In order to develop radiopharmaceuticals for targeting a serotonin receptor such as $5-HT_{1A}$, histidine-$C_n$-arylpiperazines (AP) (C = alkyl, n = 2, 3, 4) were prepared in five steps with yields of 25%, 37% and 51%, respectively, and radiolabeled with the $[^{99m}Tc(CO)_3(H_2O)+3]^+$. The $^{99m}Tc(CO)_3$-Histidine-Cn-APs were prepared with a high yield (>99%) and characterized as a tridentate complex with a neutral charge to pass through the blood-brain barrier (BBB). The rhenium complexes with $Re(CO)_3$ were also synthesised and comparative experiments were achieved to evaluate the nature of the $^{99m}Tc$ complexes.