Variation of CS salience reveals group II mGluR-dependent and -independent forms of conditioning in the rat

• Published in: Neuropharmacology Vol. 43; no. 2; pp. 205 - 214
• Main Authors: Riedel, Gernot, Harrington, Nicholas R., Kozikowski, Alan P., Sandager-Nielsen, Karin, Macphail, Euan M.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01-08-2002; Elsevier
• Subjects: 4-Aminopyrrolidine-2,4-dicarboxylic acid; Animal; Animals; Biological and medical sciences; Central nervous system; Central neurotransmission. Neuromudulation. Pathways and receptors; Conditioning (Psychology) - drug effects; Conditioning (Psychology) - physiology; Fear conditioning; Fundamental and applied biological sciences. Psychology; Group II mGluRs; Hippocampus; Learning; Learning. Memory; Male; Motor Activity - drug effects; Motor Activity - physiology; Nerve Net - drug effects; Nerve Net - physiology; Neuronal Plasticity - drug effects; Neuronal Plasticity - physiology; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rat; Rats; Receptors, Metabotropic Glutamate - agonists; Receptors, Metabotropic Glutamate - physiology; Vertebrates: nervous system and sense organs; Group II mGluRs; Rat; 4-Aminopyrrolidine-2,4-dicarboxylic acid; Hippocampus; Fear conditioning; Agonist; Intraperitoneal administration; Memory; Rodentia; Central nervous system; Glutamate receptor; Learning; Vertebrata; Mammalia; Acquisition process; Metabotropic receptor; Animal; Second messenger; Mechanism of action; Brain (vertebrata)
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/S0028-3908(02)00096-5

There is good evidence that metabotropic glutamate receptors (mGluRs) are involved in some types of learning, and we have previously suggested that this involvement may reflect the modulation by mGluRs of the signal-to-noise ratio in neural networks. This hypothesis supposes that unspecific activation of mGluRs increases background noise level, so reducing the effectiveness of behaviourally relevant stimuli as signals in the network. We report here that intraperitoneal (i.p.) injection of 4-aminopyrrolidine-2,4-dicarboxylic acid (APDC), a specific agonist of group II mGluRs, disrupts conditioning to context (but not to cue) using conventional procedures. The hypothesis predicts, however, that the effect of the drug should be counteracted by the use of more salient stimuli, which would provide stronger signals to the network. In accordance with this prediction, we find that increases in the salience of
either the CS (context)
or the UCS (shock) abolish the drug-induced disruption of conditioning. These results suggest that group II mGluRs modulate neural networks involved in association formation.