A radioautographic study of the efferent pathways of the nucleus locus coeruleus

Development of catecholaminergic phenotypic characters in the mouse locus coeruleus in vivo and in culture

While abundant studies have begun to elucidate ontogeny of the peripheral nervous system, molecular mechanisms underlying brain development remain obscure. To approach this problem, we initiated parallel in vivo and in vitro studies of the mouse locus coeruleus (l.c.), a brainstem noradrenergic nucleus. The catecholaminergic enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) were used to monitor phenotype expression and development. TH catalytic activity and immunocytochemical reactivity were initially detectable on gestational Day 13 (E-13) in vivo, and adult levels of activity were approximately by the third postnatal week. Immunotitration studies indicated that the developmental increase was due to accumulation of enzyme molecules and not enzyme activation. The in vivo developmental profile of DBH approximated that of TH. To begin defining regulatory mechanisms, explants of embryonic brainstem were placed in culture. Explantation on E-12, prior to expression of TH or DBH, resulted in the de novo appearance of these phenotypic characters after 4 days. Explantation on E-18, after the enzymes are already expressed, was followed by a striking sixfold rise in TH activity. Immunotitration studies revealed that the increase in TH activity in E-18 cultures was attributable to increased molecule number, reproducing the in vivo results. Moreover, the E-18 explants, cultured for 3 weeks, attained higher plateau levels of TH activity than E-12 cultures, and this differences was due to increased molecule number. Morphometric analysis indicated that 3-week E-12 cultures actually had more l.c. cells than E-18 cultures, indicating that differences in TH were not due to increased cells in the E-18 l.c. Finally, systemic study revealed that the development of TH activity in culture increased progressively from E-11 to E-12 to E-13, suggesting that critical regulatory events occur at this time. Our studies suggest that the l.c. is an excellent model for the study of brain development in vivo and in vitro. Initial phenotypic expression and dramatic development occur in culture in the absence of normal targets, normal afferent innervation and, presumably, normal humoural milieu.

Unilaterally activated systems in rats self-stimulating at sites in the medial forebrain bundle, medial prefrontal cortex, or locus coeruleus

Rats with electrodes in either the posterior medial forebrain bundle (MFB), the anterior MFB, the medial prefrontal cortex, or the locus coeruleus self-stimulated during a 45 min period following the injection of [14C]2-deoxyglucose. They were then sacrificed and their brains prepared for autoradiography. The autoradiographs were analyzed for unilaterally activated neural systems, using a computerized image analyzing system to compare the darkness of neural structures on the stimulated side with the darkness of the same structures on the unstimulated side. There was extensive overlap in the neural structures unilaterally activated by stimulation in the anterior and posterior MFB; but there was no overlap between the structures activated by MFB stimulation and the structures activated by stimulation at either of the extradiencephalic sites; nor did the forebrain, diencephalic, and midbrain sites have any readily apparent bilateral effects in common. If there is a substrate common to MFB self-stimulation and extradiencephalic self-stimulation, its activation is not revealed by 2-deoxyglucose autoradiography.

Atlas of catecholamine perikarya, varicosities and pathways in the brainstem of the cat

By application of a modified glyoxylic acid--paraformaldehyde histofluorescence technique, catecholamine perikarya, varicosities, and pathways were delineated within the brainstem of kittens that were either untreated, pretreated pharmacologically, or injected intracerebrally with 6-OHDA. Three principle catecholamine cell groups were identified within the medulla and pons; the dorsomedial medullary cell group, the dorsolateral pontine cell group, and a ventrolateral cell group extending from the medulla into the pons. Induced axonal accumulation of catecholamines with intracerebral 6-OHDA injections revealed a major longitudinal catecholamine bundle which courses in a dorsolateral position through the entire brainstem tegmentum. The dorsomedial medullary and dorsolateral pontine cell groups contribute ascending and descending fibers to this bundle. Axons of the ventrolateral pontomedullary cells also feed into the bundle at successive levels through radially coursing transverse fibers. Via this major dorsolateral conduit and its ventrally and medially coursing tributaries, catecholamine fibers and terminals are distributed to multiple nuclei through the brainstem. The regions of the catecholamine cell groups and the serotonin raphe nuclei all receive a dense catecholamine innervation. Varicosities are also dense in the visceral cranial nerve nuclei, moderately dense in most somatic spinal and cranial nerve motor nuclei, and moderate to light in sensory cranial nerve and relay nuclei. The lateral and ventromedial reticular formation are moderately innervated by varicose catecholamine fibers that traverse these regions. The longitudinal catecholamine bundle continues caudally into the lateral funiculus to descend into and innervate the spinal cord. Rostrally it continues into the tegmental fascicles of the midbrain to ascend into and innervate the diencephalon and there join the medial forebrain bundle to ascend into the telencephalon. Thus, the catecholamine neurons utilize this dorsolateral longitudinal bundle to distribute collaterals to multiple bulbar nuclei and to travel beyond the brainstem to innervate the spinal cord and forebrain.

