A renal countercurrent system in marine elasmobranch fish: a computer-assisted reconstruction.

Computer-aided techniques were used to reconstruct the complex renal tubular system in the dorsal kidney region of a marine elasmobranch fish, the little skate (Raja erinacea), from a series of light micrographs of serial sections. It was established that five individual segments of one nephron, consisting of two loops and a distal tubule, are arranged in parallel within an elongated closed tissue sac. Capillaries, which form a network around these nephron segments, enter and exit this sac at the same end. This anatomical arrangement suggests that a complex renal countercurrent multiplier system may be important in fluid regulation in these fish.

Effects of restraint and haloperidol on sensory gating in the midbrain of awake rats.

Deficits in sensory processing have been reported to be associated with an array of neuropsychiatric disorders including schizophrenia. Auditory sensory gating paradigms have been routinely used to test the integrity of inhibitory circuits hypothesized to filter sensory information. Abnormal dopaminergic neurotransmission has been implicated in the expression of schizophrenic symptoms. The aim of this study was to determine if inhibitory gating in response to paired auditory stimuli would occur in putative dopaminergic and non-dopaminergic midbrain neurons. A further goal of this study was to determine if restraint, a classic model of stress known to increase extracellular dopamine levels, and systemic haloperidol injections affected inhibitory mechanisms involved in sensory gating. Neural activity in the rat midbrain was recorded across paired auditory stimuli (first auditory stimulus (S1) and second auditory stimulus (S2)) under resting conditions, during restraint and after systemic haloperidol injections. Under resting conditions, a subset of putative GABA neurons showed fast, gated, short latency responses while putative dopamine neurons showed long, slow responses that were inhibitory and ungated. During restraint, gated responses in putative GABAergic neurons were decreased (increased S2/S1 or ratio of test to conditioning (T/C)) by reducing the response amplitude to S1. Systemic haloperidol decreased the T/C ratio by preferentially increasing response amplitude to S1. The results from this study suggest that individual neurons encode discrete components of the auditory sensory gating paradigm, that phasic midbrain GABAergic responses to S1 may trigger subsequent inhibitory filtering processes, and that these GABAergic responses are sensitive to restraint and systemic haloperidol.

Electrical signs of new membrane production during cleavage of Rana pipiens eggs.

Rana pipiens eggs dividing normally in diluted Ringer's solution show an increase in transmembrane potential inside negative, a decrease in resistance, and no change in total surface membrane capacitance at the appearance of a division furrow. Furrows of eggs in solutions with the tonicity of full Ringer develop partially, then regress so that the surface is again spherical. The potential and resistance changes are greater and substantial increases in capacitance occur when furrowing is so inhibited. It is proposed that the electrical changes at division are due to the introduction of new plasma membrane, between the blastomeres, having selective permeability to K and a low resistance compared to the outer spherical membrane. A narrow gap between blastomeres limits current flow through new membrane during normal division. A direct exposure of new membrane to the bathing medium when furrowing is disrupted results in larger changes in potential and resistance and permits the capacitance of new membrane to be detected.

Measures of gender differences in the human brain and their relationship to brain weight.

A series of gross brain linear measurements and cross-sectional surface areas were obtained in a sample of 69 postmortem adult human brains. Data indicate that a subset of these measurements are sexually dimorphic and can be used to discriminate between male and female brains. Results further suggest that studies on gender differences in neuromorphometry can be greatly enhanced if they account for sample variance in brain weight. Using 19 of the gross brain measures delineated in this study, it is possible to accurately predict brain weight. It is believed that the measures obtained in this study will facilitate expanded correlative studies of brain morphology and neuropsychological profiles using either postmortem material or in vivo magnetic resonance imaging scans.

5'-nucleotidase in the rodent ventral striatum: relation to the distribution of leu-enkephalin, cell clusters, and infralimbic cortical innervation.

