The gut-brain axis mediates bacterial driven modulation of reward signaling.

OBJECTIVE: Our goal is to investigate if microbiota composition modulates reward signaling and assess the role of the vagus in mediating microbiota to brain communication. METHODS: Male germ-free Fisher rats were colonized with gastrointestinal contents from chow (low fat (LF) ConvLF) or HF (ConvHF) fed rats. RESULTS: Following colonization, ConvHF rats consumed significantly more food than ConvLF animals. ConvHF rats displayed lower feeding-induced extracellular DOPAC levels (a metabolite of dopamine) in the Nucleus Accumbens (NAc) as well as reduced motivation for HF foods compared to ConvLF rats. Dopamine receptor 2 (DDR2) expression levels in the NAc were also significantly lower in ConvHF animals. Similar deficits were observed in conventionally raised HF fed rats, showing that diet-driven alteration in reward can be initiated via microbiota. Selective gut to brain deafferentation restored DOPAC levels, DRD2 expression, and motivational drive in ConvHF rats. CONCLUSIONS: We concluded from these data that a HF-type microbiota is sufficient to alter appetitive feeding behavior and that bacteria to reward communication is mediated by the vagus nerve.

ADAR1 deficiency protects against high-fat diet-induced obesity and insulin resistance in mice.

Obesity is an important independent risk factor for type 2 diabetes, cardiovascular diseases, and many other chronic diseases. The objective of this study was to determine the role of adenosine deaminase acting on RNA 1 (ADAR1) in the development of obesity and insulin resistance. Wild-type (WT) and heterozygous ADAR1-deficient (Adar1+/-) mice were fed normal chow or a high-fat diet (HFD) for 12 wk. Adar1+/- mice fed with HFD exhibited a lean phenotype with reduced fat mass compared with WT controls, although no difference was found under chow diet conditions. Blood biochemical analysis and insulin tolerance test showed that Adar1+/- improved HFD-induced dyslipidemia and insulin resistance. Metabolic studies showed that food intake was decreased in Adar1+/- mice compared with the WT mice under HFD conditions. Paired feeding studies further demonstrated that Adar1+/- protected mice from HFD-induced obesity through decreased food intake. Furthermore, Adar1+/- restored the increased ghrelin expression in the stomach and the decreased serum peptide YY levels under HFD conditions. These data indicate that ADAR1 may contribute to diet-induced obesity, at least partially, through modulating the ghrelin and peptide YY expression and secretion.NEW & NOTEWORTHY This study identifies adenosine deaminase acting on RNA 1 as a novel factor promoting high-fat diet-induced obesity, at least partially, through modulating appetite-related genes ghrelin and PYY.

Age Dependency of Blood-Brain Barrier Penetration by cis- and trans-Permethrin in the Rat.

Permethrin (PER), a type I pyrethroid, is the most widely used insecticide in domestic settings in the United States. The overall objective of this study was to assess the efficiency of the blood-brain barrier (BBB) as an obstacle to the 14C-cis-permethrin (CIS) and 14C-trans-permethrin (TRANS) isomers of PER, and to determine whether its barrier function changes during maturation of the rat. Experiments were conducted to quantify brain uptake of CIS and TRANS in postnatal day 145, 21, and 90 Sprague-Dawley rats. The common carotid artery of anesthetized rats was perfused for 2 or 4 minutes with 1, 10, or 50 µM 14C-CIS or 14C-TRANS in 4% albumin. Brain deposition of each isomer was inversely related to age, with levels in the youngest animals >5 times those in adults. Brain uptake was linear over the 50-fold range of pyrethroid concentrations, indicative of passive, nonsaturable BBB permeation. The extent of uptake of toxicologically relevant concentrations of CIS and TRANS was quite similar. Thus, dissimilar BBB permeation does not contribute to the greater acute neurotoxic potency of CIS, but greater permeability of the immature BBB to CIS and TRANS may contribute to the increased susceptibility of preweanling rodents to the insecticides.

Activity in nodose ganglia neurons after treatment with CP 55,940 and cholecystokinin.