Organization of the afferent projections to the Wulst in the pigeon

The afferent connections to the Wulst, a well-defined bulge in the forebrain roof, were studied in the pigeon. Cells of origin were identified by horseradish peroxidase retrograde tracing, after placing multiple injections in the Wulst. The results demonstrate a bilateral intratelencephalic pathway arising from the archistriatum intermedium (Ai) in the basal forebrain. Labeled cells in n. superficialis parvocellularis (SPC) and n. dorsolateralis posterior (DLP) on both sides of the brain, provide anatomical evidence for a bilateral forebrain projection of the somatosensory thalamus. A sparse ipsilateral input of unknown function from the medial thalamus originates in n. dorsomedialis anterior (DMA) and n. dorsolateralis medialis (DLM). We provide confirming evidence of the bilateral thalamofugal visual pathway ascending from nuclei of the dorsolateral thalamus (DLAmc and DLL). Projections from several brainstem structures are described, including: griseum centrale (GCt), medial and lateral reticular formation (FRM and FRL), area ventralis of Tsai (AVT), n. annularis (Anl), locus coeruleus (LoC), and the avian homologue of the raphe nucleus, n. linearis caudalis (LC). The account provides a direct anatomical demonstration of a Wulst input from the basal forebrain, the somatosensory thalamus, and the brainstem. The projection cells in the brainstem reside in structures known to contribute to ascending catecholaminergic and serotoninergic pathways.

The transsynaptic regulation of the septal-hippocampal cholinergic neurons

There is not yet a complete understanding of the functional interactions among various septal nuclei which regulate hippocampal function. Nevertheless, much has been learned histologically and biochemically about the major connections of the distinct areas of the septal complex and the chemical character of some of these pathways. The cholinergic septal-hippocampal pathway serves as a well defined link between these two important structures of the limbic system. Acetylcholine turnover rates in the hippocampus have been shown to increase or decrease proportionally to the activity of the cholinergic neurons originating in the septum. Moreover, these turnover rates have been shown to be modulated by intraseptal injections of agonists or antagonists of various neurotransmitters or neuromodulators which are stored in various cell groups located in the septum. By coupling this biochemical approach with techniques to study the receptor organization, greater detail concerning the transmitter and cotransmitter interactions among the various neuromodulators can be obtained.

Evidence for the existence of alpha- and beta-adrenoceptors on neurones and glial cells of cultured rat central nervous system--an autoradiographic study

The cellular localization of the binding of radioactive noradrenaline and alpha- and beta-adrenoceptor antagonists was studied in organotypic cultures of rat cerebellum, brain stem and spinal cord using autoradiography. In cerebellar cultures, many neurones, which appeared to be Purkinje cells, were labelled by [3H]noradrenaline and by the beta-antagonists [3H]dihydroalprenolol and [3H]carazolol, whereas no binding of the alpha-antagonists [3H]prazosin and [3H]rauwolscine was detected. In cultures of spinal cord and brain stem, [3H]noradrenaline and the beta-antagonists were bound to many large neurones. Binding of [3H] alpha-antagonists was observed to a small number of brain stem and spinal neurones, the labelling being much weaker than that produced by the [3H] beta-antagonists. The antidepressant [3H]desmethylimipramine was bound to many neurones and glial cells in cerebellar, brain stem and spinal cord cultures. Glial cells also possessed binding sites for [3H]noradrenaline and alpha- and beta-adrenoceptor antagonists, findings that are consistent with recent electrophysiological observations which indicate the existence of alpha- and beta-adrenoceptors on cultured astrocytes.

The telencephalic limbic system and experimental gastric pathology: a review

The effects of lesions and stimulations of the telencephalic limbic system on experimental gastric ulcers and erosions are reviewed. It is concluded that the centromedial amygdala and the anterior cingulate gyrus are facilitatory structures, whereas the medial prefrontal cortex, posterior cingulate cortex, entorhinal cortex, hippocampus and posterolateral amygdala are inhibitory areas during stressful experiences, e.g., immobilization. Both the centromedial amygdala and the anterior cingulate gyrus may be part of an "ancillary" pain system, mediating the affective components of aversive experiences. The inhibitory structures, on the other hand, are assumed to be part of a "preventive" mechanism which is initiated by the selective nuclear binding of glucocorticoids when under stress.

Laminar, tangential and regional organization of the noradrenergic innervation of monkey cortex: dopamine-beta-hydroxylase immunohistochemistry

An antiserum directed against human dopamine-beta-hydroxylase purified from pheochromocytoma tissue was employed in an immunohistochemical study of the organization of the noradrenergic innervation of monkey neocortex. A detailed description is given of the laminar pattern of noradrenergic innervation in the dorsolateral prefrontal cortex (Brodmann areas 9 and 10) and the primary somatosensory cortex of the postcentral gyrus (Brodmann areas 3,1,2). The noradrenergic innervation of these two regions is similar in the following respects: (1) fibers are present in all six layers, (2) the innervation is dense and terminal-like in layers IV and V, and (3) layer VI is characterized by fibers oriented parallel to the pial surface which follow the contours of the subcortical white matter. However, these regions differ with respect to specific laminar patterns of fiber distribution and orientation and by virtue of the fact that the primary somatosensory cortex has a very dense noradrenergic innervation, while the density of innervation in dorsolateral prefrontal cortex is low relative to the postcentral gyrus and most other neocortical areas. The laminar pattern of noradrenergic innervation in primary visual cortex differs fundamentally from both prefrontal and primary somatosensory cortices. In a separate series of experiments, dorsolateral frontal cortex lesions were used to investigate the intracortical trajectory of noradrenergic fibers. A discrete aspiration lesion confined to the grey matter of the prefrontal cortex led to a substantial loss of noradrenergic fibers in cortical regions caudal to the lesion. The decrease in density of noradrenergic innervation was particularly pronounced in the pre- and postcentral gyri. These results demonstrate that while the noradrenergic innervation of primate cortex exhibits a far greater degree of regional variation than is present in the rat cortex, the tangential intracortical trajectory that is characteristic of the lissencephalic rat brain is also a dominant feature of the noradrenergic innervation of the gyrencephalic primate brain.

