Biomedical subjects

Robert F Lundy

Publications and source records attributed to Robert F Lundy.

5 recordsLinked to original sources

PubMed2006

Central gustatory lesions and learned taste aversions: unconditioned stimuli.

The efficacy of two different unconditioned stimuli (US) in producing conditioned taste aversion (CTA) was tested in rats after bilateral ibotenic acid (IBO) lesions of the gustatory nucleus of thalamus (TTAx) and the medial and lateral parabrachial nuclei (mPBNx, lPBNx). An initial study determined an equivalent dose for the two USs, LiCl and cyclophosphamide (CY), using non-lesioned rats. Subsequently, using a separate set of lesioned animals and their sham controls (SHAM), injections of CY were paired 3 times with one of two taste stimuli (CSs), 0.1 M NaCl for half the rats in each group, 0.2 M sucrose for the other half. After these conditioning trials, the CS was presented twice more without the US, first in a 1-bottle test, then in a 2-bottle choice with water. The acquisition and test trials had 2 intervening water-only days to assure complete rehydration. Two weeks later, the same rats were tested again for acquisition of a CTA using LiCl as the US and the opposite CS as that used during the CY trials. The SHAM and TTAx groups learned to avoid consuming the taste associated with either CY or LiCl treatment. The two PBNx groups failed to learn an aversion regardless of the US.

Animals↗

PubMed2004

A novel method for induction of salt appetite in rats.

A number of procedures exist for the experimental induction of sodium appetite. With the exception of a low sodium diet, nearly all of these methods are invasive, requiring injections, surgery, or both. In addition to stimulating intake of concentrated salt, some of them produce substantial side-effects like reduced food intake and weight gain. The present experiment was designed to evaluate the efficacy of a novel non-invasive method to induce a salt appetite. We investigated the effects of ingesting 100 microM amiloride, a diuretic and natriuretic compound, on urine quantity, electrolyte balance, 0.5 1M sodium chloride (NaCl) intake, water intake, and Na(+)-free chow intake, and weight gain in rats. A water ingestion only group served as control. Consumption of amiloride in mixture with water produced greater loss of urinary Na(+) and intake of 0.51 M NaCl compared with controls. This treatment was without effect on food intake and only modestly influenced weight gain. These results demonstrate a rapid and non-invasive method for the induction of salt appetite free of unwanted side-effects.

Amiloride↗

PubMed2004

Furosemide-induced food avoidance: evidence for a conditioned response.

Furosemide (Furo) is a potent natriuretic drug that is often used experimentally to investigate the brain mechanisms underlying salt appetite. Within this experimental paradigm, however, Furo also has anorectic activity that has received only modest attention. In Experiment 1 we varied two things-administering a 10-mg dose of Furo in a single or a divided dose and preinjection exposure to a Na-free diet. In the 24 h after Furo, all four groups of rats reduced ingestion of Na-free diet. Both the division of the Furo dose and the preexposure to Na-free diet reduced the amount of food consumed even more than a single dose or continuous access to normal chow did. The fact that preexposure to Na-free diet increased the post-Furo anorexia implied an associative component to the phenomenon. Experiments 2 and 3 investigated the ability of Furo (2 and 10 mg) to serve as an unconditioned stimulus in taste aversion learning using 0.2 M sucrose as the conditioned stimulus. A saline (Sal) injection group served as control in both experiments. The results show that animals avoided sucrose when its ingestion was immediately followed by 10 mg Furo but not with 2 mg Furo or Sal. An aversion to sucrose did not develop when 10 mg Furo was administered the day prior to sucrose access. Thus, the suppressive effects of high-dose Furo on food intake might be due to a conditioned response.

Animals↗

PubMed2003

Activity in the hypothalamus, amygdala, and cortex generates bilateral and convergent modulation of pontine gustatory neurons.

Evidence suggests that centrifugal modulation of brain stem gustatory cells might play a role in the elaboration of complex taste-guided behaviors like conditioned taste aversion and sodium appetite. We previously showed that activity in one forebrain area, the central nucleus of the amygdala (CeA), increased the chemical selectivity of taste cells in the parabrachial nucleus (PBN). The present study investigates how activity in 2 other similarly interconnected forebrain sites, the lateral hypothalamus (LH) and gustatory cortex (GC), might influence PBN gustatory processing in rats. The potential convergence of descending inputs from these sites, as well as the CeA, was also evaluated. After anesthesia (35 mg/kg Nembutal ip), 70 PBN gustatory neurons were tested before, during, and after electrical stimulation of these forebrain sites, while responding to 0.3 M sucrose, 0.1 M NaCl, 0.01 M citric acid, and 0.003 M QHCl. Although each forebrain site modulated taste-evoked responses, more PBN neurons were influenced by stimulation of the GC (67%) and CeA (73%) than of the LH (48%). Activation of cortex (71%) and amygdala (85%) most often produced inhibition, whereas inhibition and excitation occurred equally often during hypothalamic stimulation. Of the neurons tested for convergence (n = 60), 88% were influenced by > or =1 of the 3 sites. Twenty were modulated by stimulation at all 3 sites and another 17 by 2 of the 3 sites. The net effect of centrifugal modulation was to sharpen the across-stimulus response profiles of PBN cells, particular with regard to the NaCl- and citric acid-best cells.

Amygdala↗

PubMed2003

Furosemide, sodium appetite, and ingestive behavior.

Sodium appetite is often produced experimentally by using the diuretic furosemide (Furo) to induce a rapid loss of urinary sodium. The present experiments were designed to investigate the dose-dependent relationship between renal and behavioral responses to Furo. We compared the effects of five different Furo doses (0.5, 1, 2, 6, and 10 mg) on 3% NaCl intake, water intake, Na(+)-free chow intake, urine quantity, electrolyte balance, and weight gain in rats. The Na(+) loss produced by Furo injection was dose dependent from 0.5 to 10 mg and did not change across repeated depletions. There was only a weak correspondence, however, between these dose-dependent changes in renal function and subsequent sodium appetite. This suggests that net Na(+) loss is not the only determinant of sodium intake. Moreover, at the two higher doses of Furo, both food intake and weight dropped significantly, but these did not change following the three lower ones. Given these substantial side effects, the preferred dose of Furo for inducing a salt appetite should not exceed 2.0 mg.

Animals↗