Dorsal raphe serotonin neurons in mice: immature hyperexcitability transitions to adult state during first three postnatal weeks suggesting sensitive period for environmental perturbation.
Trauma during early life is a major risk factor for the development of anxiety disorders and suggests that the developing brain may be particularly sensitive to perturbation. Increased vulnerability most likely involves altering neural circuits involved in emotional regulation. The role of serotonin in emotional regulation is well established, but little is known about the postnatal development of the raphe where serotonin is made. Using whole-cell patch-clamp recording and immunohistochemistry, we tested whether serotonin circuitry in the dorsal and median raphe was functionally mature during the first 3 postnatal weeks in mice. Serotonin neurons at postnatal day 4 (P4) were hyperexcitable. The increased excitability was due to depolarized resting membrane potential, increased resistance, increased firing rate, lack of 5-HT1A autoreceptor response, and lack of GABA synaptic activity. Over the next 2 weeks, membrane resistance decreased and resting membrane potential hyperpolarized due in part to potassium current activation. The 5-HT1A autoreceptor-mediated inhibition did not develop until P21. The frequency of spontaneous inhibitory and excitatory events increased as neurons extended and refined their dendritic arbor. Serotonin colocalized with vGlut3 at P4 as in adulthood, suggesting enhanced release of glutamate alongside enhanced serotonin release. Because serotonin affects circuit development in other brain regions, altering the developmental trajectory of serotonin neuron excitability and release could have many downstream consequences. We conclude that serotonin neuron structure and function change substantially during the first 3 weeks of life during which external stressors could potentially alter circuit formation.
Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, and Department of Anesthesiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104.
Benjamin D
BD
Rood
Lyngine H
LH
Calizo
David
D
Piel
Zachary P
ZP
Spangler
Kaitlin
K
Campbell
Sheryl G
SG
Beck
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001640:Bicuculline / Q000494:pharmacology; D004777:Environment; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D011810:Quinoxalines / Q000494:pharmacology; D011903:Raphe Nuclei / Q000166:cytology* / Q000254:growth & development*; D059326:Serotonergic Neurons / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D018691:Excitatory Amino Acid Antagonists; C484684:Fev protein, mouse; D058787:GABA-A Receptor Antagonists; D008164:Luminescent Proteins; D011810:Quinoxalines; D017366:Serotonin Receptor Agonists; D014157:Transcription Factors; C054562:yellow fluorescent protein, Bacteria; D012701:Serotonin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C056723:FG 9041; C047087:5-carboxamidotryptamine; D001640:Bicuculline