Nutrient balance in humans: effects of diet composition

The purpose of this study was to examine the effect of alterations in diet composition on energy expenditure and nutrient balance in humans. Eight adults (three men, five women) ate a high-carbohydrate (60% of calories from carbohydrate) and a high-fat (60% of calories from fat) diet for 7 d each according to a randomized, crossover design. Six subjects were studied for an additional week on a mixed diet (45% of calories from fat). For each subject, total caloric intake was identical on all diets and was intended to provide the subject's maintenance energy requirements. All subjects spent days 3 and 7 of each week in a whole-room indirect calorimeter. Diet composition did not affect total daily energy expenditure but did affect daily nutrient oxidation by rapidly shifting substrate oxidation to more closely reflect the composition of the diet. These results show that diet composition can affect substrate oxidation without producing measurable effects on total energy expenditure.

Effect of the 5-HT1A receptor agonist 8-OH-DPAT on the release of 5-HT in dorsal and median raphe-innervated rat brain regions as measured by in vivo microdialysis

Recent electrophysiological studies, measurements of 5-HT synthesis and in vivo voltammetry recordings of 5-HT metabolism have suggested that serotoninergic neurones in the median raphe (MR) are less sensitive to 5-HT1A autoreceptor stimulation relative to those in the dorsal raphe (DR). To further study the putative differences in regulation between ascending 5-HT projections from the raphe nuclei we have used microdialysis to measure the release of 5-HT in ventral hippocampus, globus pallidus, dorsal hippocampus, frontal cortex, nucleus accumbens and medial septum, following systemic administration of the specific 5-HT1A agonist 8-OH-DPAT. The results show that the baseline output of 5-HT was similar in each of the areas studied. While 8-OH-DPAT decreased dialysate levels of 5-HT in all areas, the inhibition of 5-HT release seen in globus pallidus was significantly less marked compared to that observed in the other five regions. The results indicate that 5-HT1A autoreceptor-mediated control of 5-HT release is functional in all of the brain areas studied, including those receiving a preferential 5-HT innervation from the DR and MR. We find little evidence in support of the idea that brain 5-HT neuronal projections are heterogenous with respect to 5-HT1A autoreceptor regulation of 5-HT release; the globus pallidus, however representing a possible exception to this.

Application of brain microdialysis to study the pharmacology of the 5-HT1A autoreceptor

5-Hydroxytryptamine (5-HT) receptors of the 5-HT1A subtype are localized on serotoninergic cells and dendrites in the raphe nuclei of the brain stem and are believed to regulate synaptic 5-HT release through an inhibitory influence on serotoninergic impulse flow. The effects of 5-HT1A agonists on 5-HT release can, therefore, only be detected by measurement of 5-HT release from intact serotoninergic neurones. Here we review the evidence that the microdialysis technique, when applied to the anaesthetized rat, is able to detect extracellular 5-HT in the brain which derives from serotoninergic neurones and changes in accordance with serotoninergic neuronal activity. We have observed that a range of 5-HT1A agonists, including 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), inhibit 5-HT release in hippocampus, most probably by acting on somatodendritic 5-HT1A autoreceptors in the dorsal raphe nucleus. The inhibitory action of 8-OH-DPAT and several other selective 5-HT1A receptor active drugs on 5-HT release is sensitive to pindolol, further supporting the idea that the 5-HT receptor being measured is of the 5-HT1 subtype. Two drugs, BMY 7378 and NAN-190, which show 5-HT1A antagonist properties in certain models, reduce 5-HT release indicating that they have mixed agonist/antagonist actions at the 5-HT1A receptor. Our data indicate that measurement of 5-HT release in rat brain using the microdialysis technique may be a useful method to probe the pharmacology of the 5-HT1A autoreceptor in vivo.

Behavioural evidence for a functional interaction between central 5-HT2 and 5-HT1A receptors

