The effect of tongue exercise on serotonergic input to the hypoglossal nucleus in young and old rats.
OBJECTIVE
Breathing and swallowing problems affect elderly people and may be related to age-associated tongue dysfunction. Hypoglossal motoneurons that innervate the tongue receive a robust, excitatory serotonergic (5HT) input and may be affected by aging. We used a rat model of aging and progressive resistance tongue exercise to determine whether age-related alterations in 5HT inputs to the hypoglossal nucleus can be modified. We hypothesized that tongue forces would increase with exercise, 5HT input to the tongue would decrease with age, and tongue exercise would augment 5HT input to the hypoglossal nucleus.


METHODS
Young (9-10 months), middle-aged (24-25 months), and old (32-33 months) male F344/BN rats received tongue exercise for 8 weeks. Immunoreactivity for 5HT was measured in digital images of sections through the hypoglossal nucleus using ImageJ software.


RESULTS
Tongue exercise resulted in increased maximum tongue forces at all ages. There was a statistically significant increase in 5HT immunoreactivity in the hypoglossal nucleus in exercised, young rats but only in the caudal third of the nucleus and primarily in the ventral half.


CONCLUSIONS
Specificity found in serotonergic input following exercise may reflect the topographic organization of motoneurons in the hypoglossal nucleus and the tongue muscles engaged in the exercise paradigm.
University of Wisconsin–Madison, USA.
Mary
M
Behan
Adam E
AE
Moeser
Cathy F
CF
Thomas
John A
JA
Russell
Hao
H
Wang
Glen E
GE
Leverson
Nadine P
NP
Connor
D000375:Aging / Q000502:physiology*; D000818:Animals; D007002:Hypoglossal Nerve / Q000166:cytology / Q000502:physiology*; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000502:physiology*; D023421:Models, Animal; D009046:Motor Neurons / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology; D051381:Rats; D011914:Rats, Inbred BN; D011916:Rats, Inbred F344; D055070:Resistance Training / Q000379:methods; D012701:Serotonin / Q000502:physiology*; D014059:Tongue / Q000294:innervation* / Q000502:physiology*
D012701:Serotonin