Acute and chronic stress increase salivary cortisol: a study in the real-life setting of a national examination undertaken by medical graduates.

Spanish medical graduates who apply for a medical specialty training position (MIR) must take an examination that will shape their future personal and professional lives. Preparation for the test represents an important stressor that persists for several months. The aim of this study was to elucidate the stress pattern of this group and evaluate possible changes in the circadian rhythm of cortisol release in medical graduates preparing for this test. A repeated-measures longitudinal study was performed, measuring the salivary cortisol concentrations in 36 medical graduates (13 males and 23 females; mean age of 24.2 years) on five sampling days. Five cortisol samples were collected from 07:00 to 21:00 h in order to monitor changes in the circadian rhythm. On all sampling days (except on the day of the official examination), anxiety and psychological stress were evaluated with the Spanish versions of the State-Trait Anxiety Inventory (STAI) and the Perceived Stress Scale (PSS). During the study period, participants showed higher levels of anxiety than the Spanish reference population as well as a progressive increase in self-perceived stress. A significant increase in salivary cortisol concentration was observed in both chronic (study and examination preparation) and acute (examinations) situations. Our results suggest that the cortisol awakening response (CAR) may be a good indicator of anticipatory stress but is unaffected by long-term examination preparation. Comparison of results between the official examination day and the mock examination days yielded evidence that learning may modulate the behavior of the hypothalamic-pituitary-adrenal axis.

A simple mathematical model that describes the growth of the area and the number of total and viable cells in yeast colonies.

UNLABELLED: We propose a model, based on the Gompertz equation, to describe the growth of yeasts colonies on agar medium. This model presents several advantages: (i) one equation describes the colony growth, which previously needed two separate ones (linear increase of radius and of the squared radius); (ii) a similar equation can be applied to total and viable cells, colony area or colony radius, because the number of total cells in mature colonies is proportional to their area; and (iii) its parameters estimate the cell yield, the cell concentration that triggers growth limitation and the effect of this limitation on the specific growth rate. To elaborate the model, area, total and viable cells of 600 colonies of Saccharomyces cerevisiae, Debaryomyces fabryi, Zygosaccharomyces rouxii and Rhodotorula glutinis have been measured. With low inocula, viable cells showed an initial short exponential phase when colonies were not visible. This phase was shortened with higher inocula. In visible or mature colonies, cell growth displayed Gompertz-type kinetics. It was concluded that the cells growth in colonies is similar to liquid cultures only during the first hours, the rest of the time they grow, with near-zero specific growth rates, at least for 3 weeks. SIGNIFICANCE AND IMPACT OF THE STUDY: Mathematical models used to predict microbial growth are based on liquid cultures data. Models describing growth on solid surfaces, highlighting the differences with liquids cultures, are scarce. In this work, we have demonstrated that a single Gompertz equation describes accurately the increase of the yeast colonies, up to the point where they reach their maximum size. The model can be used to quantify the differences in growth kinetics between solid and liquid media. Moreover, as all its parameters have biological meaning, it could be used to build secondary models predicting yeast growth on solid surfaces under several environmental conditions.

A mesoscopic stochastic model for the specific consumption rate in substrate-limited microbial growth.

The specific consumption rate of substrate, as well as the associated specific growth rate, is an essential parameter in the mathematical description of substrate-limited microbial growth. In this paper we develop a completely new kinetic model of substrate transport, based on recent knowledge on the structural biology of transport proteins, which correctly describes very accurate experimental results at near-zero substrate concentration values found in the literature, where the widespread Michaelis-Menten model fails. Additionally, our model converges asymptotically to Michaelis-Menten predictions as substrate concentration increases. Instead of the single active site enzymatic reaction of Michaelis-Menten type, the proposed model assumes a multi-site kinetics, simplified as an apparent all-or-none mechanism for the transport, which is controlled by means of the local substrate concentration in the close vicinity of the transport protein. Besides, the model also assumes that this local concentration is not equal to the mean substrate concentration experimentally determined in the culture medium. Instead, we propose that it fluctuates with a mostly exponential distribution of Weibull type.

Growth kinetics and physiological behavior of co-cultures of Saccharomyces cerevisiae and Kluyveromyces lactis, fermenting carob sugars extracted with whey.

