Effects of amphetamine on catecholamine levels and turnover in discrete hypothalamic areas

The lateral hypothalamic area revisited: ingestive behavior

This article discusses the role of the lateral hypothalamic area (LHA) in feeding and drinking and draws on data obtained from lesion and stimulation studies and neurochemical and electrophysiological manipulations of the area. The LHA is involved in catecholaminergic and serotonergic feeding systems and plays a role in circadian feeding, sex differences in feeding and spontaneous activity. This article discusses the LHA regarding dietary self-selection, responses to high-protein diets, amino acid imbalances, liquid and cafeteria diets, placentophagia, "stress eating," finickiness, diet texture, consistency and taste, aversion learning, olfaction and the effects of post-operative period manipulations by hormonal and other means. Glucose-sensitive neurons have been identified in the LHA and their manipulation by insulin and 2-deoxy-D-glucose is discussed. The effects on feeding of numerous transmitters, hormones and appetite depressants are described, as is the role of the LHA in salivation, lacrimation, gastric motility and secretion, and sensorimotor deficits. The LHA is also illuminated as regards temperature and feeding, circumventricular organs and thirst and electrolyte dynamics. A discussion of its role in the ischymetric hypothesis as an integrative Gestalt concept concludes the review.

Evidence that neuropeptide Y and dopamine in the perifornical hypothalamus interact antagonistically in the control of food intake

Mapping studies have revealed that the perifornical hypothalamus (PFH) is a primary locus for both the feeding-stimulatory effect of neuropeptide Y (NPY) and the anorectic effect of catecholamines (CAs), suggesting that NPY and CAs may interact antagonistically there. To investigate this, the CA-releasing agent amphetamine (AMPH) was injected through indwelling guide cannulas into the PFH of satiated adult male rats 5 min prior to injection of NPY (78 pmol/0.3 microliters) and food intake was measured 1, 2, and 4 h later. Amphetamine (50-200 nmol) dose-dependently reduced NPY feeding, usually eliminating it at the higher doses. The receptors mediating this effect were investigated by sequential injection of various CA antagonists, AMPH, and NPY into the PFH. Neither the alpha- nor beta-adrenergic receptor antagonists phentolamine (100 nmol) or propranolol (200 nmol) significantly affected AMPH suppression of NPY feeding. In contrast, the dopamine receptor antagonist haloperidol (5 nmol) abolished AMPH suppression of NPY feeding, suggesting that dopamine (DA) mediates the AMPH effect. To examine this, epinephrine (EPI, 50-200 nmol) and DA (25-200 nmol) were tested for suppression of NPY-induced feeding. While EPI had no significant effect, DA at the maximally effective dose (50 nmol) reduced the NPY feeding response by 36% or more. These findings provide convergent evidence for antagonistic interactions between endogenous DA and NPY in the control of eating behavior.

Opposite dopaminergic activity in lateral and median hypothalamic nuclei in relation to the feeding effect of D-Ser2-Leu-Enk-Thr6 (DSLET)

The Leu-enkephalin analogue D-Ser2-Leu-Enk-Thr6 (DSLET) had been shown to enhance feeding in rats, increase dopaminergic activity in the striatum like other opiate agonists, and particularly to decrease dopaminergic activity in the hypothalamus. In this study, the latter effect was found to be localized in the hypothalamic nuclei involved in the regulation of feeding such as the paraventricular (PVN), ventromedian (VMH), dorsomedian (DMH) nuclei and the lateral hypothalamus (LH). DSLET produced the same decrease in dopaminergic activity in the LH as in the whole hypothalamus. In the median nuclei (PVN and VMH and to a lesser extent in the DMH), an opposite effect was observed, resembling that in the striatum. The relevance of these opposite variations with regard to the feeding effect of DSLET is discussed. The decreased dopaminergic activity in the LH would appear to be the most specifically related to the behavioural effect given the known role of dopamine in this region. These data reconcile apparently contradictory aspects of the role of dopamine and the functional opposition between the lateral and median hypothalamus in food intake control.

Alterations in catecholamine levels and turnover in discrete brain areas after food deprivation

The present study determined the levels and turnover of norepinephrine (NE), epinephrine (EPI) and dopamine (DA) in discrete brain areas of rats after 48 hr food deprivation. The steady-state levels of NE, EPI and DA in saline-treated food-deprived rats, relative to satiated rats, remained basically unchanged. However, 48 hr deprivation caused a site-selective potentiation, specifically in the hypothalamic paraventricular nucleus, in the depletion of NE after alpha-methyl-p-tyrosine injection (IP, 200 mg/kg), indicating an increase in NE turnover. While changes in EPI turnover could not be demonstrated, an apparent increase in DA turnover was detected in the perifornical lateral hypothalamus and anterior hypothalamic nucleus after deprivation, while decreased DA turnover was seen in the hypothalamic dorsomedial nucleus and caudate nucleus. These results may reflect specific functions of hypothalamic catecholamines in control of food intake.