Previous work has shown that cannabinoids increase feeding, while cholecystokinin (CCK) has an anorexigenic effect on food intake. Receptors for these hormones are located on cell bodies of vagal afferent nerves in the nodose ganglia. An interaction between CCK and endocannabinoid receptors has been suggested. The purpose of these studies is to explore the effect of pretreatment with a cannabinoid agonist, CP 55,940, on nodose neuron activation by CCK. To determine the effect of CP 55,940 and CCK on neuron activation, rats were anesthetized and nodose ganglia were excised. The neurons were dissociated and placed in culture on coverslips. The cells were treated with media; CP 55,940; CCK; CP 55,940 followed by CCK; or AM 251, a CB1 receptor antagonist, and CP 55,940 followed by CCK. Immunohistochemistry was performed to stain the cells for cFos as a measure of cell activation. Neurons were identified using neurofilament immunoreactivity. The neurons on each slip were counted using fluorescence imaging, and the number of neurons that were cFos positive was counted in order to calculate the percentage of activated neurons per coverslip. Pretreatment with CP 55,940 decreased the percentage of neurons expressing cFos-immunoreactivity in response to CCK. This observation suggests that cannabinoids inhibit CCK activation of nodose ganglion neurons.

Agricultural Animals as Biomedical Models: Occupational Health and Safety Considerations.

The use of agricultural animals in biomedical research is increasing. Their overall size and metabolic rate, organ size, longer gestation period, and other physiological similarities make them good candidates for animal models of human disease. There are a number of special considerations for use of traditional farm animals for biomedical research. Differences in physical plant infrastructure, handling equipment, training of personnel, and potential zoonoses are some of the important considerations when traditional farm animals are used in biomedical research. This article provides an overview of some of the special considerations for using traditional agricultural animals in biomedical research. With the growing need for improved translational research, it is reasonable to predict significant growth in these animal models.

The galanin receptor agonist, galnon, attenuates cocaine-induced reinstatement and dopamine overflow in the frontal cortex.

Relapse represents one of the most significant problems in the long-term treatment of drug addiction. Cocaine blocks plasma membrane monoamine transporters and increases dopamine (DA) overflow in the brain, and DA is critical for the motivational and primary reinforcing effects of the drug as well as cocaine-primed reinstatement of cocaine seeking in rats, a model of relapse. Thus, modulators of the DA system may be effective for the treatment of cocaine dependence. The endogenous neuropeptide galanin inhibits DA transmission, and both galanin and the synthetic galanin receptor agonist, galnon, interfere with some rewarding properties of cocaine. The purpose of this study was to further assess the effects of galnon on cocaine-induced behaviors and neurochemistry in rats. We found that galnon attenuated cocaine-induced motor activity, reinstatement and DA overflow in the frontal cortex at a dose that did not reduce baseline motor activity, stable self-administration of cocaine, baseline extracellular DA levels or cocaine-induced DA overflow in the nucleus accumbens (NAc). Similar to cocaine, galnon had no effect on stable food self-administration but reduced food-primed reinstatement. These results indicate that galnon can diminish cocaine-induced hyperactivity and relapse-like behavior, possibly in part by modulating DA transmission in the frontal cortex.

Chronic exercise confers neuroprotection in experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is an autoimmune disease that affects the CNS, resulting in accumulated loss of cognitive, sensory, and motor function. This study evaluates the neuropathological effects of voluntary exercise in mice with experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Two groups of C57BL/6J mice were injected with an emulsion containing myelin oligodendrocyte glycoprotein and then randomized to housing with a running wheel or a locked wheel. Exercising EAE mice exhibited a less severe neurological disease score and later onset of disease compared with sedentary EAE animals. Immune cell infiltration and demyelination in the ventral white matter tracts of the lumbar spinal cord were significantly reduced in the EAE exercise group compared with sedentary EAE animals. Neurofilament immunolabeling in the ventral pyramidal and extrapyramidal motor tracts displayed a more random distribution of axons and an apparent loss of smaller diameter axons, with a greater loss of fluorescence immunolabeling in the sedentary EAE animals. In lamina IX gray matter regions of the lumbar spinal cord, sedentary animals with EAE displayed a greater loss of α-motor neurons compared with EAE animals exposed to exercise. These findings provide evidence that voluntary exercise results in reduced and attenuated disability, reductions in autoimmune cell infiltration, and preservation of axons and motor neurons in the lumbar spinal cord of mice with EAE.

Effect of treatment with simvastatin and cyclosporine on neurotransmitter concentrations in cerebrospinal fluid after subarachnoid hemorrhage in dogs.

