Patricia L. Faris

Effect of decreasing afferent vagal activity with ondansetron on symptoms of bulimia nervosa: a randomised, double-blind trial

BACKGROUND Several lines of evidence have led us to postulate that afferent vagal hyperactivity could be an important factor in the pathophysiology of the eating disorder bulimia nervosa. Ondansetron is a peripherally active antagonist of the serotonin receptor 5-HT3, and is marketed for prevention of vagally-mediated emesis caused by cancer chemotherapeutic agents. We investigated the effects of ondansetron on bulimic behaviours in patients with severe and chronic bulimia nervosa in a randomised, double-blind, placebo-controlled study. METHODS We enrolled patients with severe bulimia nervosa (at least seven coupled binge/vomit episodes per week). The patients were otherwise healthy, their weight was normal, and they were not receiving medical or psychiatric treatment. During the first week of the study, patients recorded all eating-behaviour events to establish a baseline. In the second week, all patients received placebo, but were told that they were receiving either placebo or active drug. At the end of this single-blind phase, patients were randomly assigned placebo or ondansetron (24 mg daily) for a further 4 weeks. The primary outcome measure was the number of binge/vomit episodes per week. Data were analysed by intention to treat. FINDINGS 29 patients met the inclusion criteria, of whom 28 completed the baseline study, and 26 completed the single-blind placebo week. 12 patients were assigned placebo, and 14 ondansetron; one patient in the ondansetron group dropped out owing to accidental injury. During the 4th week of double-blind treatment, mean binge/vomit frequencies were 13.2 per week (SD 11.6) in the placebo group, versus 6.5 per week (3.9) in the ondansetron group (estimated difference 6.8 [95% CI 4.0-9.5]; p<0.0001). The ondansetron group also showed significant improvement, compared with the placebo group, in two secondary indicators of disease severity. The amount of time spent engaging in bulimic behaviours was decreased on average by 7.6 h per week in the ondansetron group, compared with 2.3 h in the placebo group (estimated difference 5.1 [0.6-9.7]). Similarly, the number of normal meals and snacks increased on average by 4.3 normal eating episodes without vomiting per week in the ondansetron group, compared with 0.2 in the placebo group (estimated difference 4.1 [1.0-7.2]). INTERPRETATION The decrease in binge-eating and vomiting under ondansetron treatment was not achieved by compensatory changes in eating behaviour such as by a smaller number of binges of longer duration, or by not eating, or by binge-eating without vomiting. Instead, our findings indicate a normalisation of the physiological mechanism(s) controlling meal termination and satiation. Since meal termination and satiety are mainly vagally mediated functions, since binge-eating and vomiting produce intense stimulation of vagal afferent fibres, and since ondansetron and other 5-HT3 antagonists decrease afferent vagal activity, the symptom improvement may result from a pharmacological correction of abnormal vagal neurotransmission.

Opiate vs non-opiate footshock-induced analgesia (FSIA): The body region shocked is a critical factor

Previous work has demonstrated that footshock can elicit either opiate or non-opiate analgesia. The present study has demonstrated that one critical factor determining the involvement of endogenous opioids is the body region shocked. Using 90 s shock, front paw shock produced an opiate analgesia which was significantly antagonized by as little as 0.1 mg/kg systemic naloxone and morphine tolerance. In the latter experiment, a parallel recovery of the analgesic potencies of both front paw shock and morphine was observed following 2 weeks of opiate abstinence. In contrast, hind paw shock produced a non-opiate analgesia which failed to be attenuated by 20 mg/kg systemic naloxone and showed no cross-tolerance to morphine. Since identical shock parameters were used for front paw and hind paw shock in the systemic naloxone experiments, stress per se clearly cannot be the crucial factor determining the involvement of endogenous opioids in footshock-induced analgesia. These results were discussed with respect to clinical treatments of pain which utilize somatosensory stimulation.

