Development of the Gusto Facial Reflex in Perinatally Undernourished Rats

Abstract

In the rat, the taste system plays a critical role in motivating the animal to consume nutrients and avoid toxic substances. In neonatal rat the orofacial movements can be modified by the application of sucrose and quinine in the mouth, producing ingestion or rejection responses, respectively, but there is no information available on the gusto facial reflexes (GFR) under perinatal fasting. The aim of the present study was to determine how undernutrition can affect the development of orofacial responses to sucrose, quinine, and NaCl during early development. Pregnant dams were undernourished by being given 50% of a balanced diet from G6 to G12, 60% from G13 -G18, and 100% from G 19-G21. On postpartum days 0 -9, prenatally underfed (UG) pups continued the undernourishment by remaining for 12 h with a foster dam and 12 h with a nipple-ligated mother. Stimuli were presented as a single droplet of sucrose (S), sodium chloride (NaCl), quinine hydrochloride (Q), and water (W) onto the lips at 1, 3, 5, 7, and 9 days of age, and mouth-opening frequency (MO) and lip-licking frequency (LL) were analyzed. The results show consistent effects associated with age, but not with diet, except in the cases of 0.01 M Q, which provoked in the UG subjects increased MO and the reduction of LL, and 0.1 M Q, which consistently reduced both responses. Moreover, S provoked increases in both MO and LL at 0.1 M while NaCl and water elicited minimal effects on GFR. These data suggest that perinatal undernutrition affects the basic components of the gustatory system necessary to produce GFR in the first postnatal days by possibly interfereing with the integration of taste input for food learning and the hedonic aspects of gustatory cues.

Analysis of the Sensory and Hedonic Impacts of Sweet and Bitter Tastes in Perinatally Underfed Rats

“…Furthermore, current data also indicated that the reduced MOF elicited by the different taste concentrations are clearly different when compared to the increased LLF movements to the same gustatory cues. These findings suggest that the neuronal circuits underlying the MOF responses in the UG pups elicited by water and salt reflect different excitability or synaptic organization at this developmental period, because they maintain a relatively constant concentration in the amniotic fluid during gestation [11] [36]. Additionally, on PD1 the UG pups showed consistent LLF reductions in response to all tastants when compare to the CG animals; by contrast on PD3 most of the UG subjects displayed LLF movements in response to the same gustatory cues.…”

“…Additionally, on PD1 the UG pups showed consistent LLF reductions in response to all tastants when compare to the CG animals; by contrast on PD3 most of the UG subjects displayed LLF movements in response to the same gustatory cues. These findings suggest that in the UG pups the undernutrition interfered more with the synaptic connectivity and the excitability of the circuit underlying the LLF movements [11] [33] [37].…”

“…Food restriction also similarly disrupts other gustatory relays, such as those of the parabrachial nuclei and the insular cortex of the rat. Thus, these brain stem and neocortical neuronal alterations may be generating different rhythms of motor activity, such as the excessive self-grooming bouts usually associated with early undernutrition [11] [38]- [40]. Giving support to these possibilities is the fact that the basic mechanisms that trigger the motor components of reactions to taste are generated by the brainstem, since anencephalic infants and decerebrate rats show the appropriate GFR in response to sucrose or quinine [1] [40].…”

“…In the rat development of the gustatory system begins during gestation, and 1 to 3 days old rat pups reject quinine solutions, showing aversive responses accompanied by gaping and forelimb flailing. By contrast, sucrose solutions produce rhythmic mouth opening and lateral tongue protrusions [11]. However, as the animal matures, its nervous system develops and becomes more organized in order to integrate taste cues and allow appropriate ingestive behavior necessary for survival [11]- [13].…”

“…By contrast, sucrose solutions produce rhythmic mouth opening and lateral tongue protrusions [11]. However, as the animal matures, its nervous system develops and becomes more organized in order to integrate taste cues and allow appropriate ingestive behavior necessary for survival [11]- [13]. Altricial mammals dramatically change their feeding behavior in the first week of life, and taste is an important determinant of the ingestive behaviors of adult mammals [12].…”