Number Of Such Neurons Research Articles

Identification of Stress‐Activated Inputs to the Dorsomedial Hypothalamus

Acute psychological stress elicits a typical response characterized in the short term by elevated sympathetic nerve activity and increases in heart rate and blood pressure. While the primary neural circuitry that underpins these responses is still uncertain, the dorsomedial hypothalamus (DMH) is known to play a major role.1 However, the antecedent inputs responsible for DMH activation in response to stress are unknown. In the present study, retrograde tracing was combined with Fos immunohistochemistry following air jet stress (AJS) to identify neurons that both project to the DMH and are activated by stress.Sprague Dawley rats received a unilateral injection of 15–30 nl of retrograde tracer choleratoxin B subunit‐AlexaFluor 555 into the DMH. One week later rats were exposed to a 15 minute AJS protocol (n=4), while controls (n=2) were left undisturbed. Following perfusion, brain sections were processed for Fos immunohistochemistry and photographed. The distribution of retrogradely and/or Fos‐labeled neurons was mapped using a rat brain atlas.2 The number of labeled cells in key regions was counted. Data are expressed as mean ± SE cells per section.Retrogradely labeled neurons were found throughout the brainstem and forebrain (Table 1). The majority of labeled cells were located in the forebrain, in particular in the medial prefrontal cortex, lateral septal nucleus, claustrum and amygdala. Following AJS, Fos‐positive neurons were located in many, but not all, of the regions in which retrogradely labeled neurons were found. There was a significant increase in the number of Fos‐positive neurons in the Kolliker Fuse nucleus (KF) in the pons, the dorsomedial, dorsolateral and ventrolateral midbrain periaqueductal gray (PAG), amygdala, the cingulate cortex, lateral septal nucleus and the claustrum. Double‐labeled neurons were found in the brainstem in the KF and ventrolateral PAG, and in the forebrain in the amygdala, cingulate cortex, lateral septal nucleus and claustrum. However, overall there were very few double‐labeled neurons seen throughout the brain.Neurons that both project to the DMH and are activated by AJS were identified in several brain regions, particularly in the forebrain. The number of such neurons was very small, suggesting that these neurons may play a minor role in stress‐induced activation of the DMH. An alternate hypothesis is that recruitment of DMH in response to stress may be dependent upon disinhibition. Number of labeled cells in key nuclei Region CTb Fos CTb + Fos RVLM 0.7±0.4 9.2±5.1 0.0±0 RVMM 0.3±0.2 6.1±4 0.0±0 PBC 27.6±14.2 14.4±5.9 1.5±0.8 KF 20.2±14.8 11.0±4.0* 0.6±0.4* dmPAG 4.4±2.1 7.3±1* 0.2±0.2 dIPAG 4.2±1.5 10.7±0.6* 0.5±0.4 IPAG 8.6±2.7 19.9±2.4 0.3±0.1 vIPAG 12.0±1.6 18.4±3.2* 1.0±0.5* Amy 124.4±22.7 55.9±18.3* 2.4±0.7* Cingular Cor 88.8±32.1 17.0±0.3* 3.2±0.8* Lat SN 177.9±62.1 38.5±5.5* 4.9±1.8* Claustrum 148.3±55.2 35.8±11* 2.1±0.4* mPFC 192.0±79 42.4±21.1 3.3±0.8 Values are mean ± SE

Operant reflexes and expression of the c-fos gene in the amygdalar nuclei and insular cortex of rats

We studied manifestations of increased neuronal activity in the limbic structures of the rat brain related to realizations of operant reflexes by the animals. After rats had performed repeated operant foodprocuring movements, the mean numbers of Fos-immunoreactive neurons within sections of the central and basolateral amygdalar nuclei, insular cortex, substantia innominata, and paraventricular hypothalamic nucleus significantly exceeded the control values. In the ipsilateral (with respect to the working forelimb) central nucleus of the amygdala, the mean number of such neurons within a 40-μm-thick slice was nearly an order of magnitude greater than in the control (42.2 ± 2.4 and 4.5 ± 0.4 labeled units, respectively). In the agranular insular and granular/disgranular cortical zones at the contralateral site, the numbers of labeled neurons exceeded control values by about three times (94.6 ± 8.2 vs 31.6 ± 2.2 and 103.5 ± 4.5 vs 39.6 ± ± 2.4 immunopositive cells, respectively). These findings confirm the hypothesis on the direct involvement of the subcortical structures and limbic cortex zones in the control of somato-cardiovascular integration during the performance of operant reflexes by the animals.

