Ipsilateral Nucleus Research Articles

Some observations on the nature of neural intranuclear inclusions (Roncoroni bodies).

In experimental jejunal obstruction produced in cats, the neurones of the intermediate gray column of the cord showed bilateral intranuclear inclusions. They were also seen when hypertrophy and hyperplasia, produced in various elements of the bowel wall, were prevented by large doses of atropine. The latter observation implied that the afferent autonomic nerve supply is involved in the production of these unusual structures. The inclusion bodies were extremely rare or absent in control animals. In order to see whether these bodies occurred by chance even though they are regularly produced in the above-mentioned area, an effort was made to see whether they would appear unilaterally following stimulation of a unilateral afferent nerve. This was done by ligation and severance of the right common carotid artery below its bifurcation with or without severing its accompanying vagal trunk. Removal of the pulsatile blood supply to the carotid sinus and carotid body has long been known to produce afferent action potentials in the glossopharyngeal and vagus nerves. Within 6 h many neurones in the middle half of the ipsilateral nucleus of the tractus solitarius showed the inclusions. The cephalic end of this nucleus showed no inclusions. At the level of the obex the inclusions were present bilaterally. The inclusions also appeared in numerous other areas of the brain, brain stem and cervical cord in bilateral fashion. They were found in neurones of the neurohyphysis as well as in the cingulate gyrus. Their widespread but focal distribution corresponds to numerous areas of the cord and brain in which physiologists have produced striking effects with electric probing and stimulation. The inclusion bodies are at present conceived as representing the neuronal nuclear response to an afferent stimulus which causes an increase in the metabolic activity controlled by the nucleus.

Supraspinal cell populations projecting to the cerebellar cortex in the turtle (Pseudemys scripta elegans).

Neuronal cell populations giving rise to cerebellar projections in the turtle, Pseudemys scripta elegans, were analysed following injections of horseradish peroxidase into the cerebellar cortex. The most prominent retrograde cell labeling occurred bilaterally within the caudal rhombencephalon and especially in the ventral portion of the inferior reticular field. Based on the structural parameters of the labeled cells (size, dendritic tree), their location and laterality of projection, attempts were made to identify cell groups similar to the inferior olive, the lateral funicular (reticular) nucleus and the perihypoglossal complex of other vertebrates. There were some labeled neurons within the descending and principal trigeminal nuclei, but few if any within the dorsal column nuclear complex. Cerebellar projections on the other hand clearly arose from the n.vestibularis inferior and n.vestibularis dorsolateralis on both sides. While there was little evidence for labeled cells located in a similar position as the pontine nuclei of higher vertebrates, a conspicuous number of neurons were observed in meso-diencephalic regions. Confirming the findings of Reiner and Karten (1978) characteristic accumulations of cells were seen in the nucleus opticus tegmenti, in the ipsilateral mesencephalic tegmentum and lateral and ventral to the ipsilateral nucleus pretectalis. Additional neurons were found in the periventricular hypothalamus, the nucleus of the fasciculus longitudinalis medialis and in the n.interstitialis of flm on both sides as well as in the red nucleus.

Distribution and structural characterization of neurons giving rise to descending spinal projections in the turtle, Pseudemys scripta elegans.

Descending spinal projections were investigated in the turtle Pseudemys scripta elegans following injections of horseradish peroxidase and/or radioactive wheat germ agglutinin into the spinal cord at various levels. Using various planes of section the cells of origin in the brainstem, cerebellum, and diencephalon were characterized according to their size, dendritic tree, and precise location. Projections to levels as far caudal as the lumbar spinal cord were found to arise from medial and lateral rhombencephalic reticular fields, including the perihypoglossal complex, the nucleus raphe inferior, and the locus coeruleus; from certain subdivisions of the vestibular complex (ipsilateral subnucleus (subn.) ventrolateralis, contralateral subn. ventromedialis, and possibly subn. tangentialis); from the motor trigeminal nucleus; from the contralateral red nucleus, the ipsilateral nucleus (n.) interstitialis of the fasciculus longitudinalis medialis (flm) and from the hypothalamus. Fibers to high cervical levels arose from neurons within the dorsolateral and superior vestibular nuclei, the lateral cerebellar nucleus, the mesencephalic trigeminal nucleus, and from neurons of the optic tectum. Low cervical and thoracic spinal levels were reached by fibers from the torus semicircularis n. laminaris, the n. of the flm, the medial cerebellar nucleus as well as from the n. vestibularis inferior and the principal and descending trigeminal nuclei.

