Combined chemoradiotherapy with gemcitabine in patients with locally advanced inoperable transitional cell carcinoma of the urinary bladder and/or in patients ineligible for surgery: a phase I trial.

BACKGROUND: We conducted a phase I trial of gemcitabine (gem) with concurrent radiotherapy in patients with muscle-invasive bladder cancer (BC) ineligible for surgery or cisplatin or refusing organ loss. PATIENTS AND METHODS: Patients with urothelial cancer, cT2-T4, cN0-1, M0, ineligible for surgery due to local tumor extension, PS, age or co-morbidities or who refused surgery were included. After maximal transurethral resection, the treatment schedule included: twice-weekly i.v. infusion of gem [dose levels (DL) 1-6: 20, 27, 30, 33, 50 and 40 mg/m(2), respectively] for 30 min and concurrent radiotherapy (RT) to the bladder with 55.5 Gy. The primary end point was to determine the maximum-tolerated dose (MTD) and the dose recommended (RD) for further studies of this gem schedule. The secondary end point was late toxicity. The MTD was defined by dose-limiting toxicity (DLT) in 2 or more of 6 patients, discontinuation of RT and/or gem for >1 week in 2 or more of 6 patients due to grade (G) 3/4 acute and/or late toxicity in more than 2 of 18 patients. RESULTS: Thirty-five of 44 patients were assessable for toxicity and thus the primary end point. DLTs occurred in two of five patients at dose level 5: one G3 alanine aminotransferase elevation and one G3 fatigue. The MTD, therefore, was 50 mg/m(2) gem twice weekly. At DL 6 with 40 mg/m(2), the RD was established: only one of six patients developed G3 fatigue and diarrhea. Late toxicity was rare and of low grade (only G1-2). The 2-year locoregional failure rate was 32% (9/28); 10 of 28 patients (38%) were alive with an intact bladder and no evidence of recurrent disease, 9 patients developed distant metastases and 6 died of their disease. CONCLUSIONS: Gemcitabine in combination with RT is well tolerated in BC patients ineligible for surgery and/or cisplatin. The RD of gemcitabine for subsequent trials is 40 mg/m(2) twice weekly with concurrent radiation.

Gene expression in the rat cerebral cortex: comparison of recovery sleep and hypnotic-induced sleep.

Most hypnotic medications currently on the market target some aspect of GABAergic neurotransmission. Although all such compounds increase sleep, these drugs differentially affect the activity of the cerebral cortex as measured by the electroencephalogram. Whereas benzodiazepine medications such as triazolam tend to suppress slow wave activity in the cortex, the GABA(B) ligand gamma-hydroxybutyrate greatly enhances slow wave activity and the non-benzodiazepine, zolpidem, which binds to the omega1 site on the GABA(A) receptor/Cl(-) ionophore complex, is intermediate in this regard. Our previous studies have demonstrated that a small number of genes exhibit increased expression in the cerebral cortex of the mouse and rat during recovery sleep after sleep deprivation: egr-3, fra-2, grp78, grp94, ngfi-b, and nr4a3. Using these genes as a panel of biomarkers associated with sleep, we asked whether hypnotic medications induce similar molecular changes in the rat cerebral cortex to those observed when both sleep continuity and slow wave activity are enhanced during recovery sleep. We find that, although each drug increases the expression of a subset of genes in the panel of biomarkers, no drug fully replicates the molecular changes in the cortex associated with recovery sleep. Furthermore, high levels of slow wave activity in the cortex are correlated with increased expression of fra-2 whereas the expression of grp94 is correlated with body temperature. These results demonstrate that sleep-related changes in gene expression may be affected by physiological covariates of sleep and wakefulness rather than by vigilance state per se.

Subregional organization of preoptic area/anterior hypothalamic projections to arousal-related monoaminergic cell groups.