Utilização da veia glicerolada na regeneração neural: Estudo experimental em ratos

A auto-enxertia de nervo é o tratamento de escolha para grandes perdas de tecido neural que não podem ser reparadas por meio de rafia primária. A utilização do enxerto venoso previamente conservado em glicerol seria uma alternativa para diminuir o tempo operatório e a morbidade cirúrgica nesses casos. Os vasos preservados em glicerol não apresentam destruição de sua estrutura, o que permite seu uso na microcirurgia vascular, tendo a vantagem de diminuir a imunogenicidade do enxerto. O objetivo deste trabalho experimental foi comparar o grau de reparação nervosa, utilizando análise histológica, contagem do número de axônios mielinizados regenerados e análise funcional, obtida com a interposição de enxerto autógeno (grupo A) e de tubo de veia glicerolada (grupo B) em defeitos de 5 mm no nervo fibular de ratos Wistar. Somente no grupo A foi observado a formação de neuroma. O grupo B apresentou padrões histológicos compatíveis com diminuição quantitativa do número de axônios mielinizados regenerados em menor número em relação ao grupo A (controle). Na recuperação funcional, não houve diferença estatisticamente significativa entre os dois grupos.

The fate of striatal dopaminergic neurons in Parkinson's disease and Huntington's chorea

The striatum harbours a population of dopaminergic neurons that is thought to act as a local source of dopamine (DA). This neuronal population increases in size in animal models of Parkinson's disease, where striatal DA levels are low, but its fate in idiopathic Parkinson's disease and Huntington's chorea is poorly known. In this study, we used antibodies raised against the enzyme tyrosine hydroxylase (TH), a faithful marker of dopaminergic neurons, to compare, by means of stereological counting methods, the number of striatal TH+ neurons on post-mortem brain sections from Parkinson's disease patients, Huntington's disease patients and age-matched controls. Propidium iodide nuclear staining was also performed to avoid counting short TH+ axonal segments that bear a large swollen varicosity and resemble small bipolar neurons. In normal subjects, TH+ neurons were scattered throughout the striatum, but they abounded preferentially in the ventral portion of the structure and were more numerous in the putamen than in the caudate nucleus. They displayed a multipolar cell body of medium size (10-20 mum in diameter) that emitted 3-5 smooth dendrites, a typical characteristic of striatal interneurons. These TH+ cells were rarely found in the small TH-poor striosomes, most of them being embedded in the large TH-rich extrastriosomal matrix. The number of striatal TH+ neurons was also found to vary according to an inverse relation with the age of the subjects. In pathological brains, the morphological characteristics of the striatal TH+ neurons were relatively unaltered, but the number of such neurons was markedly reduced compared with controls. The striatum of Parkinson's disease patients was found to contain six times less TH+ neurons than that of controls, whereas the striatum of Huntington's disease patients was largely devoid of such neurons. These findings are at odds with the results obtained in rodent and monkey models of Parkinson's disease, in which the number of striatal TH+ neurons is reported to increase markedly following DA denervation. Since Parkinson's disease patients examined in this study were all treated with l-3,4-dihydroxyphenylalanine to compensate for the loss of striatal DA and that levels of striatal DA are reportedly higher in the striatum of Huntington's disease patients compared with controls, we hypothesize that local DA concentrations exert a negative feedback on the expression of TH phenotype by striatal interneurons. A better knowledge of factors governing the in vivo state of this ectopic neuronal population could open new therapeutic avenues for the treatment of Parkinson's disease and Huntington's chorea.