Neuropharmacology of drugs affecting food intake

The importance of the central monoamines NE, DA and 5-HT in ingestive behavior has inevitably resulted in considerable effort being expended in attempting to implicate these monoamines in the mechanism of action of anorectic drugs. The statements that amphetamine-induced anorexia is unlikely to be due to central serotoninergic systems and that central noradrenergic and dopaminergic systems are not implicated in the appetite suppressant effect of fenfluramine are in all probability correct. However, to attribute the ability of drugs to decrease food intake unequivocally to a specific effect on central monoaminergic systems is almost certainly an oversimplification, due to the fact that other putative neurotransmitters, such as GABA and peptides, play a critical role in eating. This can be achieved either directly or by modulating the release of other transmitters. An added complication in attempting to correlate a specific neurochemical process to a behavioral effect, such as anorexia, is the complexity of the central actions of the drug. At best, a predominant but not an exclusive process can be identified. Perhaps the in-built constraint of attempting to correlate a specific neurochemical effect to the desired action of a drug is accountable for the absence of a second generation of centrally acting anorectic drugs. Dramatic progress has been made in elucidating the factors involved in ingestive behavior over the last 5-10 years. This information should, and must, provide the catalyst for more efficacious anorectic drugs because obesity represents one of the few major diseases for which adequate drug therapy does not exist.

Free and conjugated 3,4-dihydroxyphenylacetic acid and homovanillic acid in brain dopaminergic areas at basal state and after pipotiazine activation

We have determined free and conjugated 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in discrete brain areas of rats. Conjugated HVA or DOPAC accounted for 22-38% of total acids in striatum, mesolimbic tissue or prefrontal cortex. Activation of dopamine (DA) metabolism by a single injection of pipotiazine palmitic ester (PPZ), a long-lasting neuroleptic, increased free acid levels (DOPAC and HVA) at either dose and conjugate levels after 32 or 50 mg/kg. 48 hours after PPZ-32 mg/kg, the observed increases of conjugates could exceed in some cases those of corresponding free acids. About half of total DOPAC and HVA were conjugated in hypothalamus, PPZ moderately increased free DOPAC (at 32 mg/kg) but did not elevate significantly the conjugated form. It is concluded that sulfation is an important pathway for DOPAC and HVA metabolism in brain and that the determination of both free and conjugated DOPAC or/and HVA may shed additional lights on regional DA metabolism and the effect of drugs thereon.

The effect of diet and chronic obesity on brain catecholamine turnover in the rat

Male Sprague-Dawley rats were fed a high calorie, high fat diet for 3 months to produce chronic diet-induced obesity (DIO) in which they gained 70% more weight than chow-fed controls. Thirty-six percent of the rats fed the DIO diet resisted the development of obesity (DR), gaining no more weight than chow-fed controls but serving as a comparison for the effects of the diet alone on the metabolism of brain catecholamines. The major influence of dietary composition was upon norepinephrine (NE) metabolism. Both DIO and DR rats had increased turnover of NE (107-217%) and/or shorter NE half-lives (42-67%) than controls in the hypothalamic paraventricular (PVN) and dorsomedial (DMN) nuclei and the median eminence (ME); dopamine (DA) turnover was similarly accelerated in the PVN. The DR rats alone exhibited decreased NE levels with increased disappearance of NE in frontal cortex and increased disappearance of DA in the ventromedial hypothalamic nucleus (VMH). The major effect of chronic obesity alone was a 31-33% decrease in DMN DA turnover and an 80% decrement in ME DA turnover associated with a 61% decrease in DA levels as compared to chow-fed controls. Therefore, the major effect of a high calorie, high fat diet was a diffuse acceleration of brain NE and DA turnover while chronic obesity led to decreased DA turnover in the DMN and ME.

Amphetamine-induced changes in immunoreactive NPY in rat brain, pineal gland and plasma

Acute injection of d-amphetamine (10 mg/kg), administered to rats 60 minutes prior to sacrifice, induced a doubling of immunoreactive NPY (NPY-IR) in pineal gland. No changes, however, could be detected in levels of NPY-IR in grossly dissected or microdissected regions of rat brain, nor were changes evident in plasma level concentrations of NPY-IR following acute amphetamine pretreatment. When amphetamine was injected twice daily for six days and once more 60 minutes prior to sacrifice, levels of NPY-IR were decreased in caudate putamen and the paraventricular and dorsomedial nuclei of the hypothalamus, while concentrations of NPY-IR were increased in medial preoptic nucleus, pineal gland, and plasma. These data indicate that levels of NPY-IR are susceptible to manipulation by amphetamine, where the extent and direction of change (increase or decrease) depends on both the frequency of drug administration and the nature of the sampled tissue. Based on the effects of amphetamine on central and peripheral norepinephrine and epinephrine disposition observed in other studies, the data also suggest that NPY-IR and catecholamine dispositions are not directly correlated and may be inversely related in some tissue.