1. The possibility of 5-HT2 receptor modulation of central 5-HT1A receptor function has been examined using the 5-hydroxytryptamine (5-HT) behavioural syndrome induced by 5-HT1A receptor active drugs in rats. 2. The 5-HT2/5-HTIC antagonist ritanserin (0.1-2 mg kg-1) increased the 5-HT behavioural syndrome induced by submaximally effective doses of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) and gepirone. 3. Pretreatment with the 5-HT2/5-HT1C antagonist ICI 170,809 (0.25-5 mg kg-1) also enhanced the behavioural syndrome induced by 8-OH-DPAT or 5-MeODMT. 4. The 5-HT2/alpha 1-adrenoceptor antagonist ketanserin in a low dose (0.25 mg kg-1) significantly increased the 5-HT behavioural syndrome induced by 8-OH-DPAT or 5-MeODMT, while in a higher dose (2.5 mg kg-1) this drug decreased the response. Experiments with prazosin indicate that the higher dose of ketanserin might reduce the 5-HT behavioural syndrome through blockade of alpha 1-adrenoceptors. 5. Ritanserin and ICI 170,809 had no effect on apomorphine-induced stereotypy or hyperactivity, indicating that these drugs do not produce non-specific behavioural activation. 6. Ritanserin and ICI 170,809 inhibited quipazine-induced wet dog shakes at doses similar to those enhancing the 5-HT behavioural syndrome. 7. We suggest that ritanserin, ICI 170,809 and ketanserin enhance 5-HT1A agonist-induced behaviour through blockade of an inhibitory 5-HT2 receptor regulating or coupled to 5-HT1A receptor-mediated function.

Changes in blood lipids during six days of overfeeding with medium or long chain triglycerides

Although medium chain triglyceride (MCT) is less calorically dense than long chain triglyceride (LCT), it produces a greater thermic effect following ingestion. We hypothesized that the previously observed high rate of thermogenesis produced by MCT overfeeding was due to hepatic de novo synthesis of long chain fatty acids (LCFA) from the excess medium chain fatty acids (MCFA). To study this, we compared the effects of overfeeding MCT- and LCT-containing diets on blood lipid profiles. Ten in-patient, nonobese males were overfed (150% of estimated energy requirements) two formula diets for 6 days each, in a randomized crossover design. Diets differed only in the composition of the fat and contained either 40% of energy as MCT or LCT (soybean oil). The major differences between diets in the resulting pattern of blood lipids were: 1) a reduction in fasting serum total cholesterol concentrations with the LCT, but not the MCT diet; and 2) a threefold increase in fasting serum triglyceride concentrations with MCT, but not LCT, diet. Moreover, 10% of the fasting triglyceride fatty acids were medium chain and 40% were 16:0 with the MCT diet. This compared to 1% and 20% for medium chain and 16:0, respectively, with the LCT diet. In addition, there were increases in 16:1, 18:0, and 18:1 in the triglycerides during MCT feeding. The changes in fatty acids in triglycerides with MCT feeding are consistent with the hypothesis that excess dietary MCT cause a significant increase in the hepatic synthesis of these fatty acids from MCFA through de novo synthesis and/or chain elongation and desaturation. These processes could account for the higher rate of postprandial thermogenesis with MCT as compared to LCT.

cis-(+)-8-OH-1-CH3-DPAT, (+)ALK-3, a novel stereoselective pharmacological probe for characterizing 5-HT release-controlling 5-HT1A autoreceptors. An in vivo brain microdialysis study

The somatodendritic 5-HT1A autoreceptor regulating 5-HT neuronal activity is currently poorly defined pharmacologically because there are no specific antagonists, but also because potent and stereoselective agonists are scarce. Moreover, there have been few, if any, attempts to specifically investigate structure-activity relationships for agonists acting at this site. Employing brain microdialysis techniques, we have examined the effects of the enantiomers of cis-8-hydroxy-1-methyl-2-(di-n-propylamino)tetralin (ALK-3; 0.01-0.3 mg/kg s.c.), its trans-1-methyl analogue (ALK-4; 0.3 mg/kg s.c.) and the pure enantiomers of the parent compound--8-OH-DPAT (0.3 mg/kg s.c.)--in an attempt to address stereochemical agonist structure-activity requirements of 5-HT release-controlling 5-HT1A autoreceptors in brain. The cis-1-methylated 8-OH-DPAT analogue (+)ALK-3 was comparable to the parent compound in reducing the 5-HT output from rat ventral hippocampus. In comparison, both (-)ALK-3 and the racemic trans-diastereomer to ALK-3, ALK-4, were inactive, while the two stereoisomers of 8-OH-DPAT strongly reduced 5-HT release. Pretreatment with (-)pindolol (8 mg/kg s.c.), which has high affinity for 5-HT1A radioligand binding sites, blocked the reduction of hippocampal 5-HT release induced by a submaximally effective dose of (+)ALK-3. The direct intrahippocampal administration of (+)ALK-3 (10 microM) via the perfusion medium did not affect 5-HT output. In summary, the data indicate that (+)ALK-3, like 8-OH-DPAT, is a very potent 5-HT receptor agonist which inhibits terminal 5-HT release in rat hippocampus, probably via activation of somatodendritic 5-HT1A autoreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Further investigation of the in vivo pharmacological properties of the putative 5-HT1A antagonist, BMY 7378

