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.