Post-synaptic GABA(B) receptors--possible controllers of coincidence detection?
Post-synaptic GABA(B) responses (slow, late hyperpolarisations which can be eliminated by perfusion with phaclofen) can be recorded in vitro from many, but not all, neurones in the intermediate medial hyperstriatum ventrale (IMHV). The IMHV is an area of the chick forebrain which is remarkable for its plasticity, and for its essential role in two specific types of early learning-imprinting, and a form of one-trial passive-avoidance learning. Post-synaptic GABA(B) responses are strongly statistically associated with other properties (such as high membrane resistance) which are, themselves, dependent on a bird's past history. There is also evidence that their incidence changes with prior training in vivo and with age. GABA(B) hyperpolarisations are always offset to a varying extent by excitatory NMDA components. These two components follow a very similar time-course, so that the duration and (to a lesser extent), the magnitude of a response is controlled by the balance between the two systems. The evidence suggests that this balance fluctuates, and that its fluctuations determine the extent to which any neurone can function as a coincidence detector.
Bradley
P M
PM
Department of Neuroscience, Medical School, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
Burns
B D
BD
Gowland
C J
CJ
Webb
A C
AC
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001418:Baclofen / Q000031:analogs & derivatives* / Q000494:pharmacology; D002645:Chickens; D017097:Electric Impedance; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D009474:Neurons / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D016548:Prosencephalon / Q000166:cytology* / Q000502:physiology; D018080:Receptors, GABA-B / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014633:Valine / Q000031:analogs & derivatives* / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D018080:Receptors, GABA-B; C052329:phaclofen; C056639:2-amino-5-phosphopentanoic acid; D001418:Baclofen; D014633:Valine