The Modulation Of Galanin On Sound Signal Process Of Inferior Collicular Neurons

In the central auditory system, the information of the frequency, intensity, temporal and spectral properties involved in the sound signal is processed through the complex integration of the excitatory and inhibitory interaction of the neural circuits. The studies performed have shown that neurotransmitters, such as y -aminobutyric acid (GABA), acetylcholine (Ach), glutamic acid (Glu), glycine (Gly), and 5-hydroxytryptamine (5-HT) play a key role in processing of sound signal in inferior colliculus (IC). Galanin (Gal), a 29 amino acid C-amidated peptide originally isolated from the porcine gut in 1983, has been found it coexists with many other neurotransmitters in central nervous system (CNS). Its modulated effect on a lot of functional activities of CNS is observed, but whether it might modulate responses of auditory neuron remain undetermined. By iontophoresis application of Gal, the effects of Gal on basic response properties such as rate-intensity functions (RIFs), frequency tuning curves (FTCs), discharge pattern of inferior collicular neurons of mouse were investigated.A total of 96 neurons were attained with single and multiunit recording method from mouse (Mus musculus, Km) IC. 30 of 96 neurons accepted iontophoresis of Gal and the effects of Gal on the neuronal basic properties, rate-intensity functions, and frequency tunings of IC neurons were investigated. The results are as follow: 1) few units (n=5/30) transformed their discharge pattern during Gal application: Two phasic responders were changed to phasic burster, 2 Two phasic burst responders to phasic ones, and one tonic responder to phasic burst. It suggest that Gal shall exert facilitating or inhibitory modulation on IC neurons; 2) The RIFs of half units (n-15/30) varied after Gal application: Of non-monotonic RIFs, one was converted to monotonic RIF, 4 to saturated monotonic, while saturated monotonic RIFs, five to monotonic and four to non-monotonic. The others remained their RIFsconfiguration; 3) Facilitated response of few units (n=7/30) by Gal application were observed. The maximal discharges of these neurons increased significantly during Gal application; 4) The FTCs of few units (n=7/25) were sharpened, while the others' (n=11/25) were broadened by Gal.Our above results indicated that the characteristics of modulation of Gal are complex. Thought a lot of neurons were unaffected, excitatory modulations and inhibitory modulations of Gal on the responses properties of IC neurons were emerged. It is suggested that for different states of neural circuits, different galanin receptors (GalRs) of Gal may be involved in the processing of sound signal. Our data add the evidence to support the notion that the neuromodulators, for better processing of complex sound stimuli of the external world, should be taken part in functionally reconfiguring a wide range of neural circuits.