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

The posterior hypothalamic area (PHa), including the supramammillary nucleus (SuM) and posterior hypothalamic nuclei, forms a crucial part of the ascending brainstem hippocampal synchronizing pathway, that is involved in the frequency programming and modulation of rhythmic theta activity generated in limbic structures. Recent investigations show that in addition to being a modulator of limbic theta activity, the PHa is capable of producing well-synchronized local theta field potentials by itself. The purpose of this study was to examine the ability of the PHa to generate theta field potentials and accompanying cell discharges in response to glutamatergic stimulation under both in vitro and in vivo conditions.

The effect of ketamine on delta-range coupling between prefrontal cortex and hippocampus supported by respiratory rhythmic input from the olfactory bulb.

Respiratory rhythm plays an important role in cognitive functions in rodents, as well as in humans. Respiratory related oscillation (RRO), generated in the olfactory bulb (OB), is an extrinsic rhythm imposed on brain networks. In rats, RRO can couple with intrinsic brain oscillations at theta frequency during sniffing and in the delta range outside of such episodes.

The Role of the Posterior Hypothalamus in the Modulation and Production of Rhythmic Theta Oscillations.

Theta rhythm recorded as an extracellular synchronous field potential is generated in a number of brain sites including the hippocampus. The physiological occurrence of hippocampal theta rhythm is associated with the activation of a number of structures forming the ascending brainstem-hippocampal synchronizing pathway. Experimental evidence indicates that the supramammillary nucleus and posterior hypothalamic nuclei, considered as the posterior hypothalamic area, comprise a critical node of this ascending pathway.

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

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.