Mechanisms of umami taste preference and aversion in rats

The influence of glutamate intake on growth and appetite, and the mechanisms of preference and aversion for monosodium L-glutamate (MSG) solutions were investigated in rats. Food intake, but not weight gain, was reduced significantly in rats fed a glutamate + glutamine (Glx)-deficient diet compared with those fed a control diet. Increase in the voluntary intake of Glx solutions was more rapid in rats fed the Glx-deficient diet. The preference and aversion for MSG solutions were distinctly different in 14 rat strains tested. Brown-Norway rats showed a strong preference for 60 mmol/L MSG and did not show aversive behavior toward solutions containing up to 600 mmol/L MSG. Sprague-Dawley (SD) rats showed a moderate preference for 60 mmol/L MSG and a weak aversion for MSG concentrations higher than 240 mmol/L; Long-Evans Agouti rats showed a moderate preference for 60 mmol/L MSG and a marked aversion for MSG concentrations higher than 120 mmol/L. Aversion was not due to nonspecific hyperosmotic effects. After section of gastric branches of the vagus nerve, MSG became aversive to SD rats. Aversion to 240 mmol/L MSG was reduced by 23-39% when combined with proline, alanine, glycine and glucose. These results show that the preference and aversion for MSG are determined by genetic factors, as well as vagus nerve function, and that the aversion to high MSG concentrations is reduced by the presence of other glucogenic amino acids and sugars.

Hypothalamic and amygdalar neuronal responses to various tastant solutions during ingestive behavior in rats

The forebrain, including the amygdala (AM) and hypothalamus, may be a higher brain center that modulates the activity of a brainstem neural system that influences ingestive behavior via descending projections. In this study, to elucidate the characteristics of sensory information processing in the forebrain in relation to this putative connection, we recorded neuronal activity in the AM and hypothalamus [lateral hypothalamic area (LHA), medial hypothalamic area (MHA)] of rats during discrimination of conditioned sensory stimuli and the ingestion of various tastant solutions. Of 420 responsive AM neurons identified, 24 were taste responsive and located mainly in the central nucleus of the AM. Multivariate analyses of these taste neurons suggested that in the AM, taste quality is processed on the basis of palatability. In the hypothalamus, of 282 LHA and MHA neurons recorded, 144 responded to one or more conditioned auditory stimuli and/or licking of one or more solutions. Stress, which is known to influence feeding behavior, increased the mean spontaneous activity of LHA neurons but decreased the mean spontaneous neuronal activity of MHA neurons. This pattern of changes in spontaneous neuronal activity correlated with alterations in feeding behavior during stress. Furthermore, the activity of both AM and LHA neurons was modulated flexibly during conditioned associative learning. Together, the data suggest that the activity of the AM and hypothalamic neurons is altered when animals must modulate ingestive behavior by learning a new stimulus associated with food and by being exposed to stress, suggesting that these forebrain areas are important modulators of the activity of a basic neural system in the brainstem that influences ingestive behavior.

Effects of L-lysine deficient diet on the hypothalamic interstitial norepinephrine and diet-induced thermogenesis in rats in vivo

Rats readily recognize an amino acid deficient diet, presumably via central mechanisms that involve hypothalamic circuits. Presently, effects of the essential amino acid L-lysine deficiency on the ventromedial (VMH) and lateral (LH) hypothalamus norepinephrine (NE) release were evaluated in free moving rats. Microdialysis measurement was undertaken once in 48 h (12:00 noon-14:00) in rats that had free access to food and drink. Significant decline in the food intake and VMH NE release were found in rats fed L-lysine diet. No changes were identified in LH NE release. Additionally, no significant differences in diet-induced spatial thermogenesis between normal and L-lysine deficient non-stressed rats were found in vivo. The results suggested that the VMH NE release was specifically involved in the integration of signals about amino acid deficiency. However, the decrease in VMH NE was not translated into changes of thermogenic responses to diet.

Potassium-current oscillation of rat megakaryocytes: As a model system for drug evaluation (Review)

Megakaryocytes respond to externally applied agonists showing a periodic K+ current that reflects oscillation in cytoplasmic calcium concentration ([Ca2+]i). We have revealed several signal transducing factors that are involved in the K+ current oscillation of megakaryocytes. In this megakaryocyte system, it is relatively easy to determine what point of the signal transduction pathway a drug affects. In addition, as a progenitor cell, megakaryocytes resemble platelets which have important roles in many diseases. Therefore, this experimental system can be used for evaluation of new drugs.

Immunological localization and ontogenetic development of inhibin alpha subunit in rat brain

This study examined the immunolocalization and ontogeny of the inhibin-specific alpha subunit in the brain of male rats. Immunohistochemistry using antiserum directed against the mature region of porcine inhibin alpha (1-19, Tyr20) revealed positive reactions in process-bearing cells resembling astroglia in several regions, especially in the dorsal region of the third ventricle, medial and ventral arcuate nucleus, hippocampal dentate gyrus, and layers 1-3 of the cerebral cortex. Generally, inhibin alpha-positive cells in the limbic cortex had larger cell bodies and longer processes than those in the hypothalamus. These inhibin alpha-positive cells were verified to be positive for glial fibrillary acidic protein (GFAP), a differentiated astroglial marker, by double immunolabelling. The expression of inhibin alpha mRNA was higher in the brains of neonatal rats than in those of adult rats, as revealed by reverse transcription-competitive polymerase chain reaction, although the similar changes of immunoreactive inhibin alpha subunit in the brain was not observed. Orchiectomy did not affect expression of inhibin alpha mRNA in the hypothalamic area. This study suggests that inhibin-related peptide is produced by differentiated astrocytes, especially in the hypothalamic arcuate nucleus, the hippocampal dentate gyrus, and the cerebral cortex, and that the expression of inhibin alpha is regulated during brain development.