Pathways mediating the generation and/or maintenance of sleep reside within the preoptic/anterior hypothalamus (POAH). Reproduction, water balance, thermoregulation, and neuroendocrine functions are also associated with POAH, but it is not fully understood whether sleep is consolidated with these behavioral and physiological functions, or whether sleep-related circuitry is segregated from other POAH regions. Recent studies indicate that sleep mechanisms may be localized to the ventrolateral preoptic area (VLPO) and that this region sends inhibitory projections to waking/arousal-related neurons in the histaminergic tuberomammillary nucleus (TM), the noradrenergic locus coeruleus (LC), and the serotonergic dorsal raphe (DR). The present study is a quantitative investigation of preoptic area efferents to these monoaminergic groups. The results demonstrate that biotinylated dextran injections in the VLPO region reveal a robust innervation of TM that was as much as five times greater than innervation derived from other POAH subregions. The innervation of TM originated almost exclusively from injection sites in the region of galanin neurons. VLPO projections to the LC were moderately dense and were greater than in other POAH regions except for equivalent input from the medial preoptic area. Projections to the dorsal raphe were equivalent to LC innervation and were generally two to three times greater from VLPO than from other POAH regions, except for projections from the lateral preoptic region, which were similar in magnitude. The rostral and caudal levels projected more to the TM, whereas the midrostral region of VLPO strongly innervated the LC core. These findings, with recent studies demonstrating medial and lateral extensions of the sleep-related VLPO neuronal group, indicate that descending arousal state control may be mediated by this specific galaninergic/gamma-aminobutyric acid (GABA)ergic cell group.

Afferent projections to the cholinergic pedunculopontine tegmental nucleus and adjacent midbrain extrapyramidal area in the albino rat. I. Retrograde tracing studies.

The afferent connections of the pedunculopontine tegmental nucleus (PPT) and the adjacent midbrain extrapyramidal area (MEA) were examined by retrograde tracing with wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Major afferents to the PPT originate in the periaqueductal gray, central tegmental field, lateral hypothalamic area, dorsal raphe nucleus, superior colliculus, and pontine and medullary reticular fields. Other putative inputs originate in the paraventricular and preoptic hypothalamic nuclei, the zona incerta, nucleus of the solitary tract, central superior raphe nucleus, substantia innominata, posterior hypothalamic area, and thalamic parafascicular nucleus. The major afferent to the medially adjacent MEA originates in the lateral habenula, while other putative afferents include the perifornical and lateral hypothalamic area, periaqueductal gray, superior colliculus, pontine reticular formation, and dorsal raphe nucleus. MEA inputs from basal ganglia nuclei include moderate projections from the substantia nigra pars reticulata, entopeduncular nucleus, and a small projection from the globus pallidus, but not the subthalamic nucleus. Dense anterograde labeling was observed in the substantia nigra pars compacta, entopeduncular nucleus, subthalamic nucleus, globus pallidus, and caudate-putamen only following WGA-HRP injections involving the MEA. The results of this study demonstrate that the PPT and MEA share many potential afferents. Remarkable differences were found that support distinguishing between these two nuclei in future studies regarding the functional organization of the midbrain and pons. The results, for example, confirm our previous observations that the largely reciprocal connections between the midbrain and basal ganglia distinguish the MEA from the PPT. Afferents from the lateral habenula and contralateral superior colliculus represent extensions of more traditional basal ganglion circuitry which further delineate the MEA from the PPT. The results are discussed with respect to the important role of the midbrain and pons in behavioral state control and locomotor mechanisms.

Ultrastructural study of cholinergic and noncholinergic neurons in the pars compacta of the rat pedunculopontine tegmental nucleus.

A group of medium-to-large cholinergic neurons situated in the dorsolateral mesopontine tegmentum comprises the pedunculopontine tegmental nucleus (PPT). The PPT pars compacta (PPT-pc), which occupies the lateral part of the caudal two-thirds of the nucleus, contains a dense aggregation of cholinergic neurons. In the present study, we have employed immunohistochemistry for choline acetyltransferase (ChAT) and electron microscopy to investigate the ultrastructure and synaptic organization of neuronal elements in the PPT-pc. Our results demonstrate that: (1) ChAT-immunoreactive (i.e., cholinergic) PPT-pc neurons are characterized by abundant cytoplasm and organelles, and have few axosomatic synapses (both asymmetric and symmetric); (2) ChAT-immunoreactive dendrites comprise 6-15% of total dendritic elements in the neuropil; the mean percentage of dendritic membrane covered by synaptic terminals is approximately 15%, and nearly all synapses with ChAT-immunoreactive dendrites are asymmetric; (3) within the boundaries described by cholinergic PPT-pc, there are noncholinergic neurons which, in contrast, exhibit a lucent cytoplasm and a higher frequency of axosomatic synapses (10.5% versus 3.7% for cholinergic neurons); and (4) noncholinergic neurons are morphologically heterogeneous with one subpopulation exhibiting a mean diameter that approximates that of cholinergic cells (i.e., > 15 microns and < 20 microns) and a very high frequency of axosomatic synapses (> 20%). Only 0.2-0.7% of terminal elements in the neuropil were ChAT-immunoreactive and these were not observed to synapse with cholinergic dendrites or somata. This relative paucity of terminal labeling and lack of cholinergic-cholinergic interactions seems inconsistent with the recognized and prominent physiological actions of acetylcholine on cholinergic PPT-pc neurons, and suggests a methodological limitation and/or a potential paracrine-like action of nonsynaptically released acetylcholine in the PPT region.

