Deep brain stimulation (DBS) is currently being investigated for the treatment of depression. Results of early clinical trials have been very promising, but the mechanisms responsible for the effects of DBS are still unknown. This article reviews behavioral findings of stimulation applied to different brain targets in rodents, with a particular focus on the ventromedial prefrontal cortex. Mechanisms and substrates involved in the antidepressant-like effects of DBS, including the role of local tissue inactivation, the modulation of fiber pathways in the vicinity of the electrodes, as well as the importance of the serotonergic system and brain derived neurotrophic factor are discussed.
KeywordsAnimal models; deep brain stimulation; depression; fiber pathways; psychiatry; radiofrequency lesions; serotonin Deep brain stimulation (DBS) has been investigated for the treatment of depression with promising clinical results (1-11). Although preclinical research using electrical stimulation to study behavior has been conducted for over 50 years, results from animal studies did not comprise the rationale for the current use of DBS in depression. Experiments i n animal models to investigate substrates and mechanisms responsible for the antidepressant-like effects of DBS were only conducted after the initial clinical trials were published (2,7,8,(10)(11)(12).This article provides an overview of current findings and some of the emerging concepts from experiments with DBS in models of depression, with a particular focus on results obtained with ventromedial prefrontal cortex (vmPFC) stimulation in rodents.
CIHR Author Manuscript
CIHR Author Manuscript
CIHR Author Manuscript
Choosing a Stimulation TargetThe medial surface of the frontal cortex in rodents has been subdivided into four cytoarchitectural regions: the agranular frontal cortex, anterior cingulate cortex (AC), prelimbic cortex (PL), and infralimbic cortex(IL)( Figure 1A)(13-15).Alternatively, it has also been subdivided into dorsal and ventral "systems," according to functional role as well as afferent and efferent projections (15). The dorsal system includes the frontal agranular cortex, AC, and dorsal PL and seems to be involved in the control of eye and head movements (14-16). The ventral system, comprises the IL and ventral aspects of the PL (vPL), projects mainly to the amygdala, hypothalamus, insula, and brainstem and has been suggested to play a role in autonomic control (17)(18)(19)(20). Vertes (21) proposed an alternative subdivision of the medial prefrontal cortex (PFC) in dorsal (frontal agranular cortex and AC) and ventral regions (PL and IL). To mimic the effects of subgenual cingulum (SCG) DBS in rodents, we have been applying stimulation to the vmPFC (12,(22)(23)(24)(25)(26), including IL and vPL.Overall, the limits of the vPL are hard to delineate. However, if an arbitrary line is traced dividing the PL into dorsal and ventral halves, the approximate anteroposterior, mediolateral, and dorsoventral dimensions of the vmPFC (including IL and vPL...