Effects of early postnatal receptor damage on dendritic development in gustatory recipient zones of the rostral nucleus of the solitary tract.
The rostral gustatory zone of the nucleus of the solitary tract (NST) exhibits extensive anatomical development during the first 3 weeks of postnatal life, and this development requires the presence of intact gustatory receptors during a critical period. We have previously shown that unilateral damage induced to fungiform papillae of the anterior tongue at postnatal day 2 (P2) alters normal migration and ramification of chorda tympani (CT) axons in the rostral NST. In addition to alterations of axonal development, P2 receptor damage decreases the intraneuronal distance between neurons that project axons to the second-order central gustatory relay, located in the caudal parabrachial nucleus (PBN). This observation suggested that P2 receptor damage may alter both axonal development and dendritic development in the rostral gustatory NST. The present study evaluated potential changes in dendritic development of PBN projection neurons following either P2 or P10 receptor damage. Morphological studies were first conducted to quantitatively define somatic characteristics of neurons that project axons to the PBN. Independent experiments used fluorescent labeling combined with subsequent Golgi-impregnation to study dendritic architecture of identified PBN projection neurons. Results confirmed that P2 receptor damage alters dendritic development of PBN projection neurons located in CT terminal fields. Anterior tongue receptor damage at P2 (1) reduces planar length of first- and second-order dendritic branches, (2) reduces the mean number of second-order branches per neuron, and (3) reduces the density of spine processes on second-order dendritic branches. A critical period exists for these effects, similar to that reported for axonal development, insofar as P2 receptor damage alters dendritic development of PBN projection neurons, whereas P10 receptor damage does not. Dendrites of identified PBN projection neurons located in regions of the NST that receive primary afferent axons from the glossopharyngeal nerve are not affected by anterior tongue damage at P2. These results show that early postnatal receptor damage influences both pre- and postsynaptic development in the rostral gustatory NST. These anatomical changes are undoubtedly related to alterations in taste-guided behaviors that are observed following P2 receptor damage.
Lasiter
P S
PS
Department of Psychology, Florida Atlantic University, Boca Raton 33431.
D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology; D002814:Chorda Tympani Nerve / Q000502:physiology; D003712:Dendrites / Q000502:physiology*; D005456:Fluorescent Dyes; D005930:Glossopharyngeal Nerve / Q000166:cytology / Q000502:physiology; D008526:Medulla Oblongata / Q000166:cytology / Q000254:growth & development*; D009411:Nerve Endings / Q000502:physiology; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D051381:Rats; D011984:Sensory Receptor Cells / Q000502:physiology*; D013194:Staining and Labeling; D013649:Taste / Q000502:physiology*; D014059:Tongue / Q000294:innervation
D005456:Fluorescent Dyes