Do bone cells behave like a neuronal network?
Bone cells are organized into an interconnected network, which extends from the osteocytes within bone to the osteoblasts and lining cells on the bone surfaces. There is experimental evidence suggesting that bone tissue exhibits basic properties of short- and long-term memory. An analogy might be made between the bone cell network and neuronal systems. For instance, recent studies suggest that the neurotransmitter glutamate may play a role in cell-to-cell communication among bone cells. Glutamate is a key neurotransmitter involved in learning and memory in reflex loops and the hippocampus. The simplest forms of memory include habituation (desensitization) and sensitization. It is argued that bone cells exhibit habituation to repeated mechanical stimuli and sensitization to mechanical loading by parathyroid hormone (PTH). Acquired long-term memory of a mechanical loading environment may influence the responsiveness of bone tissue to external stimuli. For instance, bone tissue from the skull shows markedly different responses to several stimuli, e.g., mechanical loading, disuse, and PTH, compared with long bones. We speculate that the history of weight bearing imparts long-term cellular memory to the bone cell network that modulates the cellular response to a wide variety of stimuli.