Effects of D2 dopamine receptor agonist and antagonist on brain activity in the rat assessed by functional magnetic resonance imaging

The effects of D2 dopamine receptor agonist, bromocriptine (BROMO), and antagonist, haloperidol (HPD), on brain activity were investigated in rats by functional magnetic resonance imaging. T2*-weighted signal intensity was increased in the hypothalamus at 120 min after acute administration of BROMO, and in the ventral posterior and dorsomedial nuclei of the thalamus from 30 to 120 min. In contrast, the signal intensity was decreased in the caudate-putamen at 30 min after acute administration of HPD, in the hypothalamus from 30 to 60 min, and in the perirhinal cortex at 30 min. After chronic (2 weeks) HPD treatment, acute administration of HPD decreased signal intensity in the caudate-putamen at 60 min, in the hypothalamus at 30 min, the perirhinal cortex from 2 to 120 min, the dorsomedial and ventral posterior nuclei of the thalamus from 2 to 120 min, and the medial nucleus of the amygdala from 60 to 120 min. These results suggest that (1) the D2 receptor agonist increased the activity of the thalamic nuclei and the hypothalamus, while the D2 receptor antagonist suppressed brain activity in the regions where D2 receptors were present, (2) the suppression of brain activity in the thalamic nuclei and the perirhinal cortex by acute HPD administration was enhanced by chronic HPD treatment, and (3) the effects of antipsychotic drugs on the thalamus, amygdala, and perirhinal cortex may be related to their therapeutic efficacy, since clinical improvement in schizophrenic patients appears several days after the start of HPD treatment.

Hypothalamic control of amino acid appetite

Preference for umami taste materials, such as monosodium L-glutamate (MSG) and the 5'-ribonucleotides, inosine 5'-monophosphate (IMP) and guanosine 5'-monophosphate (GMP), varies as a consequence of protein nutrition. Rats fed diets deficient in dietary protein or an essential L-amino acid (AA), L-lysine (Lys), avidly consumed Lys, glycine and NaCl but not umami substances. However, when the rats' protein nutrition was normal or when they were recovering from deficiency, a preference for umami substances was evident. These data suggest that the central mechanism for recognition of protein malnutrition may be coupled with umami taste preference. To test this, Lys-deficient and normal rats were employed as a model for taste preference changes. AA levels in plasma and brain remain essentially unchanged throughout the day while the rat is on standard chow but are altered during Lys deficiency. The recognition site for the deficit in the rats' brains was localized to the ventromedial (VMH) and lateral (LHA) hypothalamus as determined by functional magnetic resonance imaging (fMRI, 4.7 Telsa). Studies of single neuron activity in the LHA of Lys-deficient rats suggested that neuronal plasticity occurred. Following Lys deficiency, cells responded specifically to Lys, both iontophoretically applied and during ingestion of AA. Other LHA neurons of nondeficient rats differentially responded to MSG. The present results suggest that the LHA and probably the VMH play important roles in recognition of deficient nutrients. Neural plasticity of hypothalamic cells helps maintain AA homeostasis. Furthermore, a preference for umami substances may be an indicator that the organism (rat or human) is free of protein malnutrition.

Activin antiserum infused into the lateral hypothalamic area affects operant behavior of rats fed lysine-deficient diet

Rats were trained to maintain a high rate of bar pressing to receive 50-mg pellets of a complete diet when given a lysine-deficient (Lys-def) diet ad libitum. This bar-pressing behavior was significantly inhibited when rats were also allowed ad libitum access to 0.4 M Lys to drink. A brain activin system may modulate motivation to engage in bar-pressing behavior, since previous work has established that antagonism of activin by infusion of inhibin or follistatin, but not activin, into the lateral hypothalamic area (LHA) also inhibits bar-pressing behavior. The present study sought to clarify whether the effect of inhibin or follistatin might be mediated by antagonism of endogenous activin or by a separate direct effect of inhibin or follistatin. Thus, we infused an antiserum, which specifically inhibits activin A activity, into the LHA. Infusion of antiserum greatly inhibited bar-pressing behavior of rats fed a Lys-def diet and was additive with Lys consumption further to decrease bar pressing. Ad libitum Lys consumption was unchanged from control levels, indicating that it is likely that an endogenous activin system in the LHA mediates behavioral responsiveness when rats are fed a Lys-def diet but does not appear specifically to affect appetite for Lys.

[A new pharmacological and physiological aspects of L-amino acids]

Taste preferences are altered to reflect physiological needs and to support the recovery from nutritional disorders. The central mechanism both recognition for and adaptation to a deficient essential nutrient, i.e. L-lysine, have been unveiled that the feeding center in the hypothalamus is a primary center nucleus to induce a neuronal plasticity responding to dietary intake of deficient nutrient in the brain and peripherally, such as sense of taste and its concentration change. Changing preferences may act as an alarm, signaling protein malnutrition or metabolic adult disease, such as hypertension for saltiness, diabetes for sweetness, etc. In addition, our consumption of alcohol beverage is still increasing despite of one of candidate to induce the hepatic disorders, because pharmacological function of alcohol in the brain is welcome for people enjoying meal or being relieved from stresses. Preference for both L-alanine and L-glutamine was observed when alcoholic rats fell in the hepatic disorder. Acute alcohol loading induced suppression of motor activity and the hepatic dysfunction, but both amino acids did obviously protect these alcoholic symptoms. People should have to require a little bit more specific L-amino acid physiologically and pharmacologically depending upon different states among aging, lifestyle, metabolic diseases and various stresses.

Activin selectively abolishes hippocampal long-term potentiation induced by weak tetanic stimulation in vivo

Although modulation of hippocampal synaptic plasticity by neurotrophins or growth factors has recently become an extensively investigated subject, there are no reports arguing for the contribution of the transforming growth factor (TGF)-beta superfamily. In the present study, we examined the effect of activin, a member of the TGF-beta superfamily, on long-term potentiation (LTP) of the dentate gyrus in anesthetized rats. Activin significantly impaired the formation of LTP induced by tetanic stimulation (60 Hz for 0.27 sec), but not that by strong tetanic stimulation (60 Hz for 0.5 sec). These results suggest that activin selectively blocks the induction of LTP evoked by threshold tetanic stimulation.

Development of degenerative muscle weakness by chronic administration of beta,beta'-iminodipropionitrile in the drinking water to rats: a model for motorneuropathy

Progressive muscle weakness accompanied by progressive muscle atrophy was investigated in rats administered beta,beta'-iminodipropionitrile (IDPN) chronically in the drinking water. Spontaneous running wheel activity declined slowly and reached a constant low level before postural muscle weakness was apparent. The rats being offered IDPN in the drinking water showed definite postural muscle weakness about 25 weeks after first being given IDPN, and muscle strength declined gradually throughout the remainder of the experiment (to 66 weeks). Flaccid paralysis became apparent in the hind limbs in the later stages of the experiment. Neurogenic muscle atrophy, measured by group atrophy of the muscle fibers, also progressed slowly, almost in parallel with the loss of muscle strength. At the end of the experiment, muscle weight of the gastrocnemius had decreased to about 20% that of control [F(2, 12) = 40.4, p < 0.05]. Plasma creatinine in the rats given IDPN in the drinking water for 66 weeks was significantly elevated over that of controls [F(2, 12) = 20.1, p < 0.05]. On the other hand, in rats given IDPN intraperitoneally, postural muscle weakness and muscle atrophy were less apparent, and plasma creatinine was normal. However, in these animals, abnormal behaviors, such as hyperexcitement, circling, and choreic movement (ECC syndrome), were apparent. These results suggest that the present model, which administers IDPN chronically in the drinking water ad lib and does not show involuntary movements and ECC syndrome, is of potential importance for investigation of chronic diseases of progressive muscle weakness with progressive muscle atrophy, and for assessing the efficacy of drugs and therapies for treating chronic neuromuscular diseases.

