Age-related changes underlie switch in netrin-1 responsiveness as growth cones advance along visual pathway.

Retinal axons are led out of the eye by netrin-1, an attractive guidance cue which is secreted at the optic nerve head. In the optic pathway, however, netrin-1 is expressed in areas that exclude retinal axon growth. This suggests that axons may change in their responsiveness to netrin-1 as they advance along the pathway. Indeed, in our 'whole-pathway' preparation in Xenopus, a gradual change from attraction to repulsion occurred as retinal axons emerged from progressively distal points along the pathway. We also found that axons that were aged in culture without pathway experience underwent a similar change, which correlated with a decline in cyclic AMP (cAMP) and netrin-1 receptor expression. Cyclic AMP elevators and adenosine A2b receptor agonists rejuvenated the behavior of old growth cones, causing them to regain attraction to netrin-1, whereas antagonists caused young growth cones to be repelled. These findings show that netrin-1 responsiveness is developmentally regulated and suggest that intrinsic changes that lower cAMP levels underlie this regulation.

Ephrin-B regulates the Ipsilateral routing of retinal axons at the optic chiasm.

In Xenopus tadpoles, all retinal ganglion cells (RGCs) send axons contralaterally across the optic chiasm. At metamorphosis, a subpopulation of EphB-expressing RGCs in the ventrotemporal retina begin to project ipsilaterally. However, when these metamorphic RGCs are grafted into embryos, they project contralaterally, suggesting that the embryonic chiasm lacks signals that guide axons ipsilaterally. Ephrin-B is expressed discretely at the chiasm of metamorphic but not premetamorphic Xenopus. When expressed prematurely in the embryonic chiasm, ephrin-B causes precocious ipsilateral projections from the EphB-expressing RGCs. Ephrin-B is also found in the chiasm of mammals, which have ipsilateral projections, but not in the chiasm of fish and birds, which do not. These results suggest that ephrin-B/EphB interactions play a key role in the sorting of axons at the vertebrate chiasm.

Growth-cone attraction to netrin-1 is converted to repulsion by laminin-1.

Growing axons are guided by both diffusible and substrate-bound factors. Growth cones of retinal neurons exhibit chemoattractive turning towards the diffusible factor netrin-1 in vitro and are guided into the optic nerve head (ONH) by localized netrin-1. Here we report that, in Xenopus, laminin-1 from the extracellular matrix (ECM), converts netrin-mediated attraction into repulsion. A soluble peptide fragment of laminin-1 (YIGSR) mimics this laminin-induced conversion. Low levels of cyclic AMP in growth cones also lead to the conversion of netrin-induced attraction into repulsion, and we show that the amount of cAMP decreases in the presence of laminin-1 or YIGSR, suggesting a possible mechanism for laminin's effect. At the netrin-1-rich ONH, where axons turn sharply to leave the eye, laminin-1 is confined to the retinal surface. Repulsion from the region in which laminin and netrin are coexpressed may help to drive axons into the region where only netrin is present, providing a mechanism for their escape from the retinal surface. Consistent with this idea, YIGSR peptides applied to the developing retina cause axons to be misdirected at the ONH. These findings indicate that ECM molecules not only promote axon outgrowth, but also modify the behaviour of growth cones in response to diffusible guidance cues.

Patterns of alcohol use among methadone clients in a Glasgow housing estate.

Research on the relationship between methadone and alcohol has produced varying and sometimes contradictory results, such that being prescribed methadone has been associated with different patterns of drinking and degrees of problem drinking. Little is known about the mediating influence of sociocultural factors in relation to these variations. This article is an assessment of the nature and extent of alcohol use among a sample of people being prescribed methadone in a Glasgow housing estate, identifying factors which influenced alcohol use, and assessing the role of sociocultural factors. Data were collected through ethnographic methods and short self-completion questionnaire from 32 methadone clients. Typically, current problem drinking was not a feature of this sample. Most participants experimented with alcohol in their teenage years; however, their use of alcohol decreased to minimal or ended completely as they became increasingly involved with other drugs, especially opiates. Use of opiates became incompatible with use of alcohol for the following reasons: becoming an opiate user interrupts the typical process of becoming a "novice drinker" in adolescence; through a process of labeling and self-identification the "drug addict" both opts out of and is excluded from the mainstream drinking culture; if, despite these previous conditions, the opiate user does drink, adverse physical effects reported by the participants are sufficient to act at least as a partial deterrent to further use of alcohol. For most of the participants in the study, these three factors continue to influence current use of alcohol and in combination would appear to offer some explanation for the low levels of reported drinking.

