Secretion of TRH in the third cerebral ventricle during acute cold exposure in the unanesthetized rat. Effect of alpha-adrenergic drugs

The concentrations of TRH in the cerebrospinal fluid (CSF) of the 3rd ventricle were measured with push-pull cannulae in 12 conscious rats. In the basal state the level of TRH in 15 min perfusion samples (210 microliters) were low (2.69 +/- 0.05 pg) and mostly undetectable with the RIA available. However, 70 to 80 min after exposure of the rats to cold (4 degrees C) a short lived but significant rise of TRH was measured in all animals. Post cold peaks amounted to 5.15 +/- 0.5 pg/15 min (p less than 0.001 vs baseline levels). This cold response to CSF TRH was influenced neither by pretreatment of rats with the alpha-adrenergic blocker phentolamine, administered i.p. (40 mg/kg) or i. c. v. (10(-5) M) 1 h before cold exposure, nor by i. c. v. infusion of the alpha 1-adrenergic blocker prazosin (10(-5) M). In rats receiving the blockers the post-cold TRH peaks were 6.76 +/- 1.61 pg/15 min and 5.70 +/- 0.70 pg/15 min, respectively. The possible origin of CSF TRH and the resistance of its cold stimulation to alpha-adrenergic blockers, compared to TRH released into the median eminence are discussed.     

Thyrotropin-releasing hormone and cyclo (His-Pro)-like immunoreactivities in the cerebrospinal fluids of 'normal' infants and adults, and patients with various neuropsychiatric and neurologic disorders

Levels of thyrotropin-releasing hormone (TRH) - and cyclo(His-Pro) (CHP)-like immunoreactivities and the activity of enzyme Pyroglutamate aminopeptidase (PAPase) were measured in cerebrospinal fluid (CSF) of over 100 normal adults (NA) and infants, and adult patients with various neurologic and neuropsychiatric disorders (NNDA). Levels of TRH and CHP in CSF of over 70% of the NA group were below 50 and 500 pg/ml respectively. The TRH- and CHP-like immunoreactivities in the remainder of the 30% of NA specimens exhibiting higher peptide concentrations were enzymatically and chromatographically characterized and were found to behave like authentic peptides. The levels of both of these peptides were significantly elevated in the CSF of most of the NNDA patients. An elevation in the CSF level of CHP was significantly correlated with the level of TRH, but not PAPase. Results from this study suggest that CSF elevation of TRH level may be due to a nonspecific response to stress that may be associated with hospitalization, myelogram procedure, and/or the neurologic and neuropsychiatric diseases for which the patients were admitted.     

Intracisternal injection of TRH precursor, TRH-glycine, stimulates gastric acid secretion in rats

Intracisternal injection of thyrotropin-releasing hormone (TRH)-Gly (pGlu-His-Pro-Gly) produced a dose-dependent (1-100 micrograms) stimulation of gastric acid secretion in urethane-anesthetized rats implanted acutely with a gastric fistula. The peak response occurred 20-30 min after intracisternal injection and lasted for more than 2 h. Intravenous injection of TRH-Gly (100 micrograms) did not modify gastric acid secretion. Following intracisternal injection of TRH-Gly, a peak elevation of both TRH-Gly and TRH levels is observed in the cerebrospinal fluid (CSF) within 15 min. Thereafter, TRH values are returned to basal levels at 75 min after the injection, whereas TRH-Gly concentrations remain significantly elevated throughout the 2-h period of measurement. Compartmental analysis revealed that CSF conversion of TRH-Gly to TRH was only 0.0072%/min. Medullary coronal sections containing the dorsal vagal complex and the raphé nucleus revealed increased content of TRH-Gly, but not TRH, 40 min after administration of TRH-Gly at an intracisternal dose effective in stimulating gastric acid secretion (100 micrograms). In addition, TRH but not TRH-Gly (10(-7)-10(-5) M) displaced [3H]MeTRH binding from rat medullary blocks containing the dorsal vagal complex. These data suggest that the intracisternal TRH-Gly-induced stimulation of gastric acid secretion is not related to its conversion to TRH in the CSF, or direct activation of TRH receptors in the medulla. The acid secretory response of TRH-Gly may be due to the formation of TRH at the active brain sites, or alternatively to activation of its own specific receptors.     