Effect of dietary supplementation with branched-chain amino acids on spontaneous motor activity and muscle function in beta,beta'-iminodipropionitrile-treated rats: a model for motorneuropathy

Beta,beta'-iminodipropionitrile (IDPN)-induced muscle weakness in rats is a model for motorneuropathy diseases. The effects of oral administration of branched-chain amino acids on the progression of muscle weakness and muscle atrophy induced by the administration of IDPN in the drinking water, were investigated in this study. The spontaneous motor activity of the animals, as measured with a running wheel, slowly declined after IDPN administration, reaching a steady and low level at approximately week 15. Progressive muscle weakness and muscle atrophy were observed beginning at approximately 15 weeks after the initiation of administration of IDPN. Administration of branched-chain amino acids (BCAA) as a dietary supplement did not improve the lowered spontaneous motor activity seen in IDPN animals, but it did significantly improve measures of postural weakness and muscle strength [range of F values (2, 24) = 4.1-9.5, p < 0.05]. Plasma creatinine of the IDPN-treated rats was markedly elevated, and BCAA administration also significantly suppressed this elevation [F(2, 24) = 41.2, p < 0.05]. Moreover, although BCAA in plasma were elevated in the rats administered BCAA [range of F values (2, 21) = 25.7-29.7, p < 0.05], skeletal muscle showed no differences (at the p < 0.05 level) in the amounts of BCAA, whether or not BCAA were administered. These data suggest that the BCAA taken up in the skeletal muscle were utilized in the muscle of motorneuropathic rats and improved muscle function, such as energy metabolism, and that the BCAA treatment is one important therapeutic approach for retarding the progression of muscle weakness seen in certain neuromuscular disorders.

Long-term consumption of an amino acid diet reduces the pancreatic enzyme secretion response to a trypsin inhibitor in rats

We investigated pancreatic enzyme secretion in response to soybean trypsin inhibitor (SBTI) in rats fed amino acids as a nitrogen source, from the fetal stage to adulthood. Pregnant rats were divided into two groups 4 d before parturition. During gestation and nursing, one group was fed a 15% protein diet (protein-fed rats) and the other (amino acid-fed rats) a 15% amino acid mixture diet that simulated the composition of the protein diet. Each male offspring was weaned at 4 wk after parturition and fed the same diet as fed to its dam for an additional 6 wk. Pancreatic amylase secretion in response to an intraduodenal infusion of SBTI (10 mg/rat) was observed in the protein-fed rats but not in the amino acid-fed rats. Amylase secretion in response to an intravenous injection of cholecystokinin (CCK) (10 ng/kg rat) was observed in both groups, and the magnitude of the response was significantly higher in the amino acid-fed rats than in the protein-fed rats. An increase in the level of plasma CCK in response to SBTI was observed in the protein-fed rats but not in the amino acid-fed rats. These results suggest that the long-term amino acid diet, because of its ability to inhibit the SBTI-stimulated CCK-releasing process in the small intestine of rats, reduced the pancreatic enzyme secretion response to a trypsin inhibitor. Six rats fed the amino acid mixture until 1 wk after weaning were fed the protein diet for the next 5 wk. These rats showed no pancreatic amylase secretion in response to SBTI, suggesting that dietary components around the weaning stage may affect the development of the ability of small intestinal cells to recognize a trypsin inhibitor.

Activin exerts a neurotrophic effect on cultured hippocampal neurons

Activin is a member of the transforming growth factor (TGF)-beta superfamily, which comprises a growing list of multifunctional proteins that serve as regulators of cell proliferation and differentiation. Recently, activin was shown to regulate the neurotransmitter phenotype in peripheral neurons. It is also a potent survival factor for neurogenic clonal cell lines, retinal neurons and midbrain dopaminergic neurons. We have studied the effect of activin on hippocampal cells which show abundant expression of activin receptors or binding sites. Exposure of primary cultures of rat hippocampal neurons to activin supported neuronal survival. This neurotrophic action of activin was blocked by treatment with the tyrosine kinase inhibitor genistein or the protein kinase C inhibitor calphostin C. However, the Ca2+/calmodulin kinase inhibitor KN-62 had no effect. Nicardipine, a blocker of the L-type Ca2+ channel, also inhibited the neurotrophic effect of activin. Furthermore, activin potentiated the depolarization-induced elevation in intracellular Ca2+ concentration ([Ca2+]i). The neurotrophic effect and the potentiation of depolarization-induced increase of [Ca2+]i caused by activin were completely abolished by the protein synthesis inhibitor cycloheximide. These results suggest that activin supports neuronal survival by increasing the expression of voltage-dependent Ca2+ channel through the action of a tyrosine kinase and of protein kinase C, but not of Ca2+/calmodulin kinase.

Effects of lentinan on abnormal ingestive behaviors induced by tumor necrosis factor

Lentinan (LNT), a beta-glucan derived from Lentinus edodes (Berk.) Sign., is known to work positively against cachexia in patients with malignant tumors. Because the cachectin/tumor necrosis factor (TNF) is supposed to be one of the factors that mediate cancer cachexia, we tested the effects of LNT on TNF-induced cachexia in rats. First, we analyzed in detail the cachectic actions of TNF (0.2 mg/kg/day, 5 days, IV) on food and water intake, body weight, and locomotor activity. The day after the first administration of TNF (acute phase), food and water intake, as well as body weight, of all rats decreased. However, over the next few days of treatment (chronic phase), the rats gradually developed a tolerance to the cachectic actions of TNF. Specifically, after the third administration, the rats treated with TNF had a higher amount of water intake than the control rats. This was mainly due to an increase in daytime water intake. We also analyzed the effects of LNT (0.1 or 1.0 mg/kg, twice/wk. IV) on TNF-induced cachexia, and compared the data with those from the rats treated with TNF alone. The higher dosage of LNT significantly suppressed TNF-induced daytime polydipsia and increased the amount of nighttime water intake, as well as the meal size of nighttime food intake. These results suggest that LNT partially normalizes TNF-induced cachexia in rats.

