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Olfactory associative conditioning in infant rats with brain stimulation as reward. I. Neurobehavioral consequences
1Department of Psychology, University of Oklahoma, Norman 73019.
Insights
Associating an odor with medial forebrain bundle/lateral hypothalamus (MFB/LH) stimulation in infant rats creates a lasting preference for that odor. This conditioning also alters brain responses to the odor, suggesting a critical role for prolonged olfactory bulb activity.
Area of Science:
- Neuroscience
- Olfactory Learning
- Neuroplasticity
Background:
- The medial forebrain bundle/lateral hypothalamus (MFB/LH) is crucial for reward and motivation.
- Early life experiences can significantly shape sensory processing and behavior.
Purpose of the Study:
- To investigate if associative olfactory conditioning in infant rats, using MFB/LH stimulation, can modify behavioral and physiological responses to odors.
- To explore the neural mechanisms underlying olfactory learning in early development.
Main Methods:
- Infant rats (postnatal day 12) received olfactory conditioning by pairing odor presentation with MFB/LH stimulation.
- Behavioral preference, 2-deoxy-glucose (2-DG) uptake in the olfactory bulb, and mitral/tufted cell responses were assessed.
- Direct MFB/LH stimulation effects on mitral/tufted cells were also examined.
Main Results:
- Odor-MFB/LH pairings led to a behavioral preference for the conditioned odor, increased focal 2-DG uptake, and altered mitral/tufted cell responses.
- Random odor and MFB/LH presentations did not induce these changes.
- MFB/LH stimulation caused a biphasic response in mitral/tufted cells: initial suppression followed by prolonged excitation or suppression.
Conclusions:
- Pairing olfactory input with MFB/LH stimulation effectively modifies subsequent olfactory responses, both behaviorally and physiologically.
- Prolonged olfactory bulb responses to MFB/LH stimulation may be a key mechanism in this olfactory learning and memory formation.
Abstract:
In Experiment 1, infant rats were implanted with a stimulating electrode in the medial forebrain bundle/lateral hypothalamus (MFB/LH) on postnatal day 12 (PN12). Four to 6 hours later, the pups underwent associative olfactory conditioning, with half of the pups trained with 30 temporal pairings of odor (5 s) and MFB/LH stimulation (200 Hz, 300 ms), and the other half trained with random presentations of odor and MFB/LH stimulation. On PN13, pups were tested for: (1) behavioral preference for the conditioned odor; (2) focal glomerular layer 2-DG uptake to the odor; or (3) mitral/tufted cell single-unit response pattern to the odor. Odor-MFB/LH pairings produced a relative behavioral preference, enhanced focal 2-DG uptake and a modified mitral/tufted cell response pattern to the conditioned odor. Random training resulted in none of these changes. In Experiment 2, PN12 pups were anesthetized with urethane and single-unit responses of mitral/tufted cells to MFB/LH stimulation were examined. MFB/LH stimulation produced a brief suppression of mitral/tufted cell activity followed either by a prolonged excitation (18/30 cells; 8-10 s duration) or a prolonged suppression (12/30 cells; 10-30 s). These results suggest that pairing olfactory nerve input with MFB/LH stimulation modifies subsequent behavioral and physiological responses to olfactory nerve input alone. Furthermore, the prolonged olfactory bulb response to MFB/LH stimulation may be critical in this modification.