Trends in Neurosciences
Talking back: dendritic neurotransmitter release
Section snippets
Classical transmitters
It is now clear that ‘classical transmitters’ are also major players in retrograde signalling. The many sites within the CNS at which dendritic signalling has been reported to occur are depicted in Fig. 1. Dopamine 4, 5 and ATP [6] were among the first neuroactive substances shown to be released from dendrites. Activation of ionotropic NMDA receptors in the substantia nigra triggers Ca2+-dependent dendritic release of dopamine [7] and these neurons are endowed with dopamine D2 and D3
Neuropeptides – vasopressin and oxytocin
Among the best-established sites of dendritic release are the hypothalamic supraoptic nucleus (SON) and paraventricular (PVN) nuclei (Fig. 1, Fig. 2), where the magnocellular neurons (MCNs) release the peptides vasopressin and oxytocin from their somato–dendritic compartment (Fig. 2a). Studies on dendritic release from these neurons have been facilitated by the fact that their somata and dendrites are tightly grouped, making it possible to measure the dynamics of release using microdialysis
Mechanisms of dendritic release
Differential release of neurotransmitters from different compartments of a single neuron requires subtle regulatory mechanisms. Here, we present what is known about dendritic release mechanisms and contrast this with our understanding of parallel processes in the axon terminals.
Development and morphological plasticity
During development, vasopressin- and oxytocin-containing cells maintain spontaneous electrical activity via depolarization and a facilitation of their own dendritic release. This autocontrol loop is maximally active during the second postnatal week, correlating with a transient increase in dendritic branching. Dendritic branching requires interplay between release of peptides from dendrites and glutamate from presynaptic terminals 42, 50.
In the adult animal, the somata, dendrites and axon
Concluding remarks
For many years the phenomenon of dendritic transmitter release was thought to be a peculiarity of the dopaminergic neurons of the substantia nigra. With the evidence that gaseous transmitters act as signalling molecules to mediate plasticity of synaptic function during LTP, the idea of retrograde transmission gained wider credence. Here, we present evidence that retrograde synaptic communication is also a feature of the neuropeptides, which comprise the largest group of transmitters in the
Acknowledgements
This work was supported by grants from the Wellcome Trust, BBSRC (M.L.) and Canadian Institutes of Health Research (Q.J.P.). Quentin Pittman is an Alberta Heritage Foundation for Medical Research Medical Scientist. Thanks to our many colleagues who reviewed and provided constructive advice on this paper.
References (69)
- et al.
Anatomy of the dopamine system in the basal ganglia
Trends Neurosci.
(2000) Dendritic GABA release depresses excitatory transmission between layer 2/3 pyramidal and bitufted neurons in rat neocortex
Neuron
(1999)- et al.
Dendrites of hypothalamic magnocellular neurons release neurohypophysial peptides by exocytosis
Neuroscience
(1989) Dissociated central and peripheral release of vasopressin, but not oxytocin, in response to repeated swim stress: new insights into the secretory capacities of peptidergic neurons
Neuroscience
(1998)Presynaptic inhibition caused by retrograde signal from metabotropic glutamate to cannabinoid receptors
Neuron
(2001)Calcium-dependent translocation of synaptotagmin to the plasma membrane in the dendrites of developing neurones
Mol. Brain Res.
(2001)Evidence for different exocytosis pathways in dendritic and terminal dopamine release in vivo
Brain Res.
(2002)L-type calcium channels mediate dynorphin neuropeptide release from dendrites but not axons of hippocampal granule cells
Neuron
(1995)Oxytocin and vasopressin release within the supraoptic and paraventricular nuclei of pregnant, parturient and lactating rats: a microdialysis study
Neuroscience
(1993)- et al.
Calcium-channel subtypes in the somata and axon terminals of magnocellular neurosecretory cells
Trends Neurosci.
(1996)