Cardiovascular effect of intravenously administered thyrotropin-releasing hormone and its concentration in push-pull perfusion of the fourth ventricle in conscious and pentobarbital-anesthetized rats

Changes in the concentration of thyrotropin-releasing hormone (TRH) in cerebrospinal fluid (CSF) were examined by the push-pull perfusion method after intravenous (i.v.) administration of the peptide in conscious and pentobarbital-anesthetized rats. The concentration of endogenous TRH in the perfusate was not changed during the 160-min perfusion period and was similar to that in the CSF (0.92 +/- 0.26 ng/ml) collected before the perfusion in conscious as well as in anesthetized rats. After i.v. administration of TRH (5 mg/kg) to the conscious rats, the peptide concentration in the perfusate increased to 42.23 +/- 14.33 ng/ml during the first 20 min and gradually returned to the basal level 2 hr after administration. The total amount of TRH detected in the perfusate was 20.0 ng. It was reduced by 75% in the anesthetized animals. The increases in blood pressure and heart rate, seen after i.v. as well as intracerebroventricular administration of TRH in the conscious rats, was significantly inhibited in the anesthetized rats. These results indicate that systemically administered TRH exerts its cardiovascular effect at central site(s), and that the transportation and the effect of the peptide is suppressed by pentobarbital anesthesia.     

The relationship between blood and cerebrospinal fluid prolactin in nonhuman primates

We studied the relationship between plasma and cerebrospinal fluid (CSF) concentrations of prolactin (PRL) in repeated and simultaneous samples of blood and CSF from chair-restrained rhesus monkeys. Following administration of thyrotropin releasing hormone (TRH), each of 4 monkeys showed increased plasma and lumbar CSF PRL concentrations. Increases in CSF PRL concentrations were muted and delayed until 60 min after peak plasma concentrations were attained. In 3 other monkeys we compared PRL concentrations in simultaneous lateral ventricular and lumbar CSF samples. Although we found no difference in PRL concentrations under baseline conditions, a ventricular-lumbar PRL concentration gradient became apparent after TRH stimulation. These studies demonstrate that changes in plasma PRL concentrations are reflected in CSF concentrations. They suggest that a significant blood-CSF barrier exists for PRL and that PRL may enter the the CSF selectively via the ventricles.     

Increased digitalis-like activity in human cerebrospinal fluid after expansion of the extracellular fluid volume

The present study was designed to determine whether acute expansion of the extracellular fluid volume influenced the digitalis-like activity of human cerebrospinal fluid (CSF), previously described by our laboratory. Human CSF samples, drawn before and 30 minutes after the intravenous infusion of 1 liter of either saline or glucose solutions, were assayed for digitalis-like activity by inhibition of either the 86Rb+ uptake into human erythrocytes or by the activity of a purified Na+ - K+ ATPase. The CSF inhibitory activity on both systems significantly increased after the infusion of sodium solutions but did not change after the infusion of glucose. These results indicate that the digitalis-like factor of human CSF might be involved in the regulation of the extracellular fluid volume and electrolyte content and thereby in some of the physiological responses to sodium loading.     

Distribution and characterization of cyclo(His-Pro)-like immunoreactivity in human cerebrospinal fluid

The distribution of cyclo(His-Pro), thyrotropin-releasing hormone and pyroglutamate aminopeptidase activity was examined in the CSF of human and a number of other mammalian species. Cyclo(His-Pro)-like immunoreactivity was present in the CSF of all species examined, and was immunologically and chromatographically identical with the authentic cyclo(His-Pro). Cyclo(His-Pro) concentration in CSF had no significant correlation with CSF TRH or pyroglutamate aminopeptidase.     

