In Vitro Studies of Neurotoxicant Effects on Cellular Homeostasis

Homeostasis in neurons is regulated by interactions among many signaling pathways. We will loosely define the term “signaling pathways” to include any molecular mechanisms that transduce external environmental stimuli (e.g., neurotransmitters, hormones, or contact with other cells) and/or intracellular metabolic conditions (e.g., intracellular free Ca²⁺ ion concentrations, redox status, or ATP demand) into cellular responses such as process growth, synthesis of neurotransmitters and/or their receptors, or changes in cellular respiration. This definition includes the interlinked pathways that lead to alterations in protein kinase or phosphatase activity and activation or repression of gene transcription and, perhaps less familiar mechanisms such as the stimulation of mitochondrial matrix enzymes by elevations in intramitochondrial Ca²⁺ .