Ibipinabant attenuates ß-cell loss in male Zucker diabetic fatty rats independently of its effects on body weight.

AIM: To test the antidiabetic efficacy of ibipinabant, this new cannabinoid receptor 1 (CB1) antagonist was compared with food-restriction-induced weight loss, rosiglitazone (4 mg/kg) and rimonabant (3 and 10 mg/kg), using parameters of glycaemic control in male Zucker diabetic fatty (ZDF) rats. METHODS: Body weight, food and water intake, fasted and non-fasted glucose and insulin, glucose tolerance and glycosylated haemoglobin (HbA1c) were all assessed over the course of the 9-week study. Pancreatic insulin content and islet area were also evaluated. RESULTS: At the end of the study, vehicle-treated ZDF rats were severely hyperglycaemic and showed signs of ß-cell decline, including dramatic reductions in unfasted insulin levels. Ibipinanbant (10 mg/kg) reduced the following relative to vehicle controls: fasting glucose (-61%), glucose excursion area under the curve (AUC) in an oral glucose tolerance test (OGTT, -44%) and HbA1c (-50%). Furthermore, non-fasting insulin, islet area and islet insulin content were all increased (71, 40 and 76%, respectively) relative to vehicle controls by the end of the study. All of these effects were similar to those of rimonabant and rosiglitazone, where ibipinabant was slightly more effective than rimonabant at the lowest dose and somewhat less effective than rosiglitazone at all doses. These antidiabetic effects appear independent of weight loss because none of the parameters above were consistently improved by the comparable weight loss induced by food restriction. CONCLUSIONS: Ibipinabant may have weight loss-independent antidiabetic effects and may have the potential to attenuate ß-cell loss in a model of progressive ß-cell dysfunction.

Urocortin, corticotropin releasing factor-2 receptors and energy balance.

Although there is considerable information regarding the role of brain CRF in energy balance, relatively little is known about the role of urocortin (UCN), which is an equally potent anorexic agent. Therefore, the effects of intracerebroventricular (icv) administration of UCN (0.01-1 nmol/day) on food intake and body weight were assessed over a period of 13 days and compared with data from CRF-infused counterparts. Although both peptides dose dependently reduced food intake and weight gain, the effects of CRF were much greater in magnitude than those of UCN, particularly on body weight. Pair-feeding studies suggested that, while the effects of CRF on body weight could not be completely explained by appetite suppression, the effects of UCN appeared to be due to its initial impact on food intake. CRF increased brown adipose fat pad and adrenal weights, whereas it reduced thymus and spleen weights. CRF also increased serum corticosterone, triglyceride, FFA, and cholesterol levels, whereas it reduced glucose. UCN did not produce any consistent changes in any of these indices of sympathetic nervous system activation. Concurrent administration of the CRF(2)-selective antagonist, antisauvagine-30 (ASV-30) (30 nmol/day) completely reversed or attenuated the effects of UCN and CRF (1 nmol/day) on food intake and body weight. ASV-30 did not significantly attenuate any of the above CRF-induced changes in tissue weights or serum chemistry. These data suggest that the central CRF(2) receptor may primarily mediate the anorexic, but not the metabolic effects of CRF.

Models for environmentally induced eating disorders: dietary hyperphagia and anorexia nervosa.

The two protocols in this unit provide suggestions for constructing models of eating disorders that are at the opposite ends of the spectrum: dietary hyperphagia and anorexia nervosa. The greatest degree of dietary hyperphagia is induced by giving rats or mice access to a daily choice of highly palatable foods (e.g., chocolate or bread) in addition to their regular chow. Like humans, rats overeat and actually develop physiological requirements for these foods. This model can be used to test the effects of putative anorectic agents on both acute and chronic administration regimens. The second protocol describes a model of compulsive behavior that results in profound weight loss, which is produced by moderate food deprivation along with continuous access to exercise wheels.

A unique metabolic syndrome causes obesity in the melanocortin-3 receptor-deficient mouse.