Alcoholic fermentation of carob waste sugars (sucrose, glucose and fructose) extracted with cheese whey, by co-cultures of Saccharomyces cerevisiae and Kluyveromyces lactis has been analyzed. Growth and fermentation of S. cerevisiae in the carob-whey medium showed an inhibition of about 30% in comparison with water-extracted carob. The inhibition of K. lactis on carob-whey was greater (70%) when compared with the whey medium alone, due to osmolarity problems. Oxygen availability was a very important factor for K. lactis, influencing its fermentation performance. When K. lactis was grown alone on carob-whey medium, lactose was always consumed first, and glucose and fructose were consumed afterwards, only at high aeration conditions. In co-culture with S. cerevisiae, K. lactis was completely inhibited and, at low aeration, died after 3 days; at high aeration this culture could survive but growth and lactose fermentation were only recovered after S. cerevisiae became stationary. To overcome the osmolarity and K. lactis' oxygen problems, the medium had to be diluted and a sequential fermentative process was designed in a STR-3l reactor. K. lactis was inoculated first and, with low aeration (0.13vvm), consumed all the lactose in 48h. Then S. cerevisiae was inoculated, consuming the total of the carob sugars, and producing ethanol in a fed-batch regime. The established co-culture with K. lactis increased S. cerevisiae ethanol tolerance. This fermentation process produced ethanol with good efficiency (80g/l final concentration and a conversion factor of 0.4g ethanol/g sugar), eliminating all the sugars of the mixed waste. These efficient fermentative results pointed to a new joint treatment of agro-industrial wastes which may be implemented successfully, with economic and environmental sustainability for a bioethanol industrial proposal.

Reversible loss of affinity induced by glucose in the maltose-H+ symport of Saccharomyces cerevisiae.

Glucose represses and inactivates maltose transport in Saccharomyces cerevisiae. The inactivation has been described as an irreversible process involving proteolysis. We have studied the inactivation of the maltose-H+ symport in this yeast and have observed that the mechanism of inactivation depends on the physiological conditions. In resting cells there was a decrease in transport capacity. The rate of decrease was enhanced nonspecifically by the presence of a sugar, glucose being more effective than maltose. In growing cells, glucose induced a decrease in affinity of the H+-symport which could be recovered by starvation, even in the presence of cycloheximide; there was no loss in capacity or, if present, this loss could be explained fully by the dilution due to repression during growth on glucose. We submit that in growing cells inactivation consists in a reversible modification of the permease not involving proteolysis.

A model of the specific growth rate inhibition by weak acids in yeasts based on energy requirements.

Zygosaccharomyces bailii, a spoilage yeast, capable of metabolic activity in food environments with low pH, low a(w) and in the presence of weak acid preservatives was chosen for a study on the effect of benzoic acid on growth parameters. In batch cultures, under controlled pH, this food preservative inhibited growth, decreasing the specific growth rate (mu) and the yield coefficient (Y(S)) on glucose. Data obtained at pH 3.5, 4.0 and 4.5 showed that this inhibition was exclusively promoted by the undissociated form of the acid since the effect was independent of pH when the concentration of the acid was expressed in this form. Moreover, the relationship between the values for mu and Y(S), provided evidence that the specific consumption rate of glucose (q(S)) was not affected by benzoic acid, indicating that the inhibition of growth should be completely explained by a decrease of Y(S). The outcome of parallel experiments performed in continuous culture was that the decrease of Y(S) was due to an increase of the maintenance coefficient (m), defined as the fraction of q(S) diverted from growth to cope with stress, represented in this case by the presence of the preservative. Based on these results a model was built, assuming that m increased hyperbolically with the concentration of benzoic acid, from zero in the absence of the acid up to q(S) when growth was completely inhibited. The concentration of the acid, for which m=q(S)/2, is a constant (K(W)), and represents a measure of the tolerance for a preservative, in this case benzoic acid. The simple equation mu/mu(0)=1+W/K(W) predicts the value of mu for a concentration (W) of the preservative, requiring the knowledge of two parameters: the specific growth rate in the absence of the preservative (mu(0)) and K(W). The equation fitted very well the data of the effect of benzoic acid on the specific growth rate of Z. bailii, having K(W)=0.96 mM benzoic acid. The model was also validated with other spoilage yeasts grown in the presence of benzoic acid in microtiter plates in an automated spectrophotometer. The values obtained for K(W) under these conditions confirm Z. bailii as the most tolerant (K(W)=2.1 mM) followed by Pichia sp. (K(W)=0.78 mM), Saccharomyces cerevisiae (K(W)=0.53 mM) and Debaryomyces hansenii (K(W)=0.11 mM).

Kinetic and Energetic Parameters of Carob Wastes Fermentation by Saccharomyces cerevisiae: Crabtree Effect, Ethanol Toxicity, and Invertase Repression.

