Article Figures & Data
Figures
- Fig. 1.
Expression of secretin and secretin receptors in the rat cerebellum. A, In Northern blot analysis, positive signals for secretin and its receptor were detected in the cerebellum. B, In in situ hybridization, prominent secretin mRNA signals were found in Purkinje cells when using the antisense (left) probe but not the sense (right) probe. C, Purkinje cells also expressed secretin receptor mRNA. Left, Antisense probe;right, sense probe. D, Immunoreactivity for secretin was confined to the soma and dendrites of Purkinje cells (left) and was absent in consecutive control sections (right) incubated with antiserum preabsorbed with secretin. Scale bars: B,C, 100 μm;D, 40 μm. GL, Granule cell layer;ML, molecular layer; P, Purkinje cells.
- Fig. 2.
Coexpression of parvalbumin and secretin receptor mRNA in cells in the cerebellar cortex. A,B, In these consecutive sections, parvalbumin immunoreactivity and in situ hybridization signals were colocalized in Purkinje cells and some neurons in the molecular layer. The arrows indicate two corresponding neurons in the two sections. C, In another consecutive section, GFAP-immunopositive cell bodies were mainly confined in the granule cell layer and did not colocalize with cells labeled in the in situ hybridization. Scale bar, 20 μm. GL, Granule cell layer; ML, molecular layer;P, Purkinje cell layer.
- Fig. 3.
Secretin facilitates GABAergic, but not glutamatergic, synaptic transmission in the rat cerebellum.A, Raw traces showing that evoked and spontaneous IPSCs were augmented by bath application of 30 nm of secretin. Paired stimuli (arrows), separated by a 50 msec interval, were given every 4 sec. Four overlaying traces are plotted in each case. B, Top traces on theleft, which were averaged from 50 evoked IPSCs, revealed that the amplitude and waveform of parallel fiber (PF)-PSC were unaffected by secretin, in sharp contrast to the evoked IPSC shown in the bottom trace. Mean data of the effect of 30 nm secretin on PF-PSCs and evoked IPSC are shown on theright. C, On the left, the normalized IPSCs from the cell shown in A andB revealed a reduction of paired-pulse ratio (IPSC2/IPSC1).Numbers in the parentheses denote the sample size. *p < 0.05 (paired ttest); ***p < 0.001 (t test).
- Fig. 4.
Effect of secretin on miniature IPSCs and postsynaptic GABAA receptor sensitivity of Purkinje cells.A, A typical experiment showing that secretin increased the frequency of GABAA-mediated miniature IPSCs. Secretin was added to the superfusion solution for 4 min. Two sets of traces at the time points indicated are shown on a fast time-base. In this cell, recovery from the effect of secretin took 35 min. B, Concentration–response curve of the effects of secretin on the frequency (left) and amplitude (right) of the miniature IPSCs. A clear dose-dependent effect was found in the frequency only. Numbers in theparentheses denote the number of cells tested.C, The postsynaptic sensitivity of GABAAreceptor of a Purkinje cell in the absence (left) or presence (right) of 30 nm secretin was compared. Small volumes (1 μl) of 0.1 mm GABA were applied directly to the bath at a fixed distance from the recorded cell.
- Fig. 5.
Mechanism of secretin-induced potentiation of miniature IPSCs in Purkinje cells. A, The general calcium channel blocker Cd2+ at 100 μmdid not attenuate the facilitatory effect of secretin on miniature IPSC frequency (top panel). In contrast, SQ22536, a specific inhibitor of adenylyl cyclase, significantly reduced the effect of 30 nm secretin (bottom panel). B, Histogram summarizing the effects of Cd2+ and SQ22536 on miniature IPSC frequency. Results are expressed as percentage changes over the control value before addition of the drugs. Numbers in theparentheses denote the number of cells tested in each case; **p < 0.01.