Quantitative RT-PCR for inhibin/activin subunits: measurements of rat hypothalamic and ovarian inhibin/activin subunit mRNAs during the estrous cycle

Inhibins (alpha-beta(A) and alpha-beta(B)) and activins (beta(A)-beta(A), beta(A)-beta(B) and beta(B)-beta(B)) were originally isolated from ovarian follicular fluids as FSH secretion modifiers. Inhibin/activin subunits, alpha, beta(A) and beta(B), are widely distributed in several tissues, including gonads and brain, and inhibins and activins have been reported to be involved in ovarian or hypothalamic functions. In this study, we established and employed a competitive RT-PCR assay system for rat inhibin/activin subunits by capillary electrophoresis to determine rat hypothalamic and ovarian inhibin/activin subunit mRNA levels during the estrous cycle. Linearity of standards for alpha, beta(A), and beta(B) subunit assays were between 0.01-0.3 amol, 0.003-0.09 amol and 0.002-0.02 amol of each fragment DNA as a standard, respectively. Hypothalamic beta(A) subunit mRNA during the estrous morning (1000 h) tended to be increased compared with that of the proestrous evening (1700 h), although they were not significantly different. Ovarian alpha subunit mRNA levels tended to be increased during the proestrous morning (1000 h) and were significantly increased in the proestrous evening (1700 h), compared with diestrus and estrus (P < 0.05). Ovarian beta(A) subunit mRNA was also significantly higher in the proestrous evening, compared with diestrus and estrus (P < 0.05), but in the case of beta(B) subunit mRNA there was no difference among diestrus, proestrus and estrus. We thus established a sensitive competitive RT-PCR system for the measurement of inhibin/activin alpha, beta(A) and beta(B) subunits, and this assay system would be helpful for the study of inhibin/activin action in brain and other tissues where these factors are expressed at low levels.

Immunolocalization of type I or type II activin receptors in the rat brain

We have studied immunolocalization of activin receptors in the central nervous system using polyclonal antibodies (IgG) to type I (50-55 kDa, ActRI), type II (70-75 kDa, ActRII) or a subtype of type II known as type IIB (ActRIIB) receptors of activin. A total of 7 antisera to rat activin receptors was generated, i.e. 3 kinds of antisera to the extracellular domain (ActRI(81-89), ActRII(91-100), or ActRIIB(90-99)) and 4 antisera to the kinase domain (ActRI(323-333), ActRII(307-319), ActRII(407-420) or ActRIIB(306-319)). The region of aa 407-420 of ActRII is identical with that of ActRIIB. At first, we characterized these antibodies by Western blot analysis using ovarian proteins fractionated by preparative SDS-PAGE. All antibodies to ActRII and ActRIIB specifically reacted with 75 kDa-proteins which could also bind to activin-A. Anti-ActRII(91-100) antibody also reacted with 62 kDa-proteins which were capable of binding with activin-A. Although no positive reactions to anti-ActRI(81-89) antibody were seen in ovarian proteins, a positive reaction was detected at 52 kDa only when the proteins were deglycosylated. By use of these antibodies, immunolocalization of activin receptors was examined in the rat brain. The patterns of expression of activin type I and type II receptors were different. Positive reactions to anti-ActRII(91-100) antibody were detected in neurons of the cerebral cortex, hippocampus, medial amygdala and thalamus. In the hypothalamus, some neurons of the supraoptic nucleus were weakly stained, and widely scattered neurons of the lateral hypothalamic area were moderately stained. On the contrary, the most intense reactions to anti-ActRI(81-89) antibody were detected in neurons of the lateral hypothalamic area. In addition, many neurons of the cerebral cortex were also stained, but neurons of the hippocampus and the amygdala were not stained. These results suggest that activin may have physiological roles not only for hypothalamic neuroendocrinological and feeding-related systems as suggested previously but may also have functions in cortical and limbic pathways as a neuromodulator or for maintenance of neurons.

Increased cartilage and bone formation in spontaneously hypercholesterolemic rats

Spontaneously hypercholesterolemic (SHC) rats are known to exhibit accelerated bone resorption. We compared endochondral bone formation induced by implantation of demineralized bone matrix (DBM) to 4-week-old SHC rats with that of age-matched Sprague-Dawley (SD) rats. When DBM prepared from adult SD rats was implanted, the cartilageous area enlarged, and C-propeptide of type II procollagen content on day 7 was higher in SHC rats. Alkaline phosphatase activity and calcium content on day 12 and tartrate-resistant acid phosphatase activity on day 19 were higher in SHC rats. These results suggest active chondrogenesis, with a subsequent increase in osteogenesis, and stimulated osteoclastic bone resorption in SHC rats. When DBM from 10-week-old SHC rats was implanted into SD or SHC rats, the levels of bone forming parameters on day 12 were reduced to one-third, suggesting inhibiting factor(s) for bone induction in bone matrix of SHC rats. In contrast, when DBM from 6-month-old SHC rats was implanted, although bone forming parameters in SD rats were comparable to the case of implantation of DBM from SD rats, the accelerated bone formation detected in SHC rats was blocked, indicating resistance to systemic bone inducing factor(s) of SHC rats in aged bone matrix. These results suggest that age-related decrease in responses to some systemic bone inducing factor may lead to the bone loss with advancing age.

Higher concentrations of matrix metalloproteinases in bronchoalveolar lavage fluid of patients with adult respiratory distress syndrome

This study was designed to investigate possible involvement of type IV collagenolytic matrix metalloproteinases (MMPs; 72-kDa type IV collagenase [MMP-2], 92-kDa type IV collagenase [MMP-9]), and the respective specific tissue inhibitors of these MMPs (TIMP-2 and TIMP-1) in the development of adult respiratory distress syndrome (ARDS). We determined the concentrations of these enzymes in the bronchoalveolar lavage fluid (BALF) from patients with ARDS using newly developed sensitive one-step sandwich enzyme immunoassay methods. BALF obtained from the 17 patients and eight healthy volunteer control subjects were also used for the analysis of the number of the cellular component. Concentrations of the 7S portion of type IV collagen and laminin in the BALF were measured as markers of basement membrane disruption. In the BALF from the ARDS patients, the concentrations of MMP-2 (66.7 +/- 57.0 ng/ml versus < 7.0 ng/ml for controls, p < 0.01) and MMP-9 (118.0 +/- 309.3 ng/ml versus 9.0 +/- 9.5 ng/ml for controls, p < 0.05), and the specific inhibitor of MMP-9 (TIMP-1) (161.0 +/- 145.0 ng/ml versus < 50 ng/ml for controls, p < 0.01) were significantly higher compared with those for healthy control subjects. In the ARDS patients, the concentrations of MMP-2 correlated both with those of 7S collagen and laminin; MMP-9 with the concentration of 7S collagen and the number of neutrophils. These findings suggest that the increased concentration of collagenolytic MMPs in lung plays a role in the pathogenesis of ARDS.

