Morphology and electrophysiology of neurons in dog paraventricular nucleus: In vitro study

The paraventricular nucleus (PVN) of the hypothalamus plays an important role in regulating gut motility. To date, there have been no intracellular electrophysiological studies of dog PVN neurons in vitro. The aims of this study were to: (1) adapt brain slice methods developed for studies of rodent CNS tissue to canine CNS tissue; and (2) study the electrophysiology and morphology of single neurons of the dog paraventricular nucleus (PVN). Coronal hypothalamic slice preparations (400 μm thick) of dog brain were used. Three groups of PVN neurons were classified based on their firing pattern. Continuous firing neurons (n=32) exhibited continuous ongoing action potentials (APs). Burst firing neurons generated bursts of APs (n=19). Intermittent firing neurons had only a few spontaneous APs. In contrast to continuous firing neurons, 14 of 19 burst firing neurons and 3 of 7 intermittent firing neurons responded to depolarizing current with a Ca²⁺-dependent low-threshold potential. Twenty-one PVN neurons studied electrophysiologically were filled with biocytin. Continuous firing neurons (n=12) had oval-shaped soma with two or three sparsely branched dendrites. Branched axons were found in two continuous firing neurons, in which one branch appeared to terminate locally. Burst firing neurons (n=8) generally had triangular soma with 2 to 5 branched dendrites. In summary, the brain slice technique was used to study the morphology and electrophysiology of single neurons of the dog brain. Electrophysiological and morphological properties of the three neuron groups were identified and discussed.