The present study examined the actions of the putative 5-HT1A antagonist BMY 7378 on central pre- and postsynaptic 5-HT1A function in the rat in vivo. Unlike the direct acting 5-HT1A agonist 8-hydroxy-2-(di-n-pro-pylamino)tetralin (8-OH-DPAT), BMY 7378 (0.25-5 mg/kg s.c.) did not induce the full postsynaptically mediated 5-HT behavioural syndrome (forepaw treading, head weaving, flat body posture hindlimb abduction). Indeed, the maximal 5-HT behavioural syndrome scores of BMY 7378 were about 10% of those for 8-OH-DPAT. Following pretreatment, however, BMY 7378 dose dependently (0.25-5 mg/kg s.c.) reduced to undetectable levels forepaw treading and head weaving induced by 8-OH-DPAT (0.75 mg/kg s.c.). BMY 7378 also inhibited stereotypy and locomotor activity induced by 0.5 mg/kg apomorphine although this effect was only statistically significant at the highest dose tested (5 mg/kg). In contrast to its apparent 5-HT1A antagonist properties in the behavioural experiments, BMY 7378 caused a marked and dose-dependent (0.01-1.0 mg/kg s.c.) decrease of 5-HT release in ventral hippocampus of the anaesthetized rat as detected by brain microdialysis. This effect of BMY 7378 had a similar onset and duration of action but with slightly reduced efficacy compared to that previously described for 8-OH-DPAT. As with 8-OH-DPAT, the inhibitory effect of BMY 7378 on 5-HT release was attenuated by pretreatment with the 5-HT1 receptor/beta-adrenoceptor antagonist pindolol (8 mg/kg s.c.) but not its counterpart propranolol (20 mg/kg s.c.). Pretreatment with a combination of the beta 1- and beta 2-adrenoceptor antagonists metoprolol (4 mg/kg s.c.) and ICI 118 551 (4 mg/kg s.c.), respectively, did not alter the 5-HT response to BMY 7378. From these data we conclude that BMY 7378 is a mixed agonist/antagonist at central 5-HT1A receptors.

Mixed agonist/antagonist properties of NAN-190 at 5-HT1A receptors: behavioural and in vivo brain microdialysis studies

1-(2-Methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine, NAN-190, is a novel compound with putative 5-HT1A antagonist properties. In the present study, the effects of NAN-190 were examined with regard to functional pre- and post-synaptic 5-HT1A receptor-mediated events, using in vivo brain microdialysis and behavioural techniques. Our findings provide evidence that NAN-190 acts as a mixed agonist/antagonist at central 5-HT1A receptors. Thus, NAN-190 blocked (+)8-OH-DPAT-induced behaviour in reserpinized rats, indicating antagonist properties at postsynaptic 5-HT1A receptors. However, the compound was also able to decrease the release of 5-HT in vivo, tentatively due to an agonist action at somatodendritic 5-HT1A autoreceptors. These data extend previous information on the pharmacological profile of NAN-190 and further emphasizes the difference between pre- and postsynaptic 5-HT1A receptors in brain.

Release of endogenous 5-hydroxytryptamine in rat ventral hippocampus evoked by electrical stimulation of the dorsal raphe nucleus as detected by microdialysis: sensitivity to tetrodotoxin, calcium and calcium antagonists

We have utilized the brain microdialysis technique in an attempt to measure excitation-secretion coupled release of endogenous 5-hydroxytryptamine in rat brain in vivo and investigated the pharmacology of the voltage-sensitive calcium channel involved in this process. All experiments were carried out using chloral hydrate anaesthetized rats. Ascending serotoninergic neurons were electrically stimulated using an electrode implanted into the dorsal raphe nucleus. A dialysis probe was implanted into the ventral hippocampus and continuously perfused with artificial cerebrospinal fluid containing the selective 5-hydroxytryptamine uptake inhibitor citalopram (1 microM). Twenty-minute perfusates were analysed for endogenous 5-hydroxytryptamine using high performance liquid chromatography with electrochemical detection. Electrical stimulation (cathodal monophasic 1 ms pulses, 300 microA, 2-10 Hz) of the dorsal raphe nucleus for 20 min induced an immediate release of 5-hydroxytryptamine which lasted for the duration of the stimulus and was frequency-dependent. The calculated amount of 5-hydroxytryptamine release per electrical impulse was constant over the frequency range used. Addition of tetrodotoxin (10 microM) to, or omission of calcium from, the perfusion medium reduced the spontaneous output of 5-hydroxytryptamine by 60-70% and caused a near complete inhibition of the effect of low frequency (3 Hz) electrical stimulation of the dorsal raphe nucleus. Local perfusion with cadmium (30 and 300 microM), which is reported to antagonize both N- and L-type voltage-sensitive calcium channels, also caused a pronounced decrease of basal output of 5-hydroxytryptamine and a marked, but not complete inhibition of the effect of nerve stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeated ECS enhances dopamine D-1 but not D-2 agonist-induced behavioural responses in rats

