Region | Total [3H]Epibatidine Binding Population | α-CtxMII-Sensitive Population | Ki(α-CtxMII) | % α-CtxMII- Sensitive | Cytisine-Resistant Population | % Cytisine-Resistant |
---|---|---|---|---|---|---|
fmol/mg of protein | nM | fmol/mg of protein | ||||
Superior colliculus | 259 ± 5 | 67 ± 6 | 0.96 ± 0.3 | 25.9 | 84 ± 14 | 32.1 |
Thalamus | 226 ± 5 | 26 ± 4 | 5.3 ± 2.8 | 11.5 | 39.5 ± 2.6 | 17.5 |
Striatum | 118 ± 4 | 16 ± 1 | 0.83 ± 0.01 | 13.6 | 16 ± 2 | 13.6 |
Inferior colliculus | 123 ± 5 | 15 ± 1 | 7.0 ± 1.3 | 12.2 | 39 ± 1 | 31.7 |
Olfactory tubercles | 64 ± 5 | 14 ± 4 | 1.1 ± 0.1 | 21.9 | 11 ± 1 | 17.2 |
Midbrain | 159 ± 8 | 13 ± 1 | 2.4 ± 1.0 | 8.2 | 14 ± 1 | 8.8 |
Cortex | 62 ± 5 | 5 ± 2 | 1.3 ± 0.4 | 8.1 | 8 ± 1 | 12.8 |
Hippocampus | 68 ± 4 | N.D. | N/A | None | 4 ± 1 | 5.9 |
Cerebellum | 20 ± 2 | N.D. | N/A | None | 7 ± 3 | 35.0 |
Olfactory bulbs | 26 ± 8 | N.D. | N/A | None | 13 ± 4 | 50.0 |
Hindbrain | 91 ± 4 | N.D. | N/A | None | 18 ± 9 | 19.8 |
Interpeduncular nucleus | 973 ± 154 | N.D. | N/A | None | 607 ± 34 | 62.4 |
Particulate fractions were prepared from the indicated brain regions of C57BL/6 mice. The Kd and Bmaxvalues for each region were calculated from saturation binding experiments, as described under Experimental Procedures. Inhibition of [3H]epibatidine (500 pM) binding by cytisine and α-CtxMII was determined as illustrated in Figure 4. Cytisine inhibition was fitted to a two-site model, with IC50 andBmax values for the less-sensitive binding site being used to calculate the inhibition binding constant (Ki) and size of the cytisine-resistant [3H]epibatidine binding site population in each region. A one-site model was used to determine the Ki values and numbers of α-CtxMII sensitive binding sites in each region. TheKi value of α-CtxMII inhibition of [3H]epibatidine binding did not vary significantly between regions (one-way ANOVA; F(6,13) = 2.64,P > .05). All values are the mean ± S.E. of values derived from three to four independent experiments.
N.D., not detectable; N/A, not applicable.