Neurohumoral substances released from hypothalamus of the monkey during hunger and satiety

Simultaneous comparison of cerebral dialysis and push-pull perfusion in the brain of rats: a critical review

Over the last 30 years, studies of the in vivo activity of neurotransmitters and other endogenous factors in the brain have comprised a major effort in the neurosciences. Historically, the technology of push-pull perfusion was utilized as a major approach to investigations in this field. In the last 10 years, cerebral dialysis has been used as an alternative method essentially for the same scientific purpose, since the perfusion technique was viewed as difficult and excessively damaging to tissue. This review considers the representative literature in which both systems have been used to study local neurochemical responses to a drug or other chemical factor, a physiological condition or other situation. In addition, new experiments have been undertaken to compare, in the same animal and at the same time, the utility and properties inherent in the techniques of push-pull perfusion and cerebral dialysis in terms of the profile of a neurotransmitter activity and their local histopathological effects. A miniaturized 33/26 ga push-pull needle and a 24 ga dialysis probe were implanted simultaneously in the left and right caudate nuclei, respectively, in the anesthetized rat. An artificial cerebrospinal fluid (CSF) was perfused simultaneously through both devices at a rate of 10 microliters/min in the push-pull cannula and at 1.0 or 2.0 microliters/min in the dialysis probe. Within a series of 8-10 successive perfusions, excess K+ ions in a concentration of either 30 or 60 mM were incorporated in the CSF and delivered simultaneously to both the push-pull cannula and dialysis probe. Samples of perfusate and dialysate were assayed chromatographically by coulometric HPLC detector and quantitated in terms of the pg/min efflux of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). The results showed that the resting level of DA was almost undetectable in dialysate samples from either structure; in push-pull perfusates the recovery of DA ranged between 7.0 to 10.0 pg/min, which was increased threefold by excess K+ ions. The recovery of DA and the three metabolites in samples of push-pull perfusate was two to four times that in samples of dialysate during the condition of excess K+ ions. Post-mortem histological analysis of the sites of perfusion and dialysis revealed little or no differences in the cytological damage induced by either the perfusion needle or dialysis probe. Finally, the advantages and limitations of each of these two experimental approaches to in vivo analysis of neurotransmitter efflux are reviewed in relation to the selection of an open or closed system for the on-line study of in vivo neurochemical events.

Brain regions where cholecystokinin exerts its effect on satiety

The neuropeptide cholecystokinin (CCK), which is localized within the hypothalamus in integrative centers of feeding regulation, can suppress feeding behavior when exogenously applied into the lateral hypothalamus. Moreover, the endogenous peptide can be released from the same brain locus by stimuli that physiologically are associated with satiety (i.e., gastric meal loads). This endogenously released CCK contributes to the inhibition of feeding behavior during meal intake. These data strongly suggest that hypothalamic CCK may play a physiological role in the termination of feeding behavior. The presence of additional sites sensitive to CCK in extrahypothalamic regions (e.g., medial pons and lateral medulla) argue that the CCK receptor systems may functionally (1) have several links in a linear chain or (2) exist as several parallel systems. The relevance of these extrahypothalamic loci for feeding regulation will require further studies which need to be directed towards the physiological role of the endogenously released CCK in these particular areas, by use of selective CCK antagonists.

Involvement of cholecystokinin in food intake: I. Concentrations of cholecystokinin-like immunoreactivity in the cerebrospinal fluid of male rats