Carob waste is a useful raw material for the second-generation ethanol because 50% of its dry weight is sucrose, glucose, and fructose. To optimize the process, we have studied the influence of the initial concentration of sugars on the fermentation performance of Saccharomyces cerevisiae. With initial sugar concentrations (S0) of 20 g/l, the yeasts were derepressed and the ethanol produced during the exponential phase was consumed in a diauxic phase. The rate of ethanol consumption decreased with increasing S0 and disappeared at 250 g/l when the Crabtree effect was complete and almost all the sugar consumed was transformed into ethanol with a yield factor of 0.42 g/g. Sucrose hydrolysis was delayed at high S0 because of glucose repression of invertase synthesis, which was triggered at concentrations above 40 g/l. At S0 higher than 250 g/l, even when glucose had been exhausted, sucrose was hydrolyzed very slowly, probably due to an inhibition at this low water activity. Although with lower metabolic rates and longer times of fermentation, 250 g/l is considered the optimal initial concentration because it avoids the diauxic consumption of ethanol and maintains enough invertase activity to consume all the sucrose, and also avoids the inhibitions due to lower water activities at higher S0.

Ethanol challenge alters amino acid neurotransmitter release from frontal cortex of the aged rat.

In two groups of male rats having an average age of either 90 days or two years, guide cannulae for bilateral push-pull perfusion were implanted stereotaxically to rest upon the superficial frontal cerebral cortex. On post-operative recovery, either 1.5 or 3.0 g/kg 20% ethanol (V/V) was given by intragastric gavage to each unrestrained rat. Sequential samples of venous blood were obtained from the tail and analyzed for alcohol levels by gas chromatography. A set of push-pull perfusions of the cortical sites was carried out with an artificial CSF before gavage and at 25, 50 and 150 min after the administration of ethanol. An individual perfusion was continued for 5.0 min at a rate of 25 microliters/min. Using high performance liquid chromatography with electrochemical detection (HPLC-EC) each sample of perfusate was then assayed for its content of glutamate (Glu), aspartate (Asp), glutamine (Gln), glycine (Gly), taurine (Tau) and GABA with homoserine used as the internal standard. The results showed that the 3.0 g/kg dose of ethanol resulted in a higher level of blood ethanol in the older animals, which persisted over the 150 min time interval. Further, the 1.5 g/kg dose of ethanol administered to the older rats reduced the cortical activity of Glu and Gln relative to the younger animals. In addition, the 3.0 g/kg dose augmented the cortical efflux of Tau in the aged rats. Neither dose of ethanol affected the efflux of Asp or Gly from the perfused frontal cortex of either the young or old group, nor was the release of GABA detectable under either the control condition or following treatment with ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo analysis of cortical amino acid neurotransmitters collected in the rat by a new double lumen push-pull catheter system.

The release of both endogenous and newly synthesized amino acid neurotransmitters was examined simultaneously in different areas of the cerebral cortex in the freely moving rat. An array of push-pull guide tubes was implanted permanently to rest above the frontal, parietal, temporal and occipital areas of the cortex of each rat. Then a new double-lumen catheter system, specially adapted for localized push-pull perfusion of the conscious animal, was used to perfuse an artificial cerebrospinal fluid at each cortical site. For the new synthesis experiments, 0.5 microCi of [14C]glucose in a volume of 2.0 microliter was first microinjected into the perfusion site as a precursor to label amino acids. After the site was perfused at a rate of 12.0 microliter/min, each of the samples was assayed by two-dimensional thin-layer chromatography. In a second analysis, the content of six endogenous amino acids present in unlabeled samples of push-pull perfusate was quantified by high-performance liquid chromatography analysis with electrochemical detection. The results showed a notable homogeneity among each of the four cortical areas in the content of four of the six amino acids examined. Endogenous glutamine exhibited the highest proportional content in the cortical perfusates, whereas glutamic acid was proportionally higher in terms of new synthesis. An anatomical analysis revealed that the level of endogenous glutamic acid in the frontal area was significantly lower than that found in the occipital or temporal regions of the rat's cortex. An opposite result was obtained when the proportional synthesis of glutamic acid from [14C] glucose was compared in different cortical regions in that a statistically higher release occurred in the frontal than in the occipital cortex.

Quantitative and ultrastructural changes in glia and pericytes in the parietal cortex of the aging rat.