The central melanocortin system is critical for the long term regulation of energy homeostasis. Null mutations of the melanocortin-4 receptor (MC4-R) are associated with hyperphagia, obesity, and accelerated longitudinal growth in mice and humans. However, little is known about the function of another central melanocortin receptor, the MC3-R. To assess the role of the MC3-R in energy homeostasis, the majority of the mc3r coding sequence was deleted from the mouse genome. In contrast to the MC4-R knockout, which exhibits increased food intake, increased somatic growth, and defects in metabolism, mc3r-/- mice exhibit an exclusively metabolic syndrome. Homozygous null mc3r mice, while not significantly overweight, exhibit an approximately 50% to 60% increase in adipose mass. Mc3r-/- mice also exhibit an unusual increase in respiratory quotient when transferred onto high fat chow, suggesting a reduced ratio of fat/carbohydrate oxidation. Furthermore, male mc3r-/- mice also exhibit an approximately 50% reduction in locomotory behavior on the running wheel, suggesting reduced energy expenditure.

Role of corticotropin-releasing factor (CRF) receptors in the anorexic syndrome induced by CRF.

Genetic manipulations of corticotropin-releasing factor (CRF)(1) and CRF(2) receptors have resulted in data suggesting that the CRF(2) receptor could mediate the effects of CRF on appetite or satiety. We have attempted to obtain pharmacological evidence for this hypothesis by comparing the ability of a high-affinity peptide, mixed CRF antagonist [cyclo 30-33,f12,L18,21E30, A32,K33]sucker fish urotensin (12-41)NH(2) [cUTSN (12-41)] with a small-molecule CRF(1)-selective antagonist, NBI-27914, and a CRF(2)-selective peptide antagonist, antisauvagine-30, to attenuate the anorexic effects of CRF. We also monitored other behaviors that accompanied CRF-induced anorexia. CRF-induced anorexia was significantly correlated with a reduction in locomotor activity and an increase in freezing behavior and piloerection. cUTSN (12-41) and antisauvagine-30 significantly attenuated the effects of CRF (0.04 nmol) on food intake along with the behavioral syndrome that accompanied anorexia. In contrast, NBI-27914 did not attenuate either of the above-mentioned CRF-induced phenomena when given centrally at doses ranging from 0.13 to 10 nmol/2.5 microl or when given orally at 20 to 40 mg/kg. Although these data support the hypothesis that the CRF(2) receptor mediates the appetite suppression induced by CRF, they also suggest that the CRF(2) receptor could mediate the stress-like behaviors that accompany CRF-induced appetite suppression.

Systemically and topically administered leptin both accelerate wound healing in diabetic ob/ob mice.

Leptin is a 16 kD protein that is produced by adipocytes and induces weight loss in both normal and genetically obese ob/ob mice. ob/ob mice are obese, have multiple metabolic abnormalities, and exhibit impaired wound healing. Exogenous administration of leptin to these animals induces weight loss and corrects their metabolic defects. Leptin's effect on wound repair, however, has not been studied. Systemic administration of leptin at doses ranging from 0.1 to 10 mg/kg/day induced a highly significant acceleration in wound repair in ob/ob mice (p<0.0001), but not in db/db mice, indicating that leptin's effects on wound repair were mediated through the leptin receptor. We then investigated the possibility that leptin was acting directly at the wound site by administering leptin topically, and found that topical leptin also induced a dose dependent acceleration in wound repair (p<0.0001). In addition, we found that all forms of leptin receptor, including the signal transducing long form, were present in skin by RNase protection assay, and that leptin receptor localized to subcutaneous vessels of wounded skin by in situ hybridization. Finally, we investigated the possibility that leptin stimulated angiogenesis in wounds by analyzing wound hemoglobin and wound vessel density. Neither systemic nor topical leptin induced any significant changes in either parameter, suggesting that leptin accelerates wound repair by a mechanism other than stimulation of angiogenesis. In summary, both systemic and topical leptin accelerate wound repair in diabetic ob/ob mice, possibly via the direct interaction of leptin with its receptors in wounded skin, but do not appear to significantly stimulate wound angiogenesis. Further studies to better elucidate the mechanisms of leptin's effects on wound repair are warranted.

Differential effects of nucleus basalis lesions in young adult and aging rats.

To characterize age-related changes in frontal cortical plasticity, we assessed maze learning and frontal cortical pharmacology in young adult, middle-aged, and aged rats. Rats received either ibotenic acid or sham lesions of the nucleus basalis magnocellularis (NBM) and were then trained on a radial maze task. After training, we assessed [3H]desmethylimipramine (DMI), [3H]muscimol, [3H]AMPA, and [3H]QNB binding using quantitative autoradiography. Both middle-aged and aged rats were impaired on the radial maze task. DMI binding was increased in both middle-aged and aged rats, while QNB binding was decreased in aged rats. While lesions impaired maze performance at all ages, middle-aged and aged rats showed more profound lesion-induced deficits. Lesions increased GABA, and AMPA receptor binding in young adult rats only. These lesion-induced changes may reflect a compensatory response that is lost with advancing age.