Maturation of the mammalian dorsal root entry zone--from entry to no entry.

Interfaces between glial cell precursors of the PNS and CNS are established early in development and form the sites where sensory axons enter and motor axons exit the developing CNS. The molecular and cellular interactions that lead to the formation of these glial interfaces are only now becoming apparent. New in-vitro techniques are providing clues as to how the maturation of PNS-CNS glial interfaces generates barriers to regenerating axons.

Illicit use of ketamine in Scotland.

Semistructured interviews were carried out with 20 illicit users of ketamine in Scotland. Participants had used a wide range of illegal drugs. Scottish drug agencies reported limited contact with ketamine users; however, subjects were knowledgeable regarding the licit purpose of ketamine, its effects, and its legal status. Ketamine was usually obtained through diversion from legitimate sources. Three participants reported extensive use, indicating the potential for psychological dependence. A standard dose of ketamine was typically 1/8 g, usually taken intranasally. Participants reported the ketamine experience as being extremely intense and dissociative, usually lasting for approximately one hour. All participants reported using ketamine in a carefully preplanned setting, emphasizing comfort, security, and familiarity. Participants identified potential problems arising from using ketamine in a public place, or in unfamiliar surroundings, and also suggested that novice users may encounter problems through lack of knowledge concerning the intense nature of the experience. Accurate information concerning the effects and nature of ketamine as well as the importance of set and setting should be made available. However, publicizing the drug should be avoided as widespread interest could cause greater problems than currently exist.

mCD24, a glycoprotein transiently expressed by neurons, is an inhibitor of neurite outgrowth.

In the immune system, mCD24, the mouse homolog of the human glycosyl phosphatidylinositol-anchored glycoprotein CD24, may play a role in cell adhesion. In the nervous system, the function of mCD24 has not been determined, but its transient expression by neurons suggests that it may be involved in axon growth in development. Here we show that retinal ganglion cells (RGCs) and dorsal root ganglion (DRG) neurons express mCD24 in the developing but not adult mouse in vivo and in DRG neurons of the injured adult peripheral nervous system (PNS). In vitro, mCD24 was expressed by immature neurons and by a subpopulation of adult DRG neurons. To analyze the possible function of mCD24 in the nervous system, we prepared rat C6 glioma cells stably transfected or retrovirally infected with mCD24 cDNA. The cells did not exhibit changes in their adhesive properties or cell division rate after transfection or infection. When mCD24-expressing cells were used as monolayer substrates for culturing RGCs and DRG neurons, neurite outgrowth was inhibited, depending on neuronal age and on the relative levels of mCD24 in the monolayer. This inhibition, however, was not dependent on the expression of mCD24 by the neurons themselves, because DRG neurons of a mouse deleted of the mCD24 gene showed the same response. These results show that mCD24 interacts in a heterophilic manner with a developmentally regulated molecule expressed by neurons, and they suggest that in vivo, mCD24 may inhibit the further extension or collateral branching of axons in late embryonic development.

An in vitro model of the rat dorsal root entry zone reveals developmental changes in the extent of sensory axon growth into the spinal cord.