The goal of this study was to determine the compartmental organization of 5'-nucleotidase within the rodent ventral striatum and to compare the distribution of 5'-nucleotidase with that of leu-enkephalin, cell clusters, and infralimbic cortical innervation. In the core, 5'-nucleotidase is present in several contiguous patchy structures that are in register with leu-enkephalin compartments. In the shell, 5'-nucleotidase is concentrated in a longitudinal band along the septal border. This "medial band" extends from the rostral pole of the ventral striatum to the bed nucleus of stria terminalis. The ventral portion of the medial band is in register with a cluster of cells, located medial to the most dorsal island of Cajella. A second 5'-nucleotidase compartment along the border of the core and shell is in register with a cell cluster and is most evident at caudal levels of the ventral striatum. The innervation of the ventral striatum by the infralimbic cortex is denser in the shell than in the core. In the shell, fibers from the superficial layers of the infralimbic cortex tend to avoid the 5'-nucleotidase-rich cell clusters and terminate in areas of moderate 5'-nucleotidase density. By contrast, fibers from the deep layers terminate in the ventral striatum without regard to the 5'-nucleotidase-rich cell clusters. Overall, the compartmental structure of 5'-nucleotidase in the ventral striatum segregates projections from different layers of the infralimbic cortex. Dense 5'-nucleotidase compartments are innervated by neurons in the deep layers of the infralimbic cortex. The area of moderate 5'-nucleotidase density surrounding the 5'-nucleotidase compartments is innervated by neurons in both the superficial and deep layers.

Inferior olivary nuclear complex of the rat: morphology and comments on the principles of organization within the olivocerebellar system.

This study was undertaken (1) to provide a description of the normal morphology and anatomical interrelationships within the inferior olivary cell groups and (2) to determine the topographical organization of projections from this nuclear complex to the cerebellum. Conventional histological methods and the technique of retrograde transport of horseradish peroxidase (HRP) and WGA-HRP in conjunction with the sensitive chromogen tetramethyl benzidine were used in this series of experiments. In common with that of other animals, the inferior olivary nucleus of the rat consists of three subdivisions: the medial accessory olive (MAO), dorsal accessory olive (DAO), and principal olive (PO). The MAO is made of several subnuclei including a, b, c, and nucleus beta. On the basis of their common connections, the smaller subnuclei, dorsal cap, ventrolateral outgrowth, and dorsomedial cell column can be considered as parts of the MAO. The DAO is made of two subdivisions or lamellae--the dorsal and ventral folds--joined together laterally to form a twisted V-shaped structure. The principal olive consists of dorsal and ventral lamellae. A point-to-point projection was determined for four areas of the cerebellum: the anterior lobe, the posterior vermis, the intermediate and the lateral cerebellum. Analysis of the details of the projection system revealed that distinct groups of cells, here referred to as lamellae, project to sagittal zones of the cerebellum. (1) The medial accessory olive appears to be composed of three lamellae: horizontal, vertical, and rostral. The horizontal lamella (elsewhere denoted as groups a and b) projects to a sagittal zone in the vermal anterior lobe. The vertical lamella (groups c, beta, dorsal cap, ventrolateral outgrowth, and dorsomedial cell column) projects to a sagittal zone in the posterior vermis and the flocculus, and the rostral lamella projects to the lateral cerebellum. (2) The dorsal accessory olive is composed of two distinct lamellae which we have previously denoted as the dorsal and ventral folds. The dorsal fold projects to the vermal anterior lobe and receives afferents from the spinal cord, whereas the ventral fold projects to a sagittal zone in the intermediate cerebellum and receives afferents primarily from dorsal column nuclei. (3) The principal olive contains the two familiar lamellae: dorsal and ventral lamellae, each of which projects to a specific sagittal strip in the lateral cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)

Rat medulla oblongata. IV. Topographical distribution of catecholaminergic neurons with quantitative three-dimensional computer reconstruction.