Serotonergic dorsal raphe nucleus projections to the cholinergic and noncholinergic neurons of the pedunculopontine tegmental region: a light and electron microscopic anterograde tracing and immunohistochemical study.

The serotonergic dorsal raphe nucleus is considered an important modulator of state-dependent neural activity via projections to cholinergic neurons of the pedunculopontine tegmental nucleus (PPT). Light and electron microscopic analysis of anterogradely transported biotinylated dextran, combined with choline acetyltransferase (ChAT) immunohistochemistry, were employed to describe the synaptic organization of mesopontine projections from the dorsal raphe to the PPT. In a separate set of experiments, we utilized immunohistochemistry for the serotonin transporter (SERT), combined with ChAT immunohistochemistry at the light and electron microscopic levels, to determine whether PPT neurons receive serotonergic innervation. The results of these studies indicate that: (1) anterogradely labeled and SERT-immunoreactive axons and presumptive boutons invest the PPT at the light microscopic level; (2) at the ultrastructural level, dorsal raphe terminals in the PPT pars compacta synapse mainly with dendrites and axosomatic contacts were not observed; (3) approximately 12% of dorsal raphe terminals synapse with ChAT-immunoreactive dendrites; and (4) at least 2-4% of the total synaptic input to ChAT-immunoreactive dendrites is of dorsal raphe and/or serotonergic origin. This serotonergic dorsal raphe innervation may modulate cholinergic PPT neurons during alterations in behavioral state. The role of these projections in the initiation of rapid eye movement (REM) sleep and the ponto-geniculo-occipital waves that precede and accompany REM sleep is discussed.

Ultrastructure of cholinergic synaptic terminals in the thalamic anteroventral, ventroposterior, and dorsal lateral geniculate nuclei of the rat.

The principal relay nuclei of the thalamus receive their cholinergic innervation from two midbrain cholinergic groups: the pedunculopontine tegmental nucleus and the laterodorsal tegmental nucleus. The different thalamic nuclei exhibit populations of cholinergic axons which vary in density and morphology when examined at the light microscopic level. However, the ultrastructure of the cholinergic terminals in different thalamic nuclei has not been described. This study was undertaken to confirm that synaptic contacts are formed by cholinergic axons in several principal thalamic relay nuclei, to describe their ultrastructural morphology, and to identify the types of postsynaptic elements contacted by cholinergic synaptic terminals. The thalamic nuclei examined in this study are the dorsal lateral geniculate nucleus, ventroposteromedial nucleus, ventroposterolateral nucleus, and anteroventral nucleus. Our results confirm that cholinergic axons form synaptic terminals in these thalamic nuclei. Cholinergic synaptic terminals contact structures outside the characteristic synaptic glomeruli, are never postsynaptic, and have morphologies and postsynaptic targets which differ among the thalamic nuclei. In the ventroposterior nuclei, cholinergic terminals form asymmetric synaptic contacts onto larger dendrites in the extraglomerular neuropil. In the anteroventral nucleus, cholinergic terminals form both symmetric and asymmetric synaptic contacts onto dendrites and somata. Cholinergic terminals in the anteroventral nucleus are larger than those in other nuclei. In the dorsal lateral geniculate nucleus, cholinergic terminals contact both somata and dendrites in the extraglomerular neuropil, but the synaptic contacts in this nucleus are symmetric in morphology.

Differences in the retinohypothalamic tract in albino Lewis versus brown Norway rat strains.

