Suspended chlorophyll in the River Nene, a small nutrient-rich river in eastern England: long-term and spatial trends.

The distribution of suspended algae was investigated in a 69-km length of a small lowland river in the UK, the Nene, using chlorophyll as a measure of biomass. Variations in chlorophyll data collected between 1975 and 1996 by water management organisations at a downstream site (km 91.7) were evaluated against a range of physical and chemical variables. Interpretation was aided by additional sampling at eight sites on the main river (including km 91.7) and three tributaries between 1994 and 1996. Significant inter-year variation was evident in all data and was most pronounced in discharge. The latter half of the 22-year period had significantly higher temperature and light and significantly lower ammonia concentrations. Discharge, temperature and light were significant predictors of chlorophyll concentration, particularly between January and June, and spring chlorophyll maxima ranged from 106 to 276 microg l(-1). Summer chlorophyll concentrations were generally low relative to spring peaks. Some summers, however, had very low chlorophyll concentrations (average < 10 microg l(-1)) which were independent of the controlling factors at other times and inter-year variation in submerged macrophyte abundance is proposed as a causal factor for their occurrence. Spring chlorophyll peaks occurred earlier and had smaller amplitude at downstream sites compared to those further upstream. Average spring chlorophyll concentration (April-June) increased significantly between km 22.4 and 43.9, thereafter remaining high to km 91.7. Spatial trends were attributed to changes in channel morphology, retention time and longitudinal variations in velocity and temperature.

Changes in sodium channel function during postnatal brain development reflect increases in the level of channel sialidation.

Developmental changes of forebrain sodium channels were studied at three postnatal ages: P0, P15 and adult (P30/P180). Electrophysiological analysis determined that the midpoint potential of activation was -64, -75 and -81 mV for P0, P15 and adult channels, respectively. At negative potentials, gating state changes were observed in all channels; at positive potentials they were observed in most P0 (72%) and to a lower extent in older channels (25%). A long non-conductive state was displayed with a higher frequency in P0 than in older channels. Immunoblot analysis determined that the apparent molecular weight was approximately 227, approximately 241 and approximately 246 kDa for P0, P15 and adult channels, respectively. Upon neuraminidase treatment, which cleaves sialic acids, these differences in molecular weight were abolished. The data suggest that these developmental changes in the function of forebrain sodium channels correlate with changes in the channel's sialidation level.

Vasoactive intestinal peptide stimulates neuropeptide Y gene expression and causes neurite extension in PC12 cells through independent mechanisms.

Vasoactive intestinal peptide (VIP) is widely recognized as a regulator of tyrosine hydroxylase via a mechanism of trans-synaptic activation. Subsets of adrenal medullary cells and postganglionic sympathetic nerves coexpress the peptide neurotransmitter neuropeptide Y (NPY) with catecholamines. Using PC12 cells transiently expressing a fusion gene in which the bacterial enzyme chloramphenicol acetyltransferase (CAT) is under the control of 700 base pairs of the 5' flanking region of the NPY gene, we have studied the role of VIP and the related peptide pituitary adenylate cyclase activating peptide (PACAP) in regulating NPY gene transcription. Both VIP and PACAP stimulated expression of the NPY gene through activation of cAMP-dependent protein kinase. PACAP was 1000-fold more potent in eliciting this response compared to VIP and activity resided in its N-terminal 27 amino acids. Both VIP and PACAP caused a subpopulation (approximately 50%) of PC12 cells to undergo profound morphological changes in that the cells extended long, slender neurites with prominent growth cones. This change in morphology was unaffected by preincubating cells with inhibitors of either cAMP-dependent protein kinase or calcium/phospholipid-dependent protein kinase. A trophic role for either VIP or PACAP in regulating sympathetic nerve function is proposed.

Expression of sodium channels with different saxitoxin affinity during rat forebrain development.

This work characterizes the development of the saxitoxin (STX)-sensitive Na+ channels from rat whole forebrain between embryonic day 15 (E15) and postnatal day 90 (P90), both with binding studies and with single channel studies. The Na+ channel total mRNA and the individual mRNAs encoding Na+ channels I, II and III were also determined. The total STX binding rose about 40-fold from E15 to reach a plateau at P30 and its temporal course correlated with the expression of Na+ channel total mRNA. Low affinity and high-affinity STX binding sites, predominant in embryonic and postnatal forebrains, respectively, were found. The single channel studies of batrachotoxin-modified channels also revealed two main populations. In E15 only low-affinity channels (KD = 32.7 nM; 200 mM NaCl) and in P30 only high affinity ones (KD = 1.6 nM) were present. At P0 channels with intermediate affinity (KD range 3-34 nM) were observed. The increase in affinity was due to a gradual increase in the STX association rate.

Role of protein kinase C in mediating NGF effect on neuropeptide Y expression in PC12 cells.