Neonatal Estrogen Decreases Neural Density of the Septum–Midbrain Central Gray Connection Underlying the Lordosis-Inhibiting System in Female Rats

Neurons in the lateral septum (LS) with projecting axons to the midbrain central gray (MCG) exert an inhibitory influence on lordosis. The number of such neurons is greater in female than in male rats. In this experiment, effects of neonatal estrogen on the density of the LS-MCG connections and on lordosis behavior were examined in female rats. On postnatal day 4 (day 0 = day of birth), females were injected subcutaneously with 50 or 100 µg estradiol benzoate (EB) or oil. On postnatal day 60, females and control males were gonadectomized. Behavioral tests were carried out after the implantation of silicone tubes containing estradiol. Lordotic activities in both males and EB-treated females were lower than in oil-treated females. After completing the behavioral tests, the animals were injected with Fluoro-Gold (FG), a retrograde tracer, into the right-side MCG and the number of FG-labeled neurons in the LS was measured. In all groups, the right-side LS ipsilateral to the FG injection had more FG-labeled neurons than the left-side LS. The number of FG-labeled neurons in the LS of oil-treated females was larger than that of males on both right and left sides. In the females treated with 100 µg EB (EB100), the number of FG-labeled neurons was comparable with that of males and lower than that of oil-treated females. The number of FG-labeled neurons in the EB50 females was also lower than that in oil-treated females, but tended to be larger than that observed in the EB100 group. These results indicate that neonatal estrogen decreases both lordotic activity and the density of the LS-MCG neural connections in female rats.

Neuron-Specific Activation of Murine Cytomegalovirus Early Gene e1 Promoter in Transgenic Mice

The brain is the main target in congenital cytomegalovirus (CMV) infection and immunocompromised patients. No definite evidence that a CMV has special affinity for the central nervous system (CNS) has been published. Here, we generated transgenic mice with an e1 promoter/enhancer region connected to the reporter gene lacZ. Surprisingly, expression of the transgene was completely restricted to the CNS in all lines of transgenic mice. The transgene was expressed in subpopulation of neurons in the cerebral cortex, hippocampus, diencephalon, brainstem, cerebellum, and spinal cord in all of the lines. Non-neuronal cells in the CNS were negative for transgene expression. Activation of the transgene was first observed in neurons of mesencephalon in late gestation, and then the number of positive neurons increased in various parts of the brain as development proceeded. Upon infection of the transgenic mouse brains with MCMV, the location of the activated neurons became more extensive, and the number of such neurons increased. These results suggest that there are host factor(s) that directly activate the MCMV early gene promoter in neurons. This neuron-specific activation may be associated with persistent infection in the brain and may be responsible for the neuronal dysfunction and neuronal cell loss caused by CMV infection.

Brainstem Substrates of Sympatho-Motor Circuitry Identified Using Trans-Synaptic Tracing with Pseudorabies Virus Recombinants

Previous physiological investigations have suggested the existence of a neural circuit that coordinates activation of motor and autonomic efferents before or at the onset of exercise. Traditionally these circuits have been postulated to involve forebrain areas. However, overlapping populations of medullary reticular formation neurons that participate in motor or autonomic control have been described previously, suggesting that individual pontomedullary reticular formation neurons may coordinate both motor and autonomic responses. We tested this hypothesis by conducting transneuronal retrograde tracing of motor and sympathetic nervous system pathways in rats using recombinant strains of pseudorabies virus (PRV). A PRV strain expressing the green fluorescent protein (PRV-152) was injected into the left gastrocnemius muscle, which was surgically sympathectomized, whereas another recombinant (PRV-BaBlu) was injected into the left adrenal gland. Immunofluorescence methods using monospecific antisera and distinct fluorophores identified neurons infected with one or both of the recombinants. Brainstem neurons coinfected with both PRV recombinants, which presumably had collateralized projections to both adrenal sympathetic preganglionic neurons and gastrocnemius motoneurons, were observed in several areas of the pontomedullary reticular formation. The largest number of such neurons was located in the rostral ventromedial medulla within the ventral gigantocellular nucleus, gigantocellular nucleus pars alpha, raphe obscurus, and raphe magnus. These neurons are candidates for relaying central command signals to the spinal cord.

Neuronal and inducible nitric oxide synthase and nitrotyrosine immunoreactivities in the cerebral cortex of the aging rat.

