## 3 Results
### Distribution of Serotonergic Neurons in the Myenteric Ganglia of Controls  
The occurrence of 5-HT-IR myenteric neurons was calculated as the proportion of the total myenteric neuronal number that was HuCD-stained. Despite the extremely low representation of 5-HT-IR neurons in the myenteric ganglia, strong immunoreactivity was observed in the varicosities of projections within the plexus (Figure 1). In the myenteric ganglia, 5-HT-IR neurons displayed very similar distributions among the different intestinal segments (Figure 2). The proportion of 5-HT-IR neurons varied only by 2-3% in different gut segments: 2.42 \(\pm\) 0.35% in the duodenum, 2.45 \(\pm\) 0.33% in the ileum, and 2.35 \(\pm\) 0.31% in the colon. Proportion of Serotonergic Neurons in the Myenteric Ganglia of Diabetics and Insulin-Treated Diabetics  
In the myenteric ganglia of diabetic rats, the proportion of 5-HT-IR neurons was increased in each gut segment compared to the controls (Figures 3 and 4). A 2.5-fold change was observed in the duodenal ganglia of diabetics (5.97 \(\pm\) 0.7% vs. 2.42 \(\pm\) 0.35%). A similar proportional increase was observed in the colon where the percentage was 5.91 \(\pm\) 0.54% relative to 2.35 \(\pm\) 0.31% of the controls. In the ileum, a slight increasing tendency was observed (3.8 \(\pm\) 0.41% vs. 2.45 \(\pm\) 0.33%). The immediate insulin treatment maintained the proportion of 5-HT-IR myenteric neurons close to the control value in all investigated gut segments (Figures 4 and 5). \begin{table}
\begin{tabular}{c c c c c} \hline  & \multicolumn{2}{c}{**Body Weight**} & \multicolumn{2}{c}{**Blood Glucose Concentration**} \\  & **(g) \(\pm\) SEM** & \multicolumn{2}{c}{**(mmol/L) \(\pm\) SEM**} \\ \cline{2-5}  & _Initial_ & _Final_ & _Initial_ & _Final (Average)_ \\ \hline
**Controls** (n = 10) & 226.2 \(\pm\) 4.3 & 457.1 \(\pm\) 19.7 * & 5.46 \(\pm\) 0.4 & 5.56 \(\pm\) 0.1 \\
**Diabetics** (n = 7) & 226.7 \(\pm\) 6.0 & 344.4 \(\pm\) 16.0 *00 & 4.99 \(\pm\) 0.4 & 25.54 \(\pm\) 1.1 *00 \\
**Insulin-treated** & 241.3 \(\pm\) 1.9 & 398 \(\pm\) 8.9 *00 & 4.85 \(\pm\) 0.1 & 13.75 \(\pm\) 1.0 *00 \\ \hline \end{tabular}  
* \(p\) < 0.0001 vs. initial; \({}^{\circ}\)\(p\) < 0.001 and \({}^{\circ\circ}\)\(p\) < 0.0001 vs. final controls; and \({}^{\ast}\)\(p\) < 0.01 and \({}^{\ast\prime}\)\(p\) < 0.0001 vs. final diabetics.  
\end{table} 
Table 1: Weight and glycemic characteristics of the three experimental groups of rats. Figure 1: Representative fluorescent micrographs from the duodenum (**a**), ileum (**b**), and colon (**c**) of controls after 5-HT-HuCD immunohistochemistry. On the myenteric plexus whole-mount preparations, asterisks indicate neurons that are labelled for HuCD, arrowheads point to myenteric 5-HT-IR varicosities, and the arrow points to a myenteric neuron that is double-labelled for both 5-HT and HuCD. Scale bars are 100 μm (**a**), 20 μm (**b**), and 100 μm (**c**). Figure 3: Representative fluorescent micrographs from the duodenum (**a**), ileum (**b**), and colon (**c**) of diabetic rats after 5-HT-HuCD immunohistochemistry. On the myenteric plexus whole-mount preparations, asterisks indicate neurons that are labelled for HuCD, arrowheads point to myenteric 5-HT-IR varicosities, and arrows point to myenteric neurons that are double-labelled for both 5-HT and HuCD. Scale bars are 100 \(\upmu\)m (**a**), 20 \(\upmu\)m (**b**), and 50 \(\upmu\)m (**c**). Figure 2: Proportion of 5-HT-IR neurons in the myenteric ganglia of the duodenum, ileum, and colon of controls. The percentage of 5-HT-IR neurons was only 2–3% in the myenteric ganglia in all intestinal segments without any significant differences. Data are expressed as mean \(\pm\) SEM. CD—control duodenum; CI—control ileum; and CC—control colon. Figure 4: Proportion of 5-HT-IR neurons of the duodenum, ileum, and colon of controls, diabetics, and insulin-treated diabetics. The percentage of 5-HT-IR myenteric neurons was increased in each gut segment of diabetics.