Locus coeruleus projections to cortex: topography, morphology and collateralization

The relationship between individual cells of origin within the nucleus locus coeruleus (LC) and the geometry and distribution of terminal fields in cortex was examined in the albino rat. Computer-assisted 3-dimensional reconstructions of the Nissl-stained LC allowed the characterization of the spatial distribution of LC cells. Similar reconstructions of the distributions of labelled cells following cortical injections of horseradish peroxidase were created. Comparisons of such reconstructions revealed that LC cells projecting to cortex were distributed throughout the compact dorsal LC. These cells were predominantly medium sized multipolar cells. Significant labelling of other morphological sub-populations of LC did not occur following cortical injections. Simultaneous injections of multiple fluorescent retrograde tracers into different cortical regions allowed the characterization of LC axon collateralization in cortex. Individual LC cells innervate functionally and cytoarchitectonically distinct cortical regions simultaneously. LC cells arborize more extensively in the anterior-to-posterior axis of cortex and exhibit relatively minimal medial-to-lateral collateralization. Individual LC cells were also shown to innervate both superficial and deep layers of a cortical region.

The effects of neonatal pedunclectomy on [3H]noradrenaline uptake and the development of beta-adrenergic receptors in the rat cerebellum

A newly developed method for cutting the cerebellar peduncles in neonatal rats has allowed the study of the development of cerebellar beta-adrenergic receptors in the absence of noradrenergic afferents. Cutting the cerebellar peduncles of neonatal animals did not affect the pattern of development of the beta-adrenergic receptors, nor their final numbers. Pedunclectomy induced a decline in the ability of slices of cerebellar cortex to accumulate [3H]noradrenaline although high-affinity noradrenaline uptake, was never completely abolished. It is suggested that the remaining high-affinity noradrenaline uptake cannot be attributed to noradrenergic fibres from the locus coeruleus.

Differential projections from locus coeruleus to olfactory bulb and olfactory tubercle: an HRP study

The microiontophoretic administration of horseradish peroxidase (HRP) to the olfactory bulb (OB) or olfactory tubercle (OT) in cats and rats yielded similar results in both species. After an OB HRP-injection ipsilateral and contralateral labelled neurons were seen in the piriform cortex, polymorphic layer of OT, magnocellular preoptic region, lateral hypothalamus, ventromedial hypothalamic nucleus and locus coeruleus (LC). In both species more labelled structures were found after an OT HRP-injection than after an OB HRP-injection. The substantia nigra in rats was more abundantly labelled after an OT injection than after an OB one. In cats the dorsal and the ventral raphe were also labelled. In either species, OT HRP-injections resulted in a higher frequency of LC labelled neurons than after OB injections. These results favor the hypothesis that the OT plays an important role as a relay station for efferent inflow from the brain stem en route to the OB.

Cholinergic projections to the basolateral amygdala: a combined Evans Blue and acetylcholinesterase analysis

The origins and acetylcholinesterase (AChE, EC 3.1.1.7) content of neurons projecting to the AChE-rich basolateral amygdala were studied by infusing Evans Blue (EB), a retrogradely transported fluorescent label, into that neural region and, following microscopic evaluation of labelled somata, staining the same tissue sections for AChE according to the pharmacohistochemical regimen. The following basal forebrain areas contained cells labelled with EB: the lateral preoptic area, ventral pallidum, nuclei of the diagonal band, medial septal nucleus, bed nucleus of the stria terminalis, and substantia innominata. The majority of the basal forebrain neurons projecting to the basolateral amygdala stained intensely for AChE, suggesting that they were cholinergic. In the brainstem, EB-labelled neurons staining intensely for AChE were found less frequently, but a few were observed in the nucleus tegmenti pendunculopontis, locus ceruleus, subcerulear region, and reticular formation. Cells accumulating EB after basolateral amygdala infusion but demonstrating no, weak, or moderate AChE activity were seen in the orbitofrontal, anterior cingulate, temporal, and insular cortices; the mediodorsal, paraventricular, and parataenial nuclei of the thalamus; the periventricular gray substance; the ventromedial mesencephalic tegmentum; the lateral and compact portions of the substantia nigra; the dorsal raphe; the dorsal tegmental nucleus; and the dorsal parabrachial nucleus. On the basis of staining intensity, intracellular organization of the AChE reaction product, and previous results in the literature, we conclude that the major cholinergic input to the basolateral amygdala derives from the basal forebrain.

