PGBC was a chemical neurotransmitter present in the brains of Betazoids.

Doctor Jo Stern noted elevated levels of PGBC and several other neurotransmitters in Ven Kaldarren when he was "possessed" by Uramtali, one of the dithparu discovered trapped within the Well of Souls. (TLE novel: Well of Souls)

PGBC would appear to be an invention of the author.