Sarah Schimchowitsch

Systematic presence of GABA-immunoreactivity in the tubero-infundibular and tubero-hypophyseal dopaminergic axonal systems: an ultrastructural immunogold study on several mammals

SummaryImmunoreactivities for tyrosine hydroxylase (TH), gamma-aminobutyric acid (GABA) and, in some cases, glutamic acid decarboxylase (GAD) were detected by light and electron microscopy in axons projecting into the median eminence and pituitary gland of various mammals (rats, mice, guinea pigs, cats, rabbits and hares). Light microscope immunoperoxidase reactions were performed on adjacent semithin sections of plasticembedded samples. In the median eminence external zone, the distributions of the TH- and GAD- or GABA-immunoreactive endings were very similar in the anterior and lateral areas, while medially the GABA-labelled endings predominated. Comparable distribution patterns were found in the various species examined. In the pituitary gland, the distributions of GABA- and TH- immunoreactivities were superimposable in the intermediate lobes of all species examined, except in the rabbit and hare in which both types of innervation were lacking. For electron microscopy, the immunogold procedure was applied to sections of lowicryl-embedded samples; simultaneous detection of GABA- and TH-immunoreactivities was enabled by recto-verso double labelling with gold particles of distinct diameters. In the median eminence, GABA-immunoreactivity occurred systematically in the TH-positive endings, while distinct GABA-positive/TH-negative axons were also detected. In the intermediate lobe, the colocalization of TH- and GABA-immunoreactivities was a constant feature of the axons innervating the melanotrophic cells in all the species examined, except in the Leporidae. The functional significance of this colocalization remains to be determined.

Synthesis and rheological properties of hydrogels based on amphiphilic alginate-amide derivatives

New amphiphilic derivatives of sodium alginate were prepared by covalent attachment of dodecylamine onto the polysaccharide via amide linkages at different substitution ratios, using 2-chloro-1-methylpyridinium iodide (CMPI) as coupling reagent. The aim was to limit the progressive loss of associative behaviour which occurs in the case of previously described dodecyl ester alginate derivatives due to hydrolysis of ester bonds. A series of hydrogels was obtained which differed by the amount of attached dodecyl tails. The stability and viscoelastic properties were evaluated and compared to those of hydrogels obtained with alginate esters. The observed differences were discussed in relation to the synthesis procedures. The advantages of amide links are underlined, especially with regard to long-term stability of hydrogels.

Immunocytochemical evidence for intragranular processing of pro-opiomelanocortin in the melanotropic cells of the rabbit

SummaryThe immunogold technique, employing antisera with clear-cut specificities, was used to localise different processing stages of pro-opiomelanocortin (POMC) in rabbit melanotropic cells. While the antiserum against γ3-MSH labelled all the secretory granules including intrasaccular condensations in the Golgi apparatus, antisera against α-MSH only labelled extra-Golgi secretory vesicles (SV). All extra-Golgi SV were likewise labelled with the three antisera against α-MSH used, despite their different specificities for the desacetylated, N-acetylated or C-amidated forms of the peptide. The antibody against β-endorphin also labelled the extra-Golgi SV, while only some SV were labelled with the antibody against γ-endorphin. These results correlate with biochemical data in favour of mainly — if not exclusively — intragranular processing of POMC. Except for γ3-MSH, the cleavage of which could coincide with Golgi packaging of secretory material, other post-translational modifications of the precursor seem to occur when SV are discharged outside the Golgi area. The cleavage of γ-endorphin appears to be a later step in POMC processing, occurring in some mature SV.

Oxytocin-immunoreactive nerve fibers in the pars intermedia of the pituitary in the rabbit and hare

SummaryThe pars intermedia of the pituitary in the rabbit and hare is abundantly innervated by axons reacting selectively with antibodies against oxytocin. These axons contain dense secretory vesicles about 140 nm in diameter, i.e., smaller than those in the neurosecretory axons of the neural lobe. No fiber elements staining for other peptides (vasopressin, somatostatin, substance P) were observed in the pars intermedia, except rare leu-enkephalin axons restricted to the rostral zone of the gland. Dopaminergic innervation appears to be completely absent from the intermediate lobe. This was shown by the lack of reaction with an antibody against tyrosine-hydroxylase, which did reveal a well-developed tubero-infundibular system of nerve fibers. Axons reacting with an antibody against serotonin were irregularly distributed in the pars intermedia.In the absence of dopaminergic axons, the extensive oxytocin-like innervation may play a major role in regulating the melanotrophic cell activity in the Leporidae.

Hebb-Williams performance and scopolamine challenge in rats with partial immunotoxic hippocampal cholinergic deafferentation

Recent studies suggested that the cholinergic innervation of the hippocampus is not crucial for spatial learning, but it might be important for other forms of learning. This study assessed the effects of partial immunotoxic cholinergic lesions in the medial septum and concurrent scopolamine challenge in a complex learning task, the Hebb-Williams maze. Long-Evans rats were given intraseptal injections of 192 IgG-saporin (SAPO). Rats injected with phosphate-buffered saline (PBS) served as controls. Starting 25 days after surgery, behavioural performance was assessed in the Hebb-Williams maze test without prior or after injection of scopolamine (0.17 or 0.5 mg/kg, i.p.). In SAPO rats, histochemical analysis showed a 40-45% decrease in the density of hippocampal AChE staining. The number of ChAT-positive cell bodies in the medial septum was also significantly decreased (-56%) and there was a non-significant reduction of the number of parvalbumine-positive neurons. The behavioural results demonstrated that the lesions induced small but significant learning deficits. At 0.17 mg/kg, scopolamine produced more impairments in SAPO rats than in PBS-injected rats, suggesting an additive effect between the partial lesion and the drug. These observations indicate that the Hebb-Williams test may be more sensitive to alterations of septohippocampal cholinergic function, than radial- or water-maze tasks. They also show that subtle learning deficits can be detected after partial lesions of the cholinergic septohippocampal pathways. Finally, the data from the scopolamine challenge are in keeping with clinical results showing higher sensitivity to muscarinic blockade in aged subjects in whom weaker cholinergic functions can be presumed.

