Development of the rat's uncrossed retinotectal pathway and its relation to plasticity studies.

In the normal newborn rat the retinotectal pathway from each eye distributes across the whole area of both the ipsilateral and contralateral superior colliculus. Most of the ipsilateral projection retracts during the first ten postnatal days to produce the normal adult pattern, but retraction fails to occur if one eye is removed at birth.

Nitrite and nitrate are formed by endogenous synthesis in the human intestine.

Studies of nitrate balance in humans and analyses of fecal and ileostomy samples indicate that nitrite and nitrate are formed de novo in the intestine, possibly by heterotrophic nitrification. These findings significantly alter our previous conceptions of human exposure to nitrite and suggest an even wider role for nitrite in the etiology of human cancer.

A Sensitivity Analysis of the Impact of Rain on Regional and Global Sea-Air Fluxes of CO2.

The global oceans are considered a major sink of atmospheric carbon dioxide (CO2). Rain is known to alter the physical and chemical conditions at the sea surface, and thus influence the transfer of CO2 between the ocean and atmosphere. It can influence gas exchange through enhanced gas transfer velocity, the direct export of carbon from the atmosphere to the ocean, by altering the sea skin temperature, and through surface layer dilution. However, to date, very few studies quantifying these effects on global net sea-air fluxes exist. Here, we include terms for the enhanced gas transfer velocity and the direct export of carbon in calculations of the global net sea-air fluxes, using a 7-year time series of monthly global climate quality satellite remote sensing observations, model and in-situ data. The use of a non-linear relationship between the effects of rain and wind significantly reduces the estimated impact of rain-induced surface turbulence on the rate of sea-air gas transfer, when compared to a linear relationship. Nevertheless, globally, the rain enhanced gas transfer and rain induced direct export increase the estimated annual oceanic integrated net sink of CO2 by up to 6%. Regionally, the variations can be larger, with rain increasing the estimated annual net sink in the Pacific Ocean by up to 15% and altering monthly net flux by > ± 50%. Based on these analyses, the impacts of rain should be included in the uncertainty analysis of studies that estimate net sea-air fluxes of CO2 as the rain can have a considerable impact, dependent upon the region and timescale.

Dependence of cytochrome oxidase activity in the rat lateral geniculate nucleus on retinal innervation.

Patterns of cytochrome oxidase (CO) activity were examined histochemically in the dorsal lateral geniculate nucleus (LGNd) and retina of pigmented rats. CO staining was not uniform and was distributed in a pattern similar to that of retinal afferents. Portions of the LGNd receiving an exclusively crossed projection were moderately reactive whereas regions receiving an uncrossed or overlapping crossed and uncrossed projection were darkly reactive. The dependence of oxidative metabolic activity in the LGNd on retinal innervation was verified in animals with unilateral enucleation. In adults, chronic monocular enucleation led to a decrease in CO staining in portions of the LGNd deprived of retinal input; in animals enucleated at birth, normal patterns of CO reactivity failed to develop and both LGNds had a more uniform pattern of moderate CO staining. Most neurons in the ganglion cell layer of the retina were moderately reactive for CO. However, there were approximately 3,000 darkly reactive cells, most of which appear to be ganglion cells. The darkly reactive cells were more numerous in the peripheral temporal retina. The laminar pattern of CO staining in the retina was similar to that described previously for carnivores and primates. The most reactive laminae were the inner and outer plexiform layers and the photoreceptor inner segments. Within the inner plexiform layer, sublamina a was more darkly stained than sublamina b. These results suggest that the physiological properties of crossed and uncrossed visual pathways in rats are functionally dissimilar at the level of both the retina and the LGNd.

Cytochrome oxidase staining in the rat SmI barrel cortex.

Patterns of cytochrome oxidase (CO) activity were examined histochemically in the rat SmI cortex. Discrete regions of high enzymatic activity were centered upon the granule cell aggregates (barrels) in layer IV. Those barrels which correspond to the mystacial vibrissae and make up the posteromedial barrel subfield (PMBSF) were especially interesting in that CO staining revealed distinct metabolic subdivisions which do not have an easily demonstrable cytoarchitectonic counterpart. By analogy with the barrels in mouse PMBSF and with the cytoarchitectonically distinct barrels representing the smaller sinus hairs in the rat we propose that regions of high CO activity denote the "hollow" of the rat PMBSF barrels. In accord with previous physiological studies demonstrating a vertical organization in the rodent barrel cortex, we also noted columns of intense CO activity extending from layer VI through sublamina Vb. The centers of these columns coincided with the centers of the barrels in layer IV. In tangential sections through the infragranular laminae the segmentation of CO-positive zones was less distinct than in layer IV and appeared as bands of heightened activity oriented like the five rows of layer IV barrels. Highly reactive somata and dendrites were observed in both the granular and infragranular CO barrels indicating that some of the increased activity of these regions reflects oxidative metabolism of cortical neurons per se. These patterns of metabolic activity underscore the vertical and horizontal organization of the SmI vibrissa cortex and suggest that neurons located within the central core of a column have functional properties distinct from those located in zones where individual columns interface.

