REAL-TIME TELEMETRY MONITORING OF ENERGY METABOLISM AND GLUTAMATE IN THE CENTRAL COMPLEX OF FREELY-WALKING GROMPHADORHINA PORTENTOSA

BACKGROUND: Recently, the profound homology between the basal ganglia of vertebrates and the central complex (CX) of insects have been highlighted [1-3]. The CX is a fundamental structure of insect brain regulating functions such as sleep, memory or motion control. Lately, new animal models, alternative to mammalians, have been used to study neurochemistry and expand the knowledge of the basal ganglia neurophysiology and the related disorders. Here, energy metabolism has been studied in the CX of Gromphadorhina portentosa by means of amperometric microsensors and biosensors. METHODS: Oxygen microsensors and glucose, lactate and glutamate biosensors have been implanted in the CX of cockroaches [1] and connected to a telemetric unit for the wireless transmission of electrochemical data. The oxygen microsensors were carbon-based discs further modified by means of a layer of nitrocellulose, in order to make the transducer selective only for oxygen, thanks also to the application of a cathodic potential of -400 mV vs Ag/AgCl. The biosensors, however, were platinum-based and suitably modified in order to make them selective for glucose, lactate and glutamate, by loading glucose, lactate and glutamate oxidase enzymes. Biosensors were further modified in order to shield them against interfering compounds. The hydrogen peroxide (HP) produced during enzymatic reaction is easily monitored on the platinum surface by applying an anodic potential of +700 mV vs Ag/AgCl. The amount of HP is proportional to the analyte present in the matrix. RESULTS: The functionality of the biosensors was initially verified by the injection in the hemolymph or the neck of the insect of the various analytes. The increase in the currents following these injections, demonstrated the capability of the devices to monitor the analyte variations in the cockroach's CX. The functionality of oxygen microsensors was assessed by varying the concentration of oxygen in the air inspired by the animal. Physiological stimulations, as handling or immobilization, determined a decrease in oxygen, an increase in lactate and glutamate, while glucose underwent no significant modification. Interestingly, the exposition to anesthetics, as CO2 , chloroform or triethylamine produced a decrease in oxygen and lactate, a small increase in glucose, while glutamate remained practically unchanged. CONCLUSIONS: By means of this model it was possible to study the central complex oxygen, glucose, lactate and glutamate dynamics, resulting as an alternative in- vivo model.