Rostrolateral Part Research Articles

Compartmental organization and chemical profile of dopaminergic and GABAergic neurons in the substantia nigra of the rat

The substantia nigra (SN) is a midbrain center composed of dopaminergic (DA-) and gamma aminobutyric acid (GABA)ergic (GABA-) neurons. In this study, we investigated the topographical relationship between both cell populations and their chemical profile by using single and double immunostaining for tyrosine hydroxylase (TH), glutamic acid decarboxylase (GAD), cholecystokinin (CCK), calretinin (CR), calbindin (CB), parvalbumin (PV), and nitric oxide synthase (NOS). Our results showed that DA-cells are arranged in two bands, one rostrodorsal that corresponds to the SN pars compacta (SNC), and another caudoventral that corresponds to the SN pars reticulata (SNR) and emits cell bridges that make contact with the rostrodorsal one. In the SNR, GABA-cells are arranged in dorsoventrally elongated clusters that occupy DA-cell free regions. According to cytoarchitectural, topographical, and chemical criteria, we identified ten different cell groups: five dopaminergic ones, and five GABAergic ones. Within DA-cells, we found a cell group in the dorsomedial portion of the SNC which contains CCK, CR, and CB (dmSNC); DA-cells in the SN pars lateralis (SNL) which also contain CCK, CR and CB; DA-cells in the rostral half of the SNC containing CCK and CR (rSNC); DA-cells in the SNR and the caudal half of the SNC which only express CR (cSNC-SNR), and a DA-cell group in the lateral part of the SNC that contains none of the markers studied (lSNC). Within GABA-cells, we distinguished: large GABA-cells in the SNL that contain PV; large GABA-cells in the rostrolateral part of the SNR containing PV and NOS (rlSNR), small GABA-cells in the caudomedial part of the SNR containing PV (cmSNR), and two groups of small GABA-cells in the rostromedial portion of the SNR, one of them containing CR (rmcSNR), and the other containing NOS (rmnSNR). These data suggest that over a compartmental and complementary organization, DA- and GABA-nigral cells form a mosaic of neurochemically different subnuclei which probably differ in their physiological and pharmacological properties and vulnerability to aggression.

Compartmental organization and chemical profile of dopaminergic and GABAergic neurons in the substantia nigra of the rat.

The substantia nigra (SN) is a midbrain center composed of dopaminergic (DA-) and gamma aminobutyric acid (GABA)ergic (GABA-) neurons. In this study, we investigated the topographical relationship between both cell populations and their chemical profile by using single and double immunostaining for tyrosine hydroxylase (TH), glutamic acid decarboxylase (GAD), cholecystokinin (CCK), calretinin (CR), calbindin (CB), parvalbumin (PV), and nitric oxide synthase (NOS). Our results showed that DA-cells are arranged in two bands, one rostrodorsal that corresponds to the SN pars compacta (SNC), and another caudoventral that corresponds to the SN pars reticulata (SNR) and emits cell bridges that make contact with the rostrodorsal one. In the SNR, GABA-cells are arranged in dorsoventrally elongated clusters that occupy DA-cell free regions. According to cytoarchitectural, topographical, and chemical criteria, we identified ten different cell groups: five dopaminergic ones, and five GABAergic ones. Within DA-cells, we found a cell group in the dorsomedial portion of the SNC which contains CCK, CR, and CB (dmSNC); DA-cells in the SN pars lateralis (SNL) which also contain CCK, CR and CB; DA-cells in the rostral half of the SNC containing CCK and CR (rSNC); DA-cells in the SNR and the caudal half of the SNC which only express CR (cSNC-SNR), and a DA-cell group in the lateral part of the SNC that contains none of the markers studied (lSNC). Within GABA-cells, we distinguished: large GABA-cells in the SNL that contain PV; large GABA-cells in the rostrolateral part of the SNR containing PV and NOS (rlSNR), small GABA-cells in the caudomedial part of the SNR containing PV (cmSNR), and two groups of small GABA-cells in the rostromedial portion of the SNR, one of them containing CR (rmcSNR), and the other containing NOS (rmnSNR). These data suggest that over a compartmental and complementary organization, DA- and GABA-nigral cells form a mosaic of neurochemically different subnuclei which probably differ in their physiological and pharmacological properties and vulnerability to aggression.