Activity-dependent regulation of glutamic acid decarboxylase in the rat barrel cortex: effects of neonatal versus adult sensory deprivation.

Immunocytochemical techniques were used to study the effects of tactual deprivation on glutamic acid decarboxylase (GAD) containing neurons in rat somatosensory barrel cortex. In normal rats GAD immunoreactive neurons and puncta are present in all laminae, with dense patches of GAD immunoreactive puncta centered on the barrels in lamina IV. Trimming whiskers of adult rats leads to a reversible decrease of GAD immunoreactivity in barrels corresponding to trimmed hairs. Intensity of GAD staining also is reversibly altered in supragranular laminae of nondeprived barrel columns flanked by deprived barrels. This indicates that GAD levels in the barrel cortex ordinarily fluctuate with changes in sensory input. By contrast, animals whose whiskers are trimmed from birth have normal GAD staining in both deprived and nondeprived barrels. Moreover, if trimmed whiskers of neonatally deprived animals are allowed to grow to normal lengths and are retrimmed later in adulthood GAD staining is not affected. Thus early tactual deprivation disrupts mechanisms that permit modulation of transmitter enzyme levels in cortical neurons following changes in sensory experience.

Transient expression of synaptic zinc during development of uncrossed retinogeniculate projections.

The transition metal zinc is an essential dietary constituent that is believed to serve an important intercellular signaling role at certain excitatory synapses in the central nervous system. In the present study, we used histochemical techniques to investigate the distribution of synaptic zinc during postnatal development of retinogeniculate projections in rats. From postnatal day (P) 1 until P-21, the pattern of zinc histochemical staining in the dorsal lateral geniculate nucleus (LGNd) precisely matched the distribution of axon terminals from the ipsilateral eye that were labeled by anterograde transport of horseradish peroxidase. Regions of the LGNd that contained only crossed axons were devoid of zinc staining. Abnormalities in the distribution of uncrossed retinogeniculate projections in albino versus pigmented rats were paralleled by identical variations in localization of synaptic zinc. Unilateral enucleation on P-10 was followed within 5 days by loss of zinc staining in the LGNd ipsilateral to the removed eye without affecting staining in the contralateral nucleus. Finally, the ability to detect zinc histochemically in the LGNd ceased at approximately P-24. These findings provide evidence that zinc is sequestered within synaptic boutons of a subpopulation of retinal ganglion cells whose axons terminate on the ipsilateral side of the brain. The duration of zinc staining overlaps with the major period of axonal remodeling in the LGNd, suggesting that synaptically released zinc may play a role in postnatal refinement of retinogeniculate projections.

Normal and abnormal uncrossed retinotectal pathways in rats: an HRP study in adults.

Horseradish peroxidase was injected into the superior colliculus of normal pigmented and albino rats and rats which had been unilaterally enucleated at birth, in order to identify the retinal ganglion cells which contribute normal and abnormal uncrossed retinotectal axons. The results show that while in pigmented rats, the normal uncrossed pathway derives solely from the lower temporal retina and distributes to the anterior and medial parts of the colliculus, occasional cells throughout the retina of albino rats contribute to the uncrossed pathway and the terminal distribution is broader in the tectum. These findings are confirmed with orthograde pathway tracing methods. After neonatal unilateral eye enucleation, many more ganglion cells in the remaining eye of both pigmented and albino rats project ipsilaterally. It is notable from both HRP studies and from further degeneration experiments that cells in part of the lower temporal retina do not restrict their distribution to a mirror togographic position in the ipsilateral tectum but send axons across all but the posterolateral part of the colliculus. No single class of ganglion cell (defined by soma diameter) appears responsible for the expanded ipsilateral projection, although more large cells from the lower temporal retina are involved. These may be the result of enlargement of cells with expanded terminal fields rather than necessarily indicating a preferential contribution from one retinal ganglion cell class.

Barreloids in adult rat thalamus: three-dimensional architecture and relationship to somatosensory cortical barrels.

