Theta‐related gating cells in hippocampal formation: In vivo and in vitro study

Abstract

In this study we extended our earlier in vitro findings concerning the discovery of a novel type of theta-related cells, which we have termed gating cells. There were two main objectives of our present investigations. The first was to determine the distribution of theta gating cells in the separated CA1 and CA3 generators in three different pharmacological conditions: (i) the presence of a cholinergic agonist-carbachol, (ii) the presence of carbachol and GABA(A) ergic antagonist-bicuculline, (iii) the presence of carbachol and GABA(B) ergic antagonist-2-hydroxysaclofen. The second objective of our studies was to verify our earlier in vitro findings and to demonstrate, for the first time, gating cells in intact hippocampus during the generation of Type II theta in urethane anaesthetized rats. Two hundred ninety-nine theta-related cells were isolated and recorded from in vivo and in vitro hippocampal formation. Twenty out of all 299 neurons (6.6%) were classified as gating cells. The neuron was classified as a gating cell if it met one of the following criteria: (i) the cell discharges occurred precisely in the beginning and at the end of each theta epoch (gating cell A); (ii) the cell began to discharge just before the transition from non-theta interval/LIA into the theta epoch (gating cell B); (iii) the cell began to discharge just after the transition from the theta epoch into non-theta interval/LIA (gating cell C). Our data demonstrates that the appearance of theta epochs and their length, as well as the appearance of non-theta states (in vivo recorded LIA or in vitro recorded intervals between theta epochs) and their length, may require the existence of a specific population of hippocampal neurons which we termed gating cells.

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

“…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, ).…”

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

“…All recorded in vitro and in vivo cell discharges were classified according to the criteria that have been developed previously to classify cells in hippocampal formation (Colom and Bland, ; Bland and Colom, ; Bland and Colom, ), supplemented afterword by Konopacki et al () and Kowalczyk et al (b).…”

“…In short, the amplitude of theta field potential is variable, occurring as a function of a number of synchronously firing neurons expressing MPOs. Hence, a smaller amplitude of PHa theta field potential vs HPC theta rhythm (Kowalczyk et al, b; Kowalczyk et al, ) may result from a very low density of these cells in the PHa maintained in in vivo conditions. On the other hand, the increased amount of theta‐on phasic cells in the PHa maintained in vitro (vs in vivo conditions) may be reflected in an increased amplitude of in vitro recorded theta (Kowalczyk et al, ).…”

Orexinergic theta rhythm in the rat hippocampal formation: In vitro and in vivo findings

“…The appearance of HPC rhythmic field potential is determined by the specific activity patterns of a number of cells, termed “theta‐related” cells, and “theta‐gating” cells (Colom and Bland, ; Bland and Colom, ; Bland et al, ; Kowalczyk et al, ). These cells program not only the transition from theta state into large irregular activity (LIA) state, but also theta amplitude and power (Colom et al, ; Smythe et al, ; Kowalczyk et al, ). One type of “theta‐related” cells, labelled “theta‐on” phasic cells, specifically determines the appearance of theta rhythm (Bland and Colom, ).…”