A comparison of the locomotor effects induced by centrally injected TRH and TRH analogues

Thyrotrophin-releasing hormone (TRH) and its stable analogues CG3509 and RX77368 were injected directly into the nucleus accumbens, septum and striatum of the rat and locomotor activity was recorded. TRH (5-20 micrograms) caused a dose-dependent increase in locomotor activity when injected into the nucleus accumbens. TRH (20 micrograms) also increased locomotor activity after administration into the septum but not when put into the striatum. Both the TRH analogues (0.1 and 1.0 microgram) produced closely related increases in activity when injected into either the nucleus accumbens or septum but CG3509 was more potent with a longer lasting effect. Also, in contrast with TRH (20 micrograms), both TRH analogues stimulated locomotor activity when injected into the striatum at a dose of 1 microgram but the effect was less marked and delayed in onset compared to the nucleus accumbens and septum response. Dopamine (100 micrograms) injected into the accumbens or septum also produced significant increases in locomotor activity. The locomotor effects of the peptides are discussed in relation to a possible dopamine-mediated mechanism which contrasts with the actions of TRH and the analogues on barbiturate anaesthesia.     

Comparison of the effects of TRH and D-Ala2-metenkephalinamide on hippocampal electrical activity and behavior in the unanesthetized rat

Administration of TRH into the lateral ventricle of unanesthetized rats produced increases in the incidence of hippocampal theta (5.9–9.1 Hz) rhythm, locomotor activity and shaking behavior. The increase in theta rhythm produced by TRH was brief (<5 min) and was coincident with a brief, large increase in locomotor activity. Intracerebroventricular injection of either TRH or D-Ala²-metenkephalinamide (D-Ala²-ME) also induced episodes of shaking behavior. Shakes induced by D-Ala²-ME were associated with the occurrence of hippocampal epileptiform activity whereas those caused by TRH occurred in the absence of any recorded abnormalities in hippocampal activity. These results suggest that the increase in hippocampal theta rhythm after TRH is secondary to the increase in locomotor activity and, that in contrast to enkephalins, shaking behavior caused by TRH may not be related to an action on the electrographic activity of the hippocampus.     

Involvement of thyrotropin-releasing hormone (TRH) neural system of the brain in pentylenetetrazol-induced seizures

In order to study the relationship between pentylenetetrazol (PTZ)-induced seizures and the thyrotropin-releasing hormone (TRH) neural system, immunoreactive TRH (IR-TRH) and TRH receptor binding activity were determined in discrete regions of the rat brain before as well as 40 s (immediately before seizures), 150 s (during seizures) and 24 h after an intraperitoneal injection of PTZ (75 mg/kg). IR-TRH markedly increased in the septum 40 and 150 s after the injection, and also in the hippocampus and the thalamus-midbrain region 40 and 150 s after the injection, respectively. However, no significant changes were observed in the TRH receptor binding before, during or after the seizures, suggesting that the increased IR-TRH was not released into the synaptic cleft. This speculation was supported by the dose-dependent inhibition of PTZ-induced generalized seizures by the pre-treatment with TRH or its analogue DN-1417 into the cerebral ventricle.     

Homeostatic role of the active transport in elimination of [3H]benzylpenicillin out of the cerebrospinal fluid system