Neuropeptide Y (NPY) is a 36 amino acid peptide present in the central and peripheral nervous systems. Treatment with Nerve Growth Factor (NGF) induces an increase in NPY mRNA in PC12 cells, a rat pheochromocytoma cell line extensively used as a model of neuronal differentiation. Stimulators of both cAMP and calcium-phospholipid dependent protein kinases (PKA and PKC respectively) increase NPY mRNA levels in a similar way to NGF. Nevertheless, H-89, a specific inhibitor of PKA failed to block NGF stimulated NPY mRNA accumulation. Furthermore, direct measurement of PKA activity in cell extracts showed no increase following NGF, in contrast to forskolin. H7, an inhibitor of both PKC and PKA systems completely abolished the NGF induced increase in NPY mRNA, suggesting that PKC is necessary for NGF induction of the NPY gene. NGF also increased PKC activity in cell extracts in a similar way to phorbol myristate acetate (PMA). Use of a reporter function, chloramphenicol acetyl transferase, controlled by 700 base pairs of the 5' flanking region of the NPY gene demonstrated that NGF and phorbol ester stimulated transcription of the NPY gene. This stimulation could be blocked by pre-incubating PC12 cells with calphostin C, a specific inhibitor of PKC. Our results indicate that NGF induces NPY gene expression via activation of PKC system. Although an increase in adenylate cyclase activity affects the expression of the NPY gene, activation of PKA appears not to be involved in mediating the NGF effects.

Reconstitution of sodium channels in large liposomes formed by the addition of acidic phospholipids and freeze-thaw sonication.

Phosphatidylcholine (PC) alone or with phosphatidylethanolamine (PE) are sufficient for the reconstitution of Na+ channels in planar lipid bilayers. However, when Na+ channels were first reconstituted into liposomes using the freeze-thaw-sonication method, addition of acidic phospholipids, such as phosphatidylserine (PS), to the neutral phospholipids was necessary to obtain a significant toxin-modulated 22Na uptake. To further investigate the acidic phospholipid effect on reconstitution into liposomes, Na+ channels purified from Electrophorus electricus electrocytes were reconstituted into liposomes of different composition by freeze-thaw sonication and the effect of batrachotoxin and tetrodotoxin on the 22Na flux was measured. The results revealed that, under our experimental conditions, the presence of an acidic phospholipid was also necessary to obtain a significant neurotoxin-modulated 22Na influx. Though neurotoxin-modulated 22Na fluxes have been reported in proteoliposomes made with purified Na+ channels and PC alone, the 22Na fluxes were smaller than those found using lipid mixtures containing acidic phospholipids. Electron microscopy of negatively stained proteoliposomes prepared with PC, PC/PS (1:1 molar ratio), and PS revealed that the acidic phospholipid increases the size of the reconstituted proteoliposomes. The increment in size caused by the acidic phospholipid, due to the associated increase in internal volume for 22Na uptake and in area for Na+ channel incorporation, appears to be responsible for the large neurotoxin-modulated 22Na fluxes observed.

TSH circadian secretions in aged men and effect of phosphatidylserine treatment.

In 20 euthyroid aged men (from 65 to 85 years of age) no significant circadian periodicity of thyrotropin (TSH) secretion has been shown by the population mean cosinor method. At the end of a period of 30 days of hospitalization the cosinor evaluation of TSH secretion showed a restored highly significant (p less than 0.001) circadian rhythmicity in phosphatidylserine (PS) (400 mg/daily) treated group (10 aged subjects). By contrast, hospitalization seems to further deteriorate the periodicity of the hormone secretion in 10 placebo-treated subjects.

Thyrotropin and prolactin responses to different doses of thyrotropin-releasing hormone in depression.

The effects of low doses of thyrotropin-releasing hormone (TRH, 50 and 200 micrograms) on thyrotropin (TSH) and prolactin levels have been studied in depressed women and compared with the depressive condition and with the results of the dexamethasone suppression test (DST). TRH administration elicited blunted hormonal responses that were not correlated either with the age of the patients or with DST results. Different effects were observed in subgroups of depressive patients classified according to DSM III and ICD. No correlation was found between hormone responses and the scores of Hamilton Rating Scale and Montgomery Depression Scale. The effects of 50 micrograms on TSH were significant and inversely correlated with Anxiety Rating Scale scores. No dose-response effect was apparent of prolactin and TSH in depressed patients, suggesting an impaired function of pituitary TRH receptors.

Thyroid-stimulating hormone and prolactin responses to thyrotropin-releasing hormone in common migraine.

Intravenous administration of 50 micrograms or 200 micrograms thyrotropin-releasing hormone (TRH) to men with common migraine elicited blunted prolactin (PRL) responses, when compared with healthy controls. The thyroid-stimulating hormone (TSH) response was enhanced after 50 micrograms TRH in the migraineurs, but not after 200 micrograms. The physiologic TSH dose-response relationship was abolished in migraine sufferers. The data may be interpreted in the light of dopaminergic and noradrenergic supersensitivity, for PRL and TSH, respectively. The TSH response in migraine differs from the one that occurs in depression.