Potentiation by neurosteroids of muscimol/adenosine interactions in rat hippocampus

Differential effect of kinase A and C blockers on lordosis facilitation by progesterone and its metabolites in ovariectomized estrogen-primed rats

Dose response curves for lordosis behavior was obtained for progesterone (P) and its two ring A-reduced metabolites: 5alpha-pregnanedione (alpha-DHP) and 5alpha,3alpha-pregnanolone (5alpha,3alpha-Pgl) by infusing these progestins in the right lateral ventricle (rlv) of ovariectomized (ovx) estradiol-treated rats (2 microg estradiol benzoate; EB), 40 h before intracerebro-ventricular (icv) injection. Effective doses 50 (ED50) revealed that ring A-reduced progestins were more potent than P itself to induce lordosis behavior. Two dose levels, one producing the maximal effect and the other one producing a submaximal response (ED50-ED60), were selected for testing the capacity of RpAMPS, a kinase A blocker, and H7, a kinase C blocker, to modify the response to the three progestins. rlv injection of RpAMPS significantly depressed the lordosis response to the two dose levels of P and alpha-DHP but failed to significantly inhibit that of 5alpha,3alpha-Pgl. The administration of H7 prevented the effect of both 5alpha-reduced progestins without affecting the response to P. The results suggest that P and its ring A-reduced metabolites stimulate lordosis behavior through different cellular mechanisms: P acting mainly through the cAMP-kinase system; alpha-DHP through both kinase A and kinase C signaling pathways and 5alpha,3alpha-Pgl through the kinase C system.

Hippocampal synaptic plasticity and cognition

Discoveries made over the past 20 years have greatly improved our understanding of how the brain functions. This article focuses on the relation between memory and cellular mechanisms of neuronal and synaptic plasticity in the hippocampus. Several studies indicate that the hippocampal formation is a crucial element of the neurobiological bases of higher cognitive function. Severe damage to the hippocampal formation is known to produce seemingly permanent anterograde amnesia. A generally accepted hypothesis in neurobiology has been that long-lasting activity-dependent changes in the efficacy of synaptic transmission in the mammalian brain are considered to be of fundamental importance for the development of neural circuitry and for the storage of information. The most compelling and reliable model for such changes has been long-term potentiation (LTP) and long-term depression (LTD) in the hippocampus. Therefore, the possibility of the discovery and development of compounds that, by modulating hippocampal synaptic plasticity, would be useful for the management of dementia and amnesia.