Histochemical staining for cytochrome oxidase (CO) and axonal transport of horseradish peroxidase (HRP) were used to investigate thalamocortical connections in the vibrissa-barrel system of adult rats. CO staining revealed that the medial division of the ventrobasal thalamic nucleus (VBm) consists of intensely stained rod-like configurations, containing thalamocortical projection neurons and intervening neuropil, separated by lighter-stained septa. CO-dark rods span the thickness of VBm, are arranged in a pattern of rows and arcs that resembles the distribution of vibrissae on the mystacial pad, and are similar to the cytoarchitectonic structures termed "barreloids" in the mouse thalamus. Based upon the dimensions of CO-dark structures and the numerical density of neurons in VBm we estimated that a barreloid in the rat may contain 250-300 neurons. HRP injections into lamina IV of the somatosensory cortex led to retrograde labeling of neurons within one or more barreloids. When injections were centered within the CO-dark hollows of cortical barrels about 95% of retrogradely labeled neurons were located in the barreloid that is isomorphic to the injected barrel; up to 5% of labeled neurons were located within a single adjacent barreloid. Barrel hollow injections that also included a barrel side yielded a larger proportion of labeled neurons in non-isomorphic barreloids. Interestingly, such extra-barreloid labeling was topologically consistent in that HRP-labeled neurons were distributed among barreloids that corresponded to cortical barrels nearest the injected barrel side. Injections into the septa between barrels similarly resulted in labeling within barreloids that corresponded to cortical barrels flanking the septal injection site. Following lamina IV injections the density of labeled neurons tended to be highest in the ventrolateral one-half to two-thirds of VBm. Retrograde labeling of neurons in the dorsomedial one-third to one-half of VBm was more often observed after HRP injections at the lamina V/VI border. Thus, barreloid neurons may be heterogeneous with respect to their laminar pattern of terminations within the somatosensory cortex. Some HRP injections in the cortex resulted in orthograde labeling of corticothalamic axons in the barreloids. When observed, labeled corticothalamic axons arborized principally within the barreloid isomorphic to the injected barrel column. Indeed, terminal labeling was densest in the vicinity of neurons retrogradely labeled by the same injection.

Chronic sensory deprivation affects cytochrome oxidase staining and glutamic acid decarboxylase immunoreactivity in adult rat ventrobasal thalamus.

The rodent ventrobasal thalamus (VB) contains groups of vibrissa-related neurons (barreloids) that are highly reactive for the enzyme cytochrome oxidase. The present experiments show that each barreloid also contains a dense accumulation of glutamic acid decarboxylase (GAD) immunoreactive terminals. Chronic vibrissa trimming results in parallel declines in staining for both cytochrome oxidase (CO) and GAD in barreloids associated with the trimmed hairs. Thus, thalamic metabolism like that in the cortex is dependent upon normal sensory input. This includes projection neurons as well as neurons in the reticular nucleus, which are the major source of gamma-aminobutyric acid (GABA)ergic input to the rat VB.

Exogenous monoamines affect the segregation of retinogeniculate fibers in developing rats.

The development of retinogeniculate projections was examined in rats which had norepinephrine levels altered by subcutaneous administration of 6-hydroxydopamine (6-OHDA) or exogenous norepinephrine (NE) during early postnatal life. NE, but not 6-OHDA, treatment resulted in an abnormal segregation of crossed and uncrossed axons at postnatal day 10, such that projections from the two eyes occupied extensively overlapping territory. This effect is at least partially reversible since in animals examined 30 days after cessation of NE treatment the retinogeniculate projections ultimately became segregated.

Metabolic activity in SmI cortical barrels of adult rats is dependent on patterned sensory stimulation of the mystacial vibrissae.

Cytochrome oxidase (CO) histochemistry was used to examine the effect of sensory deprivation on metabolic activity in the somatosensory cortex (SmI) of adult rats. Chronic trimming of one or several rows of mystacial vibrissae resulted in a decrease in CO reactivity in the corresponding barrels in layer IV. Reduced CO staining also was observed in cortical laminae superficial and deep to the affected layer IV barrels, suggesting that patterned deflections of the whiskers are important for maintaining the metabolic activity of neurons at least 3 and perhaps 4 synapses removed from the periphery.

Prenatal development of the optic projection in albino and hooded rats.

The development of retinofugal projections has been examined in albino and hooded rat embryos from embryonic day 16 to birth (E21.5). Horseradish peroxidase (HRP) was injected intraocularly through the uterine wall and its anterograde transport revealed with TMB and DAB. The retrograde transport of HRP or the fluorescent dyes Nuclear yellow, Fast blue and propidium iodide from optic tract, superior colliculus (SC) or lateral geniculate body (LG) injections was used to demonstrate the origin of the projections. Superficial projections to the contralateral SC were first identified at E16. A light projection to the entire medio-lateral extent of the ipsilateral SC could be detected a day later. The optic axons grow over the surface of the diencephalon at E16 and it was only at later stages that the fibers were observed to invade successively deeper parts of the LG. A superficial projection to the ipsilateral LG could first be detected at E17. Both the ipsilateral and contralateral projections grew through the entire dorso-ventral extent of the lateral geniculate body: some restriction of the axons to their normal adult termination zones could be detected by E21. No difference in the distribution of projections could be detected between the albino and pigmented rats although the projections were lighter, and possibly because of this were detected later, in the albino rats. At all the ages examined in this study labeled retinal ganglion cells were observed in the non-injected eyes after injection of label into the contralateral eye. The use of persistent fluorescent dyes showed that these retinal ganglion cells did not survive for more than 5 days postnatally. The projection to the uninjected eye came preferentially from ganglion cells in the lower nasal retina while the ipsilateral central projections came predominantly but not exclusively from the lower temporal retina of the injected eye. It appears, therefore, that the initial projections of optic axons in the rat are not limited to their normal termination zones and that the choice of pathway at the chiasm appears to be only loosely controlled.