Neuronal and inducible nitric oxide synthase (nNOS and iNOS) and nitrotyrosine immunoreactivities were localized and semiquantitatively assessed in the cerebral cortex of aged rats by means of light microscopic immunocytochemistry and Western blotting, using a new series of specific polyclonal antibodies. In the aged rats the strongly nNOS-immunoreactive multipolar neurons found in layers II-VI of the cortex of young rats were seen in similar numbers, but showed varicose, vacuolated, and fragmented processes, with an irregular outline and loss of spines. A large number of more weakly nNOS-positive neurons, characterized by a ring of immunoreactive cytoplasm, and not seen in young rats, were observed in layers II-VI of aged rat cortex. While no iNOS-immunopositive neurons were found in the cortex of young rats, a large number of such neurons appeared throughout the aged rat cortex. Nitrotyrosine-positive cells outnumbered total NOS-positive neurons in the cortex of young rats, but this relation was inverted in the aged rats, although these showed a slight increase in the number and staining intensity of nitrotyrosine-positive cells. Western blots of brain extracts showed a several-fold increase in both nNOS- and iNOS-immunoreactive bands in the aged rat, but a less marked increase in nitrotyrosine-containing proteins. The results suggest that while nNOS and iNOS expression is substantially increased in the aged rat cortex, this is not necessarily accompanied by a proportionate increase in nitric oxide synthesis. The mechanisms underlying the increased expression of nNOS and iNOS, and the functional implications of this increase, require elucidation.

Expression of Glutamate Receptor Subunit 1 and Nitric Oxide Synthase in the Hypoglossal Nucleus and Dorsal Vagal Nucleus in the Rat After Neurectomy

Using nitric oxide synthase (NOS) and glutamate receptor subunit 1 (GluRl) immunohistochemistry. the present study demonstrated changes in the expression of NOS and GluR 1 in the hypoglossal (HN) and dorsal vagal nucleus (DVN) after neurectomy. Two and 7 days after sectioning the left hypoglossal nerve, NOS expression was seen in a few neurons but GluRl immunoreactivity was drastically reduced in the ipsilateral HN. The upregulation of NOS immunoreactivity in the HN appeared to peak at 14 days postoperation (dpo). At this period, however, the GluRl immunoreactivity almost completely disappeared. Twenty-one, 35 and 56 days after neurectomy, NOS immunoreactivity was still expressed in the ipsilateral HN; at the same time, GluRl immunoreactivity reappeared in a few neurons of the nucleus. Ninety days after operation, NOS immunoreactivity completely disappeared on the operated side of the nucleus, but GluRl immunoreactivity was re-expressed in many hypoglossal neurons. The number of such neurons was obviously less than that on the unoperated side. After sectioning the left vagus nerve in the same animals, the expression of NOS immunoreactivity in the ipsilateral DVN resembled that in the HN. on the unoperated side, NOS immunoreactivity was demonstrated in some neurons in the DVN, like that in the normal. In both normal and operated rats, only a few neurons expressed GluRl immunoreactive products on both the operated and unoperated sides of the DVN. Combining with previous results on protein synthesis observed at 14 dpo, the present investigation suggested that in the early stages after neurectomy, the expression of NOS immunoreactivity and loss of GluRl expression in the HN may indicate the organism's double protective mechanism. Lastly, the reappearance of GluRl in the same nucleus from 21 to 90 days after operation may reflect functional recovery of the hypoglossal neurons.

What do retinal Müller (glial) cells do for their neuronal ‘small siblings’?

Müller (radial glial) cells are the predominant glia of the vertebrate retina. They arise, together with rod photoreceptor cells, bipolar cells, and a subset of amacrine cells, from common precursor cells during a late proliferative phase. One Müller cell and a species-specific number of such neurons seem to form a columnar unit within the retinal tissue. In contrast, ‘extracolumnar neurons’ (ganglion cells, cone photoreceptor cells, horizontal cells, and another subset of amacrine cells) are born and start differentiation before most Müller cells are generated. It may be essential for such neurons to develop metabolic capacities sufficient to support their own survival, whereas late-born (‘columnar’) neurons seem to depend on a nursing function of their ‘sisterly’ Müller cell. Thus, out of the cell types within a retinal column it is exclusively the Müller cell that possesses the enzymes for glycogen metabolism. We present evidence that Müller cells express functional insulin receptors. Furthermore, isolated Müller cells rapidly hydrolyse glycogen when they are exposed to an elevated extracellular K +ion concentration, a signal that is involved in the regulation of neuronal-glial metabolic cooperation in the brain. Müller cells are also thought to be essential for rapid and effective retinal K + homeostasis. We present patch-clamp measurements on Müller cells of various vertebrate species that all demonstrate inwardly rectifying K + channels; this type of channel is well-suited to mediate spatial buffering currents. A mathematical model is presented that allows estimation of Müller cell-mediated K + currents. A simulation analysis shows that these currents greatly limit lateral spread of excitation beyond the borders of light-stimulated retinal columns, and thus help to maintain visual acuity.