We examined serial 40 micron vibratome, immunoperoxidase-stained sections of the medulla with tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) antisera followed by Nissl staining to locate catecholaminergic neurons in cytoarchitectonic regions followed by a three-dimensional (3D) computer reconstruction of these cell groups to determine their spatial organization. Overlay drawings of low and high power photomicrographs showing cell bodies and nuclear boundaries were entered into a digital computer storage system. Every section in the series was plotted to yield an accurate representation of regional densities of cells and location of nuclei, as revealed by two-dimensional plots of individual sections as well as three-dimensional plots of groups of sections. Data files were scanned in a number of ways to obtain total cell counts of TH-, DBH-, and PNMT-immunoreactive cells within a designated area or cell counts of only one type of immunoreactive cell. This combination of data manipulation produced the following results: (1) A1 group is a homogeneous population of noradrenergic neurons at levels caudal to the obex, and at the obex it is mixed with adrenergic cells. The dimensions of the A1 cell group are 1.3 X 2.7 mm, extending from -2.5 to +0.2. Part of this cell group lies in the lateral reticular nucleus. (2) A2 group is not purely noradrenergic as previously suspected. It is a very mixed cell group containing mainly dopaminergic neurons in the area postrema (periventricular region) and the dorsal motor nucleus of the vagus, mainly noradrenergic neurons in the medial subnucleus of the nucleus of the tractus solitarius (nTS), mainly adrenergic neurons in the dorsal strip and dorsal subnucleus of the nucleus of the tractus solitarius, and a mixture of all three catecholaminergic neurons in the other subnuclei of the nTS. The dimensions of this group are 0.4 X 3 mm extending from -2.7 to +0.3. (3) C1 group is a homogeneous population of adrenaline cells extending from +1 to +2.5 with dimensions of 1.5 X 1.5 mm and consisting of scattered neurons some of which occupy the gigantocellular reticular nucleus. (4) C2 group is a homogeneous population of adrenaline neurons extending from +1 to +3 with dimensions of 2.5 X 3 mm. Accurate visual imaging and quantitation of the spatial organization of medullary catecholaminergic neurons within the classical anatomical framework of cytoarchitecture provides an enhanced comprehension of the organization of this region of the central nervous system.

An autoradiographic study of the postnatal development of sensorimotor and visual components of the corticopontine system.

Standard autoradiographic tracing methods which employed intracortical injections of 3H-leucine were used to describe the time course of development in those components of the corticopontine system which originate in sensorimotor (SM) or visual (VIS) cortices. These studies were performed using male or female pigmented rats ranging in age from 1 to 24 days (birth = day 0). Labeled axons could easily be recognized within the cerebral peduncle at the level of the basilar pons on postnatal day 1 following either an SM or a VIS cortical injection. Labeling over the basilar pontine neuropil suggestive of axonal ingrowth could also be seen on day 1 following SM injections but not until day 3 in cases with VIS injections. During the latter part of the first postnatal week, both SM and VIS axon terminal fields were established in the pontine neuropil in locations generally similar to those described in the adult. However, at this time they occupied a larger area and appeared more diffusely organized than in the adult. Subsequently during the second postnatal week, both SM and VIS projection fields gradually became more focused and circumscribed until by day 16 in the case of the SM system, and day 18 for the VIS projection, an adultlike configuration was attained. At no time during development was there any evidence of a more substantial contralateral projection than that described for the adult. Correlation of these events with previous Golgi observations and ongoing electron microscopic studies on pontine synaptogenesis suggest that the focusing or constriction of corticopontine axon terminal fields might be the result of a selective degeneration process in which the presynaptic (corticopontine axon) and postsynaptic (basilar pontine neurons) elements both play an active role. Furthermore, the absence of a stage in development characterized by an increase in the density of the contralateral component of the projection confirms the interpretation of earlier studies which suggested that the aberrant contralateral corticopontine projections observed following neonatal cortical lesions were the result of sprouting from the intact corticopontine system and not due to failure of retraction in one component of a system which in fact distributes bilaterally for a time during development.

The distribution of neocortical projection neurons in the locus coeruleus.

