Stress-induced alterations in neurotensin, somatostatin and corticotropin-releasing factor in mesotelencephalic dopamine system regions

The effects of exposure to acute mild footshock stress on concentrations of neurotensin-, somatostatin-, and corticotropin-releasing factor-like immunoreactivity (li) in mesotelencephalic dopamine system regions of the rat were examined. Mild stress exposure resulted in a selective and regionally specific increase in neurotensin-li concentrations in the ventral tegmental area (VTA), source of the dopaminergic innervation of the mesocortical and mesolimbic dopaminergic terminal fields. Concentrations of somatostatin- or corticotropin-releasing factor-li were not changed in any area examined. Levels of the dopamine metabolite, 3,4-dihydroxyphenylacetic acid, were increased only in the VTA and medial prefrontal cortex. These data suggest that neurotensin in the VTA may be involved in environmentally elicited activation of certain mesotelencephalic dopamine neurons.

CSF corticotropin-releasing factor-like immunoreactivity in depression and schizophrenia

To further investigate the hypothesis that hyperactivity of the hypothalamic-pituitary-adrenal axis in patients with depression may be mediated by hypersecretion of corticotropin-releasing factor (CRF), the authors measured CRF-like immunoreactivity in CSF samples from 138 neurological control, 54 depressed, and 27 nondepressed (23 schizophrenic and four manic) subjects. The CSF CRF concentration was markedly higher (almost twofold) in depressed patients than in control subjects and nondepressed psychiatric patients. The concentration of CSF CRF was slightly but significantly higher in schizophrenic patients than in control subjects. These findings provide further support for the hypothesis that CRF hypersecretion occurs in major depression.

Centrally administered neurotensin inhibits pentobarbital metabolism in mice but not in rats

Neurotensin (NT), a tridecapeptide with a widespread and uneven distribution within the central nervous system of mammals, is known to be involved in a variety of physiological, behavioral, endocrine and biochemical functions. Groups of rats and mice were given i.p. injections of pentobarbital followed by intracisternal administration of NT or saline. Following decapitation, the plasma, liver and brain concentrations of pentobarbital were measured with a gas chromatographic/mass fragmentographic method. In the mice, but not in the rats, the NT injection caused a substantial inhibition of the pentobarbital metabolism and a prolongation of the sleeping time. The mechanism(s) behind this inhibition still remains unclear.

Alterations in cerebrospinal fluid concentrations of somatostatinlike immunoreactivity in neuropsychiatric disorders

The concentration of somatostatinlike immunoreactivity in cerebrospinal fluid (CSF) from normal, healthy volunteers (n = 10) and patients with DSM-III diagnoses of major depression (n = 17), schizophrenia (n = 11), or dementia (n = 29) was measured by a sensitive and specific radioimmunoassay. Statistically significant decreases in CSF concentrations of somatostatinlike immunoreactivity were seen in all three patient populations when compared with controls. These findings confirm previous reports of decreased concentrations of somatostatinlike immunoreactivity in the CSF of patients with depression and dementia and extend this observation to patients with schizophrenia as well. These findings are concordant with the view that reductions in somatostatinlike immunoreactivity concentrations are associated with diseases in which cognitive function is disturbed.

Alterations in corticotropin-releasing factor-like immunoreactivity in discrete rat brain regions after acute and chronic stress

Corticotropin releasing factor (CRF) may regulate endocrine, autonomic, and behavioral responses to stress. Evidence indicates that CRF-like immunoreactivity (CRF-LI) is widely distributed throughout the CNS. In this study, the distribution of CRF-LI was determined in 36 rat brain regions by combined radioimmunoassay-micropunch dissection techniques and the effect of stress on CRF-LI was investigated, using a chronic stress model that induces endocrine changes in rats similar to those seen in depressed humans. A control group of rats was handled daily. An acute stress group was subjected to 3 hr of immobilization at 4 degrees C, while a chronic stress group was exposed to unpredictable stressors. Thirty-six brain regions were microdissected by the technique of Palkovits and assayed for CRF-LI, using a specific antiserum to ovine CRF. CRF-LI was detected in most regions. In controls, the highest concentrations were found in the arcuate nucleus/median eminence, the hypothalamic paraventricular (PVN) nucleus, and the periventricular nucleus. The next highest levels were found in the raphe nuclei and dorsal vagal complex. CRF-LI was well represented in the locus coeruleus (LC); in the central, cortical, and medial amygdaloid nuclei; and in the bed nucleus of the stria terminalis. Low concentrations occurred in the hippocampus and cerebrocortical regions. Appreciable concentrations were detected in midbrain and brain stem regions. Acute stress reduced CRF-LI in the arcuate nucleus/median eminence (ME) (by 52%) and in the median preoptic (MPO) nucleus (by 32%) and doubled its concentration in the locus coeruleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of corticotropin-releasing factor from rat brain regions in vitro