Localization of NADPH diaphorase in neurons of the rostral ventral medulla: possible role of nitric oxide in central autonomic regulation and oxygen chemoreception

We studied whether neurons containing nitric oxide synthase (NOS) are localized to the rostral ventrolateral medulla (RVM) and, if so, whether they are distinct from the adrenergic neurons of the C1 group. NOS-containing neurons and/or C1 neurons were visualized using NADPH diaphorase histochemistry and phenylethanolamine N-methyltransferase (PNMT) immunohistochemistry, respectively. A column of NADPH diaphorase-positive neurons, extending 2 mm in the rostrocaudal plane, was observed lateral to the inferior olive and medial to the C1 neurons. Double labelling studies showed that NADPH diaphorase-positive neurons were not immunoreactive for PNMT, indicating that the two enzymes were localized in the different cells. Furthermore, only a small fraction of NADPH diaphorase neurons were retrogradely labelled after injections of fluorogold into the thoracic cord. We conclude that the RVM contains a well-defined group of neurons endowed with NOS that are distinct from the adrenergic neurons of the C1 group and have only limited monosynaptic projections to the spinal cord. Since the RVM is involved in the control of arterial pressure and in oxygen-conserving reflexes, the findings raise the possibility that nitric oxide participates in central autonomic regulation and oxygen chemoreception.

Functional neuroimaging of gastric distention.

This study aimed to measure brain activation during gastric distention as a way to investigate short-term satiety. We estimated regional cerebral blood flow with positron emission tomography (15O-water) during gastric balloon inflation and deflation in 18 healthy young women. The contrast between inflated minus deflated conditions showed activation in the following four key regions that were identified a priori: dorsal brain stem; left inferior frontal gyrus; bilateral insula; and right subgenual, anterior cingulate cortex. Extant neuroimaging literature provides context for these areas as follows: the brain stem represents vagal projection zones for visceral afferent processing; the inferior frontal gyrus serves as a convergence zone for processing food-related stimuli; and both the insula and subgenual anterior cingulate cortex respond to emotional stimulation. The identification of neural correlates of gastric distention is a key step in the discovery of new treatments for obesity. New therapies could intervene by modifying the perception of gastric distention, an important contributor to meal termination and short-term satiety. This first study of brain activation during nonpainful, proximal gastric distention provides the groundwork for future research to discover novel treatments for obesity.

Characterization of the extent of pontomesencephalic cholinergic neurons' projections to the thalamus: comparison with projections to midbrain dopaminergic groups.

We sought to determine whether pontomesencephalic cholinergic neurons which we have been shown previously to project to the substantia nigra and ventral tegmental area also contribute to the thalamic activation projection from the pedunculopontine and laterodorsal tegmental nuclei. Retrograde tracing, immunohistochemical localization of choline acetyltransferase and statistical methods were used to determine the full extent of the cholinergic projection from the pedunculopontine and laterodorsal tegmental nuclei to the thalamus. Progressively larger Fluoro-Gold injections in to the thalamus proportionally labeled increasing numbers of pontomesencephalic cholinergic cells both ipsi- and contralaterally in the pedunculopontine and laterodorsal tegmental nuclei. Multiple large thalamic injections left only a small fraction of the ipsilateral pontomesencephalic cholinergic group unlabeled. This small remainder did not correspond to the populations which project to the substantia nigra and ventral tegmental area, thereby indicating that substantia nigra- and ventral tegmental area-projecting cholinergic neurons must also project to the thalamus. We examined whether there existed any set of cholinergic neurons in the pedunculopontine and laterodorsal tegmental nuclei which did not innervate a thalamic target. The distribution of descending projections of the pedunculopontine and laterodorsal tegmental nuclei demonstrated that the unlabeled remainder cannot correspond to a purely descending group. We also show that substance P-positive cholinergic cells in the laterodorsal tegmental nucleus project to the thalamus. Further studies demonstrated that the small population of cholinergic cells left unlabeled from the thalamus were the smallest sized cholinergic cells, and included two groups of small, light-staining cholinergic cells located in the parabrachial area and central gray, adjacent to the main pedunculopontine and laterodorsal tegmental nuclei cholinergic groups. These small cells, in contrast to thalamic-projecting cholinergic cells, did not stain positively for reduced nicotinamide adenine dinucleotide phosphate-diaphorase. Taken together, these results indicated that all of the reduced nicotinamide adenine dinucleotide phosphate diaphorase-positive/choline acetyltransferase-positive neurons of the pedunculopontine/laterodorsal tegmental nuclei ascend to innervate some portion of the thalamus, in addition to the other targets they innervate. These findings indicate that the diverse physiological and behavioral effects attributed to the activity of pontomesencephalic cholinergic neurons should not be dissociated from their activating effects in the thalamus.