The development of callosal projections in normal and one-eyed rats.

The course of callosal development in area 17 of rats suggests that, unlike immediately adjacent regions, axons of callosal origin do not normally gain access to upper cortical layers, and this results in the loss of an early exuberant callosal pathway. Removal of optic input, however, permits invasion of these layers of area 17 by callosal axons and results in survival of callosally projecting neurons in area 17.

Neonatal auditory cortex lesions result in aberrant crossed corticotectal and corticothalamic projections in rats.

Ablation of one auditory cortex at birth in rats results in the formation of aberrant crossed projections from the intact hemisphere. These aberrant projections extend throughout most of the corticorecipient zone of the contralateral inferior colliculus and can be traced as far rostral as the contralateral medial geniculate nucleus. The aberrant crossed corticothalamic axons arise from layer V pyramidal neurons in the intact auditory cortex.

Experience-dependent alteration of zinc-containing circuits in somatosensory cortex of the mouse.

Histochemical staining was used to localize zinc-sequestering terminals in somatosensory barrel cortex of normal mice and mice subjected to tactile deprivation by simple whisker trimming from birth. In normal mice, density of synaptic zinc was highest in laminae I, II and V, intermediate in laminae III and VI, and lowest in lamina IV barrel hollows. Whisker trimming from birth led to increased density of synaptic zinc specifically within deprived barrel hollows.

A reliable technique for marking the location of extracellular recording sites using glass micropipettes.

A simple and highly reliable technique is described for marking the locations of extracellularly recorded neurons using double-barreled glass micropipettes. One barrel contains 3 M NaCl for recording; the other contains horseradish peroxidase (HRP) that is iontophoretically ejected using low currents. With appropriate processing of the tissue, small well-localized spots are produced that contain a small number of HRP-filled neurons. The technique is effective in marking sequential recording sites within individual electrode tracks and in multiple penetrations using the same microelectrode.

Serotonin immunoreactivity in the circumesophageal nervous system of Hermissenda crassicornis.

Immunohistochemical techniques were used to examine the distribution of serotonin-immunoreactive (5-HT-IR) neurons and processes in the circumesophageal nervous system of Hermissenda. Both the pedal and the cerebropleural ganglia contained immunoreactive neuronal somata, with the majority occurring in the pedal ganglia. Immunoreactive fibers and varicosities were identified in portions of the central neuropil, where we noted a consistent and specific relationship between 5-HT-IR axons, the optic nerve and the synaptic region in the neuropil near the photoreceptor terminals.

Metabolic and structural correlates of the vibrissae representation in the thalamus of the adult rat.

Cytochrome oxidase (CO) histochemistry was used to examine patterns of metabolic activity in the ventral posteromedial nucleus of the adult rat thalamus. In sections cut in an oblique horizontal plane, CO staining reveals distinct patches of heightened activity arranged in a fashion remniscent of the pattern of vibrissae on the contralateral face and which corresponds to the known somatotopic organization of the nucleus. The CO-reactive zones coincide with oval cylinders of thalamic neurons that appear to be anatomically linked with corresponding barrels in the contralateral somatosensory cortex.

Cocaine and benzoylecgonine excretion in humans.

Maximal urinary excretion of unchanged cocaine occurred within 2 h of the intranasal absorption of 1.5 mg/kg body weight of cocaine hydrochloride, and diminished rapidly thereafter. Excretion of benzoylecgonine was maximal 4 to 8 h following administration of the drug and diminished slowly over an interval of several days. Peak cocaine and benzoylecgonine concentrations observed were 24 and 75 microgram/ml, respectively. Benzoylecgonine/cocaine ratios were too varied to allow estimation of cocaine concentrations from benzoylecgonine concentration data or vice versa. Benzoylecgonine concentrations generally exceeded the corresponding cocaine values by a wide margin, but excretion of free cocaine in the absence of benzoylecgonine was observed in one subject. Cocaine was generally detected for only approximately 8 h, and for a maximum of 12 h, whereas benzoylecgonine was generally detected by chromatographic or enzyme immunologic assays for 48 to 72 h. Benzoylecgonine was positively identified in urine by raidoimmunoassay for 96 to 144 h after dosing.