In addition to its endocrine action in the anterior pituitary, corticotropin-releasing factor (CRF) also appears to play a role in regulating higher central nervous system function(s). To investigate further the role of CRF in brain, a specific RIA was used to measure in vitro CRF release during incubation of various rat brain regions in Krebs-Henseleit buffer. Increasing the potassium concentration to 56 mM resulted in a 10-fold increase in CRF release from minced hypothalamus. However, the high K+ concentrations had no effect in the presence of calcium-free buffer containing 1 mM EGTA. Scorpion venom also stimulated CRF release in a calcium-dependent manner. CRF-like immunoreactivity was detected in extrahypothalamic brain regions using RIA and HPLC. Significant calcium-dependent CRF release from the rat amygdala and midbrain was observed in response to 56 mM K+ or scorpion venom. These results indicate that depolarizing agents induce the release of CRF-like immunoreactivity not only from the hypothalamus but also from other rat brain regions and lend further support to the hypothesis that CRF may be a neurotransmitter or neuromodulator in the central nervous system.

Adaptation to cold antagonizes neurotensin-induced hypothermia in mice

Intracerebrally-administered neurotensin produces a marked hypothermia in a variety of mammals. In this study, prior adaptation to a cold environment was found to significantly antagonize the hypothermia produced by intracisternally-administered neurotensin in mice. This antagonism required both previous exposure to cold ambient temperatures and cold exposure immediately prior to, or simultaneously with, neurotensin administration. The antagonism of neurotensin-induced hypothermia by prior cold-adaptation was blocked by indomethacin, but not by acetylsalicylic acid, suggesting that brain prostaglandin synthesis may be essential for this newly-discovered phenomenon.

Corticotropin-releasing factor-like immunoreactivity in senile dementia of the Alzheimer type. Reduced cortical and striatal concentrations

The concentration of corticotropin-releasing factor-like immunoreactivity (CRF-LI) in the human central nervous system was measured by radioimmunoassay in postmortem tissue of control patients and in those with histologically confirmed senile dementia of the Alzheimer type (SDAT). In the controls, CRF-LI was found in high concentrations in the hypothalamus and frontal cortex (Brodmann's area 10), in moderate concentrations in amygdala, substantia innominata, temporal and parietal cortex (Brodmann's areas 38 and 7), and the caudate nucleus, and in low concentrations in posterior hippocampus and nucleus accumbens. A marked reduction in the concentration of CRF-LI was observed in the frontal and temporal cortex (approximately 50%) as well as in the caudate nucleus (approximately 70%) in the SDAT group. The present findings suggest that neurons containing corticotropin-releasing factor are pathologically altered in SDAT, in addition to the previously described cholinergic and somatostatinergic neuronal degeneration.

Effects of intrahypothalamic injection of quinolinic acid on anterior pituitary hormone secretion in the unanesthetized rat

Bilateral intrahypothalamic injections of the brain metabolite quinolinic acid (QUIN) were made in an attempt to examine its effects on the secretion of LH, PRL, GH and TSH. Quin, a neuroexcitatory amino acid with close structural similarities to glutamate, kainate and N-methylaspartate, was infused into unanesthetized male rats, the animals sacrificed 7.5 min later, and serum hormone concentrations determined by radioimmunoassay. QUIN caused surges in LH, PRL and GH release (316, 607 and 1,134% of control, respectively, at 50 micrograms QUIN) without affecting the serum concentrations of TSH. At lower doses, a preferential effect of QUIN on PRL release was observed. All QUIN-induced hormonal changes were inhibited by concomitant administration of the specific antagonist (-)-2-amino-7-phosphonoheptanoic acid, indicating the presence of QUIN-sensitive receptors on neurons which are intimately associated with endocrine regulation. Moreover, because QUIN-treated animals exhibited behavioral signs of seizure activity and neuroendocrine dysfunction has been reported to occur in human convulsive disorders, the data are also of interest in view of a possible mechanistic link between epileptic phenomena and hormone secretion.

