GABA vs. glutamate or dopamine. Indeed LTP is increased medially with HFS, and the effect is dependent on the blockade of GABAA receptors, as well as the elimination of dopaminergic input from nigrostriatal synapses [35]. Next, the age of the animal is also an important factor for the switch between the induction of LTP and LTD in corticostriatal synapses. For example, the dorsolateral region of the striatum tends to express LTP in animals that are 12–14 days old, whereas LTD was found in slices from rats aged 15–34 days [26]. Interestingly, these authors also found that the type of synaptic plasticity is not altered by age in dorsomedial striatum, as NMDA-dependent LTP was found in both age groups. Lastly, the location of the stimulating electrode used for HFS to activate corticostriatal afferents influences the degree of synaptic plasticity in the striatum. For instance, if the stimulating electrode is located near the white matter it can directly cause the release of certain neurotransmitters such as dopamine or GABA. This may induce an LTD in the corticostriatal afferents. Conversely, if the stimulating electrode is located dorsally to the dorsomedial striatum on the cortical side, LTP is easily induced. This minimal current spread