Functional organization of climbing fibre projection to the cerebellar anterior lobe of the rat

1. The input characteristics and distribution of climbing fibre field potentials evoked by electrical stimulation of various parts of the skin were investigated in the cerebellum of barbiturate anaesthetized rats. 2. Climbing fibre responses were recorded in sagittally oriented microelectrode tracks across the mediolateral width of the anterior lobe. Climbing fibres with similar response latencies and convergence patterns terminated in sagittal bands with widths of 0.5-1.5 mm. The principal organization of the anterior lobe with respect to input characteristics and locations of sagittal zones was similar to that in the cat and ferret. Hence, the sagittal bands in the rat were tentatively named the a, b, c1, c2 and d1 zones. 3. In contrast to the cat and ferret, the a zone of the rat was characterized by short latency ipsilateral climbing fibre input. Furthermore, it was divisible into a medial 'a1' zone with convergent, proximal input and a lateral 'ax' zone with somatotopically organized input. A forelimb area with similar location and input characteristics as the X zone of the cat was found, but it formed an integral part of the ax zone. A somatotopic organization of ipsilateral, short latency climbing fibre input was also found in the c1 zone. 4. Rostrally in the anterior lobe, climbing fibres activated at short latencies from the ipsilateral side of the body terminated in a somatotopically organized transverse band which extended from the midline to the lateral end of the anterior lobe. 5. The absence of the C3 and Y zones may be interpreted as a reflection of differences in the organization of the motor systems in the rat as compared with the cat. Skilled movements, which in the cat are controlled by the C1, C3 and Y zones via the anterior interposed nucleus, may in the rat be partly controlled by the ax zone via the rostrolateral part of the fastigial nucleus.

Localization of extratectally evoked visual response in the corpus and valvula cerebelli in carp, and cerebellar contribution to 'dorsal light reaction' behavior.

In carp with the optic tectum removed bilaterally, the optic nerve stimulation evoked a surface positive response on the cerebellum, which originated in the granular layer. In the corpus cerebelli, the response was composed of a single component, well localized at the rostromedial part, supporting previous electrophysiological and morphological findings. In the valvula cerebelli, on the other hand, the response consisted of two wave components of oligo-synaptic and poly-synaptic transmission. The former distributed diffusely and was comparable to the corporeal response, while the latter localized at the rostrolateral part of the ventral valvula. Dorsal light reaction (DLR), which remained after optic tectum ablation, was slightly impaired by a lesion of the visual projection area in the corpus cerebelli, but recovered within a few days. The impairment was marked due to a lesion of the valvula cerebelli and recovery was prolonged. When above lesions were combined, the impairment was not summative but recovered much earlier, suggesting a complex neural network for DLR regulation mechanism.

Topographic organization of the corticonuclear projections from the paraflocculus in the albino rat: an autoradiographic orthograde tracing study.

The topographic organization of corticonuclear projections from the paraflocculus was studied in rats by an autoradiographic orthograde tracing method. The corticonuclear fibers from the paraflocculus terminated primarily in the caudoventral part of the lateral cerebellar nucleus and in the lateral part of the posterior interpositus nucleus. The rostrolateral part of the ventral paraflocculus projected only to the lateral nucleus, and the caudomedial part projected only to the posterior interpositus nucleus. Although differential projections from the dorsal and ventral paraflocculi were not clearly observed, the dorsal paraflocculus appeared to project to slightly more dorsal parts of the lateral and posterior interpositus nuclei than did the ventral paraflocculus. The lateral, medial, rostral, and caudal parts of each sublobule tended to project to the ventral, dorsal, rostral, and caudal regions within the caudoventral part of the lateral nucleus, respectively, despite massive overlap in the individual terminal fields. The corticonuclear projection from the dorsal and ventral paraflocculi to the posterior interpositus nucleus were organized in different directions; those from the dorsal paraflocculus were organized rostrocaudally, while those from the ventral paraflocculus were organized mediolaterally. These results suggest that in rats the corticonuclear projections from the paraflocculus are topographically organized in the mediolateral and rostrocaudal directions as well as in the dorsoventral direction.