Projections of the medial terminal nucleus of the accessory optic system upon pretectal nuclei in the pigmented rat.

The projections of the medial terminal nucleus (MTN) of the accessory optic system (AOS) upon pretectal nuclei have been studied in pigmented rats by means of (i) the anterograde transport of 3H-leucine with the use of light autoradiography and (ii) the retrograde transport of horseradish peroxidase (HRP). Injections of 3H-leucine largely restricted to the MTN and minimally involving adjacent ventral midbrain structures, produced heavy terminal axonal labeling within the ipsilateral nucleus of the optic tract (NOT) and the dorsal terminal nucleus (DTN) of the AOS. Terminal labeling was observed in all superficial portions of the NOT, except for a small ventromedial segment in the rostral two thirds and a larger medial segment in the caudal one third of this nucleus. Thus the MTN-NOT projections we describe entirely overlap the retinal-NOT projection and partially overlap the visual cortical-NOT, as reported by others. Within the DTN, the dense terminal fields covered the entire nucleus. After postinjection survival times of 3-7 days, the pattern of axonal labeling showed that the MTN-NOT projection consisted of three bundles: (i) a superficial mesencephalic bundle coursing within the superior fasciculus, posterior fibers of the AOS which enters the caudal portions of the NOT and the DTN; (ii) a deep mesencephalic bundle that traversed the midbrain tegmentum dorsolaterally, also reaching the caudal one-half of the NOT and all of the DTN; and (iii) a mesodiencephalic bundle that passed first laterally through midbrain tegmentum and then dorsally through lateral thalamus to enter the rostral one-half of the NOT. Pretectal injections of HRP that invade the NOT and DTN produced retrograde labeling of most (ca. 75%) of the neurons of the ipsilateral MTN, without labeling the adjacent substantia nigra or ventral tegmental area. This finding confirms our autoradiographic data by showing that the MTN provides the major, ventral tegmental projection to the NOT and DTN. The present finding of a MTN-NOT projection, combined with available anatomical and physiological data, suggests that the MTN may play a more significant role in visual-vestibular aspects of oculomotor control than formerly thought.

Electrical activity of septal neurones during suckling and the milk ejection reflex in the lactating rat.

Extracellular recordings from neurones in the lateral septum were performed in urethane anaesthetised lactating rats to study the eventual role of the septum in the control of suckling-induced oxytocin release. The connections of these neurones with the supraoptic nucleus, which contains cells secreting oxytocin, were assessed electrophysiologically by single pulse stimulation of the ipsilateral supraoptic nucleus. The neurones were thus classified into four categories: antidromically activated, orthodromically activated or inhibited, and unresponsive neurones. One hundred septal neurones were recorded in animals not exposed to suckling. A second group of 40 cells were analysed during suckling and one or more reflex milk ejections. The mean firing rates of each category of septal neurone did not differ significantly during suckling from the values observed in the absence of suckling. During suckling, almost all the recorded septal cells showed no significant alteration in their level of firing in relation to milk ejections. Two neurones presented an activation in the period between two milk ejections that seemed related to arousal. One neurone was clearly inhibited at the time of milk ejection. Our observations suggest that the septum does not represent an essential component of the pathways necessary for the milk ejection reflex induced by suckling, although it could exert an inhibitory action modulating either the intervals between two successive milk ejections, or the amount of oxytocin released.

Basal ganglia pathways to the tectum: the afferent and efferent connections of the lateral spiriform nucleus of pigeon.