OBJECTIVE: To measure concentrations of glutamate, aspartate, γ-aminobutyric acid (GABA), and glycine in CSF of dogs with experimentally induced subarachnoid hemorrhage (SAH) and to assess effects of cyclosporine and simvastatin on these concentrations. SAMPLE: CSF samples from 13 dogs. PROCEDURES: In a previous study, SAH was induced in dogs via 2 injections of autologous blood into the cerebellomedullary cistern 24 hours apart. Dogs were untreated (control; n = 5) or received simvastatin alone (4) or simvastatin in combination with cyclosporine (4). Samples of CSF were collected before the first blood injection (baseline; time 0), before the second blood injection, and on days 3, 7, and 10. For the study reported here, neurotransmitter concentrations in CSF were analyzed via high-performance liquid chromatography. Data were analyzed with a repeated-measures model with adjustments for multiple comparisons by use of the Tukey method. RESULTS: In control dogs, the glutamate concentration peaked on day 3 and there was a significant increase in GABA and glutamate concentrations. Glutamate concentrations were significantly lower and glycine concentrations significantly higher on day 3 after administration of simvastatin alone or simvastatin in combination with cyclosporine, compared with concentrations for the control group. No significant differences in GABA and aspartate concentrations were detected among treatment groups at any time point. CONCLUSIONS AND CLINICAL RELEVANCE: Glutamate concentrations were increased in the CSF of dogs with SAH. Simvastatin administration attenuated high glutamate concentrations. A combination of immunosuppression and upregulation of nitric oxide synthase may be useful in lowering high glutamate concentrations in ischemic CNS conditions.

Comparison of concentrations of γ-aminobutyric acid and glutamate in cerebrospinal fluid of dogs with idiopathic epilepsy with and without seizure-related magnetic resonance imaging hyperintense areas in the limbic system.

OBJECTIVE: To investigate differences in CSF concentrations of excitatory and inhibitory neurotransmitters in dogs with and without T2-weighted (T2W) MRI hyperintense areas in the limbic system. SAMPLE: Archived CSF samples and stored brain MRI images of 5 healthy research dogs (group 1), 8 dogs with idiopathic epilepsy (IE) with no abnormal MRI findings (group 2), and 4 dogs with IE with hyperintense areas in the limbic system detected by means of T2W MRI (group 3). PROCEDURES: Archived CSF samples and stored MRI images obtained from all dogs were evaluated. Dogs in groups 2 and 3 were matched on the basis of age and breed. High-performance liquid chromatography was used to evaluate glutamate and γ-aminobutyric acid (GABA) concentrations in CSF samples. RESULTS: Glutamate concentrations were higher in CSF of both groups of dogs with IE than in healthy dogs. However, glutamate concentrations in CSF were not significantly higher in dogs with IE and with hyperintense areas than in dogs with IE but no abnormal MRI findings. Concentrations of GABA in CSF were higher in group 3 than in group 2 and in group 2 than in group 1. CONCLUSIONS AND CLINICAL RELEVANCE: No significant difference was evident between glutamate concentrations in CSF of dogs with IE and with and without hyperintense areas detected by means of T2W MRI. However, glutamate concentrations typically were higher in CSF of dogs with IE and MRI hyperintense areas. Future studies with larger sample sizes should be conducted to confirm this finding and to determine the clinical importance of high glutamate concentrations in CSF of dogs with IE.

Assessment of plasma uracil-to-dihydrouracil concentration ratio as an indicator of dihydropyrimidine dehydrogenase activity in clinically normal dogs and dogs with neoplasia or renal insufficiency.