Cerebral acidic metabolites and penicillin are organic anions which can be carried by active transport into capillaries of the central nervous system (CNS). However, it is generally believed that these metabolites are mainly delivered from CNS to cerebrospinal fluid (CSF) and eliminated by CSF circulation over cortex and its absorption into dural venous sinuses. To test this hypothesis we studied fate of penicillin ([3H]benzylpenicillin) in the CSF under control conditions and when its active transport was blocked by probenecid. After application of penicillin into cisterna magna of control dogs, it is distributed only in traces to lumbar, ventricular and cortical CSF. However, when active transport of penicillin across capillary wall is blocked by probenecid, its disappearance from cisterna is slowed down and its distribution is greatly enhanced so that at 300 min penicillin concentrations in cisternal, lumbar and cortical CSF approach or equal each other. Disappearance of penicillin from cisternal CSF shows a single exponential course (half-time 30 min) in control, while in probenecid pretreated dogs this is a slow multiexponential process. The results indicate that the active transport across capillary wall in CNS, but not generally postulated unidirectional CSF circulation over cortex and its absorption into dural venous sinuses, is instrumental in elimination of cerebral acidic metabolites and in such a way homeostasis in brain and cerebrospinal fluid is maintained.     

Diazepam-binding inhibitor-like activity in rat cerebrospinal fluid after stimulation by an aversive quinine taste

Cerebrospinal fluid (CSF) taken from rats after stimulation by an aversive quinine taste (hereafter called quinine CSF) administered into the fourth ventricle of mice suppressed their intake of 5% sucrose solution. We examined the effects of CSF on glutathione-induced tentacle ball formation (TBF) of hydra to determine the change in CSF components associated with aversive taste stimuli. The suppressive activity of quinine CSF on TBF in the presence of 3 microM S:-methyl-glutathione (GSM) was markedly lower than that of CSF obtained from control rats (control CSF). Pronase-treated quinine CSF had suppressive activity similar to that of control CSF. The active principle passed through an ultrafiltration membrane, with a molecular weight cut-off of 30 kDa, but not through one with a cut-off of 3 kDa. A peptide fragment of diazepam-binding inhibitor (DBI) nullified the suppression of TBF at 3 microM GSM by control CSF. The nullifying activity of quinine CSF was not observed after treatment with a benzodiazepine receptor preparation that was able to bind DBI. When flumazenil, a benzodiazepine receptor antagonist, was given to mice, the suppression of the intake of 5% sucrose solution by quinine CSF was partially reversed. It is suggested that quinine CSF contains a DBI-like substance.     

Chemotactic activity of cerebrospinal fluid in experimental cryptococcal meningitis

Cerebrospinal fluid from rabbits with chronic cryptococcal meningitis was tested for its chemotactic activity towards polymorphonuclear cells and monocytes. CSF chemotactic activity was present; it peaked 5-8 days after infection, coinciding with the time when the number of inflammatory cells in CSF was greatest. However, little chemotactic activity could be found in the early stages of infection, during the initial ingress of inflammatory cells. The chemotactic activity appeared to be host-derived, with characteristics consistent with lymphokine(s) or C5a. Treatment with cortisone significantly reduced the CSF chemotactic activity for both cell types; this reduction may contribute to the severe CSF leukopenia observed in cortisone-treated animals, which are unable to eradicate this yeast infection. Modulation of CSF chemotactic activity may be important to the success or failure of the host central nervous system response to Cryptococcus neoformans.     

Cells with natural killer activity in the cerebrospinal fluid of normal mice and athymic nude mice with acute Sindbis virus encephalitis

Sindbis virus causes an acute, nonfatal inflammatory encephalitis in weanling BALB/c mice. Mononuclear inflammatory cells are present in the cerebrospinal fluid (CSF) as well as in the parenchyma of the brain. Both aspects of this inflammatory response were eliminated by treatment with cyclophosphamide. Athymic nude (nu/nu) mice developed no inflammation in the brain, but did develop a CSF pleocytosis that peaked on day 2 after infection. The time course of the appearance of cells in the CSF was earlier in nu/nu mice than their heterozygote (nu/+) littermates. The pleocytosis in nu/nu mice reached a peak on day 2, whereas in nu/+ mice the peak was on day 4, as it is in normal BALB/c mice. To determine whether some of the CSF cells in nu/nu mice may be natural killer (NK) cells, NK activity was measured in a 4-hr assay by using a YAC-1 target cell. NK cell activity in the spleen and peripheral blood was induced by infection with Sindbis virus in nu/nu mice with a similar time course to that of nu/+ mice (peak 1 day after infection). CSF from nu/nu mice had NK activity present 2 days after infection that was greater than that present in either the peripheral blood or spleen. BALB/c and nu/+ mice had insufficient cells present for assay at day 2, but BALB/c mice had NK activity present in the CSF 3 and 5 days after infection that exceeded that in the peripheral blood or spleen. Brain interferon was detectable on day 1 in nu/nu mice, but not until day 2 in nu/+ mice even though the amounts of brain virus were the same in the two groups at all time points. It is concluded that cells with NK activity contribute to the CSF pleocytosis induced by acute Sindbis virus encephalitis.     