Bombesin-like immunoreactivity in the central nervous system of capsaicin-treated rats: a radioimmunoassay and immunohistochemical study

The neuroanatomical distribution of bombesin-like immunoreactivity (BLI) in the rat central nervous system was investigated using radioimmunoassay and immunohistochemistry. Whereas cross-reactivity of the bombesin antiserum with substance P was problematic in the immunohistochemical experiments, no significant cross-reactivity with substance P was apparent in the radioimmunoassay. Results from the radioimmunoassay studies reveal particularly high concentrations of BLI in the hypothalamus, thalamus, medulla and spinal cord. Adult rats treated neonatally with capsaicin displayed significant depletions of somatostatin-like and substance P-like immunoreactivity and a small, statistically significant, reduction of BLI in the cervical spinal cord. Capsaicin treatment significantly reduced substance P-like immunoreactivity, but not somatostatin-like immunoreactivity, in the medulla and resulted in a small BLI depletion of borderline statistical significance in this brain region. Neonatally administered capsaicin treatment had no effect on the thalamic concentration of any of these three neuropeptides and neurotensin-like immunoreactivity was unchanged in all brain regions studied. These results suggest that the source of some of the BLI found in the spinal cord may be capsaicin-sensitive dorsal root ganglion cells.

Alterations in regional brain concentrations of neurotensin and bombesin in Parkinson's disease

Frozen samples of postmortem human brain tissue from patients with Parkinson's disease (n = 25) and control patients who died without neurological disease (n = 25) were assayed for neurotensin and bombesin by specific radioimmunoassay. Twelve brain regions were examined: substantia nigra, ventral tegmental area, periaqueductal gray matter, caudate nucleus, putamen, globus pallidus, amygdala, hippocampus, nucleus accumbens, frontal cortex, cingulate cortex, and entorhinal cortex. In patients with Parkinson's disease, the concentration of bombesin was significantly decreased in the caudate nucleus and globus pallidus, and the concentration of neurotensin was significantly reduced in the hippocampus. The concentration of neither peptide was significantly altered in the substantia nigra or ventral tegmental area, two regions known to exhibit reductions in other neurotransmitter substances.

Elevated concentrations of CSF corticotropin-releasing factor-like immunoreactivity in depressed patients

The possibility that hypersecretion of corticotropin-releasing factor (CRF) contributes to the hyperactivity of the hypothalamo-pituitary-adrenal axis observed in patients with major depression was investigated by measuring the concentration of this peptide in cerebrospinal fluid of normal healthy volunteers and in drug-free patients with DSM-III diagnoses of major depression, schizophrenia, or dementia. When compared to the controls and the other diagnostic groups, the patients with major depression showed significantly increased cerebrospinal fluid concentrations of CRF-like immunoreactivity; in 11 of the 23 depressed patients this immunoreactivity was greater than the highest value in the normal controls. These findings are concordant with the hypothesis that CRF hypersecretion is, at least in part, responsible for the hyperactivity of the hypothalamo-pituitary-adrenal axis characteristic of major depression.

Monosodium glutamate lesions in rat hypothalamus studied by immunohistochemistry for gonadotropin releasing hormone, neurotensin, tyrosine hydroxylase, and glutamic acid decarboxylase and by autoradiography for [3H] estradiol

Adult male and female rats treated neonatally with monosodium glutamate (MSG) exhibit lesions in the arcuate nucleus of the hypothalamus. Immunohistochemical analysis of the distribution of tyrosine hydroxylase (TH), glutamic acid decarboxylase (GAD), neurotensin (NT) and gonadotropin-releasing hormone (GnRH) reveals substantial destructions of tuberoinfundibular dopamine and NT systems accompanied by a marked reduction of immunoreactivity in the median eminence. GAD immunoreactivity in the arcuate nucleus and median eminence is greatly reduced, while GnRH containing structures in the mediobasal hypothalamus are not noticeably affected. Evaluation of autoradiograms after intravenously administered [3H] estradiol in the ventral hypothalamus indicate an almost complete loss of target neurons in the arcuate nucleus but not in the nearby ventromedial nucleus. The results suggest that: (a) NT- and dopamine-containing neurons of the arcuate nucleus project to the median eminence via tuberoinfundibular NT and dopaminergic pathways; (b) GABA in the median eminence originates to a major extent from neurons of the arcuate nucleus through a tuberoinfundibular GABAergic system; (c) GnRH is produced in the rat outside the arcuate nucleus; (d) the MSG-induced lesion in the basal tuberal region abolishes or strongly diminishes estradiol target neurons in the arcuate nucleus.