OBJECTIVE: To determine and compare the ratio of uracil (U) to dihydrouracil (UH(2)) concentrations in plasma as an indicator of dihydropyrimidine dehydrogenase activity in clinically normal dogs and dogs with neoplasia or renal insufficiency. ANIMALS: 101 client- and shelter-owned dogs. PROCEDURES: Study dogs included 74 clinically normal dogs, 17 dogs with neoplasia, and 10 dogs with renal insufficiency. For each dog, a blood sample was collected into an EDTA-containing tube; plasma U and UH(2) concentrations were determined via UV high-performance liquid chromatography, and the U:UH(2) concentration ratio was calculated. Data were compared among dogs grouped on the basis of sex, clinical group assignment, reproductive status (sexually intact, spayed, or castrated), and age. RESULTS: Mean ± SEM U:UH(2) concentration ratio for all dogs was 1.55 ± 0.08 (median, 1.38; range, 0.4 to 7.14). In 14 (13.9%) dogs, the U:UH(2) concentration ratio was considered abnormal (ie, > 2). Overall, mean ratio for sexually intact dogs was significantly higher than that for neutered dogs; a similar difference was apparent among males but not females. Dogs with ratios > 2 and dogs with ratios ≤ 2 did not differ significantly with regard to sex, clinical group, reproductive status, or age. CONCLUSIONS AND CLINICAL RELEVANCE: Determination of the U:UH(2) concentration ratio was easy to perform. Ratios were variable among dogs, possibly suggesting differences in dihydropyrimidine dehydrogenase activity. However, studies correlating U:UH(2) concentration ratio and fluoropyrimidine antimetabolite drug tolerability are required to further evaluate the test's validity and its appropriate use in dogs.

PRTFDC1 is a genetic modifier of HPRT-deficiency in the mouse.

Lesch-Nyhan disease (LND) is a severe X-linked neurological disorder caused by a deficiency of hypoxanthine phosphoribosyltransferase (HPRT). In contrast, HPRT-deficiency in the mouse does not result in the profound phenotypes such as self-injurious behavior observed in humans, and the genetic basis for this phenotypic disparity between HPRT-deficient humans and mice is unknown. To test the hypothesis that HPRT deficiency is modified by the presence/absence of phosphoribosyltransferase domain containing 1 (PRTFDC1), a paralog of HPRT that is a functional gene in humans but an inactivated pseudogene in mice, we created transgenic mice that express human PRTFDC1 in wild-type and HPRT-deficient backgrounds. Male mice expressing PRTFDC1 on either genetic background were viable and fertile. However, the presence of PRTFDC1 in the HPRT-deficient, but not wild-type mice, increased aggression as well as sensitivity to a specific amphetamine-induced stereotypy, both of which are reminiscent of the increased aggressive and self-injurious behavior exhibited by patients with LND. These results demonstrate that PRTFDC1 is a genetic modifier of HPRT-deficiency in the mouse and could therefore have important implications for unraveling the molecular etiology of LND.

Disulfiram attenuates drug-primed reinstatement of cocaine seeking via inhibition of dopamine ß-hydroxylase.

The antialcoholism medication disulfiram (Antabuse) inhibits aldehyde dehydrogenase (ALDH), which results in the accumulation of acetaldehyde upon ethanol ingestion and produces the aversive 'Antabuse reaction' that deters alcohol consumption. Disulfiram has also been shown to deter cocaine use, even in the absence of an interaction with alcohol, indicating the existence of an ALDH-independent therapeutic mechanism. We hypothesized that disulfiram's inhibition of dopamine ß-hydroxylase (DBH), the catecholamine biosynthetic enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic neurons, underlies the drug's ability to treat cocaine dependence. We tested the effects of disulfiram on cocaine and food self-administration behavior and drug-primed reinstatement of cocaine seeking in rats. We then compared the effects of disulfiram with those of the selective DBH inhibitor, nepicastat. Disulfiram, at a dose (100 mg/kg, i.p.) that reduced brain NE by ∼40%, did not alter the response for food or cocaine on a fixed ratio 1 schedule, whereas it completely blocked cocaine-primed (10 mg/kg, i.p.) reinstatement of drug seeking following extinction. A lower dose of disulfiram (10 mg/kg) that did not reduce NE had no effect on cocaine-primed reinstatement. Nepicastat recapitulated the behavioral effects of disulfiram (100 mg/kg) at a dose (50 mg/kg, i.p.) that produced a similar reduction in brain NE. Food-primed reinstatement of food seeking was not impaired by DBH inhibition. Our results suggest that disulfiram's efficacy in the treatment of cocaine addiction is associated with the inhibition of DBH and interference with the ability of environmental stimuli to trigger relapse.

Lesion of the lateral parabrachial nucleus attenuates the anorectic effect of peripheral amylin and CCK.