Abstract To investigate the role of central neural cholecystokinin in food intake the concentration of cholecystokinin-like immunoreactivity was measured by radioimmunoassay in the cerebrospinal fluid of male rats. Characterization of the molecular forms of Cholecystokinin was made by high-performance liquid chromatography before radioimmunoassay. Four molecular forms of cholecystokinin corresponding to standards of the tetra-, penta- and sulphated octapeptide and a late eluting peak probably corresponding to cholecystokinin-58 were found. The concentration of cholecystokinin-like immunoreactivity in the cerebrospinal fluid decreased in response to 48 h of food deprivation and was restored after 1 h of food intake, the main increase occurring within 30 min after the onset of feeding. Cholecystokinin-like immunoreactivity increased in the cerebrospinal fluid 10 min after an intraperitoneal injection of 5 mug cholecystokinin octapeptide, a dose which also suppressed the amount of food consumed during 1 h in rats deprived of food for 48 h. Intraperitoneal injection of the peripheral, cholecystokinin A receptor antagonists lorglumide (450 mug) or L-364. 718 (20 mug) reversed the inhibitory effect of cholecystokinin octapeptide on food intake and prevented the increase of cholecystokinin-like immunoreactivity in the cerebrospinal fluid. It is suggested that central neural cholecystokinin is involved in the control of food intake and that this is reflected in the alterations in cholecystokinin-like immunoreactivity in the cerebrospinal fluid which occur in response to food deprivation and food intake. However, a variety of ways of intracerebral administration of Cholecystokinin octapeptide failed to affect food intake in food-deprived rats. The possibility is raised that Cholecystokinin octapeptide acts in concert with another transmitter in the brain to affect food intake.

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)

Monoamine transmitter activity in lateral hypothalamus during its perfusion with insulin or 2-DG in sated and fasted rat

A unique profile of neurochemical events is proposed to occur in the diencephalon which is contingent upon the nutrient status of the animal. In this first of a series of investigations, we selected the lateral hypothalamus (LH) in order to determine its specific resting profile of monoaminergic neurotransmitters and their principal metabolites. The neuronal pattern of activity was studied during sated and fasted conditions as well as during a local glucoprivic challenge to the LH. After permanent guide cannulae for push-pull perfusion were implanted in female Sprague-Dawley rats, the LH was perfused repeatedly with an artificial CSF, at a rate of 20 microliters/min, in order to collect a series of 5.0 min samples. Aliquots of each perfusate were assayed directly using a high performance liquid chromatography system with electrochemical detection (HPLC-EC) for pg/microliter concentrations of norepinephrine (NE), dopamine (DA) and serotonin (5-HT). In comparison to the basal levels of amines during the sated condition, when the rat was food-deprived for 20-22 hr, the release of NE, DA, and 5-HT was significantly lower than that observed under the sated condition. Further, the turnover of NE in the LH was concurrently attenuated as reflected by the lower levels of MHPG in the perfusate, thus demonstrating the modification in catecholamine activity produced in the LH by the condition of hunger. When either 10 micrograms/microliters 2-deoxy-D-glucose (2-DG) or 4.0 mU/microliter insulin was incorporated into the CSF perfused in the LH, the efflux of DA was significantly enhanced independent of the state of satiation. In addition, the proportion of both NE and DA to 5-HT was likewise increased by either of these centrally acting substances, while the turnover of 5-HT was enhanced and NE and DA turnovers were reduced. Perfusion of 2-DG in the LH of the fasted rat caused a significant reduction in catecholamine turnover in terms of MHPG/NE, VMA/NE, DOPAC/DA and HVA/DA ratios. Moreover, 2-DG increased NE/5-HT while lowering the NE/DA ratio, and enhanced simultaneously the 5-HTOL/5-HT ratio. In the sated rat, 2-DG attenuated the release of 5-HT from the animal's LH, whereas insulin caused a shift in the proportions of NE/5-HT and DA/5-HT. Further, the peptide served to reduced the efflux of 5-HT, enhanced the turnover of 5-HT while diminishing DA turnover, and shifted the metabolism of NE from MHPG to VMA.(ABSTRACT TRUNCATED AT 400 WORDS)

RNA content of neurons in the ventromedial nuclei and lateral hypothalamic area relative to feeding status

