Effects of carnosine on olfactory bulb EEG, evoked potentials and DC potentials

Carnosine is a dipeptide found in great quantities in the primary olfactory nerve and has been suggested to be the neurotransmitter of the olfactory receptor axons. The aim of the present study was to describe some of its electrophysiological actions in the olfactory bulb (OB) of rabbits under anesthesia. Carnosine as a 10% solution in amounts of 2-5 microliter was injected to the OB at the level of the glomerular layer by means of a pipette attached to a Hamilton syringe. Average evoked potentials (AEPs) on the stimulation of the lateral olfactory tract (LOT-AEP), electroencephalographic (EEG) activity and slow potential (DC) recordings were obtained. The LOT-AEPs were analyzed by fitting damped sine waves to them. The parameters of amplitude, frequency, decay rate, phase and rise rate were measured and statistically compared to the values obtained prior to the carnosine injection. An increase in frequency and decreases in the phase and the decay rate of the AEP were found. Carnosine also produced a sustained oscillation in the EEG and a surface negative, deep positive shift in the DC recording. The changes were maximal within the first minute after injection and lasted 2-7 min. Tyrodes' solution, which was used as the carnosine vehicle, did not produce any changes, nor did beta-alanine, which is one of the constituents of carnosine, at equivalent osmotic concentrations. It is concluded that carnosine has an excitatory action on the mitral/tufted cells, and that this effect is obscured by a secondary increase in granule cell (inhibitory) activity.