Amylin and CCK activate the area postrema (AP)/nucleus of the solitary tract (NTS) - lateral parabrachial nucleus (LPBN) - central amygdala (CeA) pathway. However, except for the brainstem structures the role of these nuclei for the anorectic effect of these peptides is not yet well characterized. The current study investigated the role of the LPBN in mediating the inhibitory effect of peripheral amylin and CCK on feeding behavior. Rats with electrolytic lesions in the LPBN (LPBN-X) were used in behavioral as well as in immunohistological c-Fos studies. LPBN-X significantly reduced the anorectic effect of amylin (5 microg/kg, i.p.). The effect of a higher amylin dose (10 microg/kg, i.p.) was only slightly attenuated in the LPBN-X rats. In agreement with previous studies, LPBN lesions also reduced the inhibitory effect of CCK on food intake. In the immunohistological experiments, amylin and CCK induced c-Fos expression in the AP, NTS, LPBN and CeA in the SHAM rats. Both the amylin- and CCK-induced activation of the CeA was completely abolished in the animals with a LPBN lesion. These results clearly suggest that the signal transduction pathway between the AP/NTS and CeA has been disrupted by the LPBN ablation. We conclude that the LPBN is a crucial brain site mediating the anorectic effect of amylin and CCK. Furthermore, an intact LPBN seems to be essential for the c-Fos response in the CeA induced by these peptides.

Fiber but not conjugated linoleic acid influences adiposity in dogs.

Feeding obese dogs a high-fiber food with or without added conjugated linoleic acid (CLA) resulted in reduced caloric consumption, reduced body weight, and a 3.3% reduction in body fat, whereas feeding a low-fiber food resulted in a comparable increase in caloric consumption and a 2.4% gain in body fat. The addition of CLA did not significantly affect food intake, energy intake, final lean body percent, change in lean body percent, or final fat percent. These results suggest that the addition of dietary fiber but not CLA to foods may be helpful in the treatment of canine obesity.

Area postrema-lesions increase operant responding to sucrose in rats.

Rats with lesions of the area postrema (APX) are known to exhibit an enhanced intake of highly palatable foods such as sweetened condensed milk and cookies. These observations suggest the possibility that APX rats find these foods more rewarding and will work harder to obtain these foods. Sham and APX rats were tested on fixed ratio (FR) and progressive ratio (PR) schedules. APX rats consistently pressed more times to receive sucrose solution and attained both FR 3 and FR 5 criteria significantly faster than sham-lesioned control rats. Furthermore, rats with APX had significantly higher break points than sham-lesioned control rats on a progressive ratio schedule. These results support the hypothesis that rats with lesions of the area postrema will consistently work harder to obtain a highly palatable food reward.

Cardiovascular drift is related to reduced maximal oxygen uptake during heat stress.

INTRODUCTION/PURPOSE: This study investigated whether the progressive rise in heart rate (HR) and fall in stroke volume (SV) during prolonged, constant-rate, moderate-intensity exercise (cardiovascular drift, CVdrift) in a hot environment is associated with a reduction in VO(2max). METHODS: CVdrift was measured in nine male cyclists between 15 and 45 min of cycling at 60% VO(2max) in 35 degrees C that was immediately followed by measurement of VO(2max). VO(2max) also was measured after 15 min of cycling on a separate day, so that any change in VO(2max) between 15 and 45 min could be associated with the CVdrift that occurred during that time interval. This protocol was performed under one condition in which fluid was ingested and there was no significant body weight change (0.3 +/- 0.4%), and under another in which no fluid was ingested and dehydration occurred (2.5 +/- 1%, P < 0.05). RESULTS: Fluid ingestion did not affect CVdrift or change in VO(2max). A 12% increase in HR (151 +/- 9 vs 169 +/- 10 bpm, P < 0.05) and 16% decrease in SV (120 +/- 12 vs 101 +/- 10 mL.beat(-1), P < 0.05) between 15 and 45 min was accompanied by a 19% decrease in VO(2max) (4.4 +/- 0.6 vs 3.6 +/- 0.4 L.min(-1), P < 0.05) despite attainment of a higher maximal HR (P < 0.05) at 45 min (194 +/- 5 bpm) vs 15 min (191 +/- 5 bpm). Submaximal VO(2) increased only slightly over time, but VO(2max) increased from 63 +/- 5% at 15 min to 78 +/- 8% at 45 min (P < 0.05). CONCLUSION: We conclude CVdrift during 45 min of exercise in the heat is associated with decreased VO(2max) and increased relative metabolic intensity. The results support the validity of using changes in HR to reflect changes in relative metabolic intensity during prolonged exercise in a hot environment in which CVdrift occurs.

