Evoked field responses, recurrent inhibition, long-term potentiation and immobility-related nonrhythmical EEG in the dentate gyrus of fimbria-fornix-lesioned and control rats.
The effects of complete fimbria-fornix (FF) lesioning, bilateral medial-FF lesioning and systemic administration of a novel noradrenergic alpha 2-antagonist, atipamezole, on electrophysiological properties of the hippocampal formation were studied in the rat. In the hilus of the dentate gyrus (DG) complete FF lesioning abolished the long-term potentiation (LTP) of the population spike (PS), which in control rats could be induced by the application of high-frequency stimulus trains on the medial perforant pathway (PP). Several other electrophysiological properties examined in the medial-FF-lesioned rats changed as well. These changes included a decrease in the efficacy of recurrent inhibition and slight differences in granular cell population response evoked by perforant path stimulation. Also, in the DG the power of awake immobility-related nonrhythmical electroencephalogram (EEG) was significantly lower in FF-lesioned rats than in controls. In the DG of control rats systemic administration of atipamezole (1 mg/kg) shifted the population spike-field postsynaptic potential response curve towards the left. In FF-lesioned rats this drug had no effects. The slight effects of atipamezole would be in line with earlier studies, which have shown that noradrenergic activation facilitates neuronal transmission in the DG. Possible explanations for the changes seen in FF-lesioned rats include deafferentation of different subcortical projections and increased epileptic activity. These established changes in synaptic plasticity, recurrent inhibition, nonrhythmical EEG and evoked responses would indicate that information processing is severely hampered in the first stage of the hippocampal trisynaptic circuit after fimbria-fornix lesioning. Thus, the results show that aminergic/cholinergic projections have a significant role in information processing in the dentate gyrus of hippocampal formation.
Department of Neurology, University of Kuopio, Finland.
A
A
Valjakka
K
K
Lukkarinen
E
E
Koivisto
R
R
Lammintausta
M M
MM
Airaksinen
P
P
Riekkinen
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D004569:Electroencephalography; D005071:Evoked Potentials / Q000187:drug effects; D007839:Functional Laterality; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
D000319:Adrenergic beta-Antagonists; D007093:Imidazoles; C050701:atipamezole