Hemorrhage-induced regional brain thyrotropin-releasing hormone release in conscious rats measured by microdialysis

The septum, nucleus accumbens and preoptic area in the brains of conscious, freely moving rats were perfused using microdialysis probes. The TRH concentration significantly increased in the septum after withdrawal of 30% of the total blood volume but remained at constant levels in the other brain areas. Also, high potassium dose-dependently stimulated TRH release in vivo. These results suggest that blood loss stimulates septal TRH release, probably by membrane depolarization of TRH-containing nerve terminals.     

Modulation of locomotor activity by substance P in rats

The effects of intraperitoneally or intracerebrally (DA A-10 area) administered substance P (SP) on locomotor activity of rats were studied in an exact 12-h light/12-h dark cycle changing from dark to light at 6 a.m. SP was administered either at 11 a.m. (light phase, minimal locomotor activity) or at 7 p.m. (dark phase, maximal locomotor activity). The effects of 12.5 micrograms/kg SP intracerebral and 125 micrograms/kg SP intraperitoneal were very similar. In the light phase SP produces excitation but inhibition of locomotion in darkness. Hence, the effect of SP depends on the internal mechanisms controlling motor activity and tends to level off the spontaneous circadian oscillation. We found a long lasting SP effect during both the light and dark period. The present experiments led us to the conclusion that SP has a levelling effect on locomotor activity. Probably this effect might be explained as SP's action on the dopaminergic pathway or dopamine metabolism, because the dopamine content in neurons also has a circadian rhythm.     

Aldosterone acts centrally to increase brain renin-angiotensin system activity and oxidative stress in normal rats

Aldosterone acts upon mineralocorticoid receptors in the brain to increase blood pressure and sympathetic nerve activity, but the mechanisms are still poorly understood. We hypothesized that aldosterone increases sympathetic nerve activity by upregulating the renin-angiotensin system (RAS) and oxidative stress in the brain, as it does in peripheral tissues. In Sprague-Dawley rats, aldosterone (Aldo) or vehicle (Veh) was infused for 1 wk via an intracerebroventricular (ICV) cannula, while RU-28318 (selective mineralocorticoid receptor antagonist), Tempol (superoxide dismutase mimetic), losartan [angiotensin II type 1 receptor (AT(1)R) antagonist], or Veh was infused simultaneously via a second ICV cannula. After 1 wk of ICV Aldo, plasma norepinephrine was increased and mean arterial pressure was slightly elevated, but heart rate was unchanged. These effects were ameliorated by ICV infusion of RU-28318, Tempol or losartan. Aldo increased expression of AT(1)R and angiotensin-converting enzyme (ACE) mRNA in hypothalamic tissue. RU-28318 minimized and Tempol prevented the increase in AT(1)R mRNA; RU-28318 prevented the increase in ACE mRNA. Losartan had no effect on AT(1)R or ACE mRNA. Immunohistochemistry revealed Aldo-induced increases in dihydroethidium staining (indicating oxidative stress) and Fra-like activity (indicating neuronal excitation) in neurons of the hypothalamic paraventricular nucleus (PVN). RU-28318 prevented the increases in superoxide and Fra-like activity in PVN; Tempol and losartan minimized these effects. Acute ICV infusions of sarthran (AT(1)R antagonist) or Tempol produced greater sympathoinhibition in Aldo-treated than in Veh-treated rats. Thus aldosterone upregulates key elements of brain RAS and induces oxidative stress in the hypothalamus. Aldosterone may increase sympathetic nerve activity by these mechanisms.     