Previous studies have demonstrated that the lateral spiriform nucleus (SpL) of the avian pretectum receives a major input from the ipsilateral basal ganglia (Karten and Dubbeldam, '73) and projects to the ipsilateral optic tectum (Brecha et al., '76). The present study has further detailed the anatomical organization of the afferent and efferent connections of SpL, with particular reference to (1) the sources of afferent inputs to SpL, (2) the projection targets of SpL, and (3) the laminar termination pattern of the SpL projection to the tectum. The SpL was found to receive clear-cut major inputs from only three nuclei: (1) the ipsilateral paleostriatum primitivum (PP) of the basal ganglia (the avian homologue of the mammalian globus pallidus), (2) the ipsilateral anterior nucleus of the ansa lenticularis (ALa) of the diencephalon, and (3) the ipsilateral nucleus tegmentipedunculopontinus (TPc) of the mesencephalon. Both TPc and ALa have previously been noted themselves to receive major inputs from the ipsilateral PP (Karten and Dubbeldam, '73). Two other cell groups may give rise to a slight projection to the ipsilateral SpL: (1) the posterior nucleus of the ansa lenticularis (ALp) of the diencephalon and (2) the nucleus semilunaris (SLu) of the isthmic brainstem. The ALp also receives a major input from PP (Karten and Dubbeldam, '73). Two other cell groups may give rise to a slight projection to the ipsilateral SpL: (1) the posterior nucleus of the ansa lenticularis (ALp) of the diencephalon and (2) the nucleus semilunaris (SLu) of the isthmic brainstem. The ALp also receives a major input from PP (Karten and Dubbeldam, '73), while SLu receives a major tectal projection (Hunt and Kunzle, '76a). The ipsilateral tectum was found to be the only projection target of SpL. The present data suggest that the SpL projection to the tectum is restricted to layers 8-13, with layers 11-13 receiving the heaviest projection from SpL. Among layers 8-10, layer 9 receives the lightest projection from SpL. The present results indicate that SpL receives only a limited number of inputs, which in all likelihood relay largely basal ganglia input to SpL. Since SpL projects only to the tectum, the sole function of SpL apparently is the transmission of ipsilateral basal ganglia influences to the avian optic tectum. Tectal layers 8-15 have been previously found to represent the layers of origin of the descending pathways of the avian tectum to hindbrain motor and "premotor" cell groups (Reiner and Karten, '82). In view of the purported involvement of the basal ganglia in motor functions, the basal ganglia pathway to the ipsilateral tectum via SpL may represent a major route by which the avian basal ganglia exert influences over motor functions.

Medullary cells of origin of physiologically identified cardiac nerves in the dog

Individual cardiac nerves from which stimulation elicited cardioinhibition (bradycardia and negative inotropism) were identified in 24 of 38 dogs. Subsequently, 3–25 μl of 30% horseradish peroxidase (HRP) were injected into an identified cardiac nerve. After a 3-day survival period, the medulla oblongata was processed for HRP histochemistry. Retrograde labeling was observed to be concentrated primarily in the ipsilateral nucleus ambiguus (NA) and in medium-sized neurons located ventral and lateral to the larger neurons of the principal NA cell column. This latter location was so characteristic that it has been designated the ventrolateral nucleus ambiguus (VLNA). Labeled neurons were found at all levels of the NA and VLNA and their distribution was similar irrespective of the cardiac nerve injected. Relatively few labeled neurons were observed in the dorsal motor nucleus of the vagus nerve (DMV) except after injections into the left and right recurrent cardiac nerves and the left cranial vagal nerve. In some dogs labeled cells were present only in and ventrolateral to the NA and not in the DMV, even though stimulation of the injected nerve elicited both bradycardia and negative inotropism. These results demonstrate that ventrolateral regions of the NA represent the major site of cardioinhibitory motor neurons in the dog and that they can regulate both rate and force.

Medullary proprioceptive neurons from extraocular muscles in the pigeon identified with horseradish peroxidase

Three to five microliters of 50% HRP in saline was injected along a central axis into one of the 6 extraocular muscles in each of 18 adult pigeons. The brain was fixed and serially sectioned 16-20 h postinjection and the HRP reacted with tetramethylbenzidine (TMB). HRP-labeled proprioceptive neurons were located in the ipsilateral nucleus descendens nervi trigemini (TTD) for all muscle injections. The labeled neurons were further subdivided into two groups based on size and shape. In each experiment the number of labeled proprioceptive cells relative to the number of labeled motoneurons ranged between 4.9 and 15.5%. There were no labeled cells in the trigeminal mesencephalic nucleus or contralateral TTD. The study suggests that at least partial afferent (proprioceptive) innervation of the extraocular muscles in the pigeon derived from neurons in the ipsilateral TTD.

