Figure 1.
Endocannabinoid contribution to the difference in group 1 mGluR-induced LTD between the perforant path (PP) and Schaffer collateral (SC) pathways.
Inset: recording setup. One stimulating electrode was placed in the site of the PP pathway, and another stimulating electrode was placed in the site of SC synapses. Somatic recordings under the whole-cell voltage clamp mode were made in CA1 pyramidal neurons. A1. Representative traces of EPSCs in response to independent PP and SC stimuli recorded from the same rat hippocampal CA1 pyramidal neuron in the absence and presence of DHPG (50 µM) and washout. A2. Time courses of DHPG-induced changes in EPSCs. A3. Mean values of EPSCs averaged from 6 to 10 (Peak) and 36 to 40 min (LTD) following DHPG application. *P<0.05, **P<0.01 compared with PP. B1. Representative traces of EPSCs recorded in slices treated with AM251 (2 µM) in the absence and presence of DHPG (50 µM) and washout. B2. Time courses of DHPG-induced changes in EPSCs in the presence of AM251. B3. Mean values of EPSCs averaged from 6 to 10 (Peak) and 36 to 40 min (LTD) following DHPG application. **P<0.01 compared with PP. C1. Time courses of DHPG-induced changes in EPSCs at PP in the absence and presence of AM251. C2. Mean values of PP EPSCs averaged from 6 to 10 (Peak) and 36 to 40 min (LTD) following DHPG application in the absence of presence of AM251. C3. Time courses of DHPG-induced changes in EPSCs at SC in the absence and presence of AM251. C4. Mean values of SC EPSCs averaged from 6 to 10 (Peak) and 36 to 40 min (LTD) following DHPG application in the absence of presence of AM251. *P<0.05 compared with DHPG.
Figure 2.
The difference in group 1 mGluR-induced LTD between the PP and SC pathways is absent in mice deficient in the CB1 receptor.
A1. Representative traces of EPSCs recorded in hippocampal CA1 pyramidal neuron from a wild-type (WT) mouse in response to independent PP and SC stimuli in the absence and presence of DHPG (50 µM) and washout. A2. Time courses of DHPG-induced changes in EPSCs. A3. Mean values of EPSCs averaged from 6 to 10 (Peak) and 36 to 40 min (LTD) following DHPG application. **P<0.01 compared with PP. B1. Representative traces of EPSCs recorded in a mouse from a CB1R knockout (KO) mouse in the absence and presence of DHPG (50 µM) and washout. B2. Time courses of DHPG-induced changes in EPSCs. B3. Mean values of EPSCs averaged from 6 to 10 (Peak) and 36 to 40 min (LTD) following DHPG application. C1. Time courses of DHPG-induced changes in EPSCs at the PP in CB1R KO and their WT littermates. C2. Mean values of PP EPSCs averaged from 6 to 10 (Peak) and 36 to 40 min (LTD) following DHPG application. C3. Time courses of DHPG-induced changes in EPSCs at the SC in CB1R KO and their WT littermates. C4. Mean values of SC EPSCs averaged from 6 to 10 (Peak) and 36 to 40 min (LTD) following DHPG application. **P<0.05 compared with WT.
Figure 3.
Endocannabinoids are involved in LFS-induced LTD at the SC of CA1 pyramidal neurons.
A1. Representative traces of EPSCs recorded before and after LFS at the PP or SC in different rat hippocampal CA1 pyramidal neurons. LFS was delivered to the PP or SC independently. A2. Time courses of LSF-induced LTD at the PP and SC. A3. Mean values of LTD averaged from 30 to 35 min following LFS. **P<0.01 compared with LFS at the PP. B1. Representative traces of EPSCs recorded before and after LFS at the PP or SC of different rat hippocampal CA1 pyramidal neurons in slices treated with rimonabant (RIM, 2 µM). B2. Time courses of LSF-induced LTD at the PP and SC in the presence of RIM. B3. Mean values of LTD averaged from 30 to 35 min following LFS. C1. Time courses of LSF-induced LTD at the PP in the absence and presence of RIM. C2. Mean values of PP LTD in control and RIM. C3. Time courses of LSF-induced LTD at the SC in the absence and presence of RIM. C4. Mean values of SC LTD in control and RIM. **P<0.01 compared with SR. Scale bars: 200 pA/30 ms.
Figure 4.
Removal of the CB1 receptor eliminates the difference in LTD between the PP and SC.