Transient cessation of female rat sexual cycle after electrolytic damage of locus coeruleus

In order to evaluate the possible participation of the locus coeruleus (LC) in the regulation of estrous cyclicity, bilateral LC electrolytic lesions were made in intact female rats. Vaginal smears were sampled daily and the estrous cyclicity was established. LC lesions resulted in a transient loss of cyclicity characterized by a sustained diestrous period. The delay in recovery was dependent on the percentage of LC destroyed. The cyclicity of sham operated rats and of nonoperated rats showed no change. Results are discussed within the context of the LC as a generalized influencing system.

Amygdalopetal projections in the cat. II. Subcortical afferent connections. A study with retrograde tracing techniques

The subcortical afferent connections of the amygdaloid complex of the cat were studied by means of retrograde tracing of horseradish peroxidase and the fluorescent substances bisbenzimid and nuclear yellow. The results of the present study indicate that structures in the basal forebrain, hypothalamus, brainstem, and thalamus project in a topographical manner to the various amygdaloid nuclei. Within the basal forebrain "ventral pallidal" structures project to the lateral and basolateral amygdaloid nuclei. The nucleus of the horizontal limb of the diagonal band and the medial part of the bed nucleus of the stria terminalis project predominantly to the medial and the medial central amygdaloid nuclei. Fibers from the substantia innominata distribute to nearly the entire expanse of the amygdaloid complex. The medial preoptic area and medial hypothalamic nuclei, including the paraventricular, ventromedial, arcuate, premammillary, and supramammillary nuclei, project most heavily to a region of the amygdala which includes the medial and the medial central nuclei. The caudal part of the lateral hypothalamic area sends strong projections to the medial central amygdaloid nucleus and more weakly projects to the basolateral nucleus. Brainstem neurons located in the cell groups A8 and A10, the dorsal raphe nucleus, the locus coeruleus, and the parabrachial nucleus project mainly to the medial central amygdaloid nucleus. Fibers originating in the medial part of the parabrachial nucleus in addition have a dense termination in the anterior amygdaloid area. Of the various midline nuclei of the thalamus which project to the amygdaloid complex, the paraventricular and ventral reuniens nuclei distribute fibers to the medial central and basolateral nuclei. The parataenial and the interventral nuclei project only to the medial central amygdaloid nucleus. Fibers from the interanteromedial nucleus exclusively reach the basolateral nucleus of the amygdala. Caudally in the ventral thalamus the subparafascicular and peripeduncular nuclei have been found to project to the medial, central, lateral, and cortical nuclei. In the posterior thalamus the medial part of the medial geniculate nucleus and the nucleus mediolateralis-suprageniculate complex give rise to fibers which reach the lateral central amygdaloid nucleus.

The medial forebrain bundle of the rat. I. General introduction

This paper is the first of a projected series of studies on the structure and composition of the medial forebrain bundle (MFB) of the rat and the relations of this fiber system to its bed nucleus, the lateral hypothalamic area. The first part of the paper comprises an extensive review of literature on the MFB from its discovery by Ganser in 1882 to the present. This review serves as the basis for an evaluation of our present-day knowledge of the organization of the MFB, which is presented in the second part of this paper. Despite the wealth of information available on the origins and sites of termination of the axons that constitute the MFB, surprisingly little attention has been given to the bundle itself, to its topographic boundaries, its fiber composition, or to the spatial arrangement of its constituent components. These features of the MFB as it extends through the lateral preoptic and lateral hypothalamic areas have been analyzed in normal Klüver-Barrera- and Bodian-stained material. From this analysis, a detailed atlas of the MFB and some of the surrounding structures has been prepared. This atlas, which forms the third section of this paper, illustrates the appearance and organization of the MFB at ten equidistant levels through the lateral preoptic and lateral hypothalamic continuum.

Behavior during hippocampal microinfusions. IV. Transmitter interactions

The interaction between noradrenergic, cholinergic, and GABAergic receptor stimulation in the dentate gyrus of the rat was investigated at the behavioral level. Awake, unrestrained rats in a holeboard/activity apparatus received continuous 40-min infusions into the dentate hilus of combined solutions of norepinephrine, the cholinergic agonist carbachol, and the GABA antagonist picrotoxin. Infusions into the dentate gyrus of either carbachol or picrotoxin have been found to produce a comparable locomotor activation of rats that is probably due to the excitation of dentate granule cells. Low dose hippocampal infusions of norepinephrine have been shown to significantly affect the quality but not the quantity of the locomotor activity or rats. Co-infusion of norepinephrine potentiated the effects of picrotoxin and blocked the effects of carbachol. It is hypothesized that the noradrenergic input to the area dentata increases the efficacy of extrinsic afferents while also facilitating recurrent granule cell inhibition mediated by GABAergic interneurons.

