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R Norgren

Publications and source records attributed to R Norgren.

90 records · Page 5Linked to original sources
PubMed1978

Chronically decerebrate rats demonstrate satiation but not bait shyness.

Taste substances applied to the oral cavity result in either ingestion or rejection, each with a characteristic muscular response pattern. These responses are the same in decerebrate and intact rats; the caudal brainstem appears to be the neural substrate of ingestion and rejection responses. The experiment determined whether decerebrates can alter these discriminative responses as a function of food deprivation or toxicosis. Food-deprived decerebrate rats, like intact ones, ingested a taste substance they had rejected when sated. However, these same decerebrates, in contrast to controls, neither rejected nor decreased ingestive reactions to a novel taste after that taste had been repeatedly paired with lithium chloride-induced illness. Although the forebrain may be important for integrating ingestion, some aspects of this control seem to be represented in caudal brain areas.

Animals↗
PubMed1978

The taste reactivity test. I. Mimetic responses to gustatory stimuli in neurologically normal rats.

One or two bottle preference tests, i.e., relative fluid consumption, constitute the primary methodology for determining acceptance or rejection of tastes in animals other than humans. These tests require organisms to initiate and maintain drinking behavior, and, therefore, can not be applied to preparations which do not eat or drink spontaneously. The taste reactivity test, a new method for assessing responses to gustatory stimuli, circumvents this shortcoming. A 50 microliter taste stimulus is injected directly into the oral cavity of a freely moving rat and the immediate response videotaped for frame by frame analysis. Each of the sapid stimuli used (4 concentrations of sucrose, NaCl, HCl, and quinine HCl) generated a stereotyped response derived from a lexicon of 4 mimetic (movements of lingual, masticatory, and facial musculature) and 5 body response components. Responses to taste stimuli were highly consistent within and between rats. For example, sapid sucrose, NaCl and HCl stimuli elicited a response sequence beginning with low amplitude, rhythmic mouth movements, followed by rhythmic tongue protrusions, and then lateral tongue movements. No body movements accompanied these mimetic responses. In contrast, quinine in concentrations at and above 3 X 10(-5) M (1/2 log step above the absolute behavioral threshold for quinine) elicited a response pattern beginning with gaping and proceeding through as many as 5 body responses. These normative data for the intact rat can be directly compared to the taste reactivity of neurally ablated preparations which do not spontaneously feed or drink. Such comparisons can be utlized in determining the neural substrates necessary for the execution and regulation of ingestive behavior.

Animals↗
PubMed1978

The taste reactivity test. II. Mimetic responses to gustatory stimuli in chronic thalamic and chronic decerebrate rats.

The taste reactivity test described in the preceding paper was used to begin determining the capacity of brain stem structures to execute and regulate ingestive behavior. Both chronic thalamic and chronic decerebrate rat preparations were examined repeatedly, and their gustatory mimetic responses compared through frame-by-frame videotape analysis with the responses of neurologically normal controls. In response to orally injected taste stimuli, chronic decerebrate rats executed the same mimetic response components, and very similar response sequences observed in intact rats. In contrast, all taste stimuli elicited a quinine-like rejection sequence from chronic thalamic rats. In thalamic rats mimetic responses associated with ingestion were completely absent. Based on the similarities in the ingestion and rejection responses of decerebrate and intact rats, it appears that discriminative responses to taste result from integrative mechanisms complete within, or caudal to, the midbrain. Since decerebrate rats have the capacity to execute both ingestion and rejection response sequences, neural mechanisms rostral to the midbrain in some way suppress ingestion and/or releaser ejection responses in the thalamic preparation.

Animals↗
PubMed1978

Neurological tests and behavioral deficits in chronic thalamic and chronic decerebrate rats.

The taste reactivity of chronic decerebrate rats is very similar to intact rats although chronic thalamic rats display only the quinine-like rejection sequence. The performance of intact (n = 12), decerebrate (n = 10) and thalamic (n = 10) preparations was further compared across a set of simple behavior tests to more broadly assess the behavioral capacities of the rodent brain stem. Decerebrate rats were immobile. They exhibited no spontaneous activity other than grooming, but often overreacted with well-coordinated movements (i.e., running, jumping and climbing) to seemingly inappropriate activating stimuli such as tail pinch, handling or water squirted on the fur. Decebrates had lower thresholds for elicited attack and grooming behaviors than thalamic or intact rats. The thalamic preparation exhibited a wider range of intact neurological responses than the decerebrate. Cage climbing, resistance to gravity, suspension and muscle tone reactions, rhythmic vibrissae movements and examination of objects with snout and mandible were difficult to distinguish from controls. Decerebrates either did not perform these responses or did so in a clearly different manner. In contrast, grooming behavior in thalamics was much less effective than in decerebrates. Thalamic rats spontaneously executed grooming sequences, but the responses were misdirected and ineffective. Desite their relative immobility, decerebrates coordinated grooming sequences and maintained their fur. No single mechanism appears to account for the constellation of deficits and capacities observed in either chronic thalamic or chronic decerebrate rats.

Animals↗
PubMed1976

Taste pathways to hypothalamus and amygdala.