The total RNA content of hypothalamic and cortex neurons in relation to the feeding status of adult male Wistar rats was studied. Experimental conditions including food deprivation (12 and 24 hours) and relative satiation (short-term refeeding, glucose or glycerol administration) changed in different ways the total RNA content of the neurons in the ventromedial hypothalamic nuclei (VMH) and in the lateral hypothalamic area (LHA) with respect to fasting or satiety. Only the long-term absence of food (24 hours) significantly increased the total RNA content of the VMH cells, while the RNA content of the LHA neurons significantly decreased in both the 12 and 24 hr fasted rats compared with those fed ad lib. The sixty minute free access to food after 12 or 24 hours of fasting fully reversed these changes. The short-term food intake significantly increased the RNA content of the LHA cells of the 12 and 24 hr fasted animals while the total RNA content of the VMH neurons significantly decreased only in the 24 hr fasted rats. The effect of glucose and glycerol administration on the RNA content of the LHA neurons (in 12 hr fasted rats) was similar to the effect of refeeding. One hour after giving glucose (1 g/kg b.wt.) or glycerol (300 mg/kg b.wt.) the total RNA content in the LHA neurons significantly increased. No changes in RNA content were observed in the neurons of the cortex when comparing the experimental and control rats. The results demonstrated the close relationship between the RNA content of the hypothalamic neurons and the feeding status.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuronal cholecystokinin-like immunoreactivity is postprandially released from primate hypothalamus

By use of the push-pull perfusion technique, release of neuronal cholecystokinin-like immunoreactivity (CCK-LI) from hypothalamus of owl monkeys was investigated in relation to an intragastric meal. In overnight fasted, halothane-anesthetized owl monkeys, levels of CCK-LI in the hypothalamic push-pull perfusate were below assay sensitivity (less than 4 pg/30 min). After intragastric administration of a carbohydrate/amino acid meal, however, a 10-fold increase in CCK-LI release (51 +/- 7 pg/30 min) was observed in 5 out of 15 perfusion sites during the first postprandial 30 min. During the subsequent two 30-min intervals, release of CCK-LI was still increased with 32 +/- 5 pg/30 min and 15 +/- 6 pg/30 min, respectively. Thereafter, CCK-LI release was below assay sensitivity again. Addition of 40 mM potassium chloride (KCl) to the perfusion solution, which causes neuronal depolarization, resulted in a second increase in CCK-LI release of 56 +/- 7 pg/30 min which was comparable to the meal-induced release. All sites that exhibited an increase in CCK-LI were located in the anterolateral aspect of the hypothalamus. In experiments without meal-induced release, KCl did not have any effect on CCK-LI in perfusate, suggesting that these particular sites did not contain CCK-releasing terminals. High performance liquid chromatography (HPLC) identified the C-terminal octapeptide of CCK (CCK-8) as the predominant molecular form of CCK within the owl monkey hypothalamus. No gastrin-17 was present.(ABSTRACT TRUNCATED AT 250 WORDS)

An intragastric meal releases the putative satiety factor cholecystokinin from hypothalamic neurons in cats

The release of cholecystokinin-like immunoreactivity (CCK-LI) from feline hypothalamus was studied in relation to a meal by use of the push-pull perfusion technique. While levels of CCK-LI in the perfusate of overnight-fasted anesthetized cats were below assay sensitivity (less than 7 pg/30 min), intragastric administration of a carbohydrate-amino acid meal elicited a 3-fold increase in CCK-LI, identified by high-performance liquid chromatography as the C-terminal octapeptide of CCK (CCK-8). Examination of an extrahypothalamic site showed no comparable release in CCK-LI. Intravenous infusions of CCK-8 at doses imitating physiological blood levels up to 400 times higher than those seen after physiological stimulation demonstrated the existence of a CCK blood-brain barrier in the lateral hypothalamus. These observations provide support that CCK may play a physiological role in termination of feeding behavior.