Fumonisin B1-induced neurodegeneration in mice after intracerebroventricular infusion is concurrent with disruption of sphingolipid metabolism and activation of proinflammatory signaling.

Fumonisin B1 (FB1), a mycotoxin produced by Fusarium verticillioides, causes equine leukoencephalomalacia, a condition not reproduced in any other species. We hypothesized that direct exposure of murine brain to FB1 will result in neurotoxicity, characterized by biochemical and pathological alterations. The present study compared the toxicity of FB1 in mouse brain after an intracerebroventricular (icv) or subcutaneous (sc) infusion. Female BALB/c mice (5/group) were infused (0.5 microl/h) with total doses of 0, 10 or 100 microg FB1 in saline over 7 days via osmotic pumps implanted either via icv cannulation of the ventricle or via the sc route. One day after the last day of treatment, brains were dissected either fresh or after intracardiac paraformaldehyde fixation. In mice given 100 microg of FB1 icv, FluoroJade B staining revealed neurodegeneration in the cortex, and anti-glial fibrillary acidic protein staining detected activated astrocytes in the hippocampus. High performance liquid chromatography indicated accumulation of free sphinganine in animals given FB1 icv in all brain regions and increased free sphingosine after the 100 microg FB1 in the cortex. The concentration of cortical sphingomyelin and complex sphingolipids remained unchanged. The icv administration of FB1 induced expression of tumor necrosis factor alpha, interleukin-1beta, interleukin-6 and interferon gamma after both doses, assayed by the real-time polymerase chain reaction. The sc administration of 100 microg FB1 caused slight sphinganine accumulation and increased IL-1beta expression in cortex only. Results indicated that icv injection of FB1 caused neurodegeneration with simultaneous inhibition of de novo ceramide synthesis, stimulation of astrocytes, and upregulation of pro-inflammatory cytokines in the murine brain. A relative lack of FB1 availability into the brain could be responsible for the absence of its neurotoxicity in mouse.

Dopamine overflow is increased in olfactory bulbectomized rats: an in vivo microdialysis study.

Olfactory bulbectomy (OBX) in rats produces behavioral, physiological, and neurochemical changes that resemble symptoms of depression in humans. The procedure thus serves as a rodent model of affective disorder. Many of the behavioral effects of OBX resemble psychomotor agitation. The possible role of dysregulation of ventral striatal dopamine (DA) systems in this phenomenon was investigated. Basal levels of DA, norepinephrine (NE), homovanillic acid, dihydroxyphenylacetic acid, and 5-hydroxyindoleacetic acid were examined in the striatum of OBX and sham-operated controls using in vivo microdialysis. OBX rats exhibited significantly higher basal DA levels (192%) and lower NE levels (12%) than sham-operated controls. Locomotor activity in response to novelty and footshock stress was elevated in OBX rats. The finding of higher DA levels in striatum may explain this "agitation-like" behavior, a commonly observed phenomenon in the OBX model.

Cannabinoid agonist, CP 55,940, facilitates intake of palatable foods when injected into the hindbrain.

Cannabinoids have been shown to influence food intake, and until recently, the neural pathways mediating these effects have remained obscure. It has been previously shown that intracerebroventricular injection of delta-9-tetrahydrocannabinol (Delta(9)-THC) causes increased consumption of palatable foods in rats, and we postulated the involvement of the hindbrain in this cannabinoid-induced food intake. Cannulated rats (both female and male groups) trained to consume sweetened condensed milk received either lateral or fourth ventricle injections of CP 55,940 and were presented with sweetened condensed milk 15 min after injection. Rats were injected over a range of doses between 100 pg and 10 microg per rat. Milk intake was recorded for a total of 3 h. Lateral ventricle injection of CP 55,940 increased milk intake at doses in the microgram range. However, CP 55,940 was effective in increasing food intake at nanogram doses when injected into the fourth ventricle. Finally, male rats appeared to be more sensitive to CP 55,940 than female rats inasmuch as milk consumption was increased at the 1 ng dose in male rats, whereas only the 10 ng dose was effective in females. These results indicate that CP 55,940 may act in the hindbrain to influence feeding behavior in rats.