Compartmental distribution of ventral striatal neurons projecting to the mesencephalon in the rat

The ventral striatum is characterized by an intricate neurochemical compartmentation that is reflected in the distribution of most of its afferent fiber systems. In the present study, the compartmental relationships of ventral striatal neurons projecting to the mesencephalon were studied by combining tract tracing with the immunohistochemical localization of leu-enkephalin. Injections of the retrograde tracer cholera toxin subunit B were placed at various sites in the ventral mesencephalon. The anterograde tracer Phaseolus vulgaris leucoagglutinin was injected in single compartments in the rostrolateral part of the nucleus accumbens. The projections from the ventral striatum to the dopaminergic cell groups in the ventral mesencephalon and those to the substantia nigra pars reticulata originate from distinct subpopulations of ventral striatal neurons that respect neurochemically defined compartmental boundaries. In the "shell" of the nucleus accumbens, neurons that project to the dopaminergic cell groups are located outside areas of high cell density and weak enkephalin immunoreactivity (ENK-IR). Rostrolaterally in the "core" of the nucleus accumbens, neurons inside large areas of strong ENK-IR surrounding the anterior commissure project to the dorsomedial part of the substantia nigra pars reticulata, whereas neurons outside these areas innervate the ventral tegmental area and/or the medial part of the substantia nigra pars compacta. By contrast, more caudally in the dorsal part of the nucleus accumbens and in the ventral part of the caudate-putamen, the relationships are reversed: neurons in- or outside small patches of strong ENK-IR project respectively to the pars compacta or the pars reticulata of the substantia nigra. Since the thalamic and cortical afferents of the ventral striatum are compartmentally ordered as well, the present results imply that through the ventral striatal compartments information from disparate combinations of cortical and thalamic sources may be conveyed to distinct mesencephalic targets. The component of the ventral striatomesencephalic system reaching the dopaminergic cell groups A10, A9, and A8 may modulate the dopaminergic input to virtually the entire striatum. The other component can, by way of the pars reticulata of the substantia nigra, participate in nigrothalamic and nigrotectal output pathways of the basal ganglia.

Regional differences in the regulation of acetylcholine release upon D 2 dopamine and [formula omitted] receptor activation in rat nucleus accumbens and neostriatum

The effect of D 2 dopamine receptor activation on either the electrically, or N- methyl- d-aspartate induced release of radiolabeled acetylcholine (ACh) was investigated in different areas of the nucleus accumbens and the neostriatum of rats, by using a superfusion technique. Sequential slices of 100 μm were chopped along either a rostrocaudal, mediolateral or dorsoventral axis. In every slice the effect of a supramaximal concentration of the selective D 2 receptor agonist quinpirole on the release of ACh was measured. In the entire neostriatum the release of ACh was reduced by approximately 70% in the presence of quinpirole. By contrast, in the nucleus accumbens, a gradual decrease in the inhibitory effect of quinpirole on the release of ACh was observed along both the rostral-to-caudal and the lateral-to-medial axes. Whereas in the rostrolateral part a 50% inhibition could be observed, in the caudomedial part no significant inhibition could be detected. Also the N- methyl- d-aspartate induced release of ACh was smaller in the caudomedial part as compared to the rostrolateral part of the nucleus accumbens. It is concluded that the nucleus accumbens is a very heterogenous structure with respect to the regulation of the release of ACh by D 2 dopamine and N- methyl- d-aspartate receptor activation.