Resistance to the anorexic and thermogenic effects of centrally administrated leptin in obese aged rats

The aim of the present study was to determine whether the anorexic and thermogenic effects of leptin were attenuated in overweight aged rats following intracerebroventricular (i.c.v.) injection of murine leptin. Male F344/BN rats of two ages (6 months: young (n=20) and 24 months: old (n=18)) were divided into three groups (control, pair-fed and leptin) and were treated with either vehicle (artificial cerebrospinal fluid) or leptin (15.6 microgram/day) for 3 days. There was an age-related increase in basal food intake (20+/-2%), serum leptin levels (363+/-106%) and leptin (OB) mRNA (72+/-16%) in perirenal white adipose tissue (PWAT). In contrast, basal expression of hypothalamic NPY mRNA and brown adipose tissue (BAT) uncoupling protein 1 (UCP1) mRNA was reduced significantly (-35+/-4% and -51+/-5%, respectively) with age. I.c.v. leptin treatment had a significantly greater effect in reducing food intake (-42+/-5% vs. -23+/-4%), serum leptin levels (-55+/-7% vs. 10+/-2%) and PWAT OB mRNA (-46+/-2% vs. 10+/-5%) in young than in old rats. Similarly, central leptin treatment also had a greater effect in suppressing hypothalamic NPY mRNA expression in young (-23+/-4%) than in old (-8+/-4%) rats compared with their age-matched pair-fed treated rats. The stimulatory effect of i.c.v. leptin treatment on BAT UCP1 mRNA expression was also significantly greater in young rats (45+/-8%) than in old rats (10+/-6%) compared with age-matched pair-fed rats. Our previous report indicated that these overweight aged rats were resistant to peripheral administered leptin. The present data extend those findings and demonstrate that the impaired anorexic and metabolic effects of leptin are centrally mediated. This leptin resistance may be due to either the elevated obesity and serum leptin with age or due to age itself or both. The development of leptin resistance with age may contribute to the hyperphagia, hyperleptinemia and impaired energy balance with age.     

Analgesic activity of substance P following intracerebral administration in rats

Substance P was found to be a potent, long-lasting analgesic in the tail flick test in rats following intracerebral administration, via chronically indwelling cannulae, into the midbrain periaqueductal gray. Substance P was approximately five times as potent as morphine sulfate on a weight basis; however, it was 25 times more potent than morphine on a molar basis. The analgesic activity produced by Substance P was significantly antagonized by pretreatment with naloxone, a narcotic antagonist. The analgesic activity of Substance P exhibited a rapid onset (1 min.), peaked by 3 minutes post infusion and its duration of activity was between 30 and 60 minutes. Thus, Substance P may be yet another endogenous analgesic peptide.     

Analgesic activity of substance P in rats: apparent mediation by met-enkephalin release

The intracerebroventricular administration of Substance P (SP) produced a marked and short-lasting increase in the threshold for vocalization and vocalization afterdischarge in the rat after electrical stimulation of the tail. This effect was blocked by naloxone and potentiated by bacitracin, a peptidase inhibitor. The analgesic effect of SP was also blocked by the concomitant intraventricular injection of the specific antibody against the opioid peptide metenkephalin but not by the antibody against beta-endorphin. Anti-met-enkephalin did not block other pharmacological actions of SP. The results suggest that SP produces an analgesic effect in rats by releasing met-enkephalin at supra-spinal levels involved in pain control.     

Effect of substance P on neonatally axotomized noradrenaline neurons in rat brain

Transection (axotomy) of the dorsal tegmental noradrenaline bundle in the neonatal stage leads to a permanent degeneration of noradrenaline nerve terminal projections distal to the lesion (e.g. in the neocortex), while projections proximal to the lesion increase their nerve terminal density (e.g. in the cerebellum). These structural changes are reflected by marked reductions and elevations respectively of the endogenous noradrenaline levels, [3H]-noradrenaline uptake in vitro and nerve density as demonstrated by fluorescence histochemistry. Intracisternal administration of substance P after the transection did not alter these noradrenaline parameters in the neocortex, whereas dose-dependent and significant increases were found in the cerebellum and pons-medulla. The results indicate that substance P may have a growth-stimulatory effect on damaged locus coeruleus noradrenaline neurons in the CNS during ontogeny.     

The effect of substance P on the neuronal activity of the antinociceptive system

The experiments on rats showed that the 1 micrograms substance P injection to dorsal raphe nucleus caused prolonged (24 hours of study) analgetic effect--it enhances the reaction latent period to thermal nociceptive stimulation, intensifies the background impulse activity, rises the middle frequency of neuron discharges and creates high-frequency neurons as well as the neurons with burst impulse activity. The supposition is being confirmed that the mechanism of antinociceptive structures activation leads to analgesia caused by substance P.     

