4 -  Excitatory and inhibitory functions
There is also a need to understand functions of the
metabolic processes that are supported by the high
rate of energy production in the auditory system, and
why the auditory system is the most active in the
brain.  Caird et al. (1991) used the deoxyglucose
method in gerbils to visualize metabolic responses to
sounds of different frequencies.  They determined
that this functionality is provided by interactions of
both excitatory and inhibitory neurons [1].  Research
of this kind attempts the difficult task of mapping
metabolic activity in neurons involved in binaural
hearing, which is the basis for the capacity to maintain
focus on a particular sound source among many that
simultaneously impinge on the ears.

Friauf et al. (1999) investigated development of
glycine transporters.  These transporters are protein
components of pre-synaptic membranes that enable
rapid removal of biochemical transmitters once they
have stimulated their post-synaptic targets.  Glycine is
an inhibitory transmitter, and re-uptake is
accomplished by two classes of transporters, GLYT-1
over wide areas of the brain and GLYT-2
predominantly in brainstem systems.  Friauf et al.
found that GLYT-2 transporters develop long before
onset of hearing and during synapse maturation in
the auditory system and thus proposed that they are
involved in maturation processes.

1. Caird D et al. (1991)
   Functional organization of
   auditory cortical fields in the
   Mongolian gerbil (Meriones
   unguiculatus): Binaural 2-
   deoxyglucose patterns.
   
2. Friauf E et al. (1999)
   Developmental expression
   of the glycine transporter
   GLYT2 in the auditory
   system of rats suggests
   involvement in synapse
   maturation.
   

References

Full References

1. Caird D, Scheich H, Klinke R (1991) Functional organization of auditory cortical fields in the
   Mongolian gerbil (Meriones unguiculatus): Binaural 2-deoxyglucose patterns. Journal of
   Comparative Physiology A 168:13-26.
   
2. Friauf E, Aragon C, Lohrke S, Westenfelder B, Zafra F. (1999) Developmental
   expression of the glycine transporter GLYT2 in the auditory system of rats
   suggests involvement in synapse maturation. J Comp Neurol. 1999 Sep 13;412
   (1):17-37.
   

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