The effect of neonatal 6-hydroxydopamine treatment on synaptogenesis in the visual cortex of the rat

It has been proposed repeatedly that the noradrenergic (NE) system may exert an influence on cortical development. We have tested this proposition by examining synaptogenesis in the visual cortex of rats whose NE afferents were selectively lesioned by injections of the neurotoxin 6-hydroxydopamine (6-OHDA). Control littermates were injected with equal volumes of vehicle. Montages of electron micrographs covering approximately 50 micrometers-wide strips of cortex were assembled from both groups of animals at 2,4,6,8,14, and 90 days of age. Synapse counts revealed a significantly higher density of synapses in the cortex of 6-OHDA-treated rats during the first week of postnatal life. The difference between the experimental and control rats was less apparent during the second postnatal week, and at day 90 the densities of synapses were similar for the two groups of animals. The enhanced density, which was the result of the increased number of Gray's type I synapses, was confined to the subplate region at day 2 but became more widespread in the cortex at subsequent stages of development. From these observations it would appear that the NE system exerts an inhibitory influence on synapse formation in the visual cortex in early postnatal life.

Brain stem generation of the hippocampal EEG

In summary, based on unit recording studies in behaving animals it appears that the brain stem cells best suited for a role in theta generation are the pontine RF neurons in the rat (Vertes, 1980, 1981) rabbit (Klemm, 1970) and dog (Arnolds, 1977) that fire selectively during the identical states in which theta is present in the hippocampus and whose discharge characteristics closely parallel properties attributed to hippocampal theta (Vertes, 1981). The omission of any description of RF cells in the behaving cat with theta-like properties (McCarley and Hobson, 1971; Hobson et al., 1974; Siegel et al., 1977, 1979) could stem from any of the following factors: (1) species differences; (2) differences in RF recording sites; (3) failure of the cat studies to specifically evaluate RF cell discharge in relation to hippocampal theta. The only other brain stem nucleus directly implicated in theta generation in unit recording studies was the raphe magnus (Sheu et al., 1974). The firing of cells within other monoaminergic nuclei including the locus coeruleus was unrelated or only loosely related to states of hippocampal synchronization or desynchronization (Sheu et al., 1974; Chu and Bloom, 1973, 1974; Hobson et al., 1975; Foote and Bloom, 1979; Aston-Jones and Bloom, 1981; Heym et al. 1981).

D-Amphetamine at low doses suppresses noradrenergic functions

This study examined the effects of d-amphetamine on the firing rate of hippocampal cells which had been shown to have an inhibitory, noradrenergic input from the nucleus locus coeruleus (LC). d-Amphetamine at low doses of 0.1 mg/kg i.v. or 0.5 mg/kg i.p. increased the firing rates of these cells. With higher doses of d-amphetamine, both increases and decreases in the firing rates of hippocampal cells were observed. These differential effects on the firing rate of hippocampal cells were statistically significant (x2 = 13.32, d.f. = 3, P less than 0.01). The increased firing rate of hippocampal cells produced by the low doses of d-amphetamine was blocked by a prior destruction of the LC indicating that the drug effect was mediated by LC neurons. d-Amphetamine also significantly attenuated the decrement in the firing rates of hippocampal cells produced by LC stimulation (P less than 0.01). These results suggest that low doses of d-amphetamine suppress rather than enhance the actions os norepinephrine.

Divergent axon collaterals of rat locus coeruleus neurons: demonstration by a fluorescent double labeling technique

The distribution of the noradrenaline-containing neurons of the rat locus coeruleus has been investigated with retrograde labeling techniques using two different fluorescent tracers. Injections were placed in the prefrontal cortex, the striatum, the thalamus, the hippocampus, the cerebellar cortex and the lumbar spinal cord. No evidence for locus coeruleus projections to the striatum was found. Injections in the cortex, thalamus and hippocampus revealed not only ipsilateral but also contralateral labeling of cells in the locus coeruleus. Following unilateral or bilateral homo- or heterotopic injections of the two tracers several cells of the locus coeruleus were double labeled. Combined injections of the two fluorophores in any of these forebrain areas and in the spinal cord also produced double labeled cells. The majority of double labeled cells was located in an area between the ventral and the dorsal parts of the locus coeruleus. These results indicate that individual neurons of the locus coeruleus have the possibility to influence adrenergic receptors at remote areas in the central nervous system.

Evoked responses of pyramidal tract neurons to stimulation of the lateral hypothalamus

The evoked responses of identified pyramidal tract neurons of the pericruciate region of the cortex arising on stimulation of the posterior, tuberal, and anterior sections of the lateral hypothalamus were investigated in acute experiments on cats anesthetized with chloralose. THe pyramidal tract neurons recorded were situated at a depth of 0.75-2.5 mm and on stimulation of the hypothalamus discharged with a latent period of 1.6-52.5 msec. They discharged most efficiently in the case of stimulation of the caudal half of the lateral hypothalamus. The pyramidal tract neurons activated by the hypothalamus were also tested by electrocutaneous stimulation of the four limbs. Of the neurons 75% responded to stimulation of several limbs, i.e., they had a broad bilateral receptive field, while 15% reacted to stimulation of one contralateral limb (either the anterior limb or the posterior limb), i.e., they had a small contralateral receptive field. Comparison of the latent periods of the anti- and orthodromic responses of the pyramidal tract neurons did not reveal any relationship between the magnitude of the latent period of the orthodromic response (on hypothalamic or electrocutaneous stimulation) and the type of pyramidal tract neuron (according to the axonal transmission velocity). No relationship between the latent period of hypothalamic stimulation and the magnitude of the latent period of the response to a peripheral stimulus was detected either.