The frequency of astrocytes, microglia plus oligodendrocytes, and pericytes displaying nuclei was analyzed and quantified in 160-microm-wide strips of the parietal cortex (Par1 region) from young and aged Wistar rats. The study was performed on two groups of rats aged 3-4 and 32-36 months. Quantifications of the glial cell types and pericytes were made in 1-microm-thick sections stained with toluidine blue. Ultrathin sections were also made to analyze the ultrastructural features of these cells during aging. Astrocytes and pericytes increased in number by about 20% and 22%, respectively, with age. These increases were most significant in layers II-IV and V for both cellular types. Clusters of astrocytes were common in these layers of aging rats. The ultrastructural analysis also indicated changes in all cell types that stored inclusions and vacuoles with age, which were particularly abundant in microglial cells. End-feet astrocytes and pericytes surrounding the vascular wall also contained vacuoles and inclusions, and consequently the vascular wall increased in thickness. In conclusion, the aging process increased astrocyte and pericyte populations, but not microglia plus oligodendrocyte populations, in the rat parietal cortex. Although no significant change in nuclear size could be observed in any cell type, all glial cells as well as pericytes underwent morphological ultrastructural changes. These modifications may result from the need to correct possible homeostatic imbalances during aging.

Cortical amino acid neurotransmitter release is altered by CCK perfused in frontal region of unrestrained aged rats.

The purpose of this study was to investigate in the aged animal the functional interaction between cholecystokinin (CCK) and amino acid neurotransmitter activity in the frontal cortex, a structure of importance in age-related disabilities. Guide cannula for repeated push-pull perfusion were implanted bilaterally in the superficial frontal cortex of male Sprague-Dawley rats. Two groups of animals were selected on the basis of their age at the time of stereotaxic surgery: 90 days and two years. Following post-operative recovery, an artificial CSF solution was perfused repeatedly within the cortex of each animal for a 5.0 min interval. The rate of perfusion was 25 microliters/min and a 5.0 min period elapsed between the collection of each sample of perfusate. After the initial control perfusions, CCK octapeptide was incorporated in a concentration of 6.0 or 18.0 ng/microliter in the CSF and perfused for 5.0 min under identical conditions. Each sample of perfusate was assayed by high performance liquid chromatography with electrochemical detection (HPLC-EC) for its content of glutamate (Glu), aspartate (Asp), glutamine (Gln), glycine (Gly), taurine (Tau) and gamma-amino-butyric acid (GABA) with homoserine used as an internal standard. Although CCK in the lower 6.0 ng/microliter concentration failed to alter significantly the profile of amino acids in the frontal cortex, the higher 18.0 ng/microliter solution of CCK enhanced the efflux of Glu as well as Asp, but only in the aged rats. Both concentrations of CCK tended also to augment the release of Gln in the older animals but these changes were not statistically significant. Both Gly and Tau were unaffected by CCK in either dose in both the young and old groups. GABA was not detectable in any of the samples of perfusate throughout the experiments. These results suggest that CCK-8 exerts a selective effect on amino acid neurotransmitter activity in the frontal cortex which is clearly age-dependent. In the older animal, this sensitivity of the cortical cells to CCK may reflect a functional attribute of the peptide in the aging process.

Neurotensin perfused in hypothalamus of sated or fasted rat: HPLC analysis of release of DA, NE and 5-HT and their metabolites.

This investigation was undertaken in the unrestrained rat to determine the localized effect of neurotensin (NT) on the profile of release and turnover of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) within the hypothalamus. Following stereotaxic implantation of a permanent guide tube, artificial CSF was perfused in the hypothalamus of the freely moving animal by means of push-pull cannulae at a rate of 20 microliters/min and for an interval of 5.0 min. After three 5.0 min control samples were collected, NT in a concentration of 0.1 micrograms/microliter was perfused followed by additional CSF controls. Assay by HPLC-EC of each perfusate showed that when the rat was sated, NT evoked a significant increase in the release of DA and DOPAC from the hypothalamus as well as augmented NE turnover, as reflected by a significant efflux in MHPG. However, when the rat was fasted for 22 hr, the perfusion of NT reduced DA and DOPAC concentrations in the diencephalic perfusate significantly as well as levels of both MHPG and VMA. Under both sated and fasted conditions, NT failed to produce notable changes in the release of 5-HT or its metabolism to 5-HIAA. These findings thus reveal a functional interaction between NT and both of the catecholamine neurotransmitters within hypothalamic neurons, which is clearly dependent upon the nutritional status of the animal.

The inactivation of hexokinase activity does not prevent glucose repression in Candida utilis.