The present study was conducted to examine the spatial organization of locus coeruleus (LC) neurons that project to rat cerebral cortex. Long-Evans hooded rats received unilateral pressure injections of horseradish peroxidase (HRP) in either frontal (n = 6) or sensorimotor (n = 11) or occipital (n = 7) cortex to determine the intranuclear location of LC neurons which project to specific neocortical regions. Coronal and sagittal sections (40-100 micron) through the LC were examined by light microscopy after carrying out the tetramethyl benzidine reaction and staining with neutral red. The locations of retrogradely labeled cells were recorded on a three-dimensional biological coordinate system maintained by a computer linked to the light microscope. LC neurons labeled from cerebrocortical injections of HRP were primarily located in the ipsilateral and to a lesser extent (fewer than 5% of total labeled cells) in the contralateral nucleus. Coeruleocortical projection neurons were concentrated in the caudal three-fifths of the dorsal division of the ipsilateral LC. Within this portion of the nucleus, HRP-filled neurons were distributed so that individual groups of cells projecting to occipital or sensorimotor or frontal cortex were coarsely aligned in a dorsal to ventral array, respectively. Moreover, in the sagittal plane of the nucleus the pattern of labeling was spatially graded so that the subset of neurons projecting to the occipital cortex was displaced more caudally in the LC than the groups of cells sending axons to sensorimotor or frontal cortex. Only the frontal area of the cortex received a projection from both dorsal and ventral divisions of the ipsilateral LC. Computer-assisted analysis of the data further suggested that neocortical projection neurons in the dorsal LC are loosely organized into two groups which run rostrocaudally through the core of the caudal nucleus. The zone of labeling resulting from injections confined to the neocortical gray matter overlapped with but was not coextensive with that observed following injections into the caudate, hippocampus, and cerebellum. These results suggest that partially overlapping subsets of LC cells might independently influence separate populations of neurons within noradrenergic terminal fields of the neocortex.

The pontocerebellar system in the rat: an HRP study. I. Posterior vermis.

This study was undertaken to determine the origin of projections from the basilar pontine nuclei (BPN) and nucleus reticularis tegmentis pontis (NRTP) to the posterior vermal lobules VI-IX of the rat cerebellum. We describe the topographical organization of this component of the pontocerebellar projection, and the congruence of the cells of origin in the basilar pons with some of the major pontine afferent systems including the corticopontine and tectopontine projections. Horseradish peroxidase (HRP) was injected into the midline cerebellar vermal zones of Long-Evans hooded rats. The more sensitive chromogens, tetramethyl benzidine and benzidine dihydrochloride, were used to reveal the location of labeled neurons. With injections located near the midline, groups of labeled cells were observed bilaterally within the BPN. The basic trend of the projections noted was: lobule VIa receives a nonfocal projection from nearly all subdivisions of the BPN throughout its rostrocaudal extent, as well as a substantial input from NRTP. Lobules VIb-c receive input from NRTP, the rostral pons, and from the ventral, lateral, and medial groups of cells in the middle BPN project to lobule VII, in addition to projections from limited groups of cells in the rostral BPN. Lobule VIII receives afferents from the caudal aspect of the pontine gray. Lobules IXa-receive afferents from the medial and peduncular groups in the midline BPN, whereas lobule IXc receives inputs from a medial group and a small lateral cluster of cells in the caudal aspect of the BPN. Pontine neurons projecting to the posterior vermis originate from areas which appear to receive descending inputs from visual, auditory, and somatosensory regions of the cerebral cortex. However, a large number of pontine and NRTP neurons projecting to lobules VI and VII are located within the terminal fields of tectal neurons, perhaps indicating a stronger input from the tectum rather than visual and auditory cerebral cortical regions.

The pontocerebellar system in the rat: an HRP study. II. Hemispheral components.