Differences in sleep-wake patterns in response to light-dark stimulation have been observed between albino Lewis and pigmented Brown Norway strains of rats, which may be associated with albinism. Since several anatomical differences have been demonstrated in the visual pathways of albino and pigmented mammals, the present study was undertaken to determine whether additional differences in visual pathways of these rat strains exist that might account for their behavioral differences. Using anterograde tracing techniques and image analysis, we have investigated the retinal projections of Lewis and Brown Norway rats. Our results demonstrate that the distribution of retinal terminals in the hypothalamic suprachiasmatic nucleus extends over a greater area in Lewis compared to Brown Norway rats. This zone of termination corresponds to a cytoarchitectonically definable ventrolateral subdivision of the suprachiasmatic nucleus (SCN), which is also greater in Lewis than in Brown Norway rats. These results may have implications for behaviors related to the SCN.

Differential increase in the expression of heat shock protein family members during sleep deprivation and during sleep.

Although sleep is thought to be restorative from prior wakeful activities, it is not clear what is being restored. To determine whether the synthesis of macromolecules is increased in the cerebral cortex during sleep, we subjected C57BL/6 mice to 6 hours of sleep deprivation and then screened the expression of 1176 genes of known function by using cDNA arrays. The expression of the heat shock proteins (HSP), endoplasmic reticulum protein (ERp72) and glucose-regulated protein (GRp78), was among the genes whose expression was significantly elevated in the cortex during sleep deprivation, whereas GRp78 and GRp94 mRNAs were elevated in the cortex during recovery sleep after sleep deprivation, as confirmed by conventional and quantitative real-time polymerase chain reaction and/or Northern analyses. A systematic evaluation of the expression of six heat shock protein family members (ERP72, GRp78, GRp94, HSP27, HSP70-1, and HSP84) in seven brain regions revealed increased mRNA levels in cortex, basal forebrain, hypothalamus, cerebellum and medulla during sleep deprivation, whereas increased mRNA levels during recovery sleep were limited to the cortex and medulla. Immunohistochemical studies identified increased numbers of GRp78-, GRp94-, and ERp72-immunoreactive cells in the dorsal and lateral cortex during sleep deprivation but, during recovery sleep, elevated numbers of these cells were found only in the lateral cortex. In the medulla, increased numbers of GRp94-immunoreactive cells were observed in nucleus tractus solitarius, dorsal motor nucleus of the vagus and the rostroventrolateral medulla during recovery sleep. The widespread increase of heat shock protein family mRNAs in brain during sleep deprivation may be a neuroprotective response to prolonged wakefulness. In contrast, the relatively limited heat shock protein family mRNA expression during recovery sleep may be related to the role of heat shock proteins in protein biogenesis and thus to the restorative function of sleep.

Sleep-waking discharge patterns of ventrolateral preoptic/anterior hypothalamic neurons in rats.

Numerous lesion, stimulation and recording studies in experimental animals demonstrate the importance of neurons within the preoptic/anterior hypothalamic area (POA) in the regulation of sleep induction and sleep maintenance. Recently, a discrete cluster of cells in the ventrolateral POA (vlPOA) of rats was found to exhibit elevated c-fos gene expression during sleep, indicating that these neurons are strongly activated during nonREM and/or REM sleep stages. We examined neuronal discharge during wakefulness and sleep throughout the dorsal to ventral extent of the lateral POA in rats, using chronic microwire technique. We found that neurons with elevated discharge rates during sleep, compared to waking, were localized to the vlPOA. As a group, vlPOA neurons displayed elevated discharge rates during both nonREM and REM sleep. Discharge of vlPOA neurons reflected the depth of sleep, i.e., discharge rates increased significantly from light to deep nonREM sleep. During recovery sleep following 12-14 h of sleep deprivation, vlPOA neurons displayed increased sleep-related discharge, compared to baseline sleep. Neurons in the vlPOA displaying increased neuronal discharge during sleep were located in the same area where neurons exhibit increased c-fos gene expression during sleep. Such neurons are likely components of a rostral hypothalamic mechanism that regulates sleep onset and sleep maintenance.

High-affinity nerve growth factor receptor (Trk) immunoreactivity is localized in cholinergic neurons of the basal forebrain and striatum in the adult rat brain.

Trk-immunoreactivity was observed in basal forebrain and striatal cholinergic neurons, whereas low-affinity NGF receptor immunoreactivity was observed in basal forebrain but not striatal cholinergic neurons. Since NGF exerts trophic actions on both basal forebrain and striatal cholinergic populations, the presence of Trk in these neurons lends strong support for an essential role of Trk in NGF-responsive neurons, but suggests that the low affinity receptor is not necessary for NGF actions in the striatum.

