Biomedical subjects

J T Laitinen

Publications and source records attributed to J T Laitinen.

At least 37 records · Page 2Linked to original sources

PubMed1997

Regulation of cyclic GMP levels in the rat frontal cortex in vivo: effects of exogenous carbon monoxide and phosphodiesterase inhibition.

A microdialysis method combined with a sensitive radioimmunoassay was used to monitor cGMP release in the frontal cortex of the anesthetized rats in vivo. We assessed the relative contribution of endogenous nitric oxide (NO), and effects of exogenous carbon monoxide (CO) and phosphodiesterase activity, as possible regulators of cortical CGMP levels. Perfusion with CO-saturated aCSF (approximately 1 mM CO) failed to significantly stimulate cortical cGMP levels. For comparison, cerebellar cGMP levels increased by 2-fold during CO stimulation, followed by a prolonged response that was fully reversible with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Cortical perfusion with zinc protopophyrin-IX (100 microM), a widely used inhibitor of the CO-generating enzyme heme oxygenase, suppressed cGMP levels by 50%, a response that spontaneously recovered in spite of the continuous presence of the metalloporphyrin. Perfusion with isobutylmethyl xanthine IBMX (1 mM) resulted in 5-fold increase in cortical cGMP levels, as compared to basal levels without IBMX. In the presence of IBMX, L-NAME suppressed basal cortical cGMP levels by 70% indicating that NO synthase activity generates the bulk of cGMP in this brain region, as previously shown for basal cGMP production in the hippocampus and the cerebellum. These data also emphasize a crucial role for phosphodiesterase activity in the maintenance of cGMP levels in vivo in the frontal cortex. The relatively weak responses to exogenous CO lend little support for a role of this gas in regulating basal cortical cGMP levels in vivo.

1-Methyl-3-isobutylxanthine↗

PubMed1996

A rhodopsin-based model for melatonin recognition at its G protein-coupled receptor.

The recent elucidation of the primary structures of different melatonin receptors as well as the deduction of the secondary structure of rhodopsin has allowed us to construct a model for melatonin recognition at its G protein-coupled receptor. To achieve this, we have used the quantum mechanics method Austin model 1 to fully optimize the structures of melatonin and several analogs. We also synthesized three compounds and used the three-dimensional analysis comparative molecular field analysis (CoMFA) to generate a model for the structure-activity relationships of melatonin and 27 melatonin-like compounds. This model predicted with good accuracy the affinities of the synthesized compounds for the melatonin receptor. We propose that recognition of the functional moieties of melatonin occurs through specific interaction of these moieties with fully conserved amino acid residues present in transmembrane helices V, VI and VII of the melatonin receptor. These residues are not found in other members of the G protein-coupled receptor family. The rhodopsin-based model can explain the importance of some structural features of melatonin and related active compounds.

Amino Acid Sequence↗

PubMed1996

Long-term induction of haem oxygenase-1 (HSP-32) in astrocytes and microglia following transient focal brain ischaemia in the rat.

Haem oxygenase-1 (HO-1) is a stress protein and a rate-limiting enzyme in haem degradation, generating ferrous iron, carbon monoxide and bile pigments. HO-1 has been suggested to be protective against oxidative stress. In the normal rodent brain the enzyme is localized in selected neuron populations, but heat shock, glutathione depletion in vivo and oxidative stress in vitro induce HO-1 predominantly in glial cells. We studied HO-1 expression in the brain following transient occlusion of the middle cerebral artery, and found increased mRNA levels in the ischaemic region from 4 h to 7 days after 90 min of ischaemia. The mRNA levels peaked at 12 h, and were localized perifocally. HO-1-immunoreactive astrocytes and microglial cells were seen in the perifocal area, in the ipsilateral and occasionally in the contralateral hippocampus. Some perifocal neurons were also HO-1-immunoreactive. In the infarcted area HO-1-positive microglia/macrophages were detected in double-labelling experiments. A microassay measuring the conversion of [14C]haem to [14C]bilirubin showed a two-fold increase in haem oxygenase activity in the infarcted core. These observations show a long-term induction of HO-1 protein and its activity following ischaemia-reperfusion brain injury, and indicate increased capacity for haem degradation and the generation of biologically active bile products, carbon monoxide and iron in astrocytes and some microglia/macrophages during focal brain ischaemia.