Suppressed bone induction by follistatin in spontaneously hypercholesterolemic rat bone

Bone inducing activity in demineralized bone matrix (DBM) of young spontaneously hypercholesterolemic (SHC) rats has been shown to be lower than that of aged SHC rats. This study examined the involvement of bone follistatin, an activin-binding protein, in bone induction. Immunoreactive follistatin was higher in DBM from 10-week-old SHC rats (DBM-10wk) than in DBM from 6-month-old SHC rats (DBM-6mo). When DBM without follistatin supplement was implanted, the C-propeptide of type II procollagen and calcium contents on day 12 in implants of DBM-6mo were 68% and 40% higher than those of DBM-10wk, respectively. In contrast, follistatin supplement to DBM decreased C-propeptide of type II procollagen and calcium contents in implants of both DBM-10wk and DBM-6mo, and the levels of these parameters were comparable between DBM-10wk and DBM-6mo, indicating reduced formation of cartilage and bone. These findings suggest that 1) follistatin content in bone matrix decreases with advancing age in SHC rats, and 2) the follistatin interferes with endochondral bone formation. We demonstrate that the lower bone induction of DBM from young SHC rats was partly due to the abundance of follistatin in bone matrix.

[Detection of numerical chromosomal aberrations in hematopoietic malignancy by in situ hybridization on bone marrow aspirate paraffin sections]

We evaluated the usefulness of in situ hybridization (ISH) with chromosome specific DNA probe on paraffin sections of bone marrow aspirates. Twenty cases of hematopoietic malignancy and eight control cases of non-hematopoietic malignancy were examined with centromere-specific probes for chromosomes 8 and 17. In the eight control cases, the mean rates of cells with more than three hybridization signals were 1.13 (2SD = 1.90) for chromosome 8, and 0.88 (2SD = 2.25) for chromosome 17. The mean rates plus 2SD were 3.03 for chromosome 8, and 3.19 for chromosome 17. Therefore, we defined cases of more than 4.0% of cells showing more than three hybridization signals per nuclei as having a numerical abnormality (trisomy). We compared these results with conventional cytogenetic results by karyotype analysis. In twenty hematopoietic malignancy cases, three cases demonstrated trisomy 8 by ISH. Two cases also demonstrated this abnormality by karyotype analysis, but one case showed no abnormality by karyotype analysis. While trisomy 17 detected in one case that did not demonstrate numerical abnormality, only structural abnormality by karyotype analysis. The rate of discrepancy between results of ISH analysis and those of karyotype analysis was only 5% (2/40) for both chromosomes. In five cases, re-examinations were performed within three months. In one case, we could not obtain adequate material for karyotype analysis. However, this case showed trisomy 8 by ISH. Structural chromosomal abnormalities such as translocation or deletion could not be detected by this ISH analysis with centromere-specific probes. However, this method has the advantage result that we can perform retrospective assessments, do not need to culture cell, and can compare with pathological findings. Thus, we conclude that ISH analysis with paraffin sections of bone marrow aspirates will provide more useful information by combining ISH analysis and karyotype analysis.

Contribution of chorda tympani and glossopharyngeal nerves to taste preferences of rat for amino acids and NaCl

To learn how the gustatory nerves convey information about the nutritionally dependent taste preference, intake of amino acid solutions and saline in rats with bilateral chorda tympani (CTX) and/or glossopharyngeal neurotomy (GPX) was determined during the feeding of a control diet (C) and a L-lysine (Lys) deficient diet (LD). Intact rats preferred L-arginine (Arg) more in C and Lys more in LD. The CTX group did not select nor ingest Lys in LD, and its intake of Arg was also low in C. The GPX group did not substantially alter its preference under both diets, while it did show an increase in total liquid intake. The preference changes in the CTX + GPX group appeared as combined effects of the CTX and the GPX groups. In an additional study, the preference for Lys shifted to higher concentrations and the total consumption of Lys increased in LD. The present data suggest that the chorda tympani nerves possibly function as discriminators of the nutritional information by altering the taste preference, and that the glossopharyngeal nerves may convey other functional taste information, such as aversive tastes, and sensory aspects of osmotic regulation. In addition, it is revealed that the animals have ability to search for a nutrient deficient in their body, and to ingest it to a level that at least nullifies the deficiency.

Increased histidine preference during specific alteration of rhythm of environmental temperature stress in rats

It has been reported that specific alteration of rhythm of environmental temperature (SART) stress induces various physiological changes. In this study, changes in taste preference during SART stress were investigated in rats. Rats were given free access to six amino acid solutions, saline, and water in a choice paradigm. During SART stress, daily food intake increased significantly by 50% whereas the rate of body weight gain decreased significantly to one third that observed during the prestress baseline period. In addition, consumption of histidine solution increased significantly, whereas intakes of water, monosodium glutamate, saline, glycine, arginine, lysine, and threonine were unaffected. Results suggest that a specific preference for histidine emerges during SART stress, which may be related to the stress-induced changes in the histamine turnover in the brain and peripheral tissues.

Increased histidine preference during specific alteration of rhythm of environmental temperature stress in rats

It has been reported that specific alteration of rhythm of environmental temperature (SART) stress induces various physiological changes. In this study, changes in taste preference during SART stress were investigated in rats. Rats were given free access to six amino acid solutions, saline, and water in a choice paradigm. During SART stress, daily food intake increased significantly by 50% whereas the rate of body weight gain decreased significantly to one third that observed during the prestress baseline period. In addition, consumption of histidine solution increased significantly, whereas intakes of water, monosodium glutamate, saline, glycine, arginine, lysine, and threonine were unaffected. Results suggest that a specific preference for histidine emerges during SART stress, which may be related to the stress-induced changes in the histamine turnover in the brain and peripheral tissues.