Sleep-waking discharge of neurons in the posterior lateral hypothalamus of the albino rat.

The sleep-waking discharge patterns of neurons in the posterior lateral hypothalamus (PLH) were investigated in the rat. Previous studies in the cat demonstrated that this region contained neurons that fired tonically at low rates (2-4 Hz) during waking, decreased firing in non-rapid eye-movement (NREM) sleep and nearly ceased firing during rapid eye-movement (REM) sleep. These "REM-off" neurons were proposed to be histaminergic neurons of the tuberomammillary nucleus (TM). Since many anatomical and physiological studies are performed in the rat, we sought to examine the sleep-waking discharge of these neurons in this animal. We found three main types of discharge patterns among PLH neurons. Waking-related neurons decreased their discharge in NREM sleep, and remained at low rates during REM sleep. A subpopulation of these neurons discharged very little during REM sleep (<0.2 Hz) (REM-off neurons). Waking/REM-related neurons decreased their discharge in NREM sleep and returned to waking rates in REM sleep. REM-related neurons decreased their discharge in NREM sleep and increased their discharge during REM sleep higher than waking rates. No NREM-related discharge patterns were recorded. Waking-related and waking/REM-related neurons were similar in location within the PLH and action potential duration. Some REM-off and other waking-related neurons were recorded within the boundaries of the histaminergic TM, however, not all waking-related and REM-off neurons were found within this region. Furthermore, neurons with waking/REM-related and state-indifferent discharge patterns were localized within the TM. These results suggest that waking-related and/or REM-off neurons may not be exclusively histaminergic in rats.

Localization of immunoreactive epidermal growth factor receptor in neonatal and adult rat hippocampus.

The regional and developmental expression of epidermal growth factor (EGF) receptor in rat hippocampus was investigated utilizing immunocytochemical techniques at the light and electron microscopic levels. EGF receptor immunoreactivity in adult hippocampus was compared to that found at postnatal day 7 (P7). While the receptor was observed in P7 hippocampus, immunostaining was more prominent in the adult hippocampus, especially in the pyramidal CA2 field. Ultrastructural analysis of this region revealed that the receptor was localized to the cell bodies of both P7 and adult neurons rather than the axons or dendrites. The expression of EGF receptor in selected regions of the adult brain was verified by Western blotting. These results demonstrate the presence of EGF receptor in rat hippocampus as early as P7, localize the receptor to the pyramidal cell body, and establish the hippocampal formation, particularly CA2, as a major site of EGF receptor expression in rat brain.

Opioid modulation of taste hedonics within the ventral striatum.

There is a long-standing interest in the role of endogenous opioid peptides in feeding behavior and, in particular, in the modulation of food reward and palatability. Since drugs such as heroin, morphine, alcohol, and cannabinoids, interact with this system, there may be important common neural substrates between food and drug reward with regard to the brain's opioid systems. In this paper, we review the proposed functional role of opioid neurotransmission and mu opiate receptors within the nucleus accumbens and surrounding ventral striatum. Opioid compounds, particularly those selective for the mu receptor, induce a potent increase in food intake, sucrose, salt, saccharin, and ethanol intake. We have explored this phenomenon with regard to macronutrient selection, regional specificity, role of output structures, Fos mapping, analysis of motivational state, and enkephalin gene expression. We hypothesize that opioid-mediated mechanisms within ventral striatal medium spiny neurons mediate the affective or hedonic response to food ('liking' or food 'pleasure'). A further refinement of this hypothesis is that activation of ventral striatal opioids specifically encodes positive affect induced by tasty and/or calorically dense foods (such as sugar and fat), and promotes behaviors associated with this enhanced palatability. It is proposed that this brain mechanism was beneficial in evolutionary development for ensuring the consumption of relatively scarce, high-energy food sources. However, in modern times, with unlimited supplies of high-calorie food, it has contributed to the present epidemic of obesity.

Preoptic area sleep-regulating mechanisms.

Evidence is summarized for the existence of a sleep-regulating mechanism within the preoptic area of the hypothalamus, including the results of lesion, stimulation, and neuronal recording studies. Recent findings employing the c-fos protein immunohistochemical method, have localized putative sleep-regulatory neurons to the ventrolateral preoptic area (vlPOA) and the median preoptic nucleus (MnPn). Electrophysiological studies have confirmed the presence of neurons with sleep-related discharge in the vlPOA. Neurons in the vlPOA that exhibit c-fos protein immunoreactivity during sleep contain the inhibitory neuromodulators galanin and gamma-aminobutyric acid (GABA). These neurons also project to monoaminergic arousal systems, particularly the histaminergic cell groups in the posterior hypothalamus. POA neurons can be hypothesized to provide sleep-related inhibitory control over multiple arousal systems in the forebrain and brainstem.