Animals↗

PubMed1996

Effects of melatonin implants on winter fur growth and testicular recrudescence in adult male raccoon dogs (Nyctereutes procyonoides).

The effects of melatonin implants were investigated on winter fur growth, monitored by counting growing and mature hairs per bundle and testicular recrudescence, judged by testis width, score count of spermatogenesis, and serum testosterone in the adult male raccoon dogs. Melatonin administration in July highly elevated melatonin concentrations in serum and urine and induced an earlier decrease in prolactin secretion (August in the treated group vs September in the control group), winter fur growth (July-beginning of November in the treated group vs. August-end of November in the control group) and testicular recrudescence (October in the treated group vs. November in the control group). In the control animals, urinary excretion of melatonin between 1500-0900 hr increased during autumn followed by a rapid fall in winter. The increase from July (1.8 +/- 0.4 ng) to August (3.9 +/- 0.5 ng) and the subsequent unchanged levels until October coincided with the period of winter fur growth. The further increase in November (6.5 +/- 1.2 ng) coincided with the significant elevation in both testis width and score count of spermatogenesis. These results suggest a role of the increase in endogenous melatonin secretion during autumn in the growth of winter fur and testicular recrudescence in this species under natural conditions. Relatively high serum concentrations of prolactin were shown in two animals, one in the control group and another in the treated group. However, the parameters for testis and winter fur growth in the two cases were similar to those in the remainder of the animals. Thereby, the role of prolactin in the winter fur growth and the initiation of testicular recrudescence, if it is truly involved, is manifested through its decreasing secretion rather than the actual blood concentrations.

Animals↗

PubMed1996

Circadian adjustment of men and women to night work.

OBJECTIVES: The aims of the present study were to define the adjustment of sleep-wakefulness and other circadian rhythms during consecutive night shifts and to study the effect of gender on the adjustment to night work. METHODS: Twenty experienced shift workers, 9 men and 11 women, were studied under controlled laboratory conditions. After a night of habituation, the subjects worked one day shift and three night shifts. Rectal temperature was measured continuously during the study. Salivary melatonin and cortisol were assessed at 2-h intervals, and subjective sleepiness was checked every hour during the work shifts. Sleep was registered by the static-charge sensitive bed (SCSB) method after the workshifts. RESULTS: Subjective sleepiness varied both between the work shifts and between the men and women. The subjects felt most alert during the day shift and were the sleepiest during the first night shift. Sleepiness decreased during the consecutive night shifts but did not reach the level of the day shift during the three nights. The sleepiness of the women decreased more than that of the men, the difference being significant during the second and third night shifts (P < 0.05). The circadian rhythm of body temperature, salivary cortisol, and time in bed changed significantly (P < 0.05) between the workshifts, but no differences were found between the men and women in the circadian adjustment of the physiological variables to night work. CONCLUSIONS: The men felt sleepier than the women during the consecutive night shifts, although no physiological differences were found between the genders. However, since normal social and domestic factors were excluded, the findings cannot be considered as evidence of women's better adaptation to night work in everyday life.

Adaptation, Physiological↗

PubMed1995

Endogenous serotonin modulates histamine release in the rat hypothalamus as measured by in vivo microdialysis.

