Oromotor Behaviors Research Articles

Swallowing during ongoing fluid ingestion in the rat

In order to identify fixed versus flexible aspects of swallowing and oromotor control, we developed a method for the concurrent analysis of swallow frequency, swallow volume, and the temporal correlation between swallowing and rhythmic orolingual movements during prolonged bouts of fluid ingestion in unanesthetized, unreestrained rats. Rats actively ingested 0.1 M sucrose solutions infused intraorally: (a) at a constant rate within sessions; and (b) during separate sessions across which the rate of intraoral infusion (=ingestion rate) was varied. Salient characteristics of ‘intraoral intake’ included: (1) covariation of swallow frequency and swallow volume to mediate adjustments in the rate of ingestion; (2) emission of rhythmic coupled movements (5–7 Hz) of the jaw and tongue that serve to transport fluid through the mouth; (3) a 20–40 ms increase in the duration of the rhythmic movement cycle associated with swallow onset; and (4) emergence of pauses between bursts of rhythmic oromotor behavior with increases in cumulative intake. That intraoral intake and fluid ingestion via spout-licking (Weijnen et al., Brain Behav. Evol., 25, 1985) share all of these features suggests strongly that common neural processes, relatively uninfluenced by sources of sensory feedback attending contact with an environmental fluid source, underlie these aspects of normal fluid ingestion. The dynamic adjustment of swallow frequency and swallow volume presents a challenge to traditional models of reflexive swallow initiation derived primarily from the neurophysiological study of acute, non-behaving preparations.

Taste reactivity as a dependent measure of the rapid formation of conditioned taste aversion: A tool for the neural analysis of taste-visceral associations.

Several explanations may account for deficits in the ability of animals to form taste aversions following neural manipulations. These encompass impairments in conditioned stimulus (CS) and unconditioned stimulus (US) processing, conditioned response (CR) measurement, and expression, memory, and taste-visceral integration. A behavioral procedure that aids in the distinction between some of these possibilities is presented. In Experiment 1, 10 rats received seven intraoral (IO) infusions of sucrose (30 s, 0.55 ml) spaced every 5 min starting immediately after the injection of 3.0 mEq/kg of lithium chloride (LiCl). Control rats (n = 12) were treated identically except that they were injected with sodium chloride (NaCl). Oromotor and somatic taste reactivity behaviors were videotaped and analyzed. Lithium-injected rats systematically decreased their ingestive taste reactivity behavior over time, whereas aversive behavior increased. Control rats maintained high and stable levels of ingestive responding and demonstrated virtually no aversive behavior over the 30-min period following sodium injection. Rats were tested several days later for the presence of a conditioned taste aversion (CTA). Rats previously injected with lithium during sucrose infusions demonstrated significantly more aversive behavior than the control group, which demonstrated none. There were no differences in the level of ingestive behavior displayed by the two groups on the CTA test. Experiment 3 revealed that when similarly treated rats were tested for a CTA while in a lithium-induced state, a difference in the ingestive behavior between the two groups was observed. In Experiment 2, naive rats were injected with either NaCl or LiCl but did not receive their first sucrose infusion until 20 min later. These rats also received sucrose infusions at 25 and 30 min postinjection. There were no differences in the taste reactivity behavior displayed by lithium- or sodium-injected rats during any of the sucrose infusions. Collectively, these findings indicate that rats dramatically change their oromotor responses to sucrose during the period following LiCl administration, provided that the infusions start immediately after injection. Furthermore, this time-related behavioral change is predominantly attributable to associative processes. This paradigm can be useful in distinguishing between neural manipulations that affect the establishment of taste-visceral associations from others that affect the animal's ability to retain such associations over the commonly employed 24-hr conditioning-test interval.

Cat trigeminal motor nucleus: rhytmic units firing in relation to opening movements of the mouth

Oromotor behavior results from the complex interaction between jaw, facial, and lingual muscles. The experiments in this and subsequent papers identify the sources of multisynaptic input to the trigeminal, facial, and hypoglossal motor nuclei. In the current experiments, pseudorabies virus (PRV-Ba) was injected into the jaw-opening (anterior digastric and mylohyoid) and jaw-closing muscles (masseter, medial pterygoid, and temporalis) in bilaterally sympathectomized rats. Injection volumes ranged from 2 to 21 μl with average titers of 2.8×108 pfu/ml and maximum survival times of 96 h. The labeling patterns and distributions were consistent between each of the individual muscles and muscle groups. A predictable myotopic labeling pattern was produced in the trigeminal motor nucleus (Mo 5). Transneuronally labeled neurons occurred in regions known to project directly to Mo 5 motoneurons including the principal trigeminal sensory and supratrigeminal areas, Kölliker-Fuse region, nucleus subcoeruleus, and the parvicellular reticular formation. Maximum survival times revealed polysynaptic connections from the periaqueductal gray, laterodorsal and pedunculopontine tegmental areas, and the substantia nigra in the midbrain, ventromedial pontine reticular regions including the gigantocellular region and pars alpha and ventralis in the pons and medulla, and the nucleus of the solitary tract, paratrigeminal region, and paramedian field in the medulla. Thus, the results define the structure of the multisynaptic brainstem neural circuits controlling mandibular movement in the rat.