Follistatin and activin in bone: expression and localization during endochondral bone development

The involvement of activin and follistatin, an activin-binding protein, in endochondral bone development was examined by sc implantation of demineralized bone matrix in rats. Immunoreactive follistatin was localized in proliferating chondrocytes and round osteoblasts, whereas it was not detected in hypertrophic chondrocytes and osteoblasts surrounding bone marrow. Western blot analysis also revealed that immunoreactive follistatin was higher during the initial stages of chondrogenesis (day 5) and osteogenesis (days 11 and 14) and lower during the conversion from cartilage to bone (day 9). These results suggest that follistatin is produced by proliferating cells, and the expression decreases with differentiation of the cells. Implants injected with follistatin on days 9 and 10 contained lower calcium levels on day 14 than those injected with rat albumin. Furthermore, the follistatin-injected implants were still mainly composed of cartilage, suggesting that the disappearance of follistatin is necessary for the conversion of cartilage to bone. In contrast, immunoreactive activin beta A (55-60 kDa) was continuously detected in implants on days 7-14. The content of C propeptide of type II procollagen was increased and cartilageous area was enlarged on day 7 by activin A injections on days 5 and 6, suggesting a chondrogenic effect of activin in the initial stage of cartilage formation. These results indicate that proliferating chondrocytes and round osteoblasts produce follistatin, and that the activity of activin is regulated by changes in the expression of follistatin at the stages of chondrogenesis and transition from cartilage to bone.

Changes in responsiveness to serotonin on rat ventromedial hypothalamic neurons after food deprivation

The effects of food deprivation on responsiveness of neurons in the ventromedial nucleus of the hypothalamus (VMH) to serotonin (5-HT), norepinephrine (NE), gamma-aminobutyric acid (GABA), and neuropeptide Y (NPY) were investigated using brain slices in vitro along with behavioral changes in vivo during fasting. Adult male rats were fasted for 48 h starting at the beginning of the dark phase (lights on: 0700-1900 h). The animals showed a significant loss of body weight on the second day of fasting and an increase in food consumption on the first day of refeeding. During fasting, voluntary locomotor activity was significantly increased in the light phase but not during the dark phase. Plasma catecholamine levels were not affected by fasting. In vitro electrophysiological study showed that, in normally fed rats, 5-HT and NE induced both excitatory and inhibitory responses, while GABA and NPY intensively suppressed unit activity in the VMH. Food deprivation for 48 h significantly changed the responsiveness of VMH neurons to 5-HT, for instance, the ratio of neurons whose activity was facilitated by 5-HT was significantly decreased. The responsiveness of VMH neurons to NE, GABA, and NPY was not affected by food deprivation. These results suggest that food deprivation decreases the facilitatory response of VMH neurons to 5-HT, and that this change in responsiveness to 5-HT is at least partially involved in the increase in food intake motivation and locomotor activity during fasting.

Alanine protects liver from injury caused by F-galactosamine and CCl4

The liver is the main organ involved in amino acid metabolism, and it utilizes glucogenic amino acids as substrates for glucose or adenosine triphosphate (ATP), but this process is impaired in clinical and experimental liver diseases. In this study, we administered high doses of amino acids in rats or cultured hepatocytes with experimental models of liver injury to examine whether such supplementation could attenuate liver damage. We found that the addition of alanine reduced enzyme leakage from primary cultured rat hepatocytes treated with D-galactosamine (D-gal), while other amino acids did not. A significant decrease of lactate dehydrogenase (LDH) leakage was observed when cells were cultured with >6 from mmol/L alanine. Alanine also reduced enzyme leakage from normal hepatocytes that were not treated with D-gal. In D-gal-treated rats, constant infusion of a high dose of alanine significantly reduced the plasma transaminase and total bilirubin levels when compared with infusion of an amino acid mixture. Bolus administration of alanine significantly prevented the elevation of plasma transaminase levels and histological liver damage in CCl4-treated rats, while fructose-1,6 bisphosphate (FDP) had little effect. Alanine might promote the restoration of damaged liver in hepatotoxicant-treated rats, because significant effect was found after the elevation in plasma transaminase levels. Alanine also prevented the decrease of cellular ATP caused by D-gal and appeared to promote ATP production in primary cultured rat hepatocytes. These results indicate that alanine reduces experimental liver damage by a direct effect on hepatocytes.

Increased NaCl preference of rats fed low-protein diet

Four studies were conducted to assess the effect of a low-protein diet on NaCl intake. Young rats fed either control (20% casein) or low-protein (5% casein) high-carbohydrate (CHO) diet were allowed to drink either water alone or water and 300 mM NaCl. Relative to rats fed control diet, rats fed the low-protein diet progressively increased NaCl intake so that, despite lower food and water intakes, they drank 180% more NaCl during the last 3 days of the 21-day test. Additional studies found that rats fed low-protein diet always maintained positive sodium balance, were neither sodium depleted nor hypovolemic, and had normal plasma renin activity and aldosterone concentrations. The elevated NaCl intake was not secondary to calcium deficiency and was unaffected by mineral supplementation of the protein-deficient diet. Increases in the diet's CH and/or fat content incidental to decreases in its protein content influenced, but could not completely account for, the effect of protein deficiency on NaCl intake. We conclude that protein deficiency is the primary cause of the elevated NaCl preference produced by being fed a low-protein diet and that a novel physiological mechanism underlies this behavior.

Unique recognition of activin and inhibin by polyclonal antibodies to inhibin subunits

Inhibin-A is a glycoprotein composed of an alpha subunit containing a glycosylation site and a beta A subunit, whereas activin-A is a homodimer of two inhibin beta A subunits. We examined the recognition of activin-A and inhibin-A by several antisera to the alpha or beta A subunit, and factors affecting the recognition. A total of six polyclonal antibodies to inhibin subunits, i.e., two antisera to a peptide fragment of the alpha subunit [alpha (1-19) and alpha (1-26)], and four antisera to the beta A subunit [beta A (1-10), beta A (70-79), beta A (87-99), and beta A (94-105)], was generated. On Western blot analysis, the anti-beta A (87-99) and beta A (94-105) sera recognized recombinant human activin-A but not inhibin-A under non-reducing conditions. When inhibin-A was deglycosylated with N-glycosidase-F, inhibin-A could be recognized by the anti-beta A (87-99) and beta A (94-105) sera. In addition, when activin-A bound to a nitrocellulose membrane was pre-incubated with recombinant human follistatin, the recognition of activin-A by the anti- beta A (87-99) and beta A (94-105) sera was decreased. These results suggested that the lower affinity of follistatin to inhibin-A than to activin-A might be likely explained as reflecting a site associated with the glycosylation of inhibin-A. However, the exposure of amino acids 87-105 of the inhibin beta A subunit on the molecular surface through deglycosylation did not increase the affinity of inhibin-A for follistatin but rather resulted in poor binding with follistatin. The present data suggest that (1) amino acids 87-105 of the inhibin/activin beta A subunit are located on the molecular surface, although this region of inhibin-A is concealed by the carbohydrate chain of the alpha subunit, (2) the region responsible for follistatin binding within the activin beta A subunit is spanned by amino acids 87-105, and (3) the mode of binding of inhibin-A to follistatin is quite different from that of activin-A to follistatin, and the former may be influenced by glycosylation.