Disposition of Erlotinib and Its Metabolite OSI420 in a Patient with High Bilirubin Levels.

Erlotinib is an oral epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor approved for the treatment of non-small cell lung cancer and when combined with gemcitabine for pancreatic cancer. Dose reduction of erlotinib in patients with severe hepatic impairment has been established. We present the case of a male patient suffering from an adenocarcinoma of the pancreas with metastases in the liver and lung, whose disease progression led to highly elevated bilirubin levels of >14 mg/dl accompanied by icterus and pruritus. Despite the known contraindication, the patient agreed to be treated with 150 mg erlotinib p.o. per day. We performed therapeutic drug monitoring of erlotinib on day 1 after the first ingestion of erlotinib and then over a period of 19 days. One-compartment pharmacokinetics on day 1 were calculated, and, based on these data, a pharmacokinetic simulation for the following 19 days was run. On day 1 after the first erlotinib ingestion, plasma concentrations were identical to those described in the literature. On the following days, erlotinib plasma concentrations remained at a similar order of magnitude after daily ingestion. Compared with published data, OSI420 plasma concentrations were clearly higher from day 1 to 16. Due to disease progression, the last intake of erlotinib was on day 16, but plasma concentrations of the drug and metabolite increased excessively thereafter. The data give evidence that total bilirubin levels up to 14 mg/dl do not necessarily cause elevated plasma concentrations of erlotinib when given in doses of 150 mg per day.

Sleep-related c-Fos protein expression in the preoptic hypothalamus: effects of ambient warming.

Preoptic area (POA) neuronal activity promotes sleep, but the localization of critical sleep-active neurons is not completely known. Thermal stimulation of the POA also facilitates sleep. This study used the c-Fos protein immunostaining method to localize POA sleep-active neurons at control (22 degrees C) and mildly elevated (31.5 degrees C) ambient temperatures. At 22 degrees C, after sleep, but not after waking, we found increased numbers of c-Fos immunoreactive neurons (IRNs) in both rostral and caudal parts of the median preoptic nucleus (MnPN) and in the ventrolateral preoptic area (VLPO). In animals sleeping at 31.5 degrees C, significantly more Fos IRNs were found in the rostral MnPN compared with animals sleeping at 22 degrees C. In VLPO, Fos IRN counts were no longer increased over waking levels after sleep at the elevated ambient temperature. Sleep-associated Fos IRNs were also found diffusely in the POA, but counts were lower than those made after waking. This study supports a hypothesis that the MnPN, as well as the VLPO, is part of the POA sleep-facilitating system and that the rostral MnPN may facilitate sleep, particularly at elevated ambient temperatures.

Restricted daily consumption of a highly palatable food (chocolate Ensure(R)) alters striatal enkephalin gene expression.

Brain opioid peptide systems are known to play an important role in motivation, emotion, attachment behaviour, the response to stress and pain, and the control of food intake. Opioid peptides within the ventral striatum are thought to play a key role in the latter function, regulating the affective response to highly palatable, energy-dense foods such as those containing fat and sugar. It has been shown previously that stimulation of mu opiate receptors within the ventral striatum increases intake of palatable food. In the present study, we examined enkephalin peptide gene expression within the striatum in rats that had been given restricted daily access to an energy-dense, palatable liquid food, chocolate Ensure(R). Rats maintained on an ad libitum diet of rat chow and water were given 3-h access to Ensure(R) daily for two weeks. One day following the end of this period, preproenkephalin gene expression was measured with quantitative in situ hybridization. Compared with control animals, rats that had been exposed to Ensure(R) had significantly reduced enkephalin gene expression in several striatal regions including the ventral striatum (nucleus accumbens), a finding that was confirmed in a different group with Northern blot analysis. Rats fed this regimen of Ensure(R) did not differ in weight from controls. In contrast to chronic Ensure(R), acute ingestion of Ensure(R) did not appear to affect enkephalin peptide gene expression. These results suggest that repeated consumption of a highly rewarding, energy-dense food induces neuroadaptations in cognitive-motivational circuits.