In vivo microdialysis was used to study the effects of serotonergic drugs on histamine release from the suprachiasmatic nuclei region of the anterior hypothalamus in anesthetized rats. Local perfusion with serotonin (5-hydroxytryptamine, 5-HT) increased histamine release significantly and dose dependently. Methysergide (10 mg/kg i.p.), a 5-HT2C/2A receptor antagonist, given 30 min before 5-HT perfusion, blocked the 5-HT-evoked histamine release. Methysergide (10 mg/kg i.p.), given alone, also suppressed basal histamine release by 33%. Dexfenfluramine (10 microM), a 5-HT releaser and uptake blocker, administered via the microdialysis probe, significantly enhanced hypothalamic histamine release. With the same dose of dexfenfluramine, 5-HT release increased 10-fold in the same brain area. These results show for the first time that endogenous 5-HT modulates histamine release in vivo and it has a tonic stimulatory effect on the histaminergic nerve terminals of the rat anterior hypothalamus.

Anesthesia↗

PubMed1995

A sensitive microassay reveals marked regional differences in the capacity of rat brain to generate carbon monoxide.

Heme oxygenase activity is the sole known physiological source for the production of carbon monoxide (CO), a gaseous messenger candidate. A sensitive radioenzymatic microassay was validated to study regional distribution of heme oxygenase activity within the rat brain. The assay utilized a 14,000 X g supernatant of brain homogenate and [14C]heme as the substrate. Thin layer chromatography revealed that incubation of cerebellar supernatant with (14C]heme yielded a single reaction product, indistinguishable from bilirubin, that was selectively extracted into toluene. Radioactivity in toluene increased linearly in respect to time and added protein, was totally dependent on NADPH and was not detected with boiled homogenate. The reaction was dose-dependently inhibited by Zn-protoporphyrin IX (IC50 0.3 microM) and by an antibody generated against rat NADPH-cytochrome P450 reductase indicating specific involvement of heme oxygenase. As little as 36 fmol [14C]bilirubin/min could be readily detected requiring only microgram-quantities of cerebellar homogenate. Heme oxygenase activity measurements from discrete brain regions revealed for the first time marked differences in enzyme activity with the increasing order: frontal cortex < cerebellum = caudate-putamen < hippocampus = hypothalamus = colliculi << trapezoid body. This activity pattern closely reflects the distribution of immunoreactivity and mRNA for heme oxygenase. The present microassay should offer a valuable tool for studies directly assessing a possible role for CO in neural signaling.

Animals↗

PubMed1995

Cholinergic signaling in the rat pineal gland.

1. Innervation of the mammalian pineal gland is mainly sympathetic. Pineal synthesis of melatonin and its levels in the circulation are thought to be under strict adrenergic control of serotonin N-acetyltransferase (NAT). In addition, several putative pineal neurotransmitters modulate melatonin synthesis and secretion. 2. In this review, we summarize what is currently known on the pineal cholinergic system. Cholinergic signaling in the rat pineal gland is suggested based on the localization of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), as well as muscarinic and nicotinic ACh binding sites in the gland. 3. A functional role of ACh may be regulation of pineal synaptic ribbon numbers and modulation of melatonin secretion, events possibly mediated by phosphoinositide (PI) hydrolysis and activation of protein kinase C via muscarinic ACh receptors (mAChRs). 4. We also present previously unpublished data obtained using primary cultures of rat pinealocytes in an attempt to get more direct information on the effects of cholinergic stimulus on pinealocyte melatonin secretion. These studies revealed that the cholinergic effects on melatonin release are restricted mainly to intact pineal glands since they were not readily detected in primary pinealocyte cultures.

Acetylcholinesterase↗

PubMed1995

Effects of melatonin implants in spring on testicular regression and moulting in adult male raccoon dogs (Nyctereutes procynoides).

