The Role of Hypothalamus in the Formation of Neural Representations of Object-Place Associations in the Hippocampus during Wakefulness and Paradoxical Sleep

We compared the formation of neural representations of object-place associations between the waking state and paradoxical sleep in the hippocampus. The activity of hippocampal neurons is affected by the supramammillary, paraventricular, and supraoptic nuclei of the hypothalamus. Sequentially complexifying representations of object-place associations are formed during signal transduction from the dentate gyrus through the CA3 to CA1 fields on the neurons of these areas in the waking state. Inputs from the supramammillary nucleus to the dentate gyrus and CA2 field, as well as inputs to the CA2 field from the paraventricular and supraoptic hypothalamic nuclei, containing vasopressin and oxytocin-secreting neurons, facilitate signal transmission into the CA1 field by promoting long-term potentiation (LTP) of the efficacy of CA3-CA2 and CA2-CA1 connections and the summation of excitation from the CA3 and CA2 fields to the neurons of CA1 field connected with the prefrontal cortex. Information about odors from the olfactory bulb entering the CA2 field through the paraventricular and supraoptic nuclei is incorporated into the representations of object-place associations. In paradoxical sleep, when the transmission of signals along the dentate gyrus-CA3-CA1 pathway is limited, the inputs from the hypothalamic nuclei facilitate LTP at each step of the dentate gyrus-CA2-CA1 pathway. As a result, during paradoxical sleep the conditions are improved in order to form new representations of object-place associations on CA2 pyramidal neurons and their target cells in the CA1 field connected with the amygdala. It follows from the analysis performed that neural representations of object-place associations formed on the hippocampal neurons during paradoxical sleep are different from those formed in the waking state.