An age-related decline in striatal taurine is correlated with a loss of dopaminergic markers.

Taurine is present in high concentration in the mammalian brain and is known to decline with aging. The present studies examined the relationship between the loss of striatal neurotransmitters and spatial learning ability in aged male Long-Evans rats. The effects of intrahippocampal infusions of neurotrophic factors-nerve growth factor (NGF) and brain-derived neurotrophic factor-were also examined for their ability to ameliorate the age-related decline in brain amino acid content. Taurine content was found to be significantly reduced in the striatum of aged rats (26 months old) that were impaired in spatial learning performance when compared to young unimpaired rats (5 months old). Aged rats that were behaviorally unimpaired had more modest reductions in taurine. Striatal dopamine content was also significantly reduced in aged learning-impaired rats. There was a significant (p < 0.001) correlation (r=0.61) between the striatal content of taurine and dopamine, but no such correlation was found for other striatal transmitters (glutamate, serotonin, norepinephrine). Treatment with neurotrophins had little effect on the age-related decline in striatal amino acids, although NGF treatment did improve spatial learning. These studies suggest (1) a link between age-related declines in striatal dopamine and taurine and (2) that NGF-induced improvement in spatial learning is not related to mechanisms involving changes in taurine or glutamate content.

Does estradiol mediate leptin's effects on adiposity and body weight?

The role of estradiol in mediating leptin's effects on body weight was assessed in ovariectomized (OVX) mice before and after the onset of obesity. Ovariectomy did not alter leptin levels before the onset of obesity, and estradiol adminstration (0.05-17 microgram/day for 14 days) did not significantly alter leptin levels if they were corrected for the estradiol-induced reduction in body fat. The converse was also true, in that leptin administration (0.4-140 microgram/day) did not alter estradiol levels in intact mice. Furthermore, neither estradiol reduction (via ovariectomy) nor addition (via exogenous administration) significantly altered leptin's ability to reduce fat mass. Leptin was equally effective in reducing body weight in lean or obese OVX mice and intact controls. Finally, estradiol did not change the magnitude of leptin's effect on fat mass reduction when it was given in combination with leptin to lean intact or OVX mice. Estradiol may have indirectly affected leptin efficacy, because leptin did not produce as large a change in fat mass at lower doses in lean OVX mice as it did in intact counterparts. Taken together, these data suggested that 1) estradiol does not directly regulate leptin secretion or its effects on fat mass and 2) leptin does not directly regulate estradiol secretion or its effects on fat mass. Leptin and estradiol, however, may interact in an indirect fashion to affect fat utilization.

Efficacy of exogenous recombinant murine leptin in lean and obese 10- to 12-mo-old female CD-1 mice.

Leptin efficacy was compared in obese and lean female CD-1 mice. Body weights in these 10- to 12-mo-old mice ranged from 29.7 to 62.0 g, and leptin levels correlated with body weight. Mice from the lean and obese ends of the weight distribution were treated with daily peripheral leptin injections (1-100 mg/kg) for a 33-day period. The half-maximal effective doses for weight loss and fat reduction were shifted 0.5-0.7 log to the right for obese mice. Leptin was less efficacious at low doses (1-3 mg/kg) in obese mice but equal to or more efficacious in obese than lean mice at high doses (30-100 mg/kg). Leptin's initial effects on weight loss could be explained by appetite suppression in both groups, but its effects on fat reduction were greater in leptin-treated than pair-fed mice, particularly in the lean group. Leptin also prevented the elevations in serum corticosterone and ketones found in pair-fed lean mice. These data allow a quantitative comparison of leptin sensitivity in obese vs. lean CD-1 mice and suggest that in mice where obesity is a function of outbreeding and age, leptin sensitivity is moderately reduced. Furthermore, although appetite suppression has a clear role in leptin's effects on body weight, leptin may also have specific effects on lipid metabolism and mobilization that are different from the metabolic compensations that normally occur with food deprivation.

Attenuation of leptin-mediated effects by monosodium glutamate-induced arcuate nucleus damage.