The projection of basilar pontine neurons to the cerebellar hemispheres was studied to pigmented rats by means of the retrograde transport of horseradish peroxidase. Injections of horseradish peroxidase were restricted to the lateral aspects of the lobulus simplex (11 cases), crus I (26 cases), crus II (23 cases), and paramedian lobule (18 cases). The main focus of labeled neurons following lobulus simplex injections of horseradish peroxidase was located in the ventral pons, at rostral levels. Interestingly, the majority of labeled cells were distributed ipsilateral to the injection site. After crus I injections, however, labeled neurons were most evident contralaterally , although labeled ipsilateral cells were conspicuous rostrally. The majority of labeled cells were characteristically distributed along the medial, ventral, and lateral perimeters of the pontine gray. This pattern of labeling contrasts with that in cases of crus II injections, in which the main focus of labeled somata occupied more central regions of medial and ventral portions of the pons. Similarly, the pattern of labeling following injections into the paramedian lobule largely avoided the medial and lateral perimeters of the pontine gray, while numerous labeled somata occupied the central region of the pons. In addition to the pontine regions described above, labeled cells were observed in various cases in the dorsal peduncular region, the lateral and dorsolateral areas, and the nuclear reticularis tegmenti pontis (NRTP) where three separate zones of labeling could be discerned in various cases. Several general organizational features were derived from these studies. Although specific quantitation procedures were not applied, the number of ipsilaterally labeled neurons was impressive in some cases, as was the mirror-image location of certain ipsi- and contralateral cell clusters. It was also noted that certain, similarly located clusters of labeled pontine neurons were present in cases in which injections were made into different cerebellar lobules, at least raising the possibility that some pontine neurons might give rise to divergent projections of multiple cerebellar locations, Moreover, it was evident that the location of certain clusters of labeled neurons was congruent with terminal zones of various pontine afferent systems, particularly those of the sensorimotor cortex. Combining the latter finding with the preceeding notion regarding pontocerebellar divergence suggests a mechanism by which sensorimotor information might be transmitted to several different cerebellar locations.

Naturally occurring alterations of cortical layers surrounding the fissura prima of rat cerebellum.

We have regularly observed alterations in the three-layered arrangement of cerebellar cortex surrounding fissura prima in normal adult and neonatal rats. In 90 of 110 rat brains analyzed, the cortical layers surrounding fissura prima were found to be altered from the four-layered (neonatal) or three-layered (adult) arrangement found in the majority of the remainder of cerebellar cortex. This common alteration extended long distances (as much as 320 microns) on either side of the midline, causing fissura prima to become more and more shallow from its lateral to medial extent. In sagittal sections at the lateral edge of the alteration in neonatal cerebellum, the external granular layer and pial cells disappeared, leaving an expanse of molecular layer lying between internal granular layer cells of lobules V and VI. Proceeding medially toward the midsagittal region, the cells of the internal granular layer of lobules V and VI were situated closer together and often merged. In such sections Purkinje cells did not usually remain in a monolayer, but were displaced, and clusters of these cells were sometimes found within the white matter. Various complex configurations of internal granular layer, molecular layer, and Purkinje cell groups surrounding fissura prima were commonplace in regions of cerebellum as far lateral as 320 microns on either side of the midsagittal plane. The greatest dorsoventral extent of such alterations measured was 400 microns. The presence of these previously unreported deviations is unrelated to experimental stress, as they occur spontaneously, possibly due to a vestigeal disorganization left in midline zones after early cell migration phases.

The tectopontine projection the the rat with comments on visual pathways to the basilar pons.

The projection from the superior and inferior colliculi to the basilar pons in the rat was studied with the technique of orthograde transport of labeled amino acids and autoradiography. Injections restricted to the medial or lateral regions of the superior colliculus gave rise to grain labeling representing terminal fields over the ipsilateral peduncular, dorsolateral, and ventrolateral regions of the caudal basilar pons and over the dorsomedial area of the contralateral nucleus reticularis tegmenti pontis (NRTP). The pontine projection from the superior colliculus to the lateral basilar pons is topographically organized; the medial superior colliculus projects primarily to the peduncular region, whereas the lateral superior colliculus terminates chiefly in ventrolateral pontine areas. A projection from the superior colliculus to the contralateral dorsomedial pontine and medial peduncular pontine regions, a previously undescribed finding, has also been shown. Descending fibers from the inferior colliculus do not appear to terminate extensively within the basilar pons but rather course adjacent to pontine cells of the dorsolateral region in the caudal pons. Pretectal nuclei project ipsilaterally to medial and lateral nuclei in the rostral and middle basilar pons, respectively. A rostrocaudal topography exists in the tectopontine projection; the pretectum projects to rostromiddle basilar pons, the superior colliculus to more caudal pontine regions, and the inferior colliculus (although sparsely) to further caudal areas. The pontine projection pattern from the colliculi and pretectum differs from the pontine afferents from the visual cortices. The findings of this study, when compared to our results from previous investigations on the pontocerebellar projection system, suggest that the tectal inputs to certain lateral cerebellar lobules are relayed primarily through NRTP rather than the basilar pons. The collicular projection to midvermal lobules of the cerebellum appear to be mediated in part by both NRTP and lateral pontine nuclei.

