Septo-hippocampal projectionsMedial Septal complex (MS-DB) Three projection bundles, reciprocal

• Diagonal band of Broca – amygdaloid complex

• Induseum griseum – hippocampus, amygdala

• Fornix – subiculum, CA3

Induseum Griseum• Developmental remnant since the supra-diencephalic hippocampal

localization • Hippocampal projection to septum

MS-DB projection to hippocampus

• From ... MS-DB ipsilateral• Via -- Dorsal projection

pathway • Fibria hippocampi• Dorsal fornix • Supracallosal area

• To ... – SUB– CA3– DG

Neurotransmitters of MS-DB projections

• ………………………• GABA: Gabaergic long projection neurons (Leranth, 2007)

– Terminate with large clustered buttons on Parvalbumin positive cells (GABA interneurons) >> see theta-oscillation pacemaker cirquits

– Densely spiny cells at CA1-3 oriens and CA3 radiata– Sparsely spiny cells in DG – Dense innervation of supragranular zone in DG, Stratum oriens in CA3– Light innervation of hilus, stratum radiata CA3

Hippocampo-septal projections• CA3 to Lateral Septum

– Partly GABAergic – Bilateral

• Subiculum To Medial Septum– Glutamatergic – GABAergic– Ipsilateral

Both pathways preferentially terminate on GABAergic interneurons of septal nuclei

• Long-range projecting GABAergic neurons

…………………………...• Sparsely spiny / smooth

somata• Densely spiny / spiny

somata• Intermediate forms in

hilus

Classification of GABAergic long projection

hippocampo-septal neurons Class I II IIISomatostatin - - +Calbindin - + +mGluR1a + - -M2R + + -Dendritic projection

trilaminar Lamina resticted Lamina resticted

Somata location L-M Oriens OriensSpiking with theta

Out of phase In phase, regular, in trains

In phase, irregular, single spike

Spiking with ripples

Out In ?

Long Range GABA projections

• Hippocamposeptal long-range GABAergic projections

• Highly myelinized, more than Glutamatergic

• Conductance of IPSPs precede EPSPs ????