The Journal of Neuroscience, September 1, 2002, 22(17):7818-7824
Facilitation of Monosynaptic and Complex PSPs in Type I
Interneurons of Conditioned Hermissenda
Terry
Crow and
Lian-Ming
Tian
Department of Neurobiology and Anatomy, University of Texas Medical
School, Houston, Texas 77225
Synaptic plasticity and intrinsic changes in neuronal excitability
are two mechanisms for Pavlovian conditioning. Pavlovian conditioning
of Hermissenda produces synaptic facilitation of monosynaptic medial B-medial A IPSPs and intrinsic changes in excitability of type A and B cells in isolated and intact sensory neurons of the conditioned stimulus (CS) pathway. Recently two types of
interneurons that receive either excitatory or inhibitory monosynaptic
or polysynaptic input from photoreceptors have been identified. On the
basis of morphological and electrophysiological criteria, the
interneurons have been classified as type Ie,
Ii (direct), and type IIe,
IIi (indirect). We have now examined synaptic facilitation
of monosynaptic PSPs in type Ie and Ii
interneurons after conditioning and pseudorandom control procedures.
Here we report that CS-elicited spike activity is increased in type
Ie interneurons and decreased in type Ii
interneurons of conditioned animals relative to their respective
baseline activity and pseudorandom control groups. Classical
conditioning resulted in synaptic facilitation of type Ie
and Ii monosynaptic PSPs elicited by lateral B spikes and
enhancement of the amplitude of complex PSPs elicited by the CS. These
results provide additional sites of plasticity in the neural circuit
involved with the expression of learned behavior produced by Pavlovian
conditioning of Hermissenda.
Key words:
Hermissenda; Pavlovian conditioning; synaptic
facilitation; intrinsic excitability; interneuron plasticity; associative learning
Copyright © 2002 Society for Neuroscience 0270-6474/02/22177818-07$05.00/0
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