The development of pre- and postsynaptic components of the noradrenergic system in the rat cerebellum

Evidence based on the ability to accumulate [3H]noradrenaline by a mechanism sensitive to desmethylimipramine suggests that there is a period of hyperinnervation of the cerebellum by noradrenergic fibres around the beginning of the second postnatal week. Different developmental profiles for specific noradrenaline uptake and noradrenaline content indicate that invasion of the tissue by noradrenergic fibres precedes their full acquisition of transmitter. Developmental increases in the density of beta-receptors and adenyl cyclase responsiveness to isoproterenol lags behind those of the presynaptic components and does not begin until the hyperinnervation is declining around day 12.

Suction lesions of the frontal cerebral cortex in the rat induce asymmetrical behavioral and catecholaminergic responses

Suction lesions of the right frontal cerebral cortex in rats induce a period of spontaneous hyperactivity. The hyperactivity, as measured by an increase in running wheel activity begins about one week post-operatively and continues throughout the remainder of a 30-day observation period. The increased activity is accompanied by a bilateral decrease in norepinephrine concentrations in both the ipsilateral and contralateral cortex and locus coeruleus. Identical lesions of the left frontal cerebral cortex produce neither the hyperactivity nor a decrease in norepinephrine concentrations. These experiments have reproduced many of the behavioral and biochemical asymmetries seen after middle cerebral artery ligation; however, suction lesions are both simpler to produce and histologically less variable in their effects.

Aminergic neurons: state control and plasticity in three model systems

Aminergic neurons have particular functions in many systems, and in this review their role is discussed and compared in three systems: those parts of the central nervous system controlling sleep and waking in the cut; the superior cervical ganglion: and the isolated nervous system of Aplysia. In the cat the aminergic neurons are most important in a waking state during which time external information is received, processed, and can be retrieved, and during which time habituation and sensitization occur. Aminergic neurons appear to have similar roles in state control in plasticity in both the Aplysia nervous system and the superior cervical ganglion. The striking similarities in the role of aminergic neurons in these three systems support the speculation that aminergic neurons have uniquely important roles in regulation of the plastic properties of neurons.

Vagal elicitation of respiratory-type and other unit responses in basal limbic structures of squirrel monkeys

Basal limbic structures (insula, amygdala, hippocampus and surrounding areas) were explored for unit responses to vagal volleys in awake, sitting, squirrel monkeys. Triple shocks were applied every 4 sec to the left cervical vagus nerve. As a control for adventitious activation by extravagal somatic afferents, units responsive to vagal volleys were also tested during shock-induced facial and cervical twitches. Under the given conditions, 16% of a population of more than 200 limbic units responded only to vagal volleys. The ratio of initially excited to initially inhibited units was about 2:3. The response latencies were indicative of both rapidly and slowly conducting, afferent pathways. The entrainment of respiration by vagal volleys revealed that 6% of the tested units discharged with a periodicity commensurate with the respiratory rhythm. Such respiratory units were found in the anterior amygdala, insula and hippocampus. In the case of the hippocampus it can be concluded that the discharge of respiratory-type units is not dependent on olfactory inputs. In the amygdala, the highest percentage of responsive units was found in the central nucleus; none were of a respiratory-type. The particular interest of the respiratory-type units found in this and the preceding study is discussed.

Mood change following left hemispheric brain injury

Eighteen patients with left hemispheric strokes were compared to 11 patients with traumatic brain injury for frequency and severity of depression, using several mood scales. More than 60% of the stroke patients had clinically significant depressions as compared with about 20% of the trauma patients, even though the two groups had comparable impairments in their activities of daily living and global cognitive functions. Analyses of brain CT scans revealed that the two groups had similar-sized lesions, but the areas of ischemic injury were more anterior than the traumatic lesions. When the results were controlled for lesion location, there were no significant differences in mood between the two groups. The severity of depression was directly correlated with the closeness of the lesion to the frontal pole. These results suggest that depression following left hemispheric brain injury may not be a nonspecific neurological or psychological response, but rather may be a symptom of injury to specific pathways, such as the catecholamine-containing ones, as they pass through the frontal cortex.

Mechanisms of norepinephrine actions on hippocampal pyramidal cells in vitro

Responses of pyramidal cells to topical application of norepinephrine (NE) were studied by intracellular recording in hippocampal slices in vitro. Norepinephrine hyperpolarized CA1 cells. Simultaneously, there was a decreased response to constant hyperpolarizing and depolarizing current pulses. The number of spikes evoked by constant depolarizing pulses was reduced. Spontaneous activity, when present, was reduced or abolished. The response to depolarizing current pulses was reduced more than the response to hyperpolarizing current pulses. The reduction of the depolarizing response was minimal for the first 6-8 msec of the pulse, whereafter it increased. The effects persisted after blocking synaptic transmission with low calcium-high magnesium concentrations in the incubation fluid. We conclude that the hyperpolarization is most likely due to a conductance increase. The mechanism behind the reduced response to depolarizing current pulses is discussed.

