Glutamatergic hippocampal formation projections to prefrontal cortex in the rat are regulated by GABAergic inhibition and show convergence with glutamatergic projections from the limbic thalamus.
Anatomic and physiologic studies in the rat have shown projections from the hippocampal formation (HF) and mediodorsal (MD) thalamic nucleus to the medial prefrontal cortex (mPFC). The authors used multi-barrel iontophoresis to: confirm the neurotransmitter used in the projection from HF to mPFC; investigate the role of GABAergic inhibition in the regulation of this projection; and examine the functional convergence of projections from HF and MD onto single mPFC neurons. During HF stimulation, nine cells (6%) showed excitation followed by prolonged inhibition, 39 cells (26%) showed prolonged inhibition alone and 100 cells (68%) showed no clear response. In a further 12 cells that showed no predrug excitation to HF stimulation (representing 16% of the cells in this category), iontophoresis of the GABAA antagonist bicuculline methiodide (BMI) revealed excitatory responses. A total of six mPFC cells (38% of the cells showing excitatory responses to HF stimulation) showed convergent excitation to HF and MD thalamic (or adjacent paratenial nucleus) stimulation. Five out of eight (63%) of the predrug or BMI-revealed excitatory responses of mPFC neurons to HF stimulation were selectively decreased after AMPA antagonist iontophoresis (either CNQX or DNQX). These data confirm that the HF projection to prefrontal cortex is, at least in part, glutamatergic; suggest that the responses of mPFC neurons to activity in this HF pathway are regulated by GABAergic inhibition; and indicate that projections from HF and MD converge onto single mPFC neurons.
Brain Research Institute, Reed Neurological Research Center, University of California, Los Angeles.
J
J
Gigg
A M
AM
Tan
D M
DM
Finch
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives / Q000494:pharmacology; D001640:Bicuculline / Q000031:analogs & derivatives / Q000494:pharmacology; D001931:Brain Mapping; D004558:Electric Stimulation; D004594:Electrophysiology / Q000379:methods; D058787:GABA-A Receptor Antagonists; D058788:GABA-B Receptor Antagonists; D018698:Glutamic Acid / Q000494:pharmacology / Q000502:physiology*; D008032:Limbic System / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009943:Organophosphorus Compounds / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D017397:Prefrontal Cortex / Q000502:physiology*; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D013788:Thalamus / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D058787:GABA-A Receptor Antagonists; D058788:GABA-B Receptor Antagonists; D009943:Organophosphorus Compounds; D010879:Piperazines; D011810:Quinoxalines; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; C052329:phaclofen; D018698:Glutamic Acid; C017069:bicuculline methiodide; D005680:gamma-Aminobutyric Acid; C056723:FG 9041; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; C066430:CGP 35348; C050592:3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid; D001418:Baclofen; C057491:2-hydroxysaclofen; D001640:Bicuculline