Effect of the N-terminal fragment of substance P on the microcirculatory system

Biomicroscopic experiments have shown that the N-terminal fragment of substance P (SP1-4), when applied to the rat mesentery, has a considerably lower injuring effect than substance P (SP1-11) itself. SP1-4 activity, as compared to SP1-11 activity regarded as 1, was 0.007 in case of microcirculatory disturbances and venular permeability increase and 0.0007 in case of mast cell degranulation increase. The data obtained suggest that the slightest damaging effect of SP1-4 on microcirculation is combined with anti-stress activity.     

Effect of substance P on the retention of a brightness discrimination task in rats

The effect of substance P (SP) on acquisition and retention of a footshock-motivated brightness discrimination was investigated in rats, 250 micrograms SP/kg were injected intraperitoneally either 30 min before or immediately after the training session. Acquisition of the brightness discrimination was not affected by SP administered 30 min before training. However, both the pre-training and post-training injections of SP resulted in a significant improvement of retention tested 24 h after training. The effect of SP on memory consolidation is discussed.     

Stimulation of brain adenylate cyclase activity by the undecapeptide substance P and its modulation by the calcium ion

Synthetic substance P stimulated adenylate cyclase activity in particulate preparations from rat and human brain.The concentration of substance P for half maximal stimulation in rat brain was 1.8 · 10⁻⁷ M.The stimulatory effect of substance P on the rat brain adenylate cyclase activity was 88% compared with 48% by noradrenalin, 163% by prostaglandin E₁ and 184% by prostaglandin E₂.Both the basal and substance P-stimulated adenylate cyclase activity in rat brain were inhibited by concentration of Ca²⁺ above 10⁻⁶ M.The chelating agent ethyleneglycol-bis-(β-aminoethylether)-N,N′-tetraacetic acid at a concentration of 0.1 mM reduced the basal adenylate cyclase activity by 64% and eliminated the substance P-stimulated activity.The inhibition by ethyleneglycol-bis-(β-aminoethylether)-N,N′-tetraacetic acid was completely reversed by increasing concentrations of Ca²⁺.     

Dual mechanism of phosphatidylinositol hydrolysis by substance P in brain

The treatment of cerebral cortex slices with substance P caused alterations in the phospholipid levels. A significant loss of phosphatidylinositol in a dose-dependent manner was observed. In contrast, the levels of the major phospholipids, phosphatidylcholine and phosphatidylethanolamine, were enhanced by the peptide. The effect of substance P on the fatty acid composition of phospholipids was also studied. The most relevant event was the decrease in the content of both stearic and arachidonic acids of phosphatidylinositol. This decrease was more evident at the lowest substance P concentration tested (65 pM). These results are consistent with the phosphatidylinositol breakdown caused by substance P in some tissues. Furthermore, our data indicate that this breakdown is selective depending on the peptide dose. Thus, in the presence of very low doses of substance P (65 pM) a preferential degradation of 1-acyl(predominantly stearoyl)-2-arachidonoylglycerophosphoinositol molecular species occurs, whereas high doses of the peptide (0.65 microM) induce a generalized hydrolysis of phosphatidylinositol without showing any preference towards molecular species rich in arachidonic acid. Hence we describe for the first time a dual, dose-dependent mechanism for phosphatidylinositol hydrolysis by substance P, suggesting the possibility that either phospholipase A2 or phospholipase C activation is involved.     

Influence of substance P on the behavioral changes induced by haloperidol in rats

Locomotor activity and grooming behavior of rats were recorded for a period of 30 min following intraventricular injections of substance P(SP) in doses of 0.60 and 2.50 microgram/rat. The lower dose of the peptide significantly increased locomotion for 10 min and time spent grooming for 25 min. The effects of the same two doses of SP on the hypokinesia induced by various pharmacological treatments modifying catecholaminergic systems were then examined. SP did not affect the behavioral depression produced by alpha-methyl-para-tyrosine (250 mg/kg), FLA-63 (25 mg/kg) and phenoxybenzamine (20 mg/kg). However, SP, in dose of 0.60 microgram/rat, systematically reversed the decrease in locomotor activity induced by a relatively small dose of haloperidol, 0.1 mg/kg. The dame dose of the peptide significantly counteracted the rigidity but not the hypokinesia and catalepsy resulting from the previous administration of a higher dose of haloperidol, 3 mg/kg. The results support the hypothesis that SP may exert direct or indirect function in motor behavior, possible via a modulatory action on brain dopaminergic systems.     