Topographical distribution of dorsal and median raphe neurons projecting to motor, sensorimotor, and visual cortical areas in the rat.

The present study was conducted to examine the spatial organization of dorsal (DR) and median (MR) raphe neurons that project to rostrocaudally aligned areas of the rat cerebral cortex. An additional goal was to determine if individual DR cells that send efferents to forelimb sensorimotor or visual regions of the neocortex also send axon collaterals to forelimb (crus II) or visual (paraflocculus) areas of the cerebellum. Long-Evans hooded rats received unilateral pressure injections of horseradish peroxidase (HRP) in either motor (n = 4) or sensorimotor (n = 5) or visual (n = 4) cortex to determine the intranuclear location of DR and MR neurons that project to specific neocortical regions. Coronal sections (40-100 microns) through the pons and midbrain were examined by light microscopy after the tetramethyl benzidine reaction and neutral red counterstaining were carried out. The locations of retrogradely labeled cells were recorded relative to a three-dimensional biological coordinate system maintained by a computer linked to the light microscope. For double labeling studies, unilateral injections of fast blue and nuclear yellow were made in paired motor (sensorimotor cortex and crus II of the lateral cerebellum) or visual (cortical area 17 and paraflocculus) areas of the CNS. Coronal tissue sections (35 microns) were collected on coverslips and examined on a Leitz fluorescence microscope (wavelength = 365 nm). DR neurons labeled from cerebrocortical injections of HRP were concentrated in the rostral two-thirds of the nucleus. HRP-filled neurons were distributed such that individual groups of neurons projecting to motor, sensorimotor, or visual cortex were aligned in a partially overlapping, rostral to caudal array. In the dorsoventral dimension, retrogradely labeled cells were clustered in three distinct groupings such that neurons projecting to the motor, sensorimotor, and visual areas were concentrated in dorsal, intermediate, and ventral portions of the DR nucleus, respectively. For all cases, the majority of HRP-filled cells were positioned along the midline or displaced to the side of the nucleus that was ipsilateral to the cortical injection site. A small number of retrogradely labeled neurons were observed in the MR following injections in the motor cortex. Computer-assisted reconstruction of the neuroanatomical data facilitated the visualization of spatial relationships between groups of DR neocortical projection neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Computer-assisted three-dimensional reconstructions of [14C]-2-deoxy-D-glucose metabolism in cat lumbosacral spinal cord following cutaneous stimulation of the hindfoot.

We report on computer-assisted three-dimensional reconstruction of spinal cord activity associated with stimulation of the plantar cushion (PC) as revealed by [14C]-2-deoxy-D-glucose (2-DG) serial autoradiographs. Moderate PC stimulation in cats elicits a reflex phasic plantar flexion of the toes. Four cats were chronically spinalized at about T6 under barbiturate anesthesia. Four to 11 days later, the cats were injected (i.v.) with 2-DG (100 microCi/kg) and the PC was electrically stimulated with needle electrodes at 2-5 times threshold for eliciting a reflex. Following stimulation, the spinal cord was processed for autoradiography. Subsequently, autoradiographs, representing approximately 8-18 mm from spinal segments L6-S1, were digitized for computer analysis and 3-D reconstruction. Several strategies of analysis were employed: 1) Three-dimensional volume images were color-coded to represent different levels of functional activity. 2) On the reconstructed volumes, "virtual" sections were made in the horizontal, sagittal, and transverse planes to view regions of 2-DG activity. 3) In addition, we were able to sample different regions within the grey and white matter semi-quantitatively (i.e., pixel intensity) from section to section to reveal differences between ipsi- and contralateral activity, as well as possible variation between sections. These analyses revealed 2-DG activity associated with moderate PC stimulation, not only in the ipsilateral dorsal horn as we had previously demonstrated, but also in both the ipsilateral and contralateral ventral horns, as well as in the intermediate grey matter. The use of novel computer analysis techniques--combined with an unanesthetized preparation--enabled us to demonstrate that the increased metabolic activity in the lumbosacral spinal cord associated with PC stimulation was much more extensive than had heretofore been observed.