The localization of the motor neurons innervating the cricothyroid muscle in the adult dog by the fluorescent retrograde axonal labeling technique.

Injection of 4'6-diamidino-2-phenylindol 2 HCl (DAPI) into the cricothyroid muscle of the adult dog resulted in blue fluorescence of cells found exclusively in the rostral part of the ipsilateral nucleus ambiguus. These labeled neurons on the average extended 1.8 mm from the level just caudal the facial nucleus to the caudal extension. In the rostral tip of the nucleus, labeled cells were located in a scattered ventral group of larger neurons of the nucleus.

Inhibition of axoplasmic transport in the developing visual system of the rat—III. Electron microscopy and golgi studies of retino-fugal synapses and post-synaptic neurons in the dorsal lateral geniculate nucleus

Quantitative light and electron microscopy, together with Golgi methodology, were used to study alterations in retino-fugal terminals and postsynaptic neurons within the dorsal lateral geniculate nucleus of the rat at various intervals following inhibition of axoplasmic transport in the optic nerve induced by intraocular injections of colchicine from 1–20 days postnatal. Colchicine concentrations used in this study ranged from 10 −5 m−10 2 m. These were selected on the basis of our measurements of axon transport suppression described in the preceding article. 61 The volume of the nucleus was determined by section planimetry and reconstruction. Growth of the contralateral dorsal lateral geniculate nucleus was significantly retarded by intraocular colchicine at 1 and 5 days of age, only achieving a volume of between 61–75% of the normal or the control (ipsilateral) nucleus depending upon dosage. Application of colchicine at 10 days of age resulted in minimal stunting of nuclear growth, (79–93% of normal). Mean numbers of neurons in the contralateral and ipsilateral nucleus remained stable throughout all postnatal ages examined suggesting that nuclear volume loss was caused principally by a reduction in the amount of neuropil. Golgi impregnation displayed dendritic stunting in relay neurons characterized by narrowing of the portion of the shaft between 40–80 μm from the soma and a reduced incidence of spinous protrusions, particularly those shown by other studies to engage the retino-fugal terminal. 27,69 A concomitant Sholl 76 analysis of dendritic branching in relay neurons demonstrated no significant differences in the number of intersections between normal and experimental nuclei. No alterations were observed in intrinsic neurons. Electron microscopy of postsynaptic neurons following concentrations ranging from 10 −4 m at birth revealed altered patterns of granular endoplasmic reticulum in many cells characterized by reduced numbers of cisternae and scattered instances of cisternal dilation, together with enhanced infolding of the nuclear membrane at 20 days postnatal. Those animals which were given 10 −3 m−10 −2 m colchicine demonstrated an increased incidence of cisternal dilation, loss of ribosomes, disruption of the nuclear membrane and occasionally, complete degeneration. A similar array of alterations took place following intraocular injection at 5 days of age; however, animals receiving colchicine at 10 days postnatal displayed minimal alterations in relay neurons. Synaptic glomeruli, which contain the retinofugal terminal, displayed dose and age-dependent reduction in the size of the presynaptic element of the complex following intraocular colchicine, together with fewer post-synaptic spinous protrusions. Synaptic vesicles remained normal in appearance and distribution and our quantitative analysis demonstrated no loss of such terminals in accordance with colchicine concentrations which were previously found not to be lethal to retinal ganglion cells and optic axons.

Corticopontine projections from the visual area of the superior temporal sulcus in the macaque monkey.

1. The projections from the superior temporal sulcus (STS) visual area to pontine nuclei were studied in the macaque monkey by the autoradiographic tracing method. Microinjections of a mixture of L-[5-3H] proline and L-[4,5-3H] leucine were carried out in the posterior band and the floor of the caudal half of the STS. Survival time was always 7 days. 2. The STS visual area projects to the dorsolateral part of ipsilateral pontine nuclei. Terminal projections are distributed in patches in the whole rostro-caudal extent of the pons. 3. These findings support the view that the STS visual area in the macaque monkey is homologous to the postero-medial lateral suprasylvian area in the cat.