Oxytocinergic neurons with tyrosine hydroxylase-like immunoreactivity in the paraventricular nucleus of the rabbit hypothalamus

Antiserum against tyrosine hydroxylase clearly reacts with two types of neurons in the rabbit paraventricular nucleus: catecholaminergic neurons, also present in rat and mouse, and neurons also staining for ocytocin and neurophysin; the latter neurons have not been reported in other species. This result raises the question of a possible aminergic potentiality of a subpopulation of oxytocinergic neurons in the rabbit hypothalamus.

Living alongside railway tracks: Long-term effects of nocturnal noise on sleep and cardiovascular reactivity as a function of age

Very few studies were devoted to permanent effects of nocturnal railway noise on sleep and cardiovascular reactivity. We investigated the effects of nocturnal railway noise on sleep and cardiovascular response in young and middle-aged adults living for many years either near a railway track or in a quiet area. Forty subjects (50% males) divided into two age groups (juniors: 26.2+/-3.6 and seniors: 56.2+/-4.2) participated in this experiment. Half of them lived near a railway track (RW group: 2.6 to 19 years) and the other half in a quiet environment (QE group: 8.1 to 14.2 years). After an adaptation night, all subjects underwent two nights in the laboratory: one control night and one noisy night (30 by-passes of a freight train). Sleep and cardiovascular modifications were assessed in response to noise. Sleep fragmentation indices were lower in RW subjects compared to QE whatever their age. In response to noise, there was a higher cardiovascular response rate to noise in RW juniors and a lower cardiovascular response rate in RW seniors compared to their age-paired QE counterparts. In conclusion, permanent exposure to nocturnal railway noise leads to decreased sleep fragmentation and to cardiovascular habituation. It is suggested that during the initial period experienced by residents living near railway tracks, nocturnal railway noise could induce a sensitization process on the autonomic response to noise reflecting a startle/defense reflex due to its functional significance, which progressively turns to habituation in the long-term if no adverse effect is experienced.

Absence of inhibitory dopaminergic control of the rabbit pituitary gland intermediate lobe.

No immunoreactive axons were detected with an antiserum against tyrosine hydroxylase in the rabbit intermediate lobe (IL), which thus appears to be devoid of dopaminergic (DA) innervation. Dopamine and its agonists, which classically inhibit alpha-MSH release have no inhibitory effects on rabbit IL superfused in vitro but, paradoxically, stimulate alpha-MSH release. D2 type DA receptors, known to mediate inhibitory control of dopamine on melanotropic cells, and detectable by their affinity for (3H)-spiroperidol, were as previously reported absent from the rabbit IL. The absence of (3H)-spiroperidol binding sites in the IL was further confirmed on rabbit pituitary sections by radioautography. The mechanism of DA stimulation is still not clear, but might be tentatively explained by interference with other receptors involved in the stimulation of the gland. The lack of DA inhibitory control over the rabbit IL is an exception among the species so far studied.

Polyamine and aminoguanidine treatments to promote structural and functional recovery in the adult mammalian brain after injury: a brief literature review and preliminary data about their combined administration.

The regeneration potential of the adult mammalian central nervous system (CNS) is very modest, due to, among other factors, the presence of either a glial scar, or myelin-associated regeneration inhibitors such as Nogo-A, MAG and OMgp, which all interact with the same receptor (NgR). After a brief review of the key proteins (Rho and PKC) implicated in NgR-mediated signalling cascades, we will tackle the implications of cAMP and Arginase I in overcoming myelin growth-inhibitory influence, and then will focus on the effects of polyamines and aminoguanidine to propose (and to briefly support this proposal by our own preliminary data) that their association might be a potent way to enable functionally-relevant regeneration in the adult mammalian CNS.

Effects of acute and chronic sleep deprivation on daytime alertness and cognitive performance of healthy snorers and non-snorers

BACKGROUND Respiratory events during sleep usually lead to micro arousals resulting in consecutive daytime sleepiness even in healthy snorers. The present study investigated the evolution of subjective and objective daytime sleepiness and reaction time in healthy snorers submitted to acute and chronic sleep deprivation. METHODS Objective sleepiness was measured by the MSLT, subjective sleepiness by the Karolinska Sleepiness Scale (KSS), and reaction time (RT) by the Psychomotor Vigilance Test. Mean sleep latencies, KSS scores and performance were analyzed through repeated measures ANOVAs with one between-factor (snorers and non-snorers) and two within-factors (sleep deprivation [baseline, acute, and chronic sleep deprivation] and time-of-day). RESULTS The findings reveal that sleep deprivation does not enhance snoring but that, during baseline, objective daytime sleepiness is higher in snorers than in non-snorers (shorter sleep latencies) with no difference in subjective assessments. The effects of acute and chronic sleep deprivation on sleep are similar in both groups, but, after acute sleep deprivation, RT and attentional lapses (RT >500 ms) are higher in snorers. Chronic sleep deprivation produces similar results in both groups. CONCLUSION These results suggest that respiratory efforts may be involved in the increased vulnerability to sleep deprivation of healthy snorers when compared to non-snorers.