Anti-activin A antibody (IgY) specifically neutralizes various activin A activities

Activin A (beta A beta A), originally isolated from ovarian follicular fluids as a follicule-stimulating hormone (FSH) secretion stimulator, has also been identified as an erythroid differentiation factor (EDF), a neuron survival factor and a mesoderm-inducing factor. Thus, activin A is a multifunctional factor, and further studies on its physiological function are important. However, it is very difficult to produce a specific antibody to neutralize the activity of activin A because of its highly conserved amino acid sequence across mammalian species. In this study, we succeeded in generating an antibody against activin A, which can neutralize several activities of activin A, such as the stimulation of FSH secretion from pituitary cells and the induction of the differentiation of erythrocytes in vitro. This antibody did not affect the activity of activin B (beta B beta B), which induces the differentiation of erythrocytes in vitro, and the activity of inhibin A (alpha beta A), which inhibits FSH secretion from pituitary in vitro, but slightly neutralized that of activin AB (beta A beta B). Western blotting analysis showed that this antibody recognized both dimeric and monomeric forms of the beta A subunit of activin and inhibin. These results suggest that this antibody recognizes the beta A subunit of activin and specifically neutralizes the activity of a dimer of the beta A subunit, activin A. Furthermore, by the addition of this antibody to the culture medium, the development of murine embryos was suppressed, suggesting that endogenous activin A plays an important role in murine development. These results indicate the usefulness of this antibody for studies of endogenous activin actions.

Effect of inhibin, follistatin, or activin infusion into the lateral hypothalamus on operant behavior of rats fed lysine deficient diet

To identify brain mechanisms which mediate hunger for amino acid (e.g. L-lysine; Lys) deficiency, rats were trained to bar press (FR30 schedule) to receive 50 mg pellets of a complete diet. Rats given a lysine deficient (Lys-def) diet ad libitum maintained a high rate of bar pressing but when allowed ad libitum access to 0.4 M Lys to drink had a significant decrease in pressing. Also, Lys continuously infused by minipump into the lateral hypothalamic area (LHA) inhibits pressing by rats given a Lys-def diet. The threshold maximal dose is between 0.1-0.5 nmol Lys/h. Therefore, animals lacking dietary Lys will work to receive complete diet, but replacement of Lys by voluntary consumption or by direct infusion into the LHA inhibits bar pressing for complete diet. The ratio of brain activin and inhibin may modulate motivation to work for a complete diet, since continuous inhibin or follistatin, but not activin, infusion into the LHA was found to inhibit bar pressing, which is normally quite strong in rats maintained on Lys-def diet. The inhibitory effect of LHA inhibin infusion was replicated, and concurrent availability of Lys solution ad libitum was additive with LHA inhibin infusion to depress responding further. This inhibitory effect of inhibin or follistatin did not result from altered ad lib. consumption of Lys-def diet. Although LHA Lys infusion did decrease consumption of a concurrently available Lys solution, inhibin did not change ad libitum Lys consumption. This indicates that inhibin may work in the LHA to inhibit bar pressing for complete diet via other mechanisms than sensation of Lys deficiency.

Recognition and neural plasticity responding to deficient nutrient intake scanned by a functional MRI in the brain of rats with L-lysine deficiency

Each L-amino acid (AA) in plasma and brain remains unchanged while normal diet is available. Once L-lysine (Lys) deficient diet was offered to rats, Lys in plasma and brain declined, and anorexia occurred. When solutions of AAs were offered, they selected the Lys solution, and their food intake and growth normalized. The single neuron activity in the lateral hypothalamic area of these rats suggested that neural plasticity occurred, specifically responding to Lys, both by iontophoretic application and during ingestion of AA. The recognition site for deficient nutrient intake in the brain of rats with Lys deficiency was identified by non-invasive magnetic resonance imaging (MRI 4.7 tesla, 40 cm bore in diameter) developed to monitor changes in cerebral blood flow and oxygenation in rat brain. Wistar strain young male rats fed with Lys deficient diet for 4 days, were adapted to be settled in the center of the bore. When they received a Lys injection intraperitoneally (0.2 M, 10 mL/kg), a signal intensity decrease in the medial and lateral hypothalamus appeared 30 minutes later in T2 weighted images, reflecting increased oxygenation which lasted for 30 minutes, and then gradually recovered. These changes never occurred in any other areas of the brain of rats with Lys deficiency, i.e., the thalamus, the cortex, the hippocampus, etc. There were no changes in the signal intensity with control injection of saline. In addition, oxygen consumption in the brain of rats without Lys deficiency was not altered by intraperitoneal Lys injection. The present results suggest that in essential AA deficiency, the medial and lateral hypothalamus may play important roles in recognition responses to particular deficient nutrients in order to maintain homeostasis.

Proline, ascorbic acid, or thioredoxin affect jaundice and mortality in Long Evans cinnamon rats

The Long Evans Cinnamon (LEC) rat spontaneously develops fulminant hepatitis, which is usually lethal due to excess copper accumulation in the liver and is considered an animal model of Wilson's disease. LEC rats show a strong appetite for proline solution. Daily oral (p.o.) administration of proline resulted in significant delay of mortality. Feeding a copper-deficient diet greatly delayed the onset of jaundice and mortality and voluntary consumption or p.o. administration of proline further delayed jaundice and prevented mortality. LEC rats also consume ascorbic acid solutions, and p.o. administration of ascorbate also results in a significant delay in the appearance of jaundice and mortality. Combined treatment with ascorbic acid and proline is additive to delay further jaundice and mortality. An endogenous antioxidant protein, thioredoxin, when infused by minipump IP, could also inhibit the incidence of jaundice. These results indicate that antioxidant treatment combined with proline may be of benefit in Wilson's disease and possibly other forms of hepatic dysfunction.

