Abstract
Classically, glia have been regarded as non-excitable cells that provide nourishment and physical scaffolding for neurons. However, it is now generally accepted that glia are active participants in brain function that can modulate neuronal communication via several mechanisms. Investigations of anatomical plasticity in the magnocellular neuroendocrine system of the hypothalamic paraventricular and supraoptic nuclei led the way in the development of much of our understanding of glial regulation of neuronal activity. In this review, we provide an overview of glial regulation of magnocellular neuron activity from a historical perspective of the development of our knowledge of the morphological changes in evident in the paraventricular and supraoptic nuclei and focus on recent data from the authors’ laboratories that were presented at the 9
th
World Congress on Neurohypophysial Hormones and that have contributed to our understanding of the multiple mechanisms by which glia modulate the activity of neurons, including: gliotransmitter modulation of synaptic transmission; trans-synaptic modulation by glial neurotransmitter transporter regulation of neurotransmitter spillover; and glial neurotransmitter transporter modulation of excitability by regulation of ambient neurotransmitter levels and their action on extrasynaptic receptors. The magnocellular neuroendocrine system secretes oxytocin and vasopressin from the posterior pituitary gland to control birth, lactation and body fluid balance and we finally speculate as to whether glial regulation of individual magnocellular neurons might co-ordinate population activity to respond appropriately to altered physiological circumstances.