Six male raccoon dogs were treated with constant-release implants of melatonin on 29 March, when the animals still had mature spermatozoa and a winter coat. Six untreated animals served as controls. High serum concentrations of melatonin were found in the treated animals throughout the study period (182.2 and 38.5 pg ml-1 in April and August, respectively). The high serum concentrations of prolactin in April and May (18.9 and 15.7 ng ml-1, respectively) in the controls were not seen in the treated animals. Testicular regression, judged by width of the testis and stage of spermatogenesis, was slowed after melatonin administration. Testis width from April to June and stage of spermatogenesis in May and June were greater in the treated animals than in the controls; however, from July onwards the differences between the two groups were no longer significant. Serum concentrations of testosterone remained low (below the detection limit in most cases) in both treated and control animals throughout the study period. Melatonin treatment also affected moulting, which was assessed by changes in the number of growing and mature underfur hairs per bundle and the percentage of bundles with a growing guard hair. The treated animals showed a more rapid shedding of mature underfur hairs and growth of new underfur hairs 6 weeks after melatonin implantation compared with the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Differential regulation of cyclic GMP levels in the frontal cortex and the cerebellum of anesthetized rats by nitric oxide: an in vivo microdialysis study.

A microdialysis method combined with a sensitive radioimmunoassay was used to monitor extracellular cyclic GMP (cGMP) levels in the frontal cortex and the cerebellum of anesthetized rats in vivo. Basal cGMP release remained constant throughout the perfusion period and was approximately 2 fmol/30 min in the frontal cortex and approximately 4 fmol/30 min in the cerebellum. The nitric oxide (NO) donor sodium nitroprusside (SNP) stimulated cGMP release transiently in both regions. However, the maximal response was 3-fold in the frontal cortex (obtained with 5 microM SNP) but 90-fold in the cerebellum (obtained with 1 mM SNP). Perfusion with the NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) suppressed cerebellar cGMP release by 74% indicating that NO is the major regulator of basal cGMP levels in the cerebellum. Quite opposite, L-NAME exhibited no potency in the frontal cortex suggesting that other activators of guanylyl cyclase may regulate basal cortical cGMP levels in vivo.

Animals↗

PubMed1994

Different patterns of light exposure in relation to melatonin and cortisol rhythms and sleep of night workers.

There is strong evidence to suggest that circadian psychophysiological adaptation processes are modified by light, depending on its intensity and timing. To characterize such modifications and determine whether they are associated with an alteration in the day/night pattern of melatonin excretion, measurements were obtained around the clock in 14 permanent night workers, each studied over a 48 hr period in the field. The light exposure behavior of these workers was studied with a newly developed light dosimetry by measuring light intensity at eye level. Physical activity was continuously registered and sleep indices were obtained by sleep logs and activity markings. Circadian rhythms of melatonin and cortisol were analysed from salivary samples collected for 24 hr at 2 hr intervals. The interindividual variation of melatonin acrophase determined by cosinor analysis was greater than 180 degrees (from around midnight to noon) and that of cortisol was about 135 degrees (from early morning to afternoon). Hormonal phase positions coincided significantly with light exposure: the more bright light pulses in the morning (maximum lux between 0600 and 0900), the less were the melatonin and cortisol acrophases shifted into the day. There was also a negative correlation between melatonin acrophase shift and duration of the overall light exposure above 1500 lux. Morning light maximum and sleep onset correlated highly significantly. Night workers were divided into those with less than ('non-shifters', n = 9) and more than 6 hr deviation from midnight ('shifters', n = 5) of the melatonin acrophase. The group comparison revealed a marked difference of the mean melatonin concentrations at night, and at 0700.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Age and adjustment to night work.

OBJECTIVE: The study was designed to examine the effects of age on sleep and the circadian rhythms during consecutive night shifts. METHODS: Two groups of letter sorters (19-29 (n = 7) and 53-59 (n = 7) years of age were studied in a sleep laboratory under closely controlled conditions. After two baseline days, circadian adjustment to three night shifts was monitored by continuous measurement of rectal temperature, salivary melatonin, and sleep-wakefulness during the night shifts. RESULTS: Age was significantly related to the adjustment to night work of rectal temperature minimum and of self rated sleepiness. Young subjects delayed their temperature phase and decreased sleepiness more than the older subjects. Age was also significantly related to an increase of alertness and to the feeling of being refreshed after the day sleep. Although there were basic differences in sleep duration and structure between the age groups, the latter did not change across the night shifts. CONCLUSION: Aging decreases the ability to recover after several, but not after the first night shift.