The projections of a third order gustatory relay in the dorsal pons of rats have been traced using tritiated proline autoradiography and antidromic activation of pontine neurons from electrodes in the thalamus and amygdala. Labelled axons collect in the central tegmental tract and ascend to the thalamic taste area in the medial extension of the ventrobasal complex. The majority of the fibers remain ipsilateral, but a few cross in the rostral pons and midbrain. The largest crossing occurs at the level of the thalamic termination. Many fascicles of fibers continue rostrally by passing beneath the thalamic taste area, piercing the medial lemniscus, and spreading out along the dorsomedial corner of the internal capsule (IC). The terminal field at this level caps IC from the subthalamic nucleus down into the far-lateral hypothalamus. Labelled axons grandually penetrate through the internal capsule, and ramify throughout the underlying substantia innominata. This terminal zone extends laterally into the rostral end of the central nucleus of the amygdala, which is densely labelled to its caudal exremity. At the caudal end of the amygdala labelled fibers are visible in one component of the stria terminalis. These fibers can be followed over the dorsal thalamus into a smaller, but equally dense terminal area in the dorsolateral bed nucleus of the stria terminalis. The electrophysiological data demonstrate that pontine gustatory units can be antidromically activated by electrodes located in or near the central nucleus of the amygdala. Since many of the same units can also be driven from the thalamic taste area, at least some of the axons traced autoradiographically probably convey gustatory information to the hypothalamus and amygdala.

Amygdala↗
PubMed1975

The pontine taste area in the rat.

The pontine taste area relays gustatory information from the rostral pole of the solitary nucleus to both the thalamus and ventral forebrain. An electrophysiological investigation of this area was carried out in 3 stages. First, multiunit responses from the dorsal pons were mapped using sapid, thermal, and tactile stimuli applied to the anterior tongue. The gustatory zone lies within and just dorsal and ventral to the brachium conjunctivum as it enters the pons from the cerebellum. Second, gustatory stimuli were applied independently to the anterior and posterior tongue to determine whether receptors in both fields are represented in the pons. Responses with characteristics similar to those obtained from the glossopharyngeal nerve were located on the dorsal edge of the pontine gustatory zone. More ventrally the responses from the posterior tongue mimicked anterior tongue responses, but were of lesser amplitude than the largest anterior responses occurring at the ventral edge of the gustatory zone. Third, 71 single units were isolated in the dorsal pons, and tested for sensitivity to gustatory stimulation of the anterior and posterior tongue separately. More than half the units responded to gustatory stimuli--some from the anterior tongue alone, some from the posterior alone, but most responded to stimuli applied to either field. In the latter instance 7 of 10 units tested continued to respond after anesthetizing the chorda tympani with Xylocaine instilled into the middle ear, thus demonstrating a true glossopharyngeal input. This proves that gustatory information from two distinct receptive fields may converge on the same central neuron.

Animals↗
PubMed1971

Taste pathways in rat brainstem.

By means of a combination of electrophysiological and anatomical procedures, the projections of the anterior portion of the solitary nucleus were traced to the parabrachial nuclei in the pons, structures hitherto not considered to be included in the taste pathway. Responses to taste stimuli were recorded from this pontine area. Lesions in the pontine taste area resulted in degeneration of fibers reaching the lingual area in the thalamus.

Animals↗
PubMedDate not supplied

Comparing salt appetites: induction with intracranial hormones or dietary sodium restriction.

To raise a natural sodium appetite in the laboratory requires approximately 10 days on a very low sodium diet. Most other regimens induce sodium appetite more rapidly, but also result in behavioral or physiological changes not observed in the deprivation-induced state. We compared the characteristics of need-free sodium appetite induced either by systemic aldosterone combined with an intracerebroventricular (ICV) injection of angiotensin II or by a single ICV injection of renin with an appetite induced by 10 days of sodium deprivation. We measured the latency to drink water and 3% NaCl, as well as the amount of these fluids consumed at 30 min, 3 h, and 24 h. Angiotensin induced the shortest latency for both water and salt drinking, but the overall salt intake was lower. In 24 h, renin and sodium deprivation both induced about 14 ml of NaCl consumption, but the time course of the fluid intake differed for the two regimens.

Aldosterone↗
PubMedDate not supplied

Parabrachial lesions disrupt responses of rats to amino acid devoid diets, to protein-free diets, but not to high-protein diets.

Normal rats "reduce" intake of diets that lack an essential amino acid (THR-DEV), are protein free (PO%), or contain a high proportion of protein (P75%). We tested the importance of the parabrachial nuclei (PBN) in signaling such adjustments of food intake by placing electrophysiologically guided lesions in these nuclei at points that responded to gustatory stimuli. When fed the THR-DEV diet, rats with PBN lesions (PBNx) decreased their food intake significantly less than the controls (78.5 vs. 44.4%). When put on a P0% diet, PBNx animals decreased their intake only 8% compared with 23% for our CONT group. When put on a P75% diet, however, both groups decreased their intake in an equivalent amount. These experiments show that the PBN is involved in the learned aversion to an amino acid devoid diet.

Amino Acids↗
PubMedDate not supplied

The gustatory system in mammals.

Taste buds occur in five distinct populations in the mammalian oral cavity. The chemical sensitivity of these receptors varies from one population to another and among species as well. Taste buds degenerate when denervated and reappear when gustatory axons reinvade an area. Branches of three cranial nerves--VII, IX, and X--convey gustatory information to the medulla, where they terminate in the rostral two thirds of the nucleus of the solitary tract. Individual gustatory afferent fibers normally respond to several classes of sapid chemicals; they are broadly tuned. The tuning, however, is not random. For a given neuron, the best stimulus predicts the order of effectiveness of other stimulus qualities. Taste neurons in the first and second central relays, in the medualla and pons, respectively, are even more broadly tuned than those on the periphery but maintain a similar orderliness in the effectiveness of different sapid qualities. Much less is known about the response properties of taste neurons in more rostral areas. Even the basic anatomy of the gustatory system in the forebrain remains in question, because its organization differs in rodents and primates.

Afferent Pathways↗