The present study examined the effect of acute and repeated administration of electroconvulsive shock (ECS) on behaviours induced by various dopamine agonists in rats. Components of behavioural arousal induced by the dopamine D-1 agonist SKF 38393, the dopamine D-2 agonist RU 24213 and the mixed D-1/D-2 agonist apomorphine were assessed using a behavioural check-list method. Also, the overall behavioural syndrome produced by these drugs was measured using rating scales. Rats receiving repeated (5 times over 10 days) but not a single ECS showed enhanced grooming and sniffing in response to SKF 38393 (7.5 mg/kg) when compared to controls. Repetitive sniffing induced by apomorphine (0.5 mg/kg) was also enhanced by repeated ECS. Neither repeated nor a single ECS significantly changed behaviours induced by RU 24213 (0.75 mg/kg), although a downward trend was evident. The behaviour rating scale measurements also demonstrated that repeated administration to ECS increased behavioural responsiveness to SKF 38393 and apomorphine but not RU 24213. These results suggest that the increase of dopamine-mediated behaviour in rats seen after chronic ECS relates to an increase in central dopamine D-1 receptor function.

Relatives' involvement in caring for the elderly mentally ill following long-term hospitalization

The involvement of relatives in patient care is frequently associated with 'good nursing practice'. However, according to recent literature it is a practice that is not widely adopted. The intention of this study was to ascertain the extent of relatives' involvement in caring for the elderly mentally ill, from both relatives' and nurses' perspectives. Following analysis of more than 130 questionnaires it was found that nursing staff responded very positively towards greater involvement of relatives wishing to encourage their participation. In comparison relatives felt that their role in patient care was negligible, but despite this did not wish to seek greater involvement. The discussion that follows examines possible reasons for these findings and the implications for future practice.

Partial postsynaptic 5-HT1A agonist properties of the novel stereoselective 8-OH-DPAT analogue (+)cis-8-hydroxy-1-methyl-2-(di-n-propylamino)tetralin, (+)ALK-3

The present study assessed the pharmacological activity of the stereoisomers of the novel 8-OH-DPAT analogue cis-8-hydroxy-1-methyl-2-(di-n-propylamino)tetralin, ALK-3, at postsynaptic 5-HT1A receptors involved in 5-HT-mediated behaviour. Reserpine-pretreated rats were injected with (+)8-OH-DPAT (0.03-1.0 mg/kg s.c.), (+)ALK-3 (0.3-10.0 mg/kg s.c.) or (-)ALK-3 (3.0-10.0 mg/kg s.c.), and components of the '5-HT behavioural syndrome' were scored. (+8-OH-DPAT dose dependently elicited forepaw treading, flattened body posture and hindlimb abduction. In this respect, (+)ALK-3 was significantly less efficacious although its behavioural action was prevented by pindolol (8 mg/kg s.c.), indicating that it was 5-HT1A receptor mediated. Following pretreatment, (+)ALK-3 dose dependently, but partially, attenuated the effect of (+)8-OH-DPAT. (-)ALK-3 did not elicit 5-HT behaviours per se, and only very weakly antagonized the behavioural actions of (+)8-OH-DPAT at the highest dose tried. Our data indicate that the (+) enantiomer of ALK-3 is a partial but stereoselective agonist at postsynaptic 5-HT1A receptors.