Neurophysiology and neuropharmacology of cardiovascular regulation and stress

Evidence has accumulated over the past several years indicating that environmental factors can have a substantial influence on cardiovascular dynamics. It has been hypothesized by many investigators that through these influence environmental stressors may be important to the etiology and maintenance of cardiovascular diseases. Since the nervous system is intimately involved in the regulation of cardiovascular function it may be assumed that environmental influences on cardiovascular dynamics are to a large extent mediated by the nervous system. This assumption is supported by the literature reviewed which indicates that there are many nervous system nuclei and neurotransmitter systems involved in the regulation of cardiovascular dynamics which are also involved in an organisms adjustment to environmental stressors. The conclusion is reached that further multidisciplinary research will reveal underlying neurophysiological and neuropharmacological mechanisms responsible for stress induced cardiovascular disease and lead to new methods of treatment.

The action of norepinephrine in the rat hippocampus: intracellular studies in the slice preparation

The ionic basis of norepinephrine (NE) action was studied with intracellular recording techniques in the rat hippocampal slice. Topical application of NE caused, in CA1 neurons, a 3-4 mV hyperpolarization associated with a 10-20% decrease in input resistance. This effect was accompanied by a decrease in spontaneous action potential discharges and, in some cells, by a reduction in EPSPs produced by stimulation of the excitatory Schaffer collateral-commissural pathway. An analysis of the voltage and concentration dependency revealed that NE may activate two different mechanisms. Experiments performed to test this hypothesis have demonstrated that a short duration hyperpolarizing action of NE was still present in a low Cl- medium. The hyperpolarizing responses to NE were absent in ouabain-treated slices and in low temperature. Cyclic AMP produced a 3-4 mV hyperpolarization associated with minimal changes in input resistance. This effect of cAMP was blocked by ouabain. IBMX potentiated responses to low concentrations of NE. It is proposed that NE activates two mechanisms; one involves activation of Cl- conductance and the other activation of a Na+-K+ pump. This latter effect might be mediated by cAMP.

Effects of 6-hydroxydopamine lesions of locus coeruleus on startle in rats

To examine the possible involvement of the norepinephrine (NE) containing neurons of the locus coeruleus in the modulation of behavioral reactivity to sensory stimulation, bilateral chemical lesions of the locus coeruleus were made by local injection of the catecholamine neurotoxin 6-hydroxydopamine. Both histochemical and biochemical analyses confirmed the effectiveness of the lesions in specifically eliminating the NE containing cell bodies of the locus coeruleus and reducing the NE content of the hippocampus and substantia nigra by 45% and 69% respectively. Rats were tested both 5 and 36 days after lesioning for their startle response to a repetitive series of tactile stimuli. On both days, locus coeruleus lesioned rats exhibited consistently reduced startle responses throughout the stimulus series. Additionally, lesioned rats showed a far more rapid rate of response habituation, particularly in the first test. The results are discussed in terms of a possible influence of the locus coeruleus on the process of sensitization to sensory stimuli.

Development of the brain stem in the rat. IV. Thymidine-radiographic study of the time of origin of neurons in the pontine region

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day 12 and 13 (E12 + 13) until the day before parturition (E21 + 22) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labeled) on specific embryonic days was determined quantitatively in 14 nuclei of the pontine region. Peak production time of neurons of the trigeminal mesencephalic nucleus was on day E11 or earlier, with a small proportion generated on day E12. Peak production time of the trigeminal motor neurons was on day E12, with a small proportion produced earlier. Neurons of the principal sensory nucleus were generated between days E13 and E16, with a peak on day E14; the late-produced neurons tended to belong to a class of intermediate and large cells. The bulk of the neurons of the supratrigeminal and infratrigeminal nuclei arose on days E15 and E16. Neurons of the locus coeruleus are produced mostly on day E12, with about 20% of the cells arising on day E13. The bulk of the neurons of the dorsal tegmental nucleus (Gudden's) are produced between days E13 and E15, whereas most of the neurons of the deep (ventral) tegmental nucleus are produced on day E15. A dorsal-to-caudal gradient was also obtained between the dorsal and ventral nuclei of the lateral lemniscus, the neurons of the former being generated between days E12 and E15; the latter, between days E13 and E17. The neurons of both the pars lateralis and the pars medialis of the parabrachial nucleus were produced simultaneously between days E13 and E15, with a peak on day E13. The heterogeneous collection of neurons of the pontine paramedial reticular formation was produced for day E11 (or earlier) until day E15. Finally, the neurons of the raphe pontis parvicellularis were generated at an even rate between days E13 and E15, whereas the bulk of the neurons of the raphe pontis magnocellularis were produced on days E15 and E16. On the basis of datings obtained for 9 subdivisions of the entire brain stem trigeminal complex, hypotheses were offered of the cytogenetic components of the system. The sequence of neuron production in the dorsal and deep tegmental nuclei was related to their connections with divisions of the mammillary and habenular nuclei on a "first come-first serve" basis.