Leptin is a protein secreted by adipocytes that is important in regulating appetite and adiposity. Recent studies have suggested the presence of leptin receptors in the arcuate nucleus of the hypothalamus (ANH). Neonatal administration of monosodium glutamate (MSG) damages the ANH, resulting in obesity and neuroendocrine dysfunction. Neonatal administration of MSG was utilized to test the hypothesis that the anatomic site for many of leptin's actions is the ANH. Female control (n = 6) and MSG-treated rats (n = 7) were implanted for 14 days with osmotic minipumps containing phosphate-buffered saline or leptin (1 mg.kg-1.day-1). Leptin suppressed (P < 0.05) body weight gain in controls but did not suppress weight gain in MSG-treated rats. Leptin decreased (P < 0.05) fat depots in controls but had no effect in MSG-treated rats. Night feeding was suppressed (P < 0.05) in leptin-treated control rats. MSG-treated rats showed a suppression in food intake that was of a smaller magnitude and appeared later in the course of leptin treatment. These findings suggest that leptin mediates some physiological actions related to fat mobilization via receptors located in the ANH.

Leptin prevents posthibernation weight gain but does not reduce energy expenditure in arctic ground squirrels.

In mammals, leptin reduces energy intake and may increase energy expenditure as a means to maintain body weight and/or adiposity at an appropriate level. Hibernating mammals seasonally alter body mass, food intake, and body composition and, therefore, represent an attractive model for investigating the physiological regulation of changing body mass and adiposity. Previous experiments in our laboratory demonstrated that administration of mouse recombinant leptin reduces food intake and body weight in arctic ground squirrels during prehibernation fattening. In addition, leptin appeared to reduce metabolic efficiency (weight gain per unit of energy intake). This result suggests that reduced food intake alone may not account for the observed weight loss. Here, we describe the effect of a 3-week constant infusion of leptin given to posthibernation arctic ground squirrels on food consumption and energy expenditure. Mouse recombinant leptin (1 mg/ml) was administered through subcutaneously implanted mini-osmotic pumps (10 microliters/hr flow rate). Resting metabolic rate was monitored before and during the 3-week leptin administration period by indirect calorimetry. Body temperature and locomotory activity were monitored continuously by abdominal radiotransmitters. At the end of the leptin administration period, thermogenic capacity was evaluated by measuring brown fat uncoupling protein-1 mRNA and protein levels. Leptin administration resulted in reduced food intake and prevented posthibernation weight gain, but it did not alter any of the measured parameters of energy expenditure.

Leptin inhibits prehibernation hyperphagia and reduces body weight in arctic ground squirrels.

The ob gene product leptin is thought to play a physiological role in the fine tuning of a homeostatic mechanism regulating satiety and adiposity. Mouse recombinant leptin was administered to seasonally hyperphagic arctic ground squirrels as a first step in demonstrating the evolutionary conservation of leptin function and the potential involvement of leptin in the seasonal regulation of adiposity in hibernators. Continuous infusion of leptin for 3 wk via miniosmotic pumps resulted in a reduction in food intake and body weight in a manner consistent with its proposed role as a satiety hormone. During the recovery period after leptin administration, squirrels that had received leptin became hyperphagic relative to controls. Percent body fat was estimated at weekly intervals by measuring total body electrical conductivity and decreased after 3 wk of leptin administration. Our observations support the role of leptin as a regulatory hormone involved in the control of satiety, adiposity, and possibly energy expenditure in hibernating mammals.

The effects of intrahippocampal BDNF and NGF on spatial learning in aged Long Evans rats.

Spatial learning rate was compared in cognitively impaired aged rats infused with either brain-derived neurotrophic factor (BDNF) or nerve growth factor (NGF). BDNF or NGF was infused into the dorsal hippocampus/third ventricle while animals were being trained on the Morris water maze. Training continued until all rats met a spatial learning criterion. Seven weeks later, they were tested for retention of the task, and sacrificed for assessment of hippocampal high-affinity choline uptake (HACU) or hypothalamic biogenic amine levels. NGF, but not BDNF, improved spatial learning rate in aged rats and increased hippocampal choline uptake weeks after withdrawal of NGF. Although BDNF did not improve spatial learning, it did induce a partial, long-term normalization of the elevated hypothalamic 5-HT levels observed in our aged rats. These data suggest that (1) intrahippocampal/intraventricular infusion of NGF can improve the learning rate of aged, spatial learning-impaired rats, and that this improvement in acquisition could be associated with increased hippocampal cholinergic activity, and (2) that the BDNF-induced normalization of hypothalamic 5-HT levels in aged rats was not sufficient to improve learning rate in aged, spatial learning-impaired rats.