Localization of neurons innervating the upper portion of the duodenum in the motor nucleus of the vagus nerve.

Using the method of the retrograde axonal transport of horseradish peroxidase and a microelectrode technique, a population of neurons sending axons to the upper portion of the duodenum was identified in the dorsal motor nucleus of the vagus nerve. It was established that the maximal number of such neurons was located 1.0-2.5 mm rostral to the obex. The effects of their stimulation on the electrical activity of the smooth muscles of the duodenum was studied.

Features of the establishment of the spontaneous activity of neurons of the trigeminal sensory nuclei of viable sections of the rat brainstem in postnatal ontogenesis.

An attempt was made to characterize the features of the development of the neurons of the sensory trigeminal nuclei, a basic structure of the sensory support of alimentary behavior, in the late stages of postnatal ontogenesis. A technique involving viable sections of the brainstem of infant rats at the ages of two, four, and eight weeks was utilized. An increase with age in the number of neurons possessing spontaneous activity (44% at two weeks; 69% at eight weeks), an increase in the frequency of discharges, the appearance by the fourth week of a population of cells with high-frequency spontaneous activity, and an increase in the number of such neurons by the eighth week. Three types of background-active neurons were distinguished: episodic, continuous, and group; and the dynamics of the change in the ratios of these types with age was demonstrated. Significant changes with age were not found in resting potentials, although a tendency to its increase takes place between the second and eighth weeks of postnatal development.

Anatomy of glutamic acid decarboxylase immunoreactive neurons and axons in the rat medial geniculate body.

This is a study of the form, density, and distribution of glutamic acid decarboxylase (GAD) immunoreactive neurons and puncta (axon terminals) in the adult rat medial geniculate complex. GAD-positive elements were stained by either the peroxidase-antiperoxidase or avidin-biotin procedures. Thalamic architectonic subdivisions were defined independently in Golgi, Nissl, plastic-embedded semi-thin, and fiber-stained preparations, and from investigations of medial geniculate connectivity. GAD-positive neurons represent only approximately 1% of medial geniculate neurons. They occur in the three major medial geniculate subdivisions (ventral, dorsal, and medial). There is variability between subdivisions in the form and number of such neurons, and among the puncta. In the ventral division, immunopositive somata may have sparsely branched dendrites as long as 300-400 microns and capped with varicose expansions or bouton-like sprays of appendages. These closely appose the somata or primary dendrites of other cells; the axons of these GAD-positive neurons are also immunostained. In the dorsal division there are fewer GAD-positive neurons and their structure is different. Their dendrites are rarely immunoreactive for more than 100-150 microns; nor can their immunostained axons be traced very far. In the medial division the number of GAD-positive neurons, considering the relatively small size of this division, was high. These neurons rarely have immunostained dendrites, and more than one type of neuron is immunoreactive. The average somatic diameter of GAD-positive neurons is about 60% of that of non-immunostained cells in semi-thin material; however, the range of somatic area and the dendritic variability of these neurons suggest that cells representing more than one population are immunopositive and include all but the largest neurons. The puncta also show regional differences. Small (0.5-2 microns in diameter), medium (2-3 microns), or large (greater than 3 microns) puncta occur. In the ventral division, the predominantly medium-sized puncta are about four times as numerous on a unit/area basis than in the dorsal division, where they are far smaller and more delicate; medial division puncta are as numerous as those in the ventral division, but are much larger and coarser, and may form perisomatic arrangements. Controls were devoid of specific immunostaining.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhanced Purkinje cell survival in granuloprival cerebellar cultures

The number of large cortical neurons that survived in cerebellar cultures in which granule cells had been destroyed by exposure to cytosine arabinoside was 3–4 times the number in normal cultures. Transplantation of granuloprival cerebellar cultures with granule cells and glia resulted in a reduction of the large cortical neuron population (predominantly Purkinje cells) to normal, while the number of such neurons remained elevated after transplantation with glia alone. These results indicated that granule cells were critical for the reduction of large cortical neurons. The rescue of large cortical neurons in granuloprival cultures was attributed to an expanded target field for Purkinje cell axon collateral projections.