Location and vestibular responses of interstitial and midbrain reticular neurons that project to the vestibular nuclei in the cat.

Experiments were performed on cats anesthetized with alpha chloralose to locate neurons in and around the interstitial nucleus of Cajal (INC) that project to the vestibular nuclei, and to study labyrinthine inputs to these neurons. Neurons that project to the vestibular nuclei were identified by microstimulation confined to the vestibular nuclei on both sides. All neurons thus identified were activated antidromically from the ipsilateral (but not contralateral) vestibular nuclei. Vestibular projecting neurons were found in the INC and the reticular formation rostral, dorsal and caudal to the INC. About 23% of these neurons were vestibular branching spinal projecting neurons. The median conduction velocity of vestibular projecting neurons was estimated to be in the neighborhood of 12-16 m/s. Stimulation of the contralateral vestibular nerve evoked firing in 29% of neurons projecting to the vestibular nuclei, but not to the spinal cord. Interstitial neurons responded more frequently than reticular neurons (45% vs 11% chi 2 test, p less than 0.001). By stimulation of individual semicircular canal nerves, it was shown that vestibular projecting neurons receive excitation from the contralateral vertical canals, but do not receive substantial inputs from the horizontal canal. Stimulation of the ipsilateral vestibular nerve excited 10% of neurons; suppression of activity was observed for six cells and four of the six were excited by stimulation of the contralateral vestibular nerve. Stimulation of ipsilateral individual semicircular canal nerve did not excite any cells tested; the activity of a few cells was suppressed by stimulation of the vertical canal nerves. One neuron received excitation from the contralateral anterior canal and suppression from the ipsilateral posterior canal. Vestibular branching spinal projecting neurons rarely received labyrinthine inputs as already reported (Fukushima et al. 1980a). These results suggested that vestibular projecting neurons may be involved in vertical vestibular reflexes.U

The brain-stem projections of pulmonary stretch afferent neurones in cats and rabbits.

1. Micro-electrode recordings were made from slowly adapting pulmonary stretch afferents within the nodose ganglia of cats and rabbits. Recordings sites were distributed throughout the ganglia. 2. The projections of these afferents to the medulla oblongata were studied by antidromic stimulation. 'Point' and 'Field' type depth--threshold curves were interpreted as corresponding to stimulation of the main afferent axons and its branches, respectively. Increases in antidromic latency in conjunction with 'field' contours was additional evidence in support of this interpretation. 3. In cats, most (six out of seven) afferents had extensive branches, and probably also terminations, within the medial subnucleus of the ipsilateral nucleus tractus solitarius (n.t.s.). Two of these, plus one other afferent, also had projections to the lateral and ventrolateral subnuclei. 4. In rabbits the projections of such afferents were similar, i.e. mainly to the medial subnucleus of the n.t.s. (eight out of eleven) but also extending into the nucleus alaris, and occasionally to lateral and ventrolateral subnuclei (two out of eleven) or to both regions (one out of eleven). 5. Branching of single afferents was seen to occur over up to 3 mm of the rostro-caudal extent of the intermediate region of the n.t.s. The significance of the observations is discussed.

The central distribution of the cervical vagus nerve and gastric afferent and efferent projections in the rat

The medullary distribution of afferent fibers and cells of origin of the cervical vagal trunk and of the vagal innervation of the stomach have been studied using the anterograde and retrograde transport of horseradish peroxidase (HRP). Injections of HRP were made into the cervical vagus nerve, the stomach wall, the proximal small intestine, or the peritoneal cavity. Two to four days following the injections, the rats were perfused and the medullae oblongatae and nodose ganglia were processed using the tetramethyl benzidine method. Cervical vagus nerve injections of HRP resulted in heavy anterograde labeling in the ipsilateral nucleus of the tractus solitarius (NTS) and the commissural nucleus. Lighter labeling was seen in these regions on the contralateral side, but did not extend as far rostrally in the NTS. Labeling was also seen in the area postrema. Retrogade labeling of somata was present in the ipsilateral side in the nodose ganglion, throughout the whole extent of the dorsal motor nucleus of the vagus, much of the nucleus ambiguus and in rostral levels of the cervical spinal cord. After stomach injections, labeling indicative of afferent fibers was observed bilaterally in the dorsomedial and medial portions of the NTS and in the commissural nucleus. Labeled efferent fibres arose from neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus and the cervical spinal cord. Retrogradely labeled somata were found bilaterally, throughout the rostrocaudal length of the dorsal motor nucleus in all cases with stomach injections. In some, but not all cases, labeled somata were seen bilaterally in compact areas within the nucleus ambiguus, particularly rostrally. Control injections of HRP into the intestinal wall and peritoneal cavity indicated that the stomach was the primary source of afferent and efferent labeling in the medulla following subdiaphragmatic injections.

