Immunohistochemical differentiation of electrophysiologically defined neuronal populations in the region of the rat hypothalamic paraventricular nucleus

Abstract

Intracellular recording and labeling were combined with neurophysin immunohistochemistry to study neurons in the paraventricular nucleus region of the rat hypothalamus. Neuronal membrane properties were examined in hypothalamic slices, and cells were labeled by injecting biocytin or Lucifer yellow. Slices were then embedded, sectioned, and immunohistochemically processed for neurophysin. Immunoreactivity patterns, and in some cases counterstaining, enabled determinations of the cytoarchitectonic positions of recorded cells to be made. Recorded cells were divided into three types according to their electrophysiological characteristics. The first type lacked low-threshold Ca2+ spikes and displayed linear current-voltage relations, a short time constant, and evidence for an A current. These were relatively large cells that were typically immunoreactive for neurophysin and were situated near other neurophysin-positive neurons. The second type had relatively small low-threshold potentials that did not generate bursts of Na+ spikes. These cells had heterogeneous current-voltage relations and intermediate time constants. They did not label for neurophysin, and most were located in the parvicellular subregion of the paraventricular nucleus. The third type had large low-threshold Ca2- spikes that generated bursts of Na+ spikes, and these cells had nonlinear current-voltage relations and long time constants. These neurons were dorsal or dorsolateral to the paraventricular nucleus and were not immunoreactive for neurophysin. These results indicate that paraventricular magnocellular neurons lack low-threshold potentials, whereas paraventricular parvicellular neurons display low-threshold potentials that generate one or two action potentials. Neurons that fire spike bursts from low-threshold potentials are adjacent to the paraventricular nucleus, confirming earlier reports.

Membrane properties of rat suprachiasmatic nucleus neurons receiving optic nerve input.

“…The LTS potentials recorded in SCN neurons did not appear as pronounced as the LTS potentials recorded in other central nervous system sites such as the thalamus (Jahnsen & Llinas, 1984), inferior olive (Llinas & Yarom, 1981) and areas near the paraventricular nucleus (Poulain & Carette, 1987;Hoffman et al 1991;. Nevertheless, the LTS potentials exhibited very similar voltage dependencies.…”

Noradrenergic Excitation of Magnocellular Neurons in the Rat Hypothalamic Paraventricular Nucleus via Intranuclear Glutamatergic Circuits

“…Putative magnocellular neurons of the PVN were distinguished from putative parvocellular neurons during recordings based on specific electrophysiological properties (Hoffman et al, 1991;Tasker and Dudek, 1991). In particular, magnocellular neurons have a prominent transient outward rectification, a relatively short membrane time constant, and linear current-voltage relations.…”

“…There are several possibilities, including a separate population of glutamatergic interneurons, a subtype of PVN parvocellular neuron that co-expresses glutamate, and other magnocellular neurons that co-express glutamate along with vasopressin or oxytocin. In the course of this study, we recorded the responses of both putative magnocellular and putative parvocellular neurons to norepinephrine, and interestingly, very few putative parvocellular neurons (ϳ2%) were depolarized by norepinephrine (Daftary et al, 1996) [note that all nonmagnocellular neurons located in the PV N were classified as parvocellular neurons; Hoffman et al (1991)]. In contrast, 23% of the putative magnocellular neurons showed a relatively robust depolarization (7.27 Ϯ 0.6 mV) in response to norepinephrine, as described above.…”

Somato-dendritic mechanisms underlying the electrophysiological properties of hypothalamic magnocellular neuroendocrine cells: A multicompartmental model study

“…Differences in electrophysiological properties between OT-secreting and VP-secreting cells are relatively few and subtle, and include differences in depolarizing after potentials (DAPs), which are more prevalent in, but not exclusive to, VP-secreting cells (Stern and Armstrong 1996); in a sustained outward rectification, found only in OT-secreting cells (Stern and Armstrong 1995;Armstrong and Stern 1997); in an A current-mediated transient outward rectification, which is more pronounced in VP-secreting cells (Stern and Armstrong 1996;Fisher et al 1998); and in a time-dependent inward rectification, more prominent in OTsecreting cells than in VP-secreting cells (Hirasawa et al 2003). Nevertheless, the electrophysiological properties of OT-and VP-secreting MNCs are, for the most part, remarkably similar, and they have been used routinely as a fingerprint to distinguish MNCs as a group from other hypothalamic neurons (Hoffman et al 1991;Tasker and Dudek 1991;Stern and Armstrong 1997).…”