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

Abstract

Theta rhythms have been recorded from rat brain slices of the posterior hypothalamic area (PHa), including the supramammillary and posterior hypothalamic nuclei. Additionally, in numerous studies theta-related neurons were identified in the PHa according to the classification of Bland and Colom (Progress in Neurobiology, 41, 157-208, 1993). It is currently widely accepted that the PHa contributes to the process of HPC theta frequency programming at least in certain behavioral states. The postnatal development of the HPC and its ability to generate theta has also been a subject of studies. Specifically, it was found that theta oscillations are present in the HPC of 8-10 days old rat pups and turn into a well-synchronized and high-amplitude activity in the following few days. In our current study, we therefore focused on the postnatal development of cholinergically-induced theta rhythm and theta-related neuronal activity in PHa slices obtained from 8 to 24 days old rat pups. Theta activity was observed in the PHa preparations at the age of 8-10 days and then progressively increased its probability of occurrence, amplitude and synchrony up to the age of 22-24 days when it reached a plateau phase. A steady increase in the number of recorded neurons correlated with local theta oscillations was also observed.

Posterior hypothalamic theta rhythm: Electrophysiological basis and involvement of glutamatergic receptors

“…On the other hand, the only type of theta‐related neurons extracellularly recorded in posterior hypothalamic slice preparations were theta‐on phasic cells. Interestingly, a similar uneven distribution of given theta‐related subtypes of neurons was observed in previous studies concerning the cellular correlates of PHa neuronal firing in relation to local cholinergic theta field oscillations (Bocian et al, 2016; Caban et al, 2018). The very low probability of recording theta‐on phasic neurons in the PHa of urethane‐anesthetized animals may seem surprising considering that a relatively large number of these cells was found in this area in some of the previous in vivo studies.…”

“…Until recently, it seemed that the only structure containing theta‐related cells within its neuronal networks and having the ability to generate local theta field potentials was the hippocampal formation (Bland & Colom, 1993; Colom & Bland, 1987; Konopacki et al, 2006; Kowalczyk et al, 2013; Smythe et al, 1991). However, studies performed during the past few years have revealed that the PHa can also be recognized as an independent theta generator in which neurons correlated with local oscillatory activity are present (Bocian et al, 2016; Caban et al, 2018). The ability of the SuM and posterior hypothalamic nuclei to generate local theta field potentials and accompanying cell discharges independently of other brain structures was discussed earlier in detail.…”

“…The function of the PHa in this ascending pathway may be to transduce the tonic pontine signal into a rhythmic pattern that facilitates the appearance of limbic theta oscillations at given frequencies (Bocian et al, 2016). Timing cells present in the PHa are postulated to play an important role in this transduction mechanism (Bocian et al, 2016; Caban et al, 2018). Interestingly, a subpopulation of septal neurons exhibiting timing cell firing properties similar to those of PHa neurons was described earlier.…”

“…Additionally, there is accumulating data showing that this diencephalic region is not only capable of controlling and modulating limbic theta rhythm but is also an independent generator of theta field potentials. Specifically, it was shown that locally recorded PHa theta rhythmic oscillations can be observed in freely moving rats (Bland & Vanderwolf, 1972; Ruan et al, 2011; Sławińska & Kasicki, 1995), anesthetized rats (Bocian et al, 2016; Grass et al, 1995; Kocsis & Vertes, 1997; Kowalczyk et al, 2014), and in vitro preparations of the PHa (Bocian et al, 2016; Caban et al, 2018; Kowalczyk et al, 2014). Unfortunately, the physiological role of PHa theta rhythmicity remains largely unknown.…”

“…Moreover, data concerning the neurochemical basis of posterior hypothalamic theta rhythm are rather sparse. It was shown that theta field potentials recorded locally in the PHa have a cholinergic (muscarinic) nature (Bocian et al, 2016; Caban et al, 2018; Kowalczyk et al, 2014), but there is still a lack of information addressing the involvement of other possible neurotransmitter systems in the generation of this EEG pattern and accompanying neuronal discharges. Taking these premises into consideration, the first aim of the present study was to examine the ability of the PHa to generate local theta field potentials and accompanying cell discharges in response to glutamatergic stimulation (kainic acid [KA] administration) both in vitro and in vivo.…”