Excitability of neurons in the ventromedial nucleus in rat hypothalamic slices: modulation by amino acids at cerebrospinal fluid levels

Free amino acid composition of cerebrospinal fluid (CSF) in the rat was measured to examine if electrical activity of neurons in the ventromedial nucleus of the hypothalamus (VMH) is modulated by amino acids at CSF levels. In CSF collected through a cannula in the cerebromedullary cistern of freely moving rats, the total concentration of amino acids was 979 microM, while that in plasma was 3.50 mM. Glutamine was the major (60%) component and each of other amino acids was less than 8.0% (lysine) of total. Among neutral amino acids, concentrations of serine, threonine and alanine were much higher than those of others. Although concentrations of basic amino acids such as lysine and arginine were also relatively high, those of acidic amino acids such as glutamate and aspartate were very low. Spontaneous firing rates of 73% of the neurons in the VMH in brain slices in vitro were facilitated by changing the perfusion medium from artificial CSF (ACSF) without amino acids to one containing each amino acid close to CSF levels (AA-ACSF). Glutamine (600 microM) alone similarly facilitated the activity in 64% of VMH neurons, though the facilitatory effect of amino acids was blocked by simultaneous application of neither AP-5 nor CNQX, antagonists for NMDA or non-NMDA receptors, respectively, to AA-ACSF at 100 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of continuous infusion of lysine via different routes and hepatic vagotomy on dietary choice in rats

The effect of continuous L-lysine (Lys) infusion on dietary choice between Lys deficient and protein-free diets in Sprague-Dawley rats was studied to determine the sensing site of Lys deficiency. After daily intake of each diet became constant, Lys was continuously infused for 11 days via intraperitoneal (IP), intragastric (IG) or intracerebroventricular (ICV) route, with an osmotic pump. Daily intake of each diet was measured. Intake of the Lys deficient diet compared with protein-free diet in either IP or IG Lys-infused group increased significantly (p < 0.001) vs. the intake in the baseline period. The selection of the Lys deficient diet was quite comparable between IP and IG groups. But the intake of the ICV group was unchanged. Hepatic vagotomy during IP infusion transiently delayed selection of the Lys deficient diet. These results imply the roles of postabsorptive mechanisms in sensing an amino acid deficiency, and possible involvement of the hepatic branch of the vagus in the sensing. However, sensing in the brain or indeed in the intestine was not excluded.

[Effect of dosing schedule on efficacy of corticosteroid inhalation in chronic asthma]

A randomized study was conducted for 4 weeks to evaluate the effect of twice daily inhalation of beclomethasone dipropionate (BDP) inhalation (group A) as compared to four times a day inhalation (group B) in chronic asthma. Patients were randomly allocated to receive BDP at a dosage of eight puffs twice daily (800 micrograms/day, group A) or four puffs four times daily (800 micrograms/day, group B). Forty four patients entered the study but eleven were excluded because of their insufficient records or unfitness to eligibility criteria. There was no significant difference in patients' characteristics such as types, and severity of diseases between the two groups. Daily keeping of symptom scores, twice daily measurement of morning and night peak expiratory flow (PEF) and checking of the drug consumption were performed throughout the study. There was no significant difference in the mean %PEF either at 2 and 4 weeks at the study between the two groups. Symptom scores, asthmatic scores, bronchial hyperresponsiveness, pulmonary function tests (FVC, FEV1, FEV1%) and serum cortisol levels also showed no significant difference between the two groups. These results indicate that twice daily inhalation of BDP (800 micrograms/day) for four weeks caused the same effects on the patients with chronic bronchial asthma as 4 times daily inhalation did. Therefore, twice daily inhalation therapy with BDP is recommended for chronic bronchial asthma patients.

Pathogenesis of thymolipoma: report of three cases

Three case reports of thymolipoma are herein presented. One patient presented with myasthenia gravis, while the other patients were asymptomatic. The tumors in our cases all had histopathologically different features: case 1, lipoma of the thymus; case 2, involuted thymic hyperplasia; and case 3, typical thymolipoma. The histopathological findings of thymolipoma are discussed in the context of the pathogenesis of thymolipoma.

Glossopharyngeal denervation alters responses to nutrients and toxic substances

Functional roles of the glossopharyngeal (GL) nerve on food and fluid intake were studied by examining effects of the GL denervation on two biologically different activities induced by specific diets using mice and rats. First, we examined whether GL section alters the acceptability of a bitter tasting essential amino acid, L-lysine (Lys), by Lys-deficiency in mice. The aversion threshold for Lys, normally about 3 uM in mice, increased to about 300 uM when mice were fed the Lys-deficient diet for 10 days. This increase of the Lys aversion threshold (increase of acceptability for Lys) by Lys-deficiency was also evident in mice with the chorda tympani denervation but was not observed in mice with the GL denervation. Next, we examined whether GL section alters the induction of a salivary protein, cystatin S (a cysteine proteinase inhibitor), by a diet containing papain (a cysteine proteinase) in rats. GL denervation largely inhibited the induction of cystatin S in the rat submandibular glands by papain. These results collectively suggest that chemosensory information conveyed by the GL nerve plays important roles on recognition of both nutrient and toxic compounds in the diet and induction of biological responses that protect the animal from both nutritional deficiency and exogenous toxic compounds.

Lysine deficient diet and lysine replacement affect food directed operant behavior

As a test for specific hunger for amino acids with the goal of identifying brain regions which might mediate motivation to alleviate L-lysine (Lys) deficiency, rats were trained to lever press to receive complete diet. Rats were given Lys deficient (Lys-def) diet ad lib. Intraperitoneal (IP) injection of Lys, 2 h before the test session, inhibited lever pressing. Lys injected animals pressed at nearly the same low rate as did animals fed ad lib complete diet, although the response of saline injected animals was also partially decreased. Next, osmotic minipumps were implanted IP and animals given Lys-def diet ad lib. Chronic Lys infusion also strongly inhibited lever pressing. Rats allowed ad lib access to Lys to drink drank significantly more Lys than when given complete diet. Lys chronically infused by minipump into the lateral hypothalamus, also inhibited pressing by rats given Lys-def diet. Therefore, animals lacking Lys in the diet will work to receive complete diet, but replacement of Lys by drinking, chronic IP infusion, or directly into the lateral hypothalamic area inhibits bar pressing behavior.