Substantia nigra pars reticulata projects to the reticular thalamic nucleus of the cat: a morphological and electrophysiological study

The projections of substantia nigra pars reticulata (SNr) toward the reticular (RE) thalamic complex of cat were studied morphologically and electrophysiologically. Numerous SNr cells were retrogradely labeled following injections of horseradish peroxidase conjugated to wheat-germ agglutinin (WGA-HRP) in the rostral and rostrolateral part of the RE thalamic nucleus. Iontophoretic injections of Phaseolus vulgaris leucoagglutinin (PHA-L) in the SNr confirmed that this retrograde labeling was not a consequence of tracer diffusion in neighboring structures, but reflected a genuine SNr projection to the RE thalamic nucleus. Indeed, widely branched and varicose PHA-L-positive fibers were found in the rostral and rostrolateral pole of the RE thalamic nucleus following PHA-L injections in the SNr. Furthermore, in agreement with previous data indicating that nigrothalamic cells are GABAergic, electrical stimulation of the SNr evoked a short-latency inhibitory effect acting on both spontaneous and cortically-evoked discharges of most RE thalamic neurons. These results are discussed in light of the possible role of the SNr and RE thalamic complex in attentional processes.

Parasagittal zonal pattern of olivo-nodular projections in rabbit cerebellum

Injection of horseradish peroxidase (HRP) into the nodulus of the rabbit retrogradely labeled cells in 5 subdivisions of the contralateral inferior olive. Localized HRP injections at each of the medial, intermediate and lateral parts of the nodulus revealed 6 longitudinal zones, two zones in each part, projected differentially from the 5 olivary subdivisions: (i) the medial-most zone projected from the β nucleus, (ii) the lateral zone of the medial part and (iii) the lateral zone of the intermediate part both from the dorsal cap, (iv) the medial zone of the intermediate part from the ventrolateral outgrowth, (v) the medial zone of the lateral part from the dorsomedial cell column, and (vi) the lateral-most zone from the rostrolateral part of the medial accessory olive. A complication is that the zones (v) and (vi) seemed to cover the dorsal lamina of the nodulus, but not the ventral lamina. The lateral part of the ventral nodulus seemed to be projected from the dorsal cap and may therefore be a lateral extension of zone (iv). There was an indication that the rostral-most area of the medial accessory olive also projects to the nodulus, but a specific receptive zone for this projection was unclear. The present results suggest that the small lateral area of the nodulus previously found to be involved in cardiovascular control is projected from the rostrolateral part of the medial accessory olive and/or the dorsomedial cell column.

Transient asymmetry in the projections of the rostral thalamus to the visual hyperstriatum of the chicken, and reversal of its direction by light exposure.

Asymmetry in the visual pathways from the rostral thalamus to the hyperstriatum of the chicken has been found after injecting the retrograde tracer, True Blue (TB), into either the left or right hyperstriatum on day 2 or 12, post-hatching. There are ipsilateral connections from the ventromedial region of the left dorsolateral thalamus, lateral part (DLL) to the left hyperstriatum, and contralateral connections from the left dorsolateral thalamus, rostrolateral part (DLAlr) and the dorsolateral thalamus, dorsal part (DLLd) to the right hyperstriatum. On the right side of the thalamus, the ipsilateral connections from DLL to the right hyperstriatum are present, but there are only very few contralateral connections to the left hyperstriatum. No asymmetry in these pathways is seen in animals injected with TB on day 21. By this age the contralateral connections from the right thalamus to the left hyperstriatum have developed. Thus, the structural asymmetry in these visual pathways is transient, a finding which explains a controversy between two papers published recently in this journal, and which adds considerably to our understanding of the behavioural asymmetries known to occur in the chicken's response to stimuli presented to either the left or right eye. The direction of the asymmetry in visual pathways depends on asymmetrical light input to the eyes of the embryo. Normally the head of the embryo is oriented such that the left eye is occluded. If the head is withdrawn from the egg so that the right eye can be occluded and the left eye exposed to light, the direction of asymmetry in the thalamo-hyperstriatal pathways is reversed.(ABSTRACT TRUNCATED AT 250 WORDS)

Entorhinal projections to the hippocampal CA1 region in the rat: An underestimated pathway

The projections of the entorhinal cortex to CA1 in relation to the entorhinal-dentate projections were studied in the rat, using the anterograde transport of Phaseolus vulgaris leucoagglutinin. It was observed that the entorhinal cortex is heterogeneous with respect to the origin of these projections. Caudomedial portions of the entorhinal cortex mainly distribute fibers to the fascia dentata, whereas only a minor projection reaches CA1. Progressively more rostral and lateral parts of the entorhinal cortex project more strongly to CA1, at the expense of the number of fibers that terminate in the fascia dentata. The rostrolateral part of the entorhinal cortex, adjacent to the olfactory cortex and the amygdaloid complex, projects only to CA1.