Ketanserin pretreatment attenuates MDMA-induced dopamine release in the striatum as measured by in vivo microdialysis

Systemic administration of the amphetamine analogue, 3,4-methylenedioxymethamphetamine (MDMA) produced a dose-dependent increase in the extracellular concentration of dopamine (DA) in the striatum as measured by in vivo microdialysis in awake, freely-moving rats. The extracellular concentration of the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), was significantly decreased in dialysate samples following the administration of MDMA (10 and 20 mg/kg, i.p.). The serotonin-2 (5-HT2) antagonist ketanserin (3 mg/kg, i.p.) had no effect on the extracellular concentration of DA or DOPAC in the striatum of vehicle- treated rats. The administration of ketanserin (3 mg/kg) 1 hr prior to MDMA (20 mg/kg) significantly attenuated the MDMA- induced increase in the extracellular concentration of DA without affecting the decrease in DOPAC concentrations. These data are suggestive that MDMA administration increases DA release in the striatum of awake, freely-moving rats. In addition, MDMA-induced increase in the extracellular concentration of DA in the striatum is mediated, in part, via 5-HT2 receptor mechanisms.     

Acute reduction of brain substance P induced by nicotine

Ten minutes after a single injection of 0.8 mg/kg nicotine SC (free base) the level of substance P-like immunoreactivity (SPLI) was reduced by 61–73% in rat caudate-putamen, nucleus accumbens, and olfactory tubercle, with smaller and not significant reductions in the frontal cortex, substantia nigra, and ventral tegmental area. The nicotinic receptor antagonist mecamylamine (1.0 mg/kg IP) prevented the reductions in SPLI. The rapidity and the degree of the changes in SPLI after nicotine exceed those previously reported for other agents and implicate substance P neurotransmission as a major component of nicotinic action.Preliminary data were presented at the 17th annual meeting of the American Society for Neurochemistry, Montreal, 1986 (1).     

Effect of passive immunization against substance P in rats with hyperprolactinemia

Substance P, an undecapeptide isolated from gut and brain tissues, was reported to stimulate prolactin release. It was suggested that substance P may play a role in the control of prolactin secretion. In this investigation we studied the effects of the blockade of endogenous substance P by the administration of a specific anti-substance P serum on serum prolactin levels in rats in the evening of proestrus, in lactating rats after suckling, and in male rats with hyperprolactinemia induced by grafting 2 anterior pituitary glands under the kidney capsule. The injection of the anti-substance P serum was followed by a significant decrease of the prolactin surge induced by 30 min suckling in lactating rats, when the antiserum was administered 24 hr but not 5.30 hr earlier. Anti-substance P serum also induced a significant decrease in serum prolactin levels in pituitary grafted rats, but induced no change in the proestrous surge of prolactin and LH. These results show that substance P may be involved in the release of prolactin induced by suckling and that this peptide may have an intrapituitary role in the process of prolactin release. On the other hand, substance P does not seem to play a significant role in the proestrous peak of prolactin and LH.     

Effect of estrogen on the response of thyroid stimulating hormone to substance P in rats

The role of substance P (SP) in the control of thyroid stimulating hormone (TSH) release and the influence of gonadal steroid were investigated. Intravenous administration of SP failed to alter plasma levels of TSH in ovariectomized (OVX) rats, whereas SP induced a significant increase in plasma TSH in estradiol benzoate-primed (Eb-primed) OVX rats (P less than 0.001). Further, intravenously administered SP did not affect the plasma TSH concentration in normal male rats, but significantly increased it in Eb-primed castrated male rats (P less than 0.01). These data suggest possible roles for SP at the level of the hypothalamus and/or the pituitary gland in stimulating TSH secretion under the influence of estrogen.