Integrated analysis of the cerebrospinal fluid peptidome and proteome

Cerebrospinal fluid (CSF) is the only body fluid in direct contact with the brain and thus is a potential source of biomarkers. Furthermore, CSF serves as a medium of endocrine signaling and contains a multitude of regulatory peptides. A combined study of the peptidome and proteome of CSF or any other body fluid has not been reported previously. We report confident identification in CSF of 563 peptide products derived from 91 precursor proteins as well as a high confidence CSF proteome of 798 proteins. For the CSF peptidome, we use high accuracy mass spectrometry (MS) for MS and MS/MS modes, allowing unambiguous identification of neuropeptides. Combination of the peptidome and proteome data suggests that enzymatic processing of membrane proteins causes release of their extracellular parts into CSF. The CSF proteome has only partial overlap with the plasma proteome, thus it is produced locally rather than deriving from plasma. Our work offers insights into CSF composition and origin.     

Interferon crosses blood-cerebrospinal fluid barrier in monkeys.

Interferon was detected in the cerebrospinal fluid (CSF) of monkeys injected iv or im with 30 million units of human leukocyte interferon. The im injection maintained a long-lasting plateau at about 1/30th of the corresponding level of interferon in the serum. Interferon injected into the serum. Interferon injected into the cerebrospinal canal was cleared from CSF at a similar rate as it disappeared from blood after iv administration of a high dose. A relatively stable serum level was maintained for 12-24 hr after the injection of interferon into the CSF space.     

Role of adrenoreceptors in the effect of thyroliberin on lymphatic vessels

Formerly we showed that TRH had simulative effect on mesenteric bovine and rat lymphatic vessels (LV) in very low concentration--10(-12)-10(-18) M. In present paper, participation of LV alpha- and beta-receptors in realization of TRH activity on rat mesenteric lymphatic vessels was studied in situ. Propranolol increased the stimulative effect of TRH, isoproterenol exerted an opposite effect. Phentolamine, prazosin eliminated the simulative effect of TRH, yohimbine resulted in additional gain of effect, which seems to testify 1) presynaptic action of TRH or 2) increase of the output of norepinephrine, which is potentiated by alpha 2-adrenoceptor antagonists. Also the participation of adrenergic receptors in positive chronotropic effects of mesenteric rat LV was studied using the method of selective destruction of dopamine-containing neurons after 6-OHDA infusion. As it occurred, desympathization hindered development of stimulating action of TRH. Thus, the efficiency of TRH as a stimulator of LV is connected with activation of adrenergic mechanisms.     

Interleukin-2 and blood brain barrier in cats: pharmacokinetics and tolerance following intrathecal and intravenous administration.

