Abstract
The dorsolateral bed nucleus of the stria terminalis (dlBNST) is a limbic structure involved in negative affective states such as anxiety, fear and aversion. However, the mechanisms how the dlBNST mediates negative emotions are still poorly understood. The BNST projects to various brain regions including the central amygdala (CeA), ventral tegmental area (VTA), lateral hypothalamus (LH), and parabrachial nucleus (PB). Recent studies have demonstrated that the BNST neurons projecting to these brain regions play important roles in mediating emotional behaviors. The dlBNST neurons can be classified into three types based on differences in responses to hyperpolarizing or depolarizing current injections. In our observation, approximately 38%, 51%, and 11% of dlBNST neurons are typeI, typeII, and typeIII neurons, respectively. In addition, we previously reported that corticotropin-releasing factor (CRF) induces neuronal excitation in typeII neurons and enhances inhibitory input into typeIII neurons, suggesting that each type of dlBNST neurons has different functions. However, it remains unclear whether the proportion of neuronal types (type I-III) is same or different between the neuronal groups projecting to the distinct brain regions. Thus, in this study, we investigate the relationship between neuronal types and projecting brain regions. We injected retrograde tracers into the CeA and VTA, and then conducted whole-cell patch-clamp recordings in the brain slices including the dlBNST. The results revealed that approximately 10%, 60%, and 30% of CeA-projecting dlBNST neurons were typeI, typeII, and typeIII neurons, respectively, and approximately 0%, 60%, and 30% of VTA-projecting dlBNST neurons were typeI, typeII, and typeIII neurons, respectively. Most of the neurons projecting to these brain regions were typeII or typeIII neurons. Especially, a large portion (60%) of VTA-projecting dlBNST neurons were typeIII. The experiments to classify the dlBNST neurons projecting to the LH and PB are now being conducted.