Glial cell line-derived neurotrophic factor sustains axotomized basal forebrain cholinergic neurons in vivo: dose-response comparison to nerve growth factor and brain-derived neurotrophic factor.

Glial cell line-derived neurotrophic factor (GDNF) was infused continuously for 2 weeks into the ventricles of male Wistar rats that had received a unilateral knife transection of the fimbria/fornix. In vehicle-treated, control animals, there was a 70% loss of choline acetyltransferase (ChAT)-positive and a 60% loss of p75-positive neurons in the septum/diagonal band ipsilateral to the axotomy as identified by immunohistochemistry, with no loss in ChAT biochemical activity. GDNF treatment at 10 micrograms/day completely prevented the loss of p75-positive neurons, significantly reduced the loss of ChAT-positive neurons to 40% of normal, and stimulated ChAT biochemical activity to 40% more than normal in an axotomy-dependent manner. GDNF is 1 order of magnitude less potent than NGF but, unlike NGF, had little or no effect on normal, uninjured neurons. GDNF was 1 order of magnitude more potent than BDNF, and BDNF had no effect on ChAT biochemical activity. GDNF and NGF inhibited weight gain, whereas BDNF induced significant weight loss and death at the dosage of 100 micrograms/day.

A role for melanin-concentrating hormone in the central regulation of feeding behaviour.

The hypothalamus plays a central role in the integrated regulation of energy homeostasis and body weight, and a number of hypothalamic neuropeptides, such as neuropeptide Y (ref. 1), galanin, CRH (ref. 3) and GLP-1 (ref. 4), have been implicated in the mediation of these effects. To discover new hypothalmic peptides involved in the regulation of body weight, we used differential display polymerase chain reaction to identify messenger RNAs that are differentially expressed in the hypothalamus of ob/+ compared with ob/ob C57B1/6J mice. We show here that one mRNA that is overexpressed in the hypothalamus of ob/ob mice encodes the neuropeptide melanin-concentrating hormone (MCH). Fasting further increased expression of MCH mRNA in both normal and obese animals. Neurons containing MCH are located in the zona incerta and in the lateral hypothalamus. These areas are involved in regulation of ingestive behaviour, but the role of MCH in mammalian physiology is unknown. To determine whether MCH is involved in the regulation of feeding, we injected MCH into the lateral ventricles of rats and found that their food consumption increased. These findings suggest that MCH participates in the hypothalamic regulation of body weight.

Y1 and Y2 receptor selective neuropeptide Y analogues: evidence for a Y1 receptor subclass.

Neuropeptide Y (NPY), a 36-residue polypeptide produced abundantly in both nervous and peripheral tissues, appears to play a significant role in the regulation of diverse biological processes, including feeding behavior and cardiovascular and psychotropic functions. The actions of NPY are mediated through effective binding to specific receptors of which two, designated Y1 and Y2, have been well characterized. A shortened cyclic analogue of NPY, des-AA10-17-cyclo-7/21[Cys7,21]NPY, was shown to retain high affinity for both human neuroblastoma SK-N-MC and SK-N-BE2 cell types (expressing Y1 and Y2 receptors, respectively). Increasing the size of the ring (des-AA10-17-cyclo-2/27[Cys2,27]NPY) in the present study produced a high-affinity analogue (Ki = 3.0 vs 0.3 nM for NPY) that bound exclusively to Y2 receptors. Using the feedback from structure-activity relationships, we also describe the optimization of specific substitutions and bridging arrangements leading to the production of other truncated, high-affinity Y1 selective analogues which bind, as does NPY itself, in the low-nanomolar range. Of greatest significance, des-AA10-17-cyclo-7/21[Cys7,21,Pro34]NPY (11) was found to possess agonistic properties with an affinity comparable to that of the native NPY molecule when tested for its ability to inhibit norepinephrine-stimulated cAMP release in SK-N-MC human neuroblastoma cells. Compound 11 also caused an increase in blood pressure in anesthetized rats. However, in two central nervous system models of Y1 receptor function, stimulation of feeding and anxiolytic activity, this analogue was inactive, which suggests the presence of a new subclass of receptors. In summary, the present results demonstrate that residues 10-17 of NPY are not directly involved in either Y1 or Y2 receptor recognition or activation. This suggests that the selectivity of NPY receptors is highly dependent on subtle conformational changes such as the substitution of residue 34 to a proline or the introduction of intramolecular constraints. Additionally, we have produced an analogue of NPY that selectively activates peripheral NPY Y1 receptors.