Single bolus doses of glycosylated human interleukin-2 (n IL-2) in the range of 2.8 x 10(3) to 2.0 x 10(6) IU/kg were administered to anesthesized cats via the cephalic vein (n = 10) or using suboccipital puncture (n = 8). CSF (cerebrospinal fluid) and blood samples were collected by repeated puncture. The n IL-2 concentration in four cats was determined on the basis of its biologic activity using 3H-thymidine incorporation into human ConA-blasts and by radioimmunoassay. In additional experiments radioactivity was determined in cerebrospinal fluid and serum after intravenous and intrathecal (i.th.) application of 5.8 x 10(3) - 3.2 x 10(3) IU/kg of 14C-acetyl-n IL-2 in regular time intervals. CSF and serum concentration time-profiles show a biexponential decline in the plasma elimination phase with half-lives of 4 min (alpha-phase) and 90 min (beta-phase) after intravenous and 20-120 min (alpha-phase) and 2-16 hours (beta-phase) after intrathecal application. There is a trend towards longer terminal elimination half-lives with increasing doses. Interleukin-2 is able to penetrate the blood brain barrier from the circulation into the cerebrospinal fluid and vice versa. Due to a slow rate of penetration and rapid elimination from blood only traces of n IL-2 (2-8 IU/ml) are detected in CSF after i.v. injection of 2 x 10(6) IU/kg, whereas concentrations between 400 and 1600 IU/ml are maintained in CSF for several hours following i.th. administration of 2-10 x 10(5) IU/kg.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electroconvulsive seizures increase levels of pGlu-Glu-Pro-NH2 (EEP) in rat brain

We have previously reported that electroconvulsive seizures (ECS) increases the level of prepro-TRH-derived peptides in hippocampus, amygdala and pyriform cortex but not the striatum of male rats and that this increase is significantly correlated with reduced immobility (increased swimming) in the Porsolt forced swim test. An abstract by Mabrouk and Bennett published in 1993 described increased locomotor activity in rats following IP injection of TRH (pGlu-His-Pro-NH2) and EEP (pGlu-Glu-Pro-NH2). We have examined the effect of three daily transcorneal ECS on the levels of EEP in various brain regions and their correlation with results from the Porsolt forced swim test. The EEP level (ng/g wet weight) was measured by RIA in 6 brain regions: amygdala (AY), hippocampus (HC), pyriform cortex (PYR), anterior cortex (AC), striatum (STR) and motor cortex (MC). ECS significantly increased EEP levels in AY, HC and PYR. The increased swim behavior following ECS, as measured in the Porsolt test, correlated significantly with the EEP levels in HC and MC within individual subjects. Intraperitoneal (IP) injection of EEP (1.0 mg/kg) resulted in a rapid and sustained rise in EEP levels throughout the brain and a clearance half-time from blood of 2.0 h. Intracardiac injection of 0.5 mg EEP resulted in a peak EEP level in CSF at 2 h followed by a t1/2 of 0.35 h. A 3 compartment model for EEP transport from blood into CSF and then brain was developed. This model revealed a 1.75 h delay in the transit time of EEP from blood to CSF followed by rapid clearance from the CSF but long retention time within various brain tissues. We conclude that (1) ECS significantly increases EEP levels in limbic regions, but not in striatum, of the rat brain, (2) EEP, like TRH, is a potential mediator of the antidepressant effect of ECS and (3) EEP, after IP or IV administration, is readily taken up by, and has a long residence time in, brain tissue.     

Influence of cerebro-spinal fluid of picrotoxin kindled rats on seizure susceptibility and locomotor activity of recipients.

Repeated picrotoxin administration (ip) in subthreshold doses in rats resulted in kindling of generalized seizures. Decrease of locomotor activity in kindled rats occurred in interictal periods. Intra-cerebroventricular microinjection to intact recipients of cerebrospinal fluid (CSF) of kindled but not intact rats or those after acute picrotoxin-induced convulsions, induced a decrease of locomotor activity and severity of acute picrotoxin induced seizures. These effects of CSF were blocked by naloxone pretreatment and were absent after injection of CSF to which protease inhibitors were not added. It is concluded that the release of endogenous opioid peptide substance(s) takes place in CSF of kindled animals which cause the interictal decrease of locomotor activity and may play the role of endogenous anticonvulsive factors controlling epileptic activity induction.