Water deprivation increases anterior hypothalamic norepinephrine metabolism in the rat

Rats were limited to 10 min of access to water per day. After 1 week, concentrations and rate of metabolism of dopamine, norepinephrine and epinephrine were determined in hypothalamic and limbic areas associated with regulation of water homeostasis. Chronic water deprivation caused hypovolemia, hypotension and ingestion of a large volume of water when water became available. Norepinephrine metabolism was consistently increased in samples containing the anterior hypothalamic nucleus, but no other catecholamine in any other brain area was significantly affected by the deprivation schedule. We conclude that the anterior hypothalamic nucleus is involved in the response to chronic disruption of water balance in the rat.

Light and electron microscopic immunocytochemistry of beta-endorphin/beta-LPH-like immunoreactive neurons in the arcuate nucleus and surrounding areas of the rat hypothalamus

beta-Endorphin/beta-LPH-like immunoreactive neurons in the hypothalamic arcuate nucleus and its surrounding areas were visualized by light and electron microscopic immunocytochemistry. Immunoreactive processes were found in the vicinity of the pia mater, in the lateral part of the external layer of the median eminence and near the lateral wall of the third ventricle. Neuronal perikarya contained immunoreactive dense granules as well as developed cell organellae. They received neuronal inputs from other neurons through axoplasmic and axodendritic synapses. Immunoreactive neuronal processes containing dense granules and mitochondria were found as preterminal elements on non-immunoreactive neuronal soma and dendrites. Immunoreactive processes also make intimate contact with capillaries in the arcuate nucleus near the median eminence.

Tolerance pattern to amphetamine anorexia after selective lesions in the hypothalamic dopaminergic projection

Tolerance to the anorexic effect of d-amphetamine was studied in rats with selective dopamine lesions in the forebrain by means of 6-hydroxy dopamine, and measuring the food intake during two consecutive 2 h periods. Lesions placed in the perifornical hypothalamus (PFH) strongly antagonised the anorexic effect, whereas, lesions produced via intraventricular injections affected the anorexia only marginally. Amphetamine anorexia observed in the first 2 h in control and lesioned groups remained persistently, without any evidence of tolerance, up to 2 weeks of treatment. The second 2 h food intake exhibited a progressive increase which contributed to the apparent tolerance seen in total 4 h food intake in the control and lesioned animals. The onset and completion of this apparent tolerance was markedly delayed in the dopamine depleted group; lesions placed in the relatively medial areas delayed the tolerance development more effectively than that of PFH lesions. The stimulant effect of amphetamine on locomotion was abolished in lesioned animals. The results indicate that an apparent tolerance to amphetamine anorexia still developed in animals with forebrain dopamine loss. Although both the beta adrenergic and dopaminergic systems act together in mediating AMPH anorexia, the onset and the rate of completion of tolerance appear to be under the influence of hypothalamic dopaminergic system.

Determination of the course of brainstem catecholamine fibers mediating amphetamine anorexia

Previous studies suggest that brainstem catecholamine (CA) fibers which mediate amphetamine (AMPH)-induced anorexia ascend through the midlateral medical forebrain bundle and perifornical region and terminate in the perifornical hypothalamic region (PFH) at the level of the hypothalamic ventromedial nucleus. Through studies of wire-knife cuts (KCs) placed in the lower brainstem, the present paper further delineates the course of fibers mediating AMPH feeding suppression, as they ascend through the medullary, pontine and midbrain tegmentum. The results indicate that the crucial CA fibers ascend through the ventrolateral medulla just dorsal to the nucleus of the seventh cranial nerve, 1.1-1.9 mm lateral to midline. In their rostral course, these fibers apparently maintain a relatively straight position in the ventral pons and then enter the ventrolateral midbrain just dorsal to the medial lemniscus, between 0.7 and 1.1 mm lateral to midline. These medullary fibers, possibly originating from the norepinephrine/epinephrine-containing ventrolateral cell group (A1/C1), then appear to join additional fibers from the scattered dopamine-containing neurons positioned in the caudal midbrain (A8 CA cell group). Together, these dopamine, epinephrine and norepinephrine systems are believed to ascend into the medial aspect of the medial forebrain bundle on their way to the PFH at the level of the ventromedial nucleus.