Amine accumulation in behavioural pathology

When nigro-striatal and meso-cortical neurons degenerate there is a loss of dopamine in the terminal fields and an accumulation of amines in the axons of these systems as they traverse the hypothalamus through the medial forebrain bundle. Traditional lines of thought have attributed the occurrence of motor and consummatory deficits which occur after dopamine neuron degeneration to the loss of functional dopamine neurotransmitter in the terminal fields. However, we have hypothesized that hypothalamic amine accumulation represents an area of brain tissue where processes such as neurotransmitter release, ephaptic transmission or local axon swelling may be affecting adjacent neurons and may thereby participate in the production of behavioural deficits. There is a considerable amount of evidence from studies on both peripheral and central catecholamine-containing neurons indicating that when their axons degenerate a release of functional neurotransmitter can occur. Information from neuropharmacological studies indicates that several drugs which facilitate behavioural recovery from dopamine-depleting lesions may do so by affecting amine release or receptor sensitivity near areas of accumulation rather than depleted terminal fields. We conclude that amine accumulation is a component of dopamine neuron degeneration which should be considered when assessing the role of the central catecholamine systems in the control of various behavioural and physiological processes.

New double-lumen polyethylene cannula for push-pull perfusion of brain tissue in vivo

A new concept in the design of a push-pull cannula device for localized perfusion of brain tissue in the conscious and/or unrestrained animal is described. A catheter, consisting of a single strand of polyethylene tubing, contains an internal dividing septum which runs longitudinally throughout its length. The orifice of each lumen is of equal diameter and provides an integrated system for simultaneous delivery and withdrawal of a perfusate from the perfusion locus. The principal features of the new cannula system are: its simplicity of fabrication due to its all-plastic construction; multiple tip configurations adapted for a specific anatomical requirement including V-shaped, slanted, horizontal and side-by-side opening; direct visualization of the perfusate monitor bubble through the wall of the transparent catheter; since there are no joints, lack of leakage of perfusate and occlusion of pull channel; ease of sterilization by liquid or gas methods; and infrequency of damage because of catheter flexibility. Using radiolabeled dopamine and norepinephrine, prototype experiments carried out with 3 flow rates and 3 tip configurations revealed differences in substrate exchange which depend upon a given experimental parameter. The practical advantages are discussed of the new perfusion system in comparison with dialysis needles as well as with more commonly used concentric, metallic push-pull cannulae. Finally, technical applications are presented of the methods for the rat and other animals in which either the pharmacological delivery of a drug over a specified interval, or recovery of a neurotransmitter released into the cerebral parenchyma is a principal experimental objective.

A role for amine accumulation in the syndrome of ingestive deficits following lateral hypothalamic lesions

Lesions of the lateral hypothalamus produce ascending catecholamine neuron degeneration which results in terminal depletion and proximal accumulation above the lesions. The occurrence of deficits in ingestive behaviour has been attributed traditionally to the loss of functional dopamine neurotransmitter in the terminal fields. However, release of functional amines may occur in the lateral hypothalamus at areas of accumulation, to produce at least some of the behavioural symptoms characterizing the lateral hypothalamic syndrome. Recovery from behavioural deficits as a result of various pharmacological treatments, after dopamine-depleting lesions, may be mediated by changes in amine release or modified sensitivity of receptors affected by released amines. We conclude that amine accumulation should be considered when interpreting experiments implicating central catecholamine systems in the control of consumatory behaviour and the regulation of body weight.