Pharmacological characterization of 8-OH-DPAT-induced inhibition of rat hippocampal 5-HT release in vivo as measured by microdialysis

1. We have previously found that the putative 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) decreases hippocampal 5-hydroxytryptamine (5-HT) release in the anaesthetized rat, as measured by brain microdialysis. The present study attempted to characterize the receptor involved in this response using a range of monoamine receptor antagonists. 2. The classical 5-HT receptor antagonists, metergoline (5 mg kg-1 s.c.), methysergide (10 mg kg-1 s.c.) and methiothepin (10 mg kg-1 s.c.) each reduced dialysate levels of 5-HT which complicated their use as antagonists in these experiments. Nevertheless, pretreatment with metergoline but not methiothepin and methysergide partially reduced the 5-HT response to a maximally effective dose of 8-OH-DPAT (0.25 mg kg-1 s.c.). 3. The mixed 5-HT 1/beta-adrenoceptor antagonist pindolol (8 mg kg-1 s.c.) was without effect on spontaneous 5-HT output but attenuated the effect of both maximally (0.25 mg kg-1 s.c.) and submaximally (0.05 mg kg-1 s.c.) effective dose of 8-OH-DPAT. In comparison, propranolol (10 mg kg-1 s.c.) did not affect 5-HT output when injected alone and did not alter the response to 8-OH-DPAT (0.25 mg kg-1 s.c.). 4. The 5-HT2 receptor antagonist ritanserin (0.2 mg kg-1 s.c.) and the 5-HT3 receptor antagonist BRL 43694 (0.5 mg kg-1 s.c.) neither altered 5-HT output alone nor significantly changed the response to 8-OH-DPAT (0.25 mg kg-1 s.c.). 5. The 8-OH-DPAT (0.25 mg kg-' s.c.) response was not affected by pretreatment with either the dopamine D2-receptor antagonist sulpiride (10mgkg-1 s.c.) or the alpha/alpha 2-adrenoceptor antagonist phentolamine (10mg kg-1 s.c.). 6. We conclude from these data that the decrease of hippocampal 5-HT output induced by 8-OHDPAT does not involve 5-HT2, 5-HT3, adrenoceptors or dopamine D2-receptors and that activation of a 5-HT1 class of receptor seems probable. Full classification of the 8-OH-DPAT response awaits development of a suitably selective 5-HT1 receptor antagonist with low intrinsic activity at the somatodendritic 5-HT autoreceptor.

Evaluation of an alternating-calorie diet with and without exercise in the treatment of obesity

This study examined the effects of calorie alternation and exercise on weight loss. Moderately obese women (130-160% of ideal body weight) were randomly assigned to an alternating- or constant-calorie diet with or without aerobic exercise. Both diets provided an average of 1200 kcal/d over a 12-wk period; daily intake of subjects in the alternating-diet condition varied in a prescribed pattern from 600 to 1800 kcal/d. Exercising subjects walked 5 d/wk. All subjects participated in an intensive outpatient behavior-modification program. At the end of the study, exercised subjects had greater reductions in body weight and body fat percentage than did nonexercised subjects. The type of caloric restriction did not affect weight or fat loss. Changes in resting metabolic rate did not differ among groups. Alternating calories was neither beneficial nor detrimental as a weight-loss strategy whereas exercise was clearly beneficial in weight-loss therapy.

In vivo measurement of extracellular 5-hydroxytryptamine in hippocampus of the anaesthetized rat using microdialysis: changes in relation to 5-hydroxytryptaminergic neuronal activity

The effect of manipulating the activity of central 5-hydroxytryptamine (5-HT) neurones on extracellular 5-HT in ventral hippocampus of the chloral hydrate-anaesthetized rat was studied using the brain perfusion method, microdialysis. Basal levels of 5-HT in the dialysates were close to the detection limits of our assay using HPLC with electrochemical detection. However, addition of the selective 5-HT reuptake inhibitor citalopram (10(-6) M) to the perfusion medium produced readily measurable amounts of dialysate 5-HT. Citalopram, therefore, was used throughout our experiments. Hippocampal dialysate levels of 5-HT sharply declined over the first hour after dialysis probe implantation, but then became constant. This stable output of 5-HT was reduced by 57% in rats treated 14 days previously with intracerebroventricular injections of the 5-HT neurotoxin 5,7-dihydroxytryptamine. Electrical stimulation (1-ms pulse width, 300 microA, 2-20 Hz) of the dorsal raphe nucleus for 20 min caused a rapid rise in hippocampal 5-HT output, which immediately declined on cessation of the stimulus and was frequency-dependent. Addition of tetrodotoxin (10(-6) M) to the perfusion medium reduced 5-HT levels to 75% of predrug values. Injection of the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (0.5 and 2.5 micrograms) into the dorsal raphe nucleus caused a dose-related fall in hippocampal output of 5-HT compared to saline-injected controls. We conclude from these data that the spontaneous output of endogenous 5-HT into hippocampal dialysates, measured under our experimental conditions, predominantly originates from central 5-HT neurones and changes in accordance with their electrical activity.