Ontogeny of brain neurotensin in the rat: a radioimmunoassay study

Concentrations of neurotensin-like immunoreactivity in several discrete brain areas were measured by radioimmunoassay in rats of different ages (2, 5, 10, 20, 30, and 60 days). Neurotensin-like immunoreactivity increased steadily from 2 to 30 days of age in the hypothalamus and then plateaued, while the preoptic area and amygdala concentrations peaked at 30 days of age. Brainstem neurotensin-like immunoreactivity concentrations increased from 2 to 10 days of age and decreased from 20 to 60 days of age. Several other regions showed no significant age-associated changes in neurotensin-like immunoreactivity.

Effects of excitotoxic amino acids on pituitary hormone secretion in the rat

The acute effects of administration of 4 excitatory amino acids (n-methyl-DL-aspartic acid (NMA), kainic acid (KA), ibotenic acid (IA) and quinolinic acid (QA] on the serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH) and prolactin (PRL) were studied in the rat. NMA-treated rats exhibited increased serum LH and GH concentrations while KA-treated rats-showed increases only in serum GH concentrations. Neither IA nor QA altered adenohypophyseal hormone levels. These endocrine alterations induced by NMA and KA are different from those previously reported after administration of glutamate, another excitatory amino acid. The finding that all of the excitatory amino acids studied did not produce identical effects on anterior pituitary hormone secretion may be due to differential permeability of these substances into the central nervous system or because they act at different subtypes of excitatory amino acid receptors.

Neurotensin-induced hypothermia: evidence for an interaction with dopaminergic systems and the hypothalamic--pituitary--thyroid axis

Neurotensin (NT), an endogenous tridecapeptide, produces significant hypothermia after intracisternal (i.c.) or intracerebroventricular (i.c.v.) administration in microgram quantities in a variety of laboratory animals. The present study sought to clarify the mechanism of the hypothermic action by utilizing pharmacological treatments which alter the function of brain neurotransmitter systems. Pretreatment of rats with anti-muscarinic (atropine), anti-noradrenergic (propranolol, a beta-blocker; phenoxybenzamine, an alpha-blocker) or anti-opiate (naloxone) agents did not significantly alter NT-induced hypothermia. Similarly depletion of brain serotonin (5-HT) with parachlorophenylalanine did not affect NT-induced hypothermia. However, depletion of brain catecholamine content with 6-hydroxydopamine resulted in a significant potentiation of NT-induced hypothermia as did pretreatment with haloperidol, a dopamine (DA) receptor antagonist. Furthermore, in rats with selective depletions of brain DA, but not norepinephrine (NE), NT-induced hypothermia was significantly augmented. Thus an interaction between brain DA systems and NT appears likely. These data indicate that NT-induced hypothermia is not dependent on intact functional activity of NE, 5-HT, muscarinic ACh or endogenous opiate systems but suggests interactions between brain DA circuits and NT. In other experiments, NT-induced hypothermia was found to be antagonized significantly by i.c. injection of thyrotropin-releasing hormone (TRH), but not by pretreatment with L-triiodothyronine. Another endogenous tripeptide (Pro--Leu--Gly--NH2, MIF-I) had no effect. Thyroidectomy (THX) significantly potentiated NT-induced hypothermia; NT administered i.c. significantly reduced the high serum TSH levels of THX rats. Thus, NT and TRH, two endogenous peptides, appear to be antagonists in certain systems.