Projections of two subclasses of vomeronasal nerve fibers to the accessory olfactory bulb in the rabbit

The organization of the projections of subclasses of vomeronasal nerve fibers to the accessory olfactory bulb was analysed using monoclonal antibodies generated against a homogenate of the rabbit olfactory bulb. Monoclonal antibody R2D5 labels all the somata of vomeronasal receptor cells in the vomeronasal organ as well as all their axons (vomeronasal nerve fibers). Another monoclonal antibody (R4B12), which has been shown to selectively bind and thus identify a subclass of olfactory nerve fibers, 7,18 also labels a subclass of vomeronasal nerve fibers. The R4B12-positive subclass of vomeronasal nerve fibers project to the glomeruli in the rostrolateral part of the accessory olfactory bulb. The third monoclonal antibody (R5A10) recognizes a complementary subclass of vomeronasal nerve fibers projecting to the glomeruli in the caudomedial part of the accessory bulb. In contrast to the clearly segregated terminations in the accessory bulb, the two subclasses of vomeronasal nerve fibers are intermingled with each other in the vomeronasal nerve bundles. Retrograde labeling of vomeronasal receptor cell somata following injection of horseradish peroxidase within the rostrolateral (R4B12-positive) part of the accessory bulb indicates that vomeronasal receptor cells of this subtype are widely distributed in the vomeronasal sensory epithelium. These results demonstrate the heterogeneity of vomeronasal receptor cells and the specificity of projections arising from subclasses of vomeronasal nerve fibers to the accessory olfactory bulb.

The retinotectal projection of quarter eyes in Xenopus laevis

Following extirpation of three quarters of the eye anlage of Xenopus laevis in stage 33 34 , the remaining quadrants developed into small eyes of normal shape. Irrespective of the different portions of the eye anlage the quarter eyes originated from, the retinotectal projection was always confined to the rostrolateral part of the tectum, forming an orderly map, and its dimensions corresponded to the size of the contralateral eye. Therefore, it was suggested that during development both size and location of the projection are independent of the existence of tectal markers. Instead, they are determined by the number of ingrowing optic fibers and the direction of their growth from the rostral origin.

A note on the projection from the rostral thalamus to the visual hyperstriatum of the chicken (Gallus gallus).

The rostral thalamo-hyperstriatal projection in young chicks was examined following large injections of wheat germ agglutin labelled with horseradish peroxidase (HRP-WGA) into the hyperstriatum. Retrograde labelling of thalamic neurons was present in the dorsolateral thalamus, rostrolateral part (DLAlr) and dorsolateral thalamus, lateral part (DLL). There was no evidence of a contralateral projection from the lateral anterior thalamic nucleus (LA) to the posterior aspect of the visual hyperstriatum as reported recently by Boxer and Stanford (1985). Furthermore, a comparison of labelled neurons in the contralateral rostral thalamus following injections into either the left or right hyperstriatum revealed no difference in the number of neurons. The study could therefore not confirm the presence of an asymmetrical LA-hyperstriatal projection, as reported by the above authors.

