as the US. ACh is believed to play a role in other models of classical conditioning such as eyeblink conditioning (Christian and Thompson, 2003), contextual fear learning, (Raybuck and Gould, 2010), auditory conditioning (Butt et al., 2009) and olfactory learning in drosophila (Gervasi et al., 2010). Dopamine has long been implicated as playing a role in the reward pathway (Schultz, 2002), which serves as the US in appetitive protocols. "
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