Effect of chronic treatment with thyrotropin-releasing hormone (TRH) or an analog of TRH (linear beta-alanine TRH) on the hypothalamic-pituitary-thyroid axis

The effects of treatment for 5 or 9 days with varying doses of thyrotropin-releasing hormone (TRH) or the linear beta-alanine TRH congener (pGlu-His-Pro-beta-Ala-NH2) on serum levels of TSH, T3, and T4 were studied in mice and rats. At low doses in rats treatment with TRH for 9 days significantly increased serum levels of T3 but not serum T4 whereas a higher dose of TRH (10 mg/kg) reduced serum T3 levels. beta-Ala TRH (0.1--10 mg/kg IP) treatment for 9 days in rats significantly reduced serum T4 levels whereas serum T3 levels were only depressed at higher doses (1--10 mg/kg IP) of the peptide. In mice treatment for 5 days with TRH (1 and 10 mg/kg IP) significantly reduced serum levels of T3 and T4. In addition, TRH (0.1--10 mg/kg IP) or beta-Ala TRH treatment (1.0--10 mg/kg IP) for 9 days significantly reduced serum TSH levels in rats. TRH (10 mg/kg IP for 9 days) also significantly reduced serum GH levels in rats. No alteration in hypothalamic content of TRH and LHRH was observed after chronic TRH treatment. Some, but not all, of our findings support the hypothesis that treatment with high doses of TRH reduce pituitary-thyroid axis functions by a direct effect on hypophysial TRH receptors.

Cholecystokinin inhibits tail pinch-induced eating in rats

Peripheral administration of the COOH-terminal octapeptide of cholecystokinin in doses from 1 to 100 micrograms per kilogram of body weight (0.25 to 25.0 micrograms per rat) significantly antagonized tail pinch-induced eating in rats, an animal model for stress-induced human hyperphagia. Centrally administered cholecystokinin was effective only in high doses (3 micrograms into the cerebral ventricle). The finding that the minimal effective dose of cholecystokinin in suppressing stress-induced appetitive behavior is smaller after peripheral than central administration suggests that the peptide is acting on peripheral, as opposed to central nervous system, substrates.

Neurotensin: central nervous system effects of a hypothalamic peptide

The central administration of neurotensin, an endogenous hypothalamic tridecapeptide, produces a marked dose-related decrease in body temperature of mice and rats at an ambient temperature of 25 degrees C. This effect is even more pronounced when mice are placed at 4 degrees C to increase the rate of decline of body temperature. Other sequelae observed after central administration of neurotensin are decreases in locomotor activity in rats and a marked dose-related enhancement in pentobarbital-induced mortality, sedation and hypothermia. This latter effect was shown to be due to a significant reduction in the metabolic degradation of the barbiturate. None of the above-mentioned effects are observed after peripheral neurotensin administration, suggesting that this peptide does not readily cross the blood-brain barrier. Neurotensin appears to be one of a growing list of neuropeptides that can affect CNS function.

Lack of effect of chronically administered thyrotropin-releasing hormone (TRH) on regional rat brain tyrosine hydroxylase activity

Chronic treatment of adult male rats with TRH (1 or 10 mg/kg IP) for 5 or 9 days failed to alter the activity of tyrosine hydroxylase (TH), the enzyme regulating the rate-limiting step in catecholamine biosynthesis. In contrast, as previously described, chronic reserpine administration (0.5 mg/kg IP: 9 days) resulted in a significant rise in TH activity in midbrain, hypothalamus, pons-medulla and forebrain. These results suggest that the enhanced brain norepinephrine turnover reported to occur after treatment with TRH is not due to synthesis of new TH enzyme protein.

Comparison of the analeptic potency of TRH, ACTH 4-10, LHRH, and related peptides

Various peptide hormones appear to exert behavioral and pharmacologic effects apart from their classical endocrine actions. Thytrotopin-releasing hormone (TRH), for example, antagonizes the sedation and hypothermia produced by barbiturate and other depressant drugs and de Wied has shown that ACTH 4-10, TRH, LHRH and certain related substances show some activity in inhibition of extinction of a pole-jumping avoidance response in the rat. These data provided the impetus for screening ACTH 4-10, LHRH, and related peptides for analeptic activity. ACTH 4-10 and ACTH 4-7 were inactive in antagonizing pentobarbital whether administered peripherally or centrally. ACTH 4-7 amide and 4-Met(O2), 8-D-Lys,9-Phe-ACTH 4-9 were active regardless of route of administration LHRH and two tripeptide fragments (pGlu-His-Trp-NH, and pGlu-His-Phe-NH2) showed analeptic activity only after intracisternal administration. Thus, some peptide fragments related to ACTH 4-10 and LHRH were shown to share to some degree the analeptic properties previously demonstrated for TRH.