The dorsal root entry zone (DREZ) forms the junction between the dorsal roots of the peripheral nervous system and the spinal cord. In rats older than 1 week, lesioned primary sensory axons regenerate within the dorsal roots but stop at the DREZ, and are thus unable to reconnect with the spinal cord. To analyze the causes of this failure, we have developed a culture model of the interaction of sensory axon growth cones with the intact DREZ, whereby dissociated dorsal root ganglion neurons from rats of various ages are grown on longitudinal cryosections of rat spinal cord, incorporating the DREZ and attached dorsal roots, from neonatal, 1-week-old (P6), or adult animals. Neurites of all ages grew along the roots to the DREZ, where their ability to cross into the spinal cord depended on both their age and that of the spinal cord substrate. Neurites from neonatal neurons failed to cross either the P6 or adult DREZ, but a substantial proportion crossed the immature neonatal DREZ. Early embryonic neurites exhibited substantial crossing on both immature and adult DREZ. These findings strongly suggest that soon after birth, the normal mammalian DREZ acquires growth inhibitory activity that is recognized by the axons of postnatal but not early embryonic sensory neurons.

Patterns of injecting and sharing in a Scottish prison.

Although the potential for prisons to act as the setting for HIV transmission has been recognised, there is an enduring lack of knowledge in this area. Data are presented on patterns of injecting and sharing in Edinburgh prison (Scotland), 1993-1994. There was a relatively low level of injecting in Edinburgh prison during this period, with 13% (8/60) of a sample of drug users having injected at some point during their current sentence. The majority (6/8) of those who had injected had shared injecting equipment. Where sharing took place, the level of HIV risk was variable, but would have been higher had cleaning fluids not been available within the prison, or had they not been used by sharers. The implications of this study for drug service provision in prisons is discussed.

Extensive regeneration in vitro by early embryonic neurons on immature and adult CNS tissue.

The failure of axon regeneration in the injured adult CNS has been ascribed to axon growth inhibitory molecules expressed by the resident glial cell populations, especially oligodendrocytes. Unlike their adult counterparts, however, early embryonic neurons are able to send lengthy axons through myelinated fiber tracts when transplanted into the adult brain. One explanation is that they have yet to express receptors for factors that inhibit the growth of older neurons. To test this possibility, we have used the cryoculture technique to study the regeneration of rat central and peripheral neurons, over a developmental period that encompasses the stages before, during, and after target contact, when cultured on either unmyelinated (neonatal) or myelinated (adult) optic nerve tissue sections. Early embryonic (days 14-15) retinal ganglion cells extended neurites on neonatal optic nerve, but few grew on adult optic nerve. In the case of early embryonic dorsal root ganglion neurons, however, neurite outgrowth on either neonatal optic nerve or on adult optic nerve was extensive. This response declined sharply with age. In contrast, neurite outgrowth by dorsal root ganglion neurons on laminin substrata remained relatively constant (> 80% extended neurites) over the same period. This suggests that (a) inhibition of neurite outgrowth within the optic nerve is mediated not only by oligodendrocytes, but also by molecules expressed prior to the onset of myelination; (b) neurons acquire receptors for these inhibitors only late in embryonic development; (c) differences exist between developing central and peripheral neurons in the response to myelin-associated axon-growth inhibitors.

Behavioural change amongst drug injectors in Scottish prisons.

A study of injecting behaviour amongst a purposive sample of drug-users in Scottish prisons found that 32% reported injecting prior to current sentence. The percentage of these who were injecting during their current prison sentence (i.e. inside the prison) had fallen to 11%. Of those who were injecting prior to imprisonment, 24% reported sharing injecting equipment at that time. Of those who were still injecting in prison, however, 76% reported sharing equipment. Overall, therefore, there were fewer injectors in prison, but a higher proportion of these shared needles. Factors most closely identified with current sharing of injecting equipment in prison were: (a) having injected a wider range of drugs in prison (during both current and previous sentences); (b) frequency of Temgesic use; and (c) being prescribed methadone in the community, then having that prescription discontinued on entry to prison.

Embryonic optic nerve tissue fails to support neurite outgrowth by central and peripheral neurons in vitro.

