Does GABA enhance or inhibit negative effects of glutamate?
Glutamate causes an EPSP (Excitatory Post Synaptic Potential,) thereby making the neuron less negative depolarize) and closer to voltage required to cause an Action Potential (AP)  and thus fire.  GABA causes an IPSP (Inhibitory Post Synaptic Potential) making the neuron more negative (hyperpolarize) and further away from the voltage required to fire and cause an AP.  GABA &amp; Glutamate receptors  are generally on different neurons that synapse with other interneurons &amp; oppose each other, although neither one is generally the end neurotransmitter of the locus,  nor the only neurotransmitter of the neuron, so basically act as neuromodulators on the post-synaptic neuron. Glutamatergic receptors generally affect Sodium Channels &amp;  GABA-ergic neurons generally  affect Chloride Channels. In theory, inhibiting an inhibitory neuron would be the equivalent of exciting an excitatory neuron, but since they primarily affect  post-synaptic neurons, the effect is cumulative, so the post-synaptic interneuron is basically adding up all the EPSPs &amp; IPSPs to get a RMP (Resting Membrane Potential) &amp; some additional stimulus must occur to get the neuron to fire (AP)