Brain stem afferents to the periabducens reticular formations (PARF) in the cat. An HRP study.

Six injections of HRP were placed in the periabducens reticular formation (PARF). Two were placed ventromedial to the caudal half of the abducens nucleus (VIn), two were placed further laterally and ventral to the rostral half of the nucleus, and two were placed rostral to the nucleus. Most injections in PARF produced cell labeling in the vestibular and perihypoglossal nuclei bilaterally and labeled cells in the reticularis gigantocellularis (Rgc) and reticularis pontis caudalis (Rpc) nuclei contralateral to the injection site. Few labeled neurons were found in the caudal part of the paramedian pontine reticular formation (PPRF). In the mesencephalon, bilateral but more numerous ipsilateral labeled cells were found in the medial mesodiencephalic region including the nuclei of Cajal, Darkschewitsch and the posterior commissure. Injections placed caudomedial to VIn resulted in a characteristic concentration of labeled cells in the ipsilateral nucleus cuneiformis and rostral half of the contralateral superior colliculus (SC). Injections placed rostral to VIn in PARF produced cell labeling in the nucleus campi Foreli. The results are related to physiological evidence which suggests that PARF is an important premotor center for coordination of oculomotor, head and body movements.

A re-examination of the rubro-olivary tract in the cat, using horseradish peroxidase as a retrograde and an anterograde neuronal tracer

Most authors using free horseradish peroxidase as a retrograde tracer have had difficulties in demonstrating a rubro-olivary tract. Injections of this tracer into the inferior olive in animals of different species resulted in only a few retrogradely labelled rubral cells within the rostral part of the ipsilateral nucleus. The present study, which is based on the highly sensitive technique of Mesulam (1978), confirms this observation. Injections of free horseradish peroxidase (Serva or Sigma VI type) into the dorsal lamella of the principal olive in eleven cats gave a positive retrograde labelling of rostral rubral cells in only three animals, with a very few cells in each case. In contrast to this, olivary injections of horseradish peroxidase labelled lectin (wheat germ agglutinin) result in an abundance of retrogradely labelled cells within the rostral part of the ipsilateral red nucleus, the great majority of these cells being of the small and medium-sized type. Many of the retrogradely labelled rubral cells are only faintly stained. However, free horseradish peroxidase appears to be well suited as an anterograde tracer for a demonstration of the rubro-olivary tract. The findings are discussed in relation to the observation that in the cat only peroxidase conjugated to lectin can be used successfully as a retrograde tracer for a visualization of the rubro-olivary connection.

Role of globus pallidus and substantia nigra efferent pathways in striatally evoked head turning in the rat.

These studies have examined the role of brain areas that receive efferent projections from the globus pallidus (GP) and substantia nigra (SN) in producing the contralateral head turning evoked by unilateral electrical stimulation of the neostriatum in the conscious rat. Two parameters were studied: the latency for a 90 degree head turn and changes in the normal latency evoked by administration of the GABA drugs picrotoxin and muscimol in GP. Electrolesions in the ipsilateral ventromedial and centromedian thalamic nuclei had no effect on the head turn parameters. Although small electrolesions in the SN slowed, but did not abolish the head turn, it prevented the changes in the response latency brought about by GABA drugs in GP. Treatment with 6-hydroxydopamine, which partly destroyed the nigro-striatal dopamine neurones, had no effect on the head turn. Areas of the brainstem that receive basal ganglia efferents were lesioned. An electrolesion of the nucleus tegmenti pedunculopontinus had no effect on the head turn latencies. The head turning was abolished by a lesion in the lateral periaqueductal grey (PAG); a more rostral PAG lesion, on the same level as SN, was ineffective. It is concluded that the head turning is mediated by basal ganglia efferents which pass close to the nigra without synapsing and project to the PAG. The GABA-sensitive GP efferents which modulate the response, probably project to SN.