The failure of axon regeneration in the injured mammalian central nervous system has been ascribed, in part, to the inhibitory effects of myelin proteins. To investigate the influence of myelination on neurite growth and regeneration by both central nervous system and peripheral nervous system neurons, isolated rat neonatal retinal ganglion cells and adult and neonatal dorsal root ganglion neurons were cultured on cryostat sections of both immature unmyelinated and mature fully myelinated adult rat optic nerve. In agreement with earlier studies using neonatal peripheral neurons, the adult optic nerve failed to support neurite outgrowth from any of the neurons tested. A new finding was that tissue sections from unmyelinated optic nerve (aged embryonic days 18 and 20, and postnatal days 1-3), also failed to support the growth of neurites from neonatal retinal ganglion cells and both neonatal and adult dorsal root ganglion neurons. Neonatal retinal ganglion cells also failed to extend neurites on sections of pre-degenerated sciatic nerve, a tissue shown in our previous work to be a good substratum for supporting neurite growth for both neonatal and adult DRG neurons. These results suggest that cells in the immature optic nerve either express widely acting axon growth inhibitory molecules unrelated to previously described myelin proteins, or do not synthesize appropriate axon growth promoting molecules. They also reveal that, for axon regeneration, central nervous system and peripheral sensory neurons require distinct substratum interactions.

The dual use of opioids and temazepam by drug injectors in Glasgow (Scotland).

In recent years much attention has been drawn to the use of buprenorphine (Temgesic) by heroin injectors in Glasgow and elsewhere. Glasgow has also witnessed a parallel increase in use of the benzodiazapine temazepam, often used as a 'cocktail' with buprenorphine. This paper presents new evidence that, although buprenorphine use among Glasgow drug injectors may now be declining, the use of temazepam-opioid cocktails has continued.

Relative changes in salivary Na+ and K+ concentrations relating to stress induction.

Three independent studies are reported in which periods of "relaxation" (A) and presumed stressors (B) were given to female students in an ABA design. The "stressors" were: (1) obligatory time-wasting activity; (2) a mental "IQ" test; and (3) delivering a speech. Saliva was collected immediately after "relaxation" and "stress" periods. "Stress" and "arousal" state were retrospectively assessed in experiments (1) and (2) by subject self-rating and in experiment 1 also by trained observers for the periods A and B. The molar [K+/Na+] ratio was determined for each saliva sample. The prediction that [K+/Na+] would increase with stress induction was supported by statistically significant results with stressors 1 and 2 (p less than 0.01), but speech delivery (3) resulted in a significant rise of [K+/Na+] after the stressor period. Correlations between [K+/Na+] and "stress" and "arousal" ratings also substantiated the prediction.

The impact of school-based drug education.

Outcome evaluation of the impact of drug education on a representative sample of 1197 pupils revealed no effects of drug education on drug-related behaviour or drug-related attitudes. However, drug education raised levels of drug-related knowledge. The long term implications of these findings would require further study. Comparison of process and outcome measures indicated that, with the exception of knowledge, teachers' positive views of drug education were misplaced. Critical aspects of good practice are discussed, both at the level of the individual teacher and in terms of whole-school factors.

Heart rate, anxiety, anger, and arousal reactions to enforced time-wasting: dependence on reactive uncontrol, work involvement, and dominance factors of 'type A'.

The factor structure of 'Type A' was examined in an experiment derived from the observation of Frankenhaeuser et al. (1980) that 'Type A' people are abnormally 'aroused' when deprived of work. Questionnaire scales were used which dissected 'Type A' (based on replicated factor analyses). The sample statistics for 21 female volunteers approximated the parent population statistics on orthogonal scales of Work Involvement (WI), Reactive Uncontrol (RU) and Dominance (D). The laboratory session involved reading for 15 min: (a) self-chosen 'useful' work material and (b) material judged by subjects (Ss) to be 'useless'. Ss and trained observers used the same scales for rating anxiety, arousal and anger states during reading periods. Observers interpreted facial expressions from video-tapes. Finger pulse amplitude and tonic heart rate (HR) were recorded during reading periods. RU (but not WI or D) correlated negatively with HR level and positively with increases in both HR and observed arousal under time-wasting conditions. Combination of changes in HR and observed arousal in a multiple R gave optimum 'prediction' of RU. While much evidence supported Frankenhaeuser's (1980) hypothesis, the multifactorial nature of 'Type A' was demonstrated.