GABA transmission in the ventral pallidum is not involved in the control of latent inhibition in the rat.
Latent inhibition describes a process of learning to ignore stimuli of no consequence, and is disrupted in acute, positive-symptomatic schizophrenia. Understanding the neural basis of latent inhibition in animals may help to elucidate the neural dysfunction underlying positive schizophrenic symptoms in man. Evidence suggests a crucial role for dopamine transmission in the nucleus accumbens in the control of latent inhibition. The present studies investigated the role of the GABA-ergic efferent from the nucleus accumbens to the ventral pallidum in latent inhibition. The GABA(A) agonist muscimol (4.56 ng/microl), and antagonist picrotoxin (0.2 microg/microl), were infused into the ventral pallidum, and effects on latent inhibition were assessed using a conditioned suppression procedure. Neither drug produced specific effects on latent inhibition when given alone and, in the case of muscimol, failed to reverse the disruption of latent inhibition induced by systemic amphetamine. In addition to significant non-specific drug effects, a positive control experiment revealed that intra-pallidal picrotoxin significantly enhanced locomotion, suggesting that our manipulations of ventral pallidal GABA function were behaviourally effective. We conclude that modulating ventral pallidal GABA transmission does not affect latent inhibition. The implications of this finding for theories of the neural circuitry mediating latent inhibition and for understanding the functional role of ventral pallidal GABA transmission are discussed.
Department of Psychology, Institute of Psychiatry, Denmark Hill, London SE5 8AF, UK. n.lawrence@iop.kcl.ac.uk
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Lawrence
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Sharp
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Peters
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Gray
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Young
D000661:Amphetamine / Q000494:pharmacology; D000818:Animals; D001288:Attention / Q000502:physiology; D001522:Behavior, Animal / Q000187:drug effects; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology*; D015259:Dopamine Agents / Q000494:pharmacology; D004525:Efferent Pathways / Q000502:physiology; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D005917:Globus Pallidus / Q000187:drug effects* / Q000502:physiology*; D007266:Inhibition, Psychological; D008124:Locomotion / Q000187:drug effects; D008297:Male; D009118:Muscimol / Q000494:pharmacology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009714:Nucleus Accumbens / Q000502:physiology; D010852:Picrotoxin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D000661:Amphetamine; D000697:Central Nervous System Stimulants; D015259:Dopamine Agents; D018755:GABA Agonists; D018756:GABA Antagonists; D009118:Muscimol; D010852:Picrotoxin; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid