Cell discharge correlates of posterior hypothalamic theta rhythm recorded in anesthetized rats and brain slices

Abstract

Kowalczyk et al. (Hippocampus 2014; 24:7-20) were probably the first to conduct a systemic study of posterior hypothalamic area (PHa) theta rhythm in anesthetized rats. They demonstrated that local PHa theta field potentials were tail-pinch resistant and could be generated in urethane-anesthetized rats independently of ongoing hippocampal formation theta rhythm. These in vivo data were also confirmed in PHa slice preparations perfused with cholinergic agonist, carbachol. In the current experiments we extend our earlier observations concerning PHa theta rhythm. Specifically, PHa field potentials were analyzed in relation to the ongoing local cell firing repertoire. Single-unit discharge patterns of cells localized in the posterior hypothalamic and supramammillary nuclei were characterized according to the criteria that was developed previously to classify theta-related cells in the hippocampal formation. The present study demonstrated that in addition to the earlier described theta-related cells (theta-on, theta-off and gating cells) the PHa also contains cells discharging in a very regular manner, which were labelled "timing cells". This type of neuron has not been previously documented. We suggest that "timing cells" form a part of the ascending brainstem synchronizing pathway, provideing a regular rhythmic signal which facilitates the transduction of tonic discharges of cells localized in the brain stem into theta-frequency rhythmic discharges. © 2016 Wiley Periodicals, Inc.

Postnatal Development of the Posterior Hypothalamic Theta Rhythm and Local Cell Discharges in Rat Brain Slices

“…It is also worth mentioning that no significant differences in local theta rhythm parameters were observed between the SuM and PH nuclei, other than a higher probability of recording theta in the SuM nucleus. This result is in line with previous observations (Kowalczyk et al, ; Bocian et al, ). In conclusion, our results indicate that PHa internal generators of local theta rhythm gradually develop from a very young age – as early as 8–10 days – until they mature completely at the age of 22–24 days.…”

“…This result was later confirmed by other authors (Sławinska and Kasicki, ). The presence of local PHa theta activity was also reported in urethane‐anesthetized rats by Grass et al () and later by other authors (Kocsis and Vertes, ; Kowalczyk et al, ; Bocian et al, ; ). Posterior hypothalamic theta rhythm has been also successfully recorded using deafferented PHa preparations for the first time by Kowalczyk et al ().…”

“…The next PHa study conducted by Bocian et at. () additionally provided evidence for a similar neuronal basis with HPC theta activity. The authors have shown that the activity of PHa neurons can also be successfully classified in regard to local PHa theta rhythm.…”

“…Most of the published data so far has suggested the role of PHa neuronal activity in HPC theta frequency programming (Vertes, ; Kirk and McNaughton, ; Bland et al, ; Kirk, ; Woodnorth et al, ; Woodnorth and McNaughton, ). Regardless however of a number of existing reports on PHa local theta rhythm observed in vivo (Bland and Vanderwolf, ; Grass et al, ; Sławinska and Kasicki, ; Kocsis and Vertes, ; Kowalczyk et al, ; Bocian et al, ; ) and in vitro (Kowalczyk et al, ; Bocian et al, ) the relevance of these oscillations is yet to be fully understood. Hence, as a continuation of our previous studies of the PHa oscillatory activity (Kowalczyk et al, ; Bocian et al, ), in this study we have investigated the postnatal development of both local theta rhythm and accompanying neuronal activity in PHa preparations obtained from rats aged 8–24 days.…”

“…In the majority of them, theta‐related cells of the PHa have been classified in regard to ongoing HPC theta rhythm. To our knowledge, Bocian et al () were the first to describe that PHa‐recorded neurons could also be classified in relation to local PHa theta oscillations. The authors demonstrated that the PHa neurons recorded from anesthetized rats and deafferented PHa preparations can be successfully classified according to ongoing local theta oscillations with the use of the well‐known theta‐related cells classification by Bland and Colom (; supplemented by Konopacki et al, and Kowalczyk et al, ).…”