Sex-Dependent Effects of Chronic Microdrive Implantation on Acquisition of Trace Eyeblink Conditioning.

Neuroscience techniques, including in vivo recording, have allowed for a great expansion in knowledge; however, this technology may also affect the very phenomena researchers set out to investigate. Including both female and male mice in our associative learning experiments shed light on sex differences on the impact of chronic implantation of tetrodes on learning. While previous research showed intact female mice acquired trace eyeblink conditioning faster than male and ovariectomized females, implantation of chronic microdrive arrays showed sexually dimorphic effects on learning. Microdrive implanted male mice acquired the associative learning paradigm faster than both intact and ovariectomized females. These effects were not due to the weight of the drive alone, as there were no significant sex-differences in learning of animals that received "dummy drive" implants without tetrodes lowered into the brain. Tandem mass tag mass spectrometry and western blot analysis suggest that significant alterations in the MAPK pathway, acute inflammation, and brain derived neurotrophic factor may underlie these observed sex- and surgery-dependent effects on learning.

Store depletion-induced h-channel plasticity rescues a channelopathy linked to Alzheimer's disease.

Voltage-gated ion channels are critical for neuronal integration. Some of these channels, however, are misregulated in several neurological disorders, causing both gain- and loss-of-function channelopathies in neurons. Using several transgenic mouse models of Alzheimer's disease (AD), we find that sub-threshold voltage signals strongly influenced by hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels progressively deteriorate over chronological aging in hippocampal CA1 pyramidal neurons. The degraded signaling via HCN channels in the transgenic mice is accompanied by an age-related global loss of their non-uniform dendritic expression. Both the aberrant signaling via HCN channels and their mislocalization could be restored using a variety of pharmacological agents that target the endoplasmic reticulum (ER). Our rescue of the HCN channelopathy helps provide molecular details into the favorable outcomes of ER-targeting drugs on the pathogenesis and synaptic/cognitive deficits in AD mouse models, and implies that they might have beneficial effects on neurological disorders linked to HCN channelopathies.

Modulation of cholinergic transmission enhances excitability of hippocampal pyramidal neurons and ameliorates learning impairments in aging animals.

Four cholinesterase inhibitors have been approved by the US Food and Drug Administration for treating behavioral symptoms of Alzheimer's disease. Here we review our experiences with two cholinesterase inhibitors (metrifonate and galanthamine) and a muscarinic acetylcholine receptor agonist (CI-1017) in behavioral pharmacological and brain slice experiments in aging and young rabbits. Aging rabbits are impaired in their ability to acquire the hippocampus-dependent trace eyeblink conditioning task, as compared to young controls. A large proportion of aging animals cannot reach behavioral criterion in this task. Those that do learn, do so more slowly. In addition, the post-burst afterhyperpolarization and spike frequency accommodation is increased in hippocampal pyramidal neurons from aging animals, i.e., cellular excitability is reduced as compared to those from young animals. Metrifonate, galanthamine, and CI-1017 reduced the learning deficits observed in aging rabbits so that they learned almost as quickly as young controls. These cholinergic compounds also enhanced the postsynaptic excitability of hippocampal pyramidal neurons in vitro. Therefore, we propose that the amelioration of learning impairment with the cholinergic compounds may in part be due to the enhanced excitability of hippocampal pyramidal neurons. The potential relevance of our studies to further understanding the cellular and behavioral changes that occur with normal aging and Alzheimer's Disease is discussed.