Adaptation, Physiological↗

PubMed1993

Dopamine stimulates K+ efflux in the chick retina via D1 receptors independently of adenylyl cyclase activation.

Dopamine (DA) stimulated K+ efflux (assessed as 86Rb+ efflux) in retinal suspensions of posthatched chicken. This effect was dose dependent (EC50 = 22 microM), was mimicked by the D1-selective agonist SKF-38393, and reversed by the D1-selective antagonist SCH-23390, indicating an involvement of D1 receptors. Analogues of cyclic AMP (cAMP) did not mimic the DA action. Moreover, DA failed to affect cAMP levels, suggesting that adenylyl cyclase (AC) was not involved. In contrast, forskolin (FSK) stimulated both K+ efflux and cAMP accumulation in the retina (EC50 of 10 microM for both effects). The FSK-elicited K+ efflux was not mimicked by 1,9-dideoxy-FSK (an analogue of FSK that does not activate AC), suggesting that FSK stimulated K+ efflux through the activation of AC. Both DA and FSK inhibited Na+,K(+)-ATPase activity in the retina. However, the DA-elicited K+ efflux was independent of this inhibition, whereas the FSK effect on K+ efflux was largely due to the inhibitory action of the diterpene of the ion pump. A possible role of protein kinase C (PKC) in the DA action was explored. The PKC activator 4 beta-phorbol 12-myristate 13-acetate (4 beta-PMA) potently (EC50 = 4 nM) stimulated K+ efflux. This action was not mimicked by the inactive isomer 4 alpha-PMA. When added together, DA and 4 beta-PMA behaved in an additive manner, suggesting separate mechanisms of action for these two drugs. Moreover, DA failed to stimulate retinal phosphoinositide hydrolysis, a well-known pathway leading to PKC activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗

PubMed1993

Renal melatonin excretion in sheep is enhanced by water diuresis.

Diurnal variation in blood melatonin levels and renal melatonin excretion was monitored in five ewes by blood sampling and quantitative urine collection at 2-h intervals. A typical secretory pattern of melatonin was seen both in blood and urine levels and in the renal excretion of melatonin. Serum melatonin levels increased from daytime values of approximately 200 pmol/l to a mean of 800 pmol/l during darkness. Urine flow rate and urine osmolality did not show any clear diurnal rhythm. To examine whether urine flow rate affects renal melatonin excretion at night, urine was collected in three consecutive 30-min fractions, and blood was sampled in the middle of each urine collection period when the sheep were in normal water balance or after hydration. Hydration increased urine flow rate over sixfold and decreased urine osmolality well below plasma osmolality. Glomerular filtration rate, measured as creatinine clearance, did not change. Serum melatonin concentrations did not differ between hydrated and non-hydrated sheep. However, urinary melatonin excretion was 1.1 +/- 0.3 (S.E.M.) pmol/min at midnight in normal water balance, and significantly higher (2.6 +/- 0.4 pmol/min) in the hydrated state. In this study, the validity of urinary melatonin determinations as an indicator of pineal function was confirmed in normal water balance. In addition, our results suggest that a high tubular fluid load during diuresis increases urinary melatonin excretion because of decreased tubular reabsorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Pineal muscarinic phosphoinositide responses: age-associated sensitization, agonist-induced desensitization and increase in melatonin release from cultured pineal glands.