Opiate Antagonistic Function of Cholecystokinin in Analgesia and Energy Balance Systems

Because several effects of cholecystokinin (CCK) are opposite to those reported for opioids, it seemed likely that CCK may function as an endogenous antagonist of opiate action. This hypothesis was tested initially by assessing the effect of CCK on opiate analgesias. Systemic administration of CCK attenuated opiate analgesias produced by morphine and footshock, but did not reduce nonopiate footshock analgesia. When delivered directly to the lumbosacral spinal cord, a critical site of opiate action, 3.6 ng of CCK-8 significantly inhibited opiate-mediated footshock analgesia; however, 3.6 ng of desulfated CCK-8 did not have an effect. Sequestering of endogenously circulating CCK by antibodies raised against CCK through an active immunization procedure resulted in a potentiation of morphine analgesia. If CCK functions to inhibit opiate involvement in behaviors other than pain responsitivity, CCK-induced satiety may result from an inhibition of opiate-stimulated feeding. In immunohistochemical studies, we have found a dense CCK fiber plexus in the dorsal PVN, a critical site for opiate-induced feeding. Direct microinjections of CCK to this region reduced short-term food intake by 28%. The findings presented here support the hypothesis that an opiate antagonistic function of CCK may account for several previously reported effects of this peptide.

Dorsolateral funiculus and intraspinal pathways mediate vaginal stimulation-induced suppression of nociceptive responding in rats

In rats, stimulation of the vaginal cervix with a glass rod reliably produces analgesia, as measured by the tail-flick test. The present studies sought to identify the neural substrates underlying this potent pain inhibition by examining the effects of decerebration, spinalization and bilateral dorsolateral funiculus (DLF) lesions on vaginal stimulation-produced analgesia (VSPA). These studies indicate that the neural circuitry mediating VSPA is contained within the caudal brainstem and spinal cord, since decerebration did not reduce VSPA when compared with sham-operated controls. A significant though markedly reduced level of analgesia was induced in spinalized rats, indicating that VSPA involves both intraspinal and descending pathways. This descending pathway, originating within supraspinal nuclei of the caudal brainstem, projects to the spinal cord via the DLF, since DLF lesions and spinalization produced equivalent reductions in VSPA compared to sham-operated controls. These results, considered in the light of previous electrophysiological and anatomical findings, indicate that the ventral medullary region may be the source of the descending DLF projection mediating VSPA.

Nociceptive, but not tactile, thresholds are elevated in bulimia nervosa

A reduction in the satiating properties of food has been postulated to be a factor responsible for the prolonged eating episodes its bulimia nerrosa (e.g., Pyle et al 1981; Geracioti and Liddle 1988; Smith 1989). With remarkably few exceptions, satiety-related information is relayed to the central nervous system via the vagus nerve (Giduck et al 1987; Kim et al 1989; Robinson et al 1988). Therefore, abnormalities in vagal function may possibly underlie the absence of the nomtal satiety response present in bulimia nervosa. Recent findings suggest that the vagus may serve as a common substrate in the peripheral control of both satiety and anti-nociception. Electrical stimulation of the vagus, including subdiaphragmatic branches, inhibits ~esponsivity to a noxious somatosensory stimulus (e.g., Pen et al 1088) and vagotomy reduces the analgesic response to peripherally administered opiates in the rat (Randich and Maixner 1984; Aicher and Randich 1988; Steinman et al 1986). Thus, we hypothesized that if bulimia nervosa