High hexokinase activity was not related to glucose repression in Candida utilis IGC 3092. The addition of Cibacron Blue 3G-A to growing cells in batch culture led to a permanent in vivo hexokinase inactivation, decreased growth rate and inhibited alcohol dehydrogenase. Hexokinase inactivation up to 90% did not alleviate glucose repression of alpha-glucosidase, as has been described for Saccharomyces cerevisiae and other yeasts. Moreover, when cells were physiologically derepressed by growing them in a chemostat at low glucose concentrations, the highest hexokinase activity was shown by the derepressed cells, and decreased as repression increased. Thus, in our strain of C. utilis, hexokinase activity was inversely proportional to glucose repression.

Rapid method for micro-analysis of endogenous amino acid neurotransmitters in brain perfusates in the rat by isocratic HPLC-EC.

A simplified method is described for the isocratic analysis of endogenous amino acid neurotransmitters contained in brain perfusates by high performance liquid chromatography (HPLC) with electrochemical detection (EC). Pre-column o-phthalaldehyde (OPA) tert-butylthiol derivatives of the amino acids were injected into a C18 3 microns column. After linear concentration curves for standard solutions were obtained, the content of 6 amino acid neurotransmitters was analyzed in push-pull perfusates obtained from the hypothalamus and cerebral cortex of the unrestrained rat. Each analysis which included the simultaneous quantification of aspartic acid, glutamic acid, glutamine, glycine, taurine and gamma-aminobutyric acid (GABA), was completed in less than 15 min. The sensitivity of the assay ranged from 1.0 to 5.0 pmol of each amino acid contained within a 20 microliters aliquot of each perfusion sample.

Decrease in cytosolic Aspartyl-aminopeptidase but not in Alanyl-aminopeptidase activity in the frontal cortex of the aged rat.

To test the neurotoxic hypothesis of excitatory amino acids, we evaluated the possible contribution to the free acidic amino acid pool of Aspartyl-aminopeptidase activity in the frontal cortex of adult (3 month old) and aged rats (3 groups of animals aged 26, 29 and 33 months). Aspartyl-aminopeptidase activity showed a significant decrease in the oldest rats (29 and 33 months old) whereas the activity of Alanyl-aminopeptidase, an unspecific enzyme, did not change with age. These data invalidate the idea that excess free acidic amino acids are released by aminopeptidases in the aged rat but do provide evidence of age-related changes in this enzymatic activity. The possible implications of our findings for general alterations in protein degradation are discussed.

Profile of NE, DA and 5-HT activity shifts in medial hypothalamus perfused by 2-DG and insulin in the sated or fasted rat.

This study was carried out in the unrestrained rat to determine the nature of the in vivo profile of monoamine neurotransmitters within the medial hypothalamus in response to the presence of a glucoprivic or metabolic challenge to neurons within this region. In these experiments, insulin or 2-deoxy-D-glucose (2-DG) was applied locally to the paraventricular nucleus (PVN), dorsomedial nucleus (DMN) and ventromedial hypothalamus (VMH). In each of 11 Sprague-Dawley rats, a guide cannula was implanted stereotaxically to rest just above these structures. Upon recovery, a concentric push-pull cannula system was used to perfuse an artificial CSF within a medial hypothalamic site. The CSF was perfused at a rate of 20 microliters/min with a 5.0 min interval intervening between the collection of each 100 microliters sample. After the rat was fasted for 20-22 hr, either 10 micrograms/microliters 2-DG or 4.0 mU/microliters of insulin was incorporated into the control CSF medium and perfused at the same locus. The aliquots of hypothalamic perfusate were assayed by high performance liquid chromatography with electrochemical detection (HPLC-EC) for the respective concentration in pg/microliter of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and each of their major metabolic products. When the rat was sated, 2-DG enhanced significantly the mean efflux of NE from the medial hypothalamus in comparison to control CSF values. However, under the fasted condition, 2-DG augmented the turnover of both the catecholamine and 5-HT as reflected by elevated levels of MHPG and 5-HIAA, respectively. On the other hand, insulin perfused within the same medial hypothalamic sites evoked a significant increase in the synthesis and release of DA from the sated rat, but did not alter its turnover. Following the interval of fast, insulin produced no immediate alteration in transmitter activity; however, in the interval following insulin's perfusion, DA and 5-HT turnover were enhanced while the efflux of 5-HT was suppressed. An analysis of the proportional values of the levels of the amines to each other revealed marked shifts in the relationships between the catechol- and indoleamine transmitters following local perfusion with both 2-DG and insulin. Overall, NE synthesis and turnover exceeded that of 5-HT following 2-DG, whereas DA predominated over NE and 5-HT during insulin's perfusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Evoked GABA release is not mediated by N-type VDCC in the frontal cortex of awake rats: effects of neomycin.