Projection of ventrolateral medullary (A1) catecholamine neurons toward nucleus tractus solitarii.

The distribution and interconnections of brainstem catecholamine cell groups thought to be important in cardiovascular control were studied using histochemical and ultrastructural techniques in the rabbit. Lesions and microinjections of horseradish peroxidase (HRP) were made in the nucleus tractus solitarii in the dorsomedial medulla, and in the ventrolateral medulla. After lesions of the dorsomedial medulla the fluorescence intensity of the A1-group of catecholamine neurons was increased, and swollen axons could be seen coursing from the ventrolateral medulla toward the lesions on the same side, but not the opposite side. Most of these axons ran in a band about 2 mm in width, centered at the level of the obex. Electron microscopically, specific cells, identified as A1-catecholamine neurons, showed evidence of chromatolysis after the dorsomedial lesions. Following injection of HRP into the nucleus tractus solitarii. A1-catecholamine cells in the ventrolateral medulla on the same side contained the reaction product. Lesions of the ventrolateral medulla did not produce evidence of a reciprocal projection of A2-catecholamine neurons toward the ventrolateral medulla. Thus axons of the A1-group of catecholamine neurons in the ventrolateral medulla project toward the ipsilateral nucleus tractus solitarii in a relatively compact band at the level of the obex. On the other hand, the A2-group of catecholamine neurons in the dorsomedial medulla does not appear to send projections toward the A1-group.

Electrophysiological evidence for connections between septal neurones and the supraoptic nucleus of the hypothalamus of the rat.

In order to see whether septal neurones are connected to the hypothalamic neurones secreting vasopressin or oxytocin, neurones in different regions of the septum were recorded during electrical stimulation of the supraoptic nucleus. The position of the stimulating electrode within the latter was verified using lactating rats in which milk ejections could be induced by a train of electrical pulses applied to the nucleus. The responses of septal neurones to single pulse stimulation were then analysed by post-stimulus time histograms. In the septum ipsilateral to the site of stimulation, 42% of the neurones were antidromically invaded, 20% were orthodromically excited and 21% were inhibited following suraoptic stimulation. In the contralateral septum, 2% of the cells tested were antidromically invaded, 3% were excited and 16% inhibited. In the medial septum, 14% of the neurones were orthodromically excited, and 48% were inhibited. These results provide electrophysiological evidence for direct connections between septal neurones and the ipsilateral supraoptic nucleus of the hypothalamus, and give further support to the hypothesis of a septal influence on the activity of vasopressin- or oxytocin-releasing cells in the magnocellular system.

Necrotizing effects of kainic acid on neurons in the pigeon brain: Histological observations

The neurotoxin kainic acid (KA) has been shown to destroy neurons in the pigeon paleostriatal complex (PC), the avian analogue of the caudato-putamen and globus pallidus. In this earlier study the movement disorders in pigeons were strikingly similar to those reported by others in rats following intracerebral injection of KA into the corpus striatum. The toxic influences of KA on other parts of the pigeon brain have not been described. Therefore, KA was injected into areas of the telencephalon, diencephalon, mesencephalon and cerebellum. Areas sensitive to KA showed a marked cell loss and the neuropil exhibited spaces that contained fragments of necrotic neurons. The injection sites were invaded by glia and granulocytes. Kainic acid had a local necrotizing effect; for example, it destroyed neurons in the PC, nucleus rotundus, nucleus spiriformis lateralis, nucleus ruber and neurons of the cerebellar cortex. An apparent long-distance effect of KA was also observed, since intracerebral injections of KA into the PC was followed by cell loss in the ipsilateral nucleus of the ansa lenticularis. Kainic acid has proved to be a potent neurotoxin with a pronounced necrotizing effect upon neurons of the pigeon brain.