Many implementations of adaptive signal processing in the nervous system are likely to require a mechanism for gain control at the single neuron level. To properly adjust the gain of an individual neuron, it may be necessary to use information carried by neurons in other parts of the system. The ability to adjust the gain of neurons in one part of the brain, using control signals arising from another, has been observed in the electrosensory system of weakly electric fish, where descending pathways to a first-order sensory nucleus have been shown to influence the gain of its output neurons. Although the neural circuitry associated with this system is well studied, the exact nature of the gain control mechanism is not fully understood. In this paper, we propose a mechanism based on the regulation of total membrane conductance via synaptic activity on descending pathways. Using a simple neural model, we show how the activity levels of paired excitatory and inhibitory control pathways can regulate the gain and baseline excitation of a target neuron.