A1. Representative traces of EPSCs recorded before and after LFS at the PP or SC in different hippocampal CA1 pyramidal neuron from WT. LFS was delivered to the PP or SC independently. A2. Time courses of LSF-induced LTD at the PP and SC in WT. A3. Mean values of LTD averaged from 30 to 35 min following LFS. **P<0.01 compared with LFS at the PP. B1. Representative traces of EPSCs recorded before and after LFS at the PP or SC of different rat hippocampal CA1 pyramidal neurons from CB1R KO. B2. Time courses of LSF-induced LTD at the PP and SC in CB1R KO. B3. Mean values of LTD averaged from 30 to 35 min following LFS. C. Summary for the differences in LFS-induced LTD at the SC and PP between WT and KO. **P<0.01 compared with KO.
Figure 5.
Depolarization-induced suppression of excitation (DSE) is present at the SC, but not at the PP.
A1. Representative traces of EPSCs recorded before and after a somatic depolarizing step from −70 to 0 mV for a 10 sec duration at the PP and SC of a rat pyramidal neuron. A2. Time courses of DSE at the PP and SC. B1. Representative traces of EPSCs recorded before and after a dendritic (200 µm from the soma) depolarizing step from −70 to 0 mV for a 10 sec duration at the SC of pyramidal neurons in the absence and presence of RIM (2 µM). B2. Time courses of DSE induced by dendritic depolarization at the SC. C1. Representative traces of EPSCs recorded before and after a dendritic (280 µm from the soma) depolarizing step from −70 to 0 mV for a 10 sec duration at the PP of a pyramidal neuron. B2. Time courses of DSE induced by dendritic depolarization at the PP. Scale bars: 200 pA/50 msec.
Figure 6.
Photolysis of caged Ca2+-induced suppression of EPSCs at the PP and SC.
A1. Representative traces of EPSCs recorded before and after a 10 sec photolysis of caged Ca2+ at the PP and SC of a rat pyramidal neuron. NP-EGTA (5 mM) was introduced into the cell via the recording patch pipette for dialysis at least 15 to 20 min before recordings were made. A2. Time courses of photolysis of caged Ca2+-induced suppression of EPSCs at the PP and SC. B1. Representative traces of EPSCs recorded before and after a 10 sec photolysis of caged Ca2+ at the PP and SC of a rat pyramidal neuron in the presence of RIM (2 µM). B2. Time courses of photolysis of caged Ca2+-induced suppression of EPSCs at the PP and SC in the presence of RIM. C. Time courses of photolysis of caged Ca2+-induced suppression of EPSCs at the SC in the absence and presence of RIM. D. Time courses of photolysis of caged Ca2+-induced suppression of EPSCs at the PP in the absence and presence of RIM. Scale bar: 200 pA/50 msec.
Figure 7.
WIN55,212-2 produces different effects on EPSCs at the PP and SC.
A1. Representative traces of paired-EPSCs recorded from a rat hippocampal CA1 pyramidal neuron in response to independent PP and SC stimuli in the absence and presence of WIN (5 µM). A2. Mean values of paired-pulse ratio (PPR) at the PP and SC in the absence and presence of WIN. A3. Time courses of WIN-induced changes in EPSCs at the PP and SC. A4. Mean values of EPSCs averaged from 20 to 25 min following WIN application. *P<0.05, **P<0.01 compared with PP. B1. Representative traces of paired-EPSCs recorded in slices treated with RIM (2 µM) in the absence and presence of WIN (5 µM). B2. Mean values of PPR at the PP and SC in the absence and presence of WIN+RIM. B3. Time courses of WIN-induced changes in EPSCs at the PP and SC in the presence of RIM. B4. Mean values of EPSCs averaged from 20 to 25 min following WIN application in RIM-treated slices. Scale bars: 200 pA/100 msec.
Figure 8.
Expression of the CB1 receptor is relatively lower in the stratum lacunosum-moleculare (SLM) when compared to that in the stratum radiatum (SR).
Rat or mouse hippocampal slices (30 µm) were prepared with cryostat, then cut and incubated with primary anti-CB1R antibody (1∶2,000) for 48 h at 4°C. Images were taken using a Zeiss deconvolution microscope. A–D. Immunostaining of rat hippocampal CB1 receptor. E1–E3. The specificity of the CB1 antibodies was determined by staining the slices from mice deficient in the CB1 receptor. SP: the stratum pyramidale; ML: molecular layer; GCL: granule cell layer; DG: dentate gyrus.