Regulation of phosphoinositide (PI) signaling through the muscarinic cholinergic receptors (mAChRs) and their possible role were explored in the rat pineal gland. A sensitization of the PI signaling pathway was seen with advancing age. Binding of the mAChR ligand [N-methyl-3H]scopolamine to pineal sections, as detected by autoradiography, significantly decreased with advancing age and thus negatively correlated with the gland's ability to respond to cholinergic stimulus. The cholinergic agonist carbachol induced a time-dependent desensitization of the muscarinic PI signaling after 2 h of pretreatment in vitro (43 and 61% dampening of the PI response after 2 and 11 h pretreatment, respectively). This homologous desensitization was not mimicked by forskolin or phorbol esters, suggesting that proteins kinases A and C were not involved. Carbachol stimulation of the pineal glands in vitro increased melatonin release 2-fold, an effect quantitatively similar to that seen after adenylyl cyclase activation. Carbachol failed, however, to affect pineal cAMP levels. These results suggest that the PI signaling through pineal mAChRs is desensitized in young rats, possibly due to higher exposure to endogenous acetylcholine. Thus acetylcholine might play a prominent role in the developing gland. Moreover, acetylcholine could modulate melatonin release from the adult pineal gland in vivo.

Aging↗

PubMed1992

Differential expression of melatonin receptors in spontaneously hypertensive rats.

Quantitative autoradiography was used to compare melatonin receptors in brain areas and arteries of young (4 weeks old) and adult (14 weeks old) spontaneously hypertensive rats (SHR) to those in age-matched normotensive controls, Wistar-Kyoto (WKY) rats. Age and strain influenced the number of melatonin receptors in an anatomically selective manner, and the most striking changes occurred in arterial receptors. Melatonin receptors were not detectable in the anterior cerebral arteries of adult SHR. In the caudal artery, melatonin receptors decreased with age in both strains, but the decrease was more pronounced in SHR. When compared to age-matched WKY rats, the number of caudal artery receptors was higher in young and lower in adult SHR. The number of melatonin receptors was higher in the area postrema of adult SHR when compared to adult WKY rats, but in the suprachiasmatic nucleus, no such differences between the two strains were present. Alterations in receptor density were not accompanied by changes in binding affinity. Our results indicate that in the rat melatonin receptors show different developmental patterns according to location and that the receptors may be expressed differentially in genetic hypertension.

Age Factors↗

PubMed1992

Differential regulation of the rat melatonin receptors: selective age-associated decline and lack of melatonin-induced changes.

To gain some understanding of the factors regulating high affinity melatonin (MT) receptors in the rat, we conducted a series of studies using quantitative autoradiography of [2-125I]iodo-MT binding in vitro with validated assay conditions. MT receptor status and the relative protein content of the autoradiographic sections were assessed in the anterior pituitary gland, the area postrema, the caudal (tail) artery (CA), the anterior cerebral artery (ACA), and the suprachiasmatic nuclei (SCN) of 9-, 96-, and 306-day-old Wistar rats. When age-associated changes in protein content were taken into account, MT receptor expression in the area postrema and the SCN remained relatively constant between 9-306 days of age. On the contrary, a dramatic loss of MT receptors was observed in the arteries of 306-day-old rats (98% and 89% loss compared to the 9-day-old rats in the ACA and CA, respectively). In the anterior pituitary gland, MT receptors were expressed only in the 9-day-old rats. The above changes reflected major changes in binding capacity and minor changes in binding affinity. Neither removal of endogenous circulating MT (acute light exposure for 24 h, pinealectomy, or superior cervical ganglionectomy) nor MT injections (1 mg/kg for 10 days 6 h after lights on) affected MT receptor status in the ACA, CA, area postrema, or SCN. Our data suggest that MT receptor expression is differentially regulated during development and that permanent alterations in MT levels do not affect rat MT receptor status.

Age Factors↗

PubMed1990

The chick retinal melatonin receptor revisited: localization and modulation of agonist binding with guanine nucleotides.

The chick retinal melatonin receptor was localized to the inner plexiform layer using 2-125I-melatonin and in vitro autoradiographic techniques. This receptor was of high affinity (Kd 19.8 pM) and specificity and showed guanine nucleotide modulation of agonist binding. It thus behaves similarly to other recently characterized high affinity melatonin receptors.

Animals↗