Fig. 5.
Selective inhibition of perforant path and hilar path neurotransmission by molecular layer and hilar administered dynorphin, respectively. To evaluate the sites of action for κ opioid inhibitory effects in the dentate, the effects of locally applied dynorphin were studied on perforant path and hilar path stimulation-induced population responses. Dynorphin B (100 μm) was pressure-ejected (20–40 psi, 50–200 msec) in the molecular layer (M) or subgranular hilus (H), and the effects on hilar and/or perforant path neurotransmission were examined. A, Scanned cresyl violet-stained guinea pig hippocampal slice schematic of the recording electrode (R) in the granule cell layer (G) and a stimulating electrode (S) in the molecular layer (M) of the dentate gyrus. For any one slice, a hilar or a molecular layer cut (represented by the two dashed lines) or no cut was made, and a pressure injection pipette was placed into both the molecular layer (Dyn PuffM) and hilus (Dyn PuffH) sequentially in a counterbalanced order across slices. Specific stimulation of the perforant path or the hilar path was performed as before, depending on which of the pathways was cut. Both pathways were assumed to be stimulated in the uncut slice.B, Dynorphin B puffs inhibited granule cell responses in the uncut (PP+HP Stimulation) slice when puffed in either the molecular layer (ML Dyn;n = 8) or the hilus (Hilar Dyn;n = 18). In cut slices, however, dynorphin B puffs inhibited PP-induced responses (PP Stimulation) only when puffed in the molecular layer (ML Dyn;n = 4) and not the hilus (Hilar Dyn;n = 4). Conversely, only dynorphin puffs in the hilus (Hilar Dyn; n = 5) and not the molecular layer (ML Dyn; n = 7) inhibited hilar path activity (HP Stimulation). In all groups of slices, nBNI (100 nm) coadministration by bath application significantly attenuated the inhibitory effects of puffed dynorphin (n = 3). Asterisksignifies a statistical difference between that group and nBNI-coadministered controls.