Effect of a bovine hypothalamic extract on glucose utilization by rat adipocytes

This study was undertaken to assess whether a hypothalamic extract has any direct metabolic action on adipose and muscle tissues. An acid bovine hypothalamic extract (HE) was tested for its effect on the utilization of D[U-14C]glucose by isolated rat adipocytes and rat hemidiaphragms. The HE was ineffective in stimulating the conversion of labeled glucose into CO2 and glycogen by rat hemidiaphragm. However, in isolated adipocytes, the HE had significant lipogenic activity. This lipogenic effect was independent of insulin and nonsuppressible by insulin antibodies. The dose-response curve was linear and saturable. That insulin and the HE were not additive at maximal concentrations suggests that they act through a common rate-limiting step, possibly a receptor site. Other hypothalamic substances tested (thyrotropin-releasing hormone, luteinizing hormone-releasing hormone, and substance P) showed no lipogenic activity. Somatostatin (6 microgram/ml) was an insulin potentiator but only when preincubated with the fat cells. It is concluded that the hypothalamic regulation of body weight may be mediated by a neurohumoral mechanism affecting adipose tissue stores.

Noradrenergic feeding system in monkey hypothalamus is altered by localized perfusion of glucose, insulin, 2-DG and eating

Hypothalamic sites in the monkey were labelled by micro-injections of 3H-NE and successive push-pull perfusions were carried out at a rate of 25 mul/min. When the monkey was fed, 3H-NE within the perifornical region increased. When 2-deoxy-D-glucose (2-DG) was added to the perfusate, 3H-NE release was also enhanced, whereas insulin perfused at the same rate caused a delated increase in catecholamine levels as reflected by increased radioactivity. Glucose supressed the release of 3H-NE, suggesting overall that the noradrenergic feeding system in the hypothalamus of the monkey is modulated by the regional level of glucose as well as the local concentration of insulin.

Release of 14C-norepinephrine into the lateral cerebroventricle of rats by exposure to a conditioned aversive stimulus

Rats chronically implanted with push-pull cannulas were injected with a pulse of 14C-norepinephrine (NE) into the lateral cerebroventricle under a variety of pretreatment and behavioral conditions. Animals pretreated intraventricularly with 6-hydroxydopamine (Group A) or ascorbic acid vehicle (Group B) were subsequently perpised imder fpur conditions: (1) presentation of a novel, visual stimulus in a one-way avoidance chamber; (2) presentation of the light (CS) followed by shock; (3) training to a high level of avoidance behavior, after which the CS was presented in the absence of opportunity for an avoidance response and in the absence of shock; and (4) after forced extinction, followed by CS without opportunity to aboid and with out presentation of shock. Samples of perfusate from rats subjected to the four test conditions were analyzed by thin-layer chromatography for total 14C in a scintillation counter and for proportion of NE and normetanephrine (NM). During Tests 1 and 4 the 14C perfusion wash-out did not differ from control values for either Group A or B. During Test 2, total radioactivity as well as the proportions of NE and NM increased in the perfusate for both Groups A and B. Presenting the CS without shock (3) resulted in 14C and NE and NM for Group B (vehicle), but not for Group A (6-OHDA). To test for non-specific release unrelated to a brain catecholaminergic function, another group of rats was subjected to identical treatments with the exception that 14C-urea replaced 14C-NE as a pulse-label. In these animals Test 2 (shock) induced an increase in 14C in the perfusate, while Tests 1, 3 and 4 yielded wash-out curves essentially identical to controls.

Changes in protein levels in perfusates of freely moving cats: relation to behavioral state

Perfusates from the brains of freely moving cats, obtained by means of a push-pull cannula, contain high concentrations of proteins. The levels vary in a cyclic fashion and are higher during rapid eye movement sleep than during the waking state. The proteins represent a distinctive class of tissue protein and their changing levels appear to reflect an alteration in the protein content of the extracellular space of brain related to behavioral state.

Feeding produced in the satiated rat by elevating the concentration of calcium in the brain

When the concentration of calcium ions in the cerebral ventricles is elevated, a fully satiated rat eats voraciously. This feeding response is not prevented by prior intraventricular administration of alpha-or beta-adrenergic blocking agents, or other pharmacological antagonists. This supports the concept of an independent ionic mechanism, rather than a neurotransmitter one, for modulating a "set-point" for weight or hunger.