Zonal organization of olivocerebellar projections to the uvula in rabbits

Olivocerebellr projections to the uvula were studied by means of retrograde axonal transport of horseradish peroxidase (HRP) in pigmented rabbits. The distribution pattern of labeled cells in the inferior olive was compared among cases following large- and micro-injectionsof HRP into the uvula. Findings indicate topographically organized projections to longitudinally oriented zones. There areleast 6 zones in the rabbit's uvula. The caudal part of the nucleus beta projects contralaterally to a most medially located zone (caudalbeta zone). The rostral part of the nucleus beta projects to a little more laterally located zone (rostral beta zone) at a distance ofabout 1 mm from the midline of the uvula. The caudolateral part of the MAO projects to a zone (caudolateral MAO zone) located laterallyto the rostral beta zone. The dorsomedial cell column projects to a zone (dorsomedial cell column zone) located in the intermediatepart of the uvula at about 2 mm from the midline. The rostrolateral part of the MAO projects to the most lateral zone (rostrolateralMAO zone) of the uvula. Finally, the ventral lamella of the PO projects to a zone (ventral lamlla of PO zone) located between therostrolateral MAO zone and the dorsomedial cell column zone.

Two groups of secondary vestibular neurons mediating horizontal canal signals, probably to the ipsilateral medial rectus muscle, under inhibitory influences from the cerebellar flocculus in rabbits

Vestibular nuclear neurons that mediate horizontal canal signals to the ipsilateral medial rectus motoneurons were explored in anesthetized and decerebrate rabbits. These neurons were identified by four criteria: (1) they were activated monosynaptically by ipsilateral vestibular nerve stimulation and (2) antidromically from the oculomotor nucleus region, while they were inhibited by (3) direct floccular stimulation and (4) ipsilateral retinal stimulation that activated floccular Purkinje cells via a climbing fiber afferent pathway. Neurons fulfilling these criteria were found in two anatomically different regions, i.e. the rostrolateral part of the medial vestibular nucleus and in the ventral part of the lateral vestibular nucleus. In decerebrate rabbits, neurons in both loci responded to horizontal rotation of the whole body with the type I pattern (excited by ipsilateral rotation). These results suggest that horizontal canal signals are conveyed to ipsilateral medial rectus motoneurons by two separate groups of vestibular nuclear neurons which may play different roles in the vestibulo-ocular reflex.

Monkey substantia nigra (pars reticulata) neuron discharges during operant feeding

Unit activity in the substantia nigra pars reticulata was recorded during monkey bar-press feeding behavior. Activity of one-third of neurons was related to motor execution such as arm extension, flexion and bar-pressing, but not to motor preparation. Motor-related neurons were distributed mainly in the rostrolateral part of the nucleus. More than one-third responded during feeding and/or drinking acts and to intra- or perioral sensory stimuli. These ingestion-related neurons were distributed mainly in the caudomedial part of the nucleus.

Cortical and brain stem afferents to the ventral thalamic nuclei of the cat demonstrated by retrograde axonal transport of horseradish peroxidase.

After horseradish peroxidase (HRP) injections into various parts of the ventral thalamic nuclear group and its adjacent areas, the distribution of labeled neurons was compared in the cerebral cortex, basal ganglia, and the brain stem. The major differences in distribution patterns were as follows: Injections of HRP into the lateral or ventrolateral portions of the ventroanterior and ventrolateral nuclear complex of the thalamus (VA-VL) produced retrogradely labeled neurons consistently in area 4 gamma (lateral part of the anterior and posterior sigmoid gyri, lateral sigmoid gyrus and the lateral fundus of the cruciate sulcus), the medial division of posterior thalamic group (POm), suprageniculate nucleus (SG) and anterior pretectal nucleus ipsilaterally, and in the nucleus Z of the vestibular nuclear complex bilaterally. Injections into the medial or dorsomedial portion of the VA-VL resulted in labeled neurons within the areas 6a beta (medial part of the anterior sigmoid gyrus), 6a delta (anterior part of ventral bank of buried cruciate sulcus), 6 if. fu (posterior part of the bank), fundus of the presylvian sulcus (area 6a beta), medial part of the nucleus lateralis posterior of thalamus and nucleus centralis dorsalis ipsilaterally, and in the entopeduncular nucleus (EPN) and medial pretectal nucleus bilaterally. Only a few neurons were present in the contralateral area 6a delta. After HRP injections into the ventral medial nucleus (VM), major labeled neurons were observed in the gyrus proreus, area 6a beta (mainly in the medial bank of the presylvian sulcus), and EPN ipsilaterally, and in the medial pretectal nucleus and substantia nigra bilaterally. Following HRP injections into the centre médian nucleus (CM), major labeled neurons were found in the areas 4 gamma, 6a beta, and the orbital gyrus ipsilaterally, and in the EPN, rostral and rostrolateral parts of the thalamic reticular nucleus, locus ceruleus, nucleus reticularis pontis oralis et caudalis and nucleus prepositus hypoglossi bilaterally. The contralateral intercalatus nucleus also possessed labeled neurons. With HRP injections into the paracentral and centrolateral nuclei, labeled neurons were observed in the gyrus proreus and the cortical areas between the caudal presylvian sulcus and anterior rhinal sulcus ipsilaterally, and in the nuclei interstitialis and Darkschewitsch bilaterally. Minor differences in the distribution pattern were observed in the superior colliculus, periaqueductal gray, mesencephalic and medullary reticular formations, and vestibular nuclei in all cases of injections.