The purpose of the present study was to analyze the Ca2+ channel involved in GABA release under resting and K(+)-evoked conditions in vivo. We used microdialysis to investigate the effects of the voltage-dependent calcium channel (VDCC) blockers neomycin, kanamycin, and omega-conotoxin GVIA, and the voltage-dependent Na+ channel blocker tetrodotoxin, in the frontal cortex of awake rats. The GABA content in frontal dialysates was analyzed by high performance liquid chromatography coupled to fluorescence detection. Basal GABA release was kanamycin, omega-conotoxin, and tetrodotoxin resistant, whereas neomycin induced a significant increase from the basal level. The K(+)-evoked release of GABA was kanamycin and omega-conotoxin resistant, but tetrodotoxin sensitive. The effects of neomycin were masked by the action of this drug on basal release. These results suggest that neomycin may affect GABA release in the frontal cortex through a mechanism independent of VDCC. In addition, the K(+)-evoked release of GABA in this cortical area was not mediated by the N-type voltage-dependent calcium channels, but was dependent on neural activity or TTX sensitive.

Putative amino acid neurotransmitters and the nucleus dorsomedialis thalamus-prefrontal cortex pathway in the rat.

Endogenous levels of putative amino acid neurotransmitters (glycine, glutamic acid, aspartic acid, and GABA) in medial and sulcal prefrontal cortex of the rat were analyzed using gas liquid chromatography. No changes were found in the levels of these amino acids in medial and sulcal prefrontal cortex after lesion of the nucleus dorsomedialis of the thalamus suggesting, therefore, that the NDMT-prefrontal cortex pathway is not mediated by these amino acids.

Cerebral cortex and amino acid neurotransmitters: higher levels of aspartic acid but not GABA in the frontal cortex of the rat.

Endogenous levels of Aspartic acid, GABA and Glutamic acid plus Glutamine were measured in the frontal, occipital, temporal and parietal cortex. Aspartic acid levels were found higher in the frontal cortex than in the rest of the cortical areas studied. GABA, however, had a homogenous distribution among all cortical areas.

CCK and other peptides modulate hypothalamic norepinephrine release in the rat: dependence on hunger or satiety.

The purpose of this investigation was to determine the functional relationship between putative satiety peptides and endogenous norepinephrine (NE) activity in the hypothalamus. Permanent guide cannulae for push-pull perfusion were implanted stereotaxically in Sprague-Dawley rats so as to rest above the medial or lateral hypothalamus (LH). Post-operatively, the animals were either satiated with food and water, both available ad lib, or fasted for 18-22 hr prior to an experiment. To perfuse a site in the LH, paraventricular (PVN) or ventromedial nucleus (VMN), a concentric 29-23 ga push-pull cannula system was lowered to a pre-determined site, in most cases after catecholamine stores had been pre-labeled with [3H]-NE. During control tests, an artificial CSF was perfused at a rate of 20-25 microliter/min for 5-8 min with a 5 min interval between each sample. The addition of cholecystokinin (CCK) in a concentration of 2.0-6.0 ng/microliter to the CSF perfused in PVN or VMN of the satiated rat enhanced the efflux of NE; however, in the fasted animal CCK often suppressed the catecholamine's release. Perfused in the LH, CCK exerted opposite effects, typically augmenting NE output when the rat was fasted but not affecting the amine's activity during the sated condition. Proglumide (1.2 micrograms/microliter) attenuated CCK's effect in releasing NE when the antagonist was perfused in the PVN of the satiated rat. Similar experiments in which neurotensin (NT) was perfused in the LH, PVN and VMN revealed virtually the same inverse effects on NE release in the fasted and satiated rat, which again were anatomically specific. Finally, insulin and 2-deoxy-D-glucose (2-DG) exerted similar state-dependent effects on the release of NE within LH and PVN. Overall, the results suggest that CCK or other neuroactive peptide could serve as a "neuromodulator" of the pre-synaptic release of NE within classical hypothalamic structures which are thought to underlie both hunger and satiety. The state-dependent nature of the peptides' activity on the noradrenergic feeding mechanism implies that these substances constitute a pivotal portion of the profile of factors which impinge functionally upon the hypothalamic neurons responsible for the feeding response and its cessation.