title: Learning-dependent plasticity of hippocampal CA1 pyramidal neuron postburst afterhyperpolarizations and increased excitability after inhibitory avoidance learning depend upon basolateral amygdala inputs.
abstract: Hippocampal pyramidal neurons in vitro exhibit transient learning-dependent reductions in the amplitude and duration of calcium-dependent postburst afterhyperpolarizations (AHPs), accompanied by other increases in excitability (i.e., increased firing rate, or reduced spike-frequency accommodation) after trace eyeblink conditioning or spatial learning, with a time-course appropriate to support consolidation of the learned tasks. Both these tasks require multiple days of training for acquisition. The hippocampus also plays a role in acquisition of single trial inhibitory avoidance learning. The current study assessed AHP plasticity in this single-trial learning task using in vitro tissue slices prepared at varying intervals posttrial using intracellular current-clamp recordings. Reduced AHPs and reduced accommodation were seen in ventral CA1 pyramidal neurons within 1 h posttraining, plasticity which persisted 24 h but was extinguished >72 h posttrial. There was also a reduction in ventral CA1 AHPs and accommodation 1 h following simple exposure to the IA apparatus (a novel context) but this change was extinguished by 24 h postexposure. Reductions in AHPs and accommodation were also seen in dorsal CA1 pyramidal neurons, but were delayed until 24 h posttrial and extinguished at >72 h posttrial. Finally, transient inactivation of the basolateral complex of the amygdala (with the local anesthetics lidocaine or bupivacaine) either immediately before or immediately posttrial blocked both learning and learning-dependent changes in excitability in the hippocampus assessed 24 h posttrial. CA3 pyramidal neurons showed no reductions in AHP peak amplitude or accommodation following IA training or context exposure.
authors.affiliation: School of Behavioral and Brain Sciences, the University of Texas at Dallas, Richardson, Texas 75080, USA.
authors.forename: George E
authors.initials: GE
authors.lastname: Farmer
authors.forename: Lucien T
authors.initials: LT
authors.lastname: Thompson
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000679:Amygdala / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001362:Avoidance Learning / Q000502:physiology*; D001767:Blinking / Q000502:physiology; D056547:CA1 Region, Hippocampal / Q000378:metabolism*; D056654:CA3 Region, Hippocampal / Q000378:metabolism; D003214:Conditioning, Classical / Q000502:physiology; D008297:Male; D009473:Neuronal Plasticity; D017966:Pyramidal Cells / Q000378:metabolism*; D051381:Rats; D020318:Rats, Long-Evans; D013997:Time Factors