Thalamic projections of nucleus reticularis thalami of cat: a study using retrograde transport of horseradish peroxidase and fluorescent tracers.

The retrograde transport of horseradish peroxidase (HRP) and fluorescent tracers after injections in various thalamic nuclei was used to investigate the relative density of retrogradely labeled cells in different districts of reticularis thalami (RE) nuclear complex of cat. The RE nucleus was left virtually free of labeling only after injections localized into the anterior nuclear group; in those experiments, heavy retrograde labeling was obtained in mammillary nuclei. The major targets of RE cells proved to be centralis lateralis-paracentralis (CL-PC) and centrum medianum-parafascicularis (CM-PF) intralaminar nuclei. The projections to various intralaminar nuclei mainly arise in the rostral pole and rostrolateral part of RE nucleus and are reciprocal to intralaminar-RE pathways disclosed by Jones ('75). The RE territories labeled following injections in relay and associational nuclei are more restricted and are located contiguously and slightly anteriorly to a given nucleus. There was a very small proportion of doubly labeled RE cells after injections with fluorescent tracers in different nuclei. This was not due to a technical failure since many double-labeled neurons were found in the same material in medial globus pallidum after thalamic and midbrain injections (see companion paper by Parent and Steriade, '84). We conclude that most individual RE axons arborize in only one thalamic nucleus or nuclear group. An additional finding was the existence of intralaminar-to-relay (CL-PC to VA-VL) projections.

Hypertensive response following stimulation of opiate receptors in the caudal ventrolateral medulla

In urethane-anesthetized rats, vasodepressor neuron pools were located bilaterally in and adjacent to the A1 area of the ventrolateral medulla by injecting the neuroexcitatory amino acid, l-glutamate. Ventrolateral vasodepressor areas included the caudolateral part of the nucleus reticularis gigantocellularis, the rostrolateral part of the nucleus reticularis ventralis, and the dorsal nucleus reticularis lateralis. In the ventrolateral vasodepressor areas l-glutamate elicited a transient fall in blood pressure (BP) and heart rate (HR). The opiate agonist ( d-ala 2-met 5)-enkephalinamide (DAME) was used to stimulate opiate receptors in vasodepressor sites, identified with l-glutamate. In these sites, bilateral injections (0.1 μl/site) of DAME caused a dose-related (2.5–500.0 ng) increase in blood pressure and heart rate, as well as exaggeration of the response to occlusion of the carotid. The effects of DAME on blood pressure were completely abolished by α-adrenergic blockade (phentolamine, 2 mg/kg, i.v.) and all effects of DAME were reversed by the administration of naloxone HCl (1 mg/kg, i.v.). Naloxone reversal was accompanied by an unexpected “rebound” hypertension. Saline had no significant effects when injected, or administered intravenously, in the absence or presence of DAME. It was concluded that stimulation of opiate receptors in the ventrolateral vasodepressor areas activated sympathetic outflow. An enkephalinergic system in this area of the brain stem may serve to modulate blood pressure, heart rate and cardiovascular reflexes.