Beta-1 adrenergic receptors mediate noradrenergic facilitation of Purkinje cell responses to gamma-aminobutyric acid in cerebellum of rat.

Norepinephrine (NE) may have a major role in modulating the responsiveness of Purkinje cells to the actions of other neurotransmitters in the cerebellum. Specifically, the catecholamine has been shown to enhance inhibitory responses of Purkinje cells to microiontophoretically applied gamma-aminobutyric acid (GABA). This noradrenergic facilitation of GABA has been shown recently to be mediated by beta-adrenergic receptors. The aim of this study was to characterize further the subtype of the beta-receptor involved. The results indicate that practolol, a selective beta-1 blocker, antagonized the NE-induced augmentation of Purkinje cell inhibitory responses to GABA. Zinterol, a selective beta-2 agonist, did not mimic the potentiating effect of NE. Furthermore, the noradrenergic facilitation of GABA-induced inhibition remained unaltered in cerebella subjected to neonatal X-irradiation. This procedure resulted in a decrease in the total cerebellar beta-receptor population yet left unchanged both the number of beta-1 receptors per cerebellum and the radio-resistant Purkinje cells. Together, the data presented here support the hypothesis that the noradrenergic facilitation of GABA-induced inhibition of Purkinje cells is mediated by the activation of cerebellar beta-1 adrenergic receptors located on the Purkinje cells.

Neuronal and behavioral correlations in the medial prefrontal cortex and nucleus accumbens during cocaine self-administration by rats.

Up to 31 neurons per animal were simultaneously recorded from the medial prefrontal cortex and nucleus accumbens in 15 rats during i.v. cocaine self-administration sessions, using a multi-channel, single-unit recording technique. Alterations of neuronal activity (both excitatory and inhibitory) were found a few seconds before each lever press for cocaine infusion; we have called these pre-lever press neuronal activations "anticipatory responses". A detailed video analysis revealed that these neuronal firing alterations were associated with specific portions of the behavioral sequence performed before each lever press in both recording areas. Some of the simultaneously recorded neurons displayed similar firing patterns in relation to a given behavioral episode within the behavioral sequence (turning, raising head, etc.), while others fired at different times relative to each behavioral event. Cross-correlational analyses revealed inter-regional and intra-regional correlated firing patterns between pairs of simultaneously recorded medial prefrontal cortex and nucleus accumbens neurons. This correlated firing occurred in the neurons with and without anticipatory responses, although the incidence of correlations between anticipatory neuron pairs was much higher than that between non-anticipatory neuron pairs (18.4% vs 3.6%). Many correlated neuron pairs displayed a time lag in the peak of correlational activity that indicated a temporal sequence in correlated activity. In contradiction to our hypothesis, the temporal pattern of correlation reveals that there are more cases in which nucleus accumbens neurons fired ahead of medial prefrontal cortex neurons. The results suggest that multiple mesocorticolimbic neuronal circuits may code sequential steps during the behavioral sequence performed to obtain an infusion of cocaine. The observed correlated firing between the medial prefrontal cortex and the nucleus accumbens indicates that dynamic, coherent activity occurs within the mesocorticolimbic circuit. Because this circuit is hypothesized to drive drug-seeking behavior, we suggest that this correlated firing between the nucleus accumbens and the medial prefrontal cortex may participate in the control of cocaine self-administration. In addition, the finding that correlated activity within the nucleus accumbens more often precedes that of the medial prefrontal cortex suggests that the nucleus accumbens may play a prime role in the initiation of cocaine self-administration.

