Multidiscriminant analysis of physiological and integrative properties of BNST neurons

Classification and discrimination of neurons based on their morphological, neurochemical and physiological properties has been a central issue of neurophysiology and such studies revealed a high degree of heterogeneity of neuron types in most brain areas. Conventionally, physiological properties of neurons in vitro have been characterized by using simplistic stimulus protocols (stepwise command waveforms) in current or voltage clamp conditions. Such experiments show important features of neuronal excitability and also reveal cell type specific biophysical properties like the expression of specific voltage-gated ionic currents. However, neurons in vivo operate under intense synaptic bombardment and classification of cell types under such conditions might be different from that observed in low-conductance states. In the present study we performed a comprehensive analysis of physiological properties of neurons of the bed nucleus of stria terminalis (BNST) using both conventional current step protocols and simulated synaptic bombardment via dynamic clamp. The BNST is a component of the extended amygdala that receives a robust glutamatergic projection from the basolateral amygdala as well as inputs from the dysgranular insular and infralimbic cortices and, in turn, sends a major GABAergic projection to the central nucleus of the amygdala. Addiction-related neuroadaptive changes in the intrinsic cellular poperties of BNST neurons have been demonstrated and such alterations might impact the classification and discriminability of cell types. Using current step protocols in whole-cell clamp configuration we measured 22 physiological parameters including input resistance, voltage sag, rheobase, afterdepolarization among others. Additionally, we studied the neurons firing responses, the reliability and precision of spike timing under the action of simulated synaptic bombardment in dynamic clamp conditions. Feature vectors from both types of experiments were generated and used for multidiscriminant analysis. In the first case we found three cell types that displayed different degree of inward rectification, afterdepolarization and postinhibitory rebound in their voltage responses. The same population of neurons were less discriminable (more diverse) when using the simulated synaptic bombardment. Furthermore, multidiscriminant analysis performed on BNST neurons from alcohol-dependent animals demonstrated partial loss of diversity that can be attributed to the downregulation of the hyperpolarization-activated nonspecific cation current.