Metabolic changes induced in rat hippocampal slices by norepinephrine

The oxidative metabolic activity of restricted regions of hippocampal slices was assessed by a continuous measurement of the fluorescence of intramitochondrial nicotinamide-adenine dinucleotide (NADH). A large increase in NADH fluorescence was triggered by substituting the oxygen supply to the slice by nitrogen gas. A large and transient increase in NADH fluorescence was also produced by superfusion of the the slice with a high (50 mM) potassium-containing medium. Addition of norepinephrine (NE) to the superfusion medium caused a propranolol-inhibited increase in NADH fluorescence. Furthermore, ouabain, which inhibits the Na-K pump, blocked the effects of NE. An analog of cyclic adenosine monophosphate (cAMP), 8-bromo cAMP, mimicked the effect of NE. Finally, effects of NE could still be produced in a kainic acid-treated hippocampus, where most neurons were previously destroyed by the drug. It is suggested that NE activates a Na-K-ATPase, that this effect might be mediated by cAMP, and that these interrelations may underly the physiological action of NE in the brain.

Cholinergic projections from magnocellular nuclei of the basal forebrain to cortical areas in rats

Acetylcholinesterase (AChE) and choline acetyltransferase (CHAc) activities were studied by quantitative histochemical (AChE) as well as biochemical methods (AChE, ChAc) in certain cortical brain areas in rats after stereotaxic lesions had been placed in several structures of the basal forebrain. After lesioning the magnocellular nuclei of the substantia innominata (nuc. basalis Meynert, NBM) the activities of AChE and ChAc decreased to moderate or low residual values in the ipsilateral cortical areas. This indicated that cholinergic pathways were directly linked to frontal, sensory-motor, auditory and visual cortex. After lesions of the globus pallidus the decrease in cortical AChE activity was less pronounced. Lesions of the caudate, accumbens or entopeduncular nucleus did not influence the cortical AChE activities. The results are discussed with respect to the similarity of the organization of the cholinergic projection to the cortex arising from NBM cells and the monoaminergic system which innervates the cortex. It is suggested that both neurotransmitter systems by their interaction might modulate and control cortical information processing and behavior in a manner analogous to the control of peripheral activity by the sympathetic and parasympathetic system.

Transplantation of embryonic occipital cortex to the tectal region of newborn rats: a light microscopic study of organization and connectivity of the transplants

Occipital cortex was taken from fetal rats and transplanted to the tectal region of newborn rats, where it developed a specific structural identity reflecting in part its cortical origin. The implants showed locally distributing intratransplant connections, and the majority formed connections with defined regions of te host cerebral cortex and the brainstem. A sparse afferent projection from the host had its origin in visual, somatosensory, and cingulate areas of te cortex, pretectum, superior colliculus, central gray, hypothalamus, pontine reticular formation, raphe nuclei, and the locus coeruleus. No input was identified from either the retina or the dorsal thalamus. Efferent fibers were observed in normal fiber preparations as compact bundles running through the host brainstem along two main routes, one group of bundles in a dorsal position and a second group more ventral. Efferent fibers traveling rostrally along the first pathway distributed in the lower part of the stratum griseum superficiale and in the intermediate laminae of the superior colliculus, and in some cases they reached the pretectum and the lateral posterior thalamic nucleus. Deep efferent fibers ran rostrally and caudally in the central gray, and in some cases laterally directed fibers were seen to distribute in the midbrain tegmentum and reticular formation, in one case reaching the pontine gray. The finding that most afferent and many efferent connections of cortical transplants are uncharacteristic of normal cortex stands in marked contrast to retina and tectum, which, when transplanted to the same region, make relatively normal connections.

Descending projections of the locus coeruleus and subcoeruleus/medial parabrachial nuclei in monkey: axonal transport studies and dopamine-beta-hydroxylase immunocytochemistry

Spinal projections originating in the dorsolateral pons in the ventral locus coeruleus and in the subcoeruleus and medial parabrachial nuclei were identified in monkeys (Macaca fascicularis) using the retrograde horseradish peroxidase tracing technique. Anterograde autoradiographic tracing studies were then carried out to determine the brain stem and spinal cord terminations of the neurons. Finally, results obtained with the axonal transport tracing methods were compared with the pattern of staining for noradrenergic cells and terminals revealed immunocytochemically with an antibody to dopamine-beta-hydroxylase (DbetaH), the synthesizing enzyme for norepinephrine. The major findings of these studies are that two presumed noradrenergic cell groups of the dorsolateral pons, one corresponding to the nucleus locus coeruleus, the second to the subcoeruleus/medial parabrachial nuclei, give rise to descending projections. They differ significantly in their patterns of termination in the lower brain stem and spinal cord. Among the major terminations of the locus coeruleus pathway are projections to parasympathetic neurons of the dorsal motor nucleus of the vagus, the region of the nucleus ambiguus, and the sacral spinal cord. The terminations of the descending subcoeruleus/medial parabrachial pathway, in contrast, include projections to sympathetic preganglionic neurons of the intermediolateral cell column of the thoracic cord and heavier projections to somatic cranial nerve nuclei. Both pathways have additional widespread and bilateral terminations in various nuclei of the reticular formation, in the spinal dorsal horn (including the marginal zone), in the region around the central canal and in the ventral spinal gray matter. Since the origins and terminations of both these pathways correspond closely to the locations and patterns of terminations of noradrenaline-containing neurons, demonstrated here with DbetaH immunocytochemistry, norepinephrine (or epinephrine) is suggested to be the transmitter in both these descending systems.