Neuronal spike activity in rat nucleus accumbens during cocaine self-administration under different fixed-ratio schedules.

Chronic ensemble recording techniques were used to investigate neuronal activity in the nucleus accumbens in freely moving rats during different cocaine self-administration schedules. The issue of concern in this study was the role of nucleus accumbens in initiating and sustaining cocaine self-administration. Specifically, to determine the nature of the neuronal activity, either motor or motivational, which precedes the multiple bar presses required to self-administer cocaine and of the post-lever press neuronal response, we used conventional fixed ratio-5, fixed ratio-10, and modified fixed ratio-3 schedules. In the modified fixed ratio-3 schedule, the first lever press resulted in retraction of the lever for 2 s; the second lever press retracted the lever and turned on a cue light; the third lever press turned off the cue light and delivered cocaine (1.0 mg/kg) intravenously. In the fixed ratio-5 and -10 schedules, rats continuously pressed the lever 5 or 10 times, respectively, to obtain a single infusion of cocaine. Phasic alterations in neural spike activity were observed in 50% of nucleus accumbens neurons before (termed "anticipatory" responses) and after lever pressing for cocaine self-administration. Neurons with anticipatory responses typically exhibited such responses for all lever presses in the modified fixed ratio-3, fixed ratio-5, and fixed ratio-10 schedules, but instances were found when the activity correlate was absent. In addition, some neurons had a prominent alteration in firing rate lasting 1-5 min after cocaine self-administration, and some of these neurons also had anticipatory responses. When cocaine was eliminated during self-administration sessions, the post-lever press inhibitory responses were largely abolished or even reversed, whereas anticipatory responses were not markedly changed when rapid lever presses occurred before behavior ceased. Post-cocaine inhibitory responses compared between self-administered and passively administered cocaine were not significantly different between these two conditions. The results suggest that nucleus accumbens may be involved in initiating general reward-seeking behaviors and action which are not exclusively associated with cocaine self-administration. Moreover, the neuronal responses in the nucleus accumbens to cocaine self-administration may play an essential role in maintaining cocaine reinforcement.

A quantitative microiontophoretic analysis of the responses of central neurones to noradrenaline: interactions with cobalt, manganese, verapamil and dichloroisoprenaline.

1. A new experimental procedure has been devised for the study of pharmacological antagonism in the central nervous sytem using automated microiontophoresis to deliver pulses of agonists and computer-generated histograms to quantify the neuronal response. The system allows study of potential antagonists having direct depressant effects and also of neurones with irregular or slow discharge rates. 2. The histogram analysis reveals the necessity for regular, periodic delivery of agonists during the assessment of agonist-antagonist interactions. Without regular repetitive delivery, many agonists, such as noradrenaline, exhibit an apparent but artifactual decrease in inhibitory potency after an interruption of agonist pulses. Examples of this phenomenon are shown, using cerebellar Punkinje cells and cerebral cortical neurones in rats anaesthetized with halothane. 3. Preliminary results with these computer-generated drug response histograms revealed manganese, cobalt, and verapamil to be generally ineffective as antagonists of noradrenaline, despite their direct depressant effects. 4. Conversely, dichloroisoprenaline (DCI), a beta-adrenoceptor antagonist, was effective in blocking noradrenaline-induced depressions of firing in the cerebral cortex at doses which caused over 50% decrease in spontaneous discharge.

Noradrenaline modulation of the responses of the cerebellar Purkinje cell to afferent synaptic activity.

Noradrenaline, applied by microiontophoresis to rat cerebellar Purkinje neurones, selectively depressed spontaneous neuronal discharge. Simple spike and complex spike excitations, evoked by stimulation of the mossy and climbing fibres, were relatively preserved during the inhibition of spontaneous activity, and the number of full-sized action potentials in the complex spike increased. Inhibition mediated by the basket and stellate cells was augmented. Thus, relative to the change in spontaneous activity, noradrenaline increased the responsiveness of the Purkinje cell to afferent input.