Transplantation of Fetal Neocortex Ameliorates Sensorimotor and Locomotor Deficits Following Neonatal Ischemic–Hypoxic Brain Injury in Rats

Ischemic brain injury in neonates can result in the degeneration of cortical and subcortical areas of brain and is associated with neurologic deficits. One approach to restoring function in conditions of ischemic brain injury is the use of neural transplants to repair damaged connections. This approach has been shown to reestablish neural circuitry and to ameliorate associated motor deficits in models of neonatal sensorimotor cortex damage. In this study, we utilized the Rice et al. rodent model of neonatal ischemic-hypoxic (IH) brain injury to assess whether transplantation of fetal neocortical tissue can promote functional recovery in tests of sensorimotor and locomotor ability throughout development and as adults. We show that animals that received neocortical grafts 3 days following the IH injury performed significantly better as adults on two measures of motor ability, the Rota-Rod treadmill and apomorphine-induced rotations, than did control animals that received sham transplants after the IH injury. Transplants were identifiable in 72% of the animals 10-12 weeks after implantation. Histochemical studies revealed that while the transplanted tissue did not establish normal cortical cytoarchitecture, cells and fibers within the grafts stained for nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), choline acetyl transferase (ChAT), cholecystokinin (CCK), and glial fibrillary acidic protein (GFAP). These results suggest that transplantation of fetal neocortical tissue following IH injury in the neonatal period is associated with amelioration of motor deficits and that the grafted tissue demonstrated a neurochemical phenotype that resembled normal neocortex. This approach warrants continued investigation in light of potential therapeutic uses.

Effect of ondansetron, a 5-HT3 receptor antagonist, on the dynamic association between bulimic behaviors and pain thresholds.

Abstract Thresholds for detection of both pressure and thermal pain are elevated in patients with bulimia nervosa. The present study was aimed at determining (1) if pressure pain detection thresholds (PDT) varied dynamically with the primary disease symptoms of binge eating and vomiting and (2) if the elevation in PDT was effected by treatment with ondansetron (ONDAN), a 5‐HT3 receptor antagonist. PDT was defined as the mean of the minimal amount of pressure (measured in g) perceived as painful when exerted by a 1 mm2 blunted point onto the center of the ventral surface of the ungual phalanx of digits 2‐5 of the non‐dominant hand. Fourteen female patients with severe bulimia nervosa (currently >seven binge/vomit episodes per week;>2 years illness duration) served as participants. PDT were evaluated at weekly intervals during the course of ongoing treatment studies (double‐blind and ‘open’ label) investigating the therapeutic effects of ONDAN. Data were analyzed by random regression analyses, allowing for the repeated‐measures and non‐orthogonal design. Data collected from 14 patients under the no‐drug condition indicated that PDT increased over the interval between binge/vomit episodes, with significant elevations occurring at times when patients had naturally exceeded their average inter‐binge interval. Eleven of these 14 patients underwent 4 weeks of ONDAN treatment. Under this drug condition, the time since the last binge/vomit episode was no longer a significant predictor of PDT. These patients also experienced a significant reduction in the frequency of bulimic behaviors, a finding reported in detail elsewhere. The above finding from untreated patients support the involvement of a common underlying mechanism driving both the increase in pain detection thresholds and the occurrence of the next bulimic episode. This possibility is further supported by the findings that ONDAN treatment is associated with a significant moderation of both variables. The effect of ONDAN may be mediated by blockade of afferent vagal neurotransmission, although other mechanisms must be considered.