Effects of the obese gene product on body weight regulation in ob/ob mice.

C57BL/6J mice with a mutation in the obese (ob) gene are obese, diabetic, and exhibit reduced activity, metabolism, and body temperature. Daily intraperitoneal injection of these mice with recombinant OB protein lowered their body weight, percent body fat, food intake, and serum concentrations of glucose and insulin. In addition, metabolic rate, body temperature, and activity levels were increased by this treatment. None of these parameters was altered beyond the level observed in lean controls, suggesting that the OB protein normalized the metabolic status of the ob/ob mice. Lean animals injected with OB protein maintained a smaller weight loss throughout the 28-day study and showed no changes in any of the metabolic parameters. These data suggest that the OB protein regulates body weight and fat deposition through effects on metabolism and appetite.

Characteristics of BDNF-induced weight loss.

There is evidence that central infusion of brain-derived neurotrophic factor (BDNF) induces weight loss in rats. We have begun to investigate the physiological basis for BDNF-induced weight loss by assessing its relationship to (a) appetite, (b) serum indices of metabolic and renal toxicity, and (c) brain monoamine activity in areas associated with feeding or motor function. BDNF (0-6 microgram/day) was infused into the lateral ventricle (LV) of male Long-Evans rats for 14 days. Body weight and food intake were monitored throughout infusion and recovery periods. BDNF induced severe, dose-dependent appetite suppression and weight loss. Although appetite began to recover after the 10th infusion day, body weight had not returned to control values at the end of the recovery period. The weight loss observed in BDNF-infused rats was related to appetite suppression, since uninfused rats that were pair-fed to high dose BDNF-treated rats showed comparable weight loss. Despite severe weight loss, serum BUN, creatinine, thyroxine, glucose, and total protein were not affected by BDNF infusion. Striatal DO-PAC/DA was similarly unaffected by BDNF. In contrast, BDNF-infused rats showed a dose-dependent increase in hypothalamic 5-HIAA/5-HT that was not observed in pair-fed rats, suggesting that the observed increase in hypothalamic 5-HIAA/5-HT was a direct effect of BDNF infusion rather than a secondary effect of food restriction. These data suggest that BDNF may induce appetite suppression and weight loss through a central mechanism.

Intraventricular administration of BDNF increases neuropeptide expression in newborn rat brain.

Brain-derived neurotrophic factor (BDNF) specifically enhances and maintains the expression of neuropeptide Y (NPY) and somatostatin (SOM) in cultured neocortical neurons (Nawa et al., 1993). In this article, we examined its effects in vivo on neuropeptide expression in various brain regions by injecting BDNF into the cerebroventricle of newborn rats. Repeated administration (2x) of BDNF increased contents of NPY-like immunoreactivity (NPY-LI) and substance P (SP)-LI most markedly in the anterior neocortex by 11- and 24-fold, respectively, in comparison to values in the animals receiving control injection. A smaller but significant increase was also observed in immunoreactivity for somatostatin (SOM), enkephalin (ENK), and cholecystokinin (CCK). mRNA for NPY, SP, and SOM was similarly upregulated in the anterior neocortex, suggesting that BDNF enhances peptide synthesis rather than inhibiting peptide release or degradation. Among the brain regions examined, however, peptidergic responses to BDNF were different with respect to their spatial distribution and time course. Induction of SP-LI, NPY-LI, and SOM-LI around the injection site was most pronounced in cortical layers II/III, layers IV-VI, and layer VI, respectively. Peptidergic immunoreactivity was also enhanced in other brain regions ipsilateral to the injection site, for example, NPY-LI in the hippocampus, thalamic nuclei, and striatum, and SOM-LI in the striatum. A single injection of BDNF elevated SP-LI to a plateau level within 12 hr while NPY-LI and SOM-LI reached maximum levels at 48 hr, and then all returned to control levels at 68 hr. In contrast, the same dose of NGF had no influences on the neuropeptide levels at 48 hr. These observations suggest that BDNF regulates the development of neuropeptide expression in the CNS in a plastic manner.