Vasopressin- and neurophysin-immunoreactive neurons in the septal region, medial amygdala and locus coeruleus in colchicine-treated rats

The distribution and morphology of neurons containing vasopressin, oxytocin and their associated neurophysins were examined immunohistochemically in rats given intracerebroventricular injections of colchicine. Under these conditions, numerous neurons containing vasopressin and neurophysin were found in several brain areas in addition to those previously described in the hypothalamus. Individual parvocellular vasopressin neurons were scattered in the medial and lateral septum and vertical limb of the nucleus of the diagonal band, while a large number of such neurons were found throughout both the bed nucleus of the stria terminals and the dorsal portion of the medial amygdala. In addition a small cluster of parvocellular vasopressin neurons was present adjacent to the top of the third ventricle in the posterior dorsal hypothalamic area and a number of such neurons were found in the ventral locus coeruleus and sub coeruleus. The mean diameters of these parvocellular vasopressin neurons ranged from 16.6 to 19.8 μm in the different regions, in contrast to the 25.4 μm mean diameter of hypothalamic magnocellular vasopressin neurons, or the 13.7 μm mean diameter of parvocellular vasopressin neurons in the suprachiasmatic nucleus. No vasopressin neurons were found in other brain and spinal cord regions under the conditions used in this study, although all regions were examined. No oxytocin neurons other than those previously described in the hypothalamus and immediately contiguous regions were found. Measurement of the mean diameter of oxytocin neurons showed that neurons in the caudal paraventricular nucleus were clearly smaller (18.9 μm) than magnocellular oxytocin neurons (24.8 μm) in other parts of the hypothalamus. These parvocellular oxytocin neurons with experimentally documented central connections were similar in both size and appearance to the parvocellular vasopressin neurons seen after colchicine treatment, which are potential sources of certain central vasopressin pathways. These findings indicate that there are at least two types of oxytocin neurons in the hypothalamus and several types of vasopressin neurons in a variety of different areas in the brain, many of which are outside of the hypothalamus.

Ectopic neurons and aberrant connections during neural development.

During the normal development of the nucleus of origin of centrifugal fibers to the chick retina (the so-called isthmo-optic nucleus) a significant number of neurons are misrouted during their migration from the neural epithelium in which they are generated. Like the cells in the isthmo-optic nucleus, these ectopic neurons can be identified by the retrograde transport of horseradish peroxidase (donor: hydrogen peroxide oxidoreductase, EC 1.11.1.7) injected into the eye. Between 500 and 600 such cells have been identified on one side of the brain of 12 to 15-day-old embryos, but only about 10% of this number is seen beyond hatching. In addition, during development some of the cells in the nucleus send their axons to the ipsilateral retina, whereas in post-hatched animals they all project to the contralateral retina. The number of such neurons with aberrant axons is greatly increased (in some cases by as much as two orders of magnitude) in chicks from which one eye was removed early in development. Although normally about 60% of the neurons in the isthmo-optic nucleus degenerate between the 13th and 17th days of incubation, they can almost all be labeled by intraocular injections of horseradish peroxidase on the 12th day, indicating that the axons of virtually all the cells, including those neurone that subsequently die, reach the retina.

A cytoarchitectonic and Golgi stody of the red nucleus in the rat

The cytology of rubral neurons was investigated using both paraffin and 1 mu thick Epon sections. The neurons were divided into four size categories which form a continuum with regard to cellular characteristics. Giant neurons (greater than 40 mu) and large neurons (26-40 mu) predominate in the caudal one-third of the nucleus. Large neurons extend up the ventral, medial and lateral borders of the nucleus into its middle one-third. The caudal one-third of the nucleus together with this extension of large cells is designated as the magnocellular part of the nucleus. The more rostral part of the nucleus contains predominantly small (less than 20 mu) and medium size (20-25 mu) neurons, and this constitutes the parvocellular part of the nucleus. The characteristics of each cell type are described. Camera lucida drawings of the rubral neurons were made in three different planes of section, and the extent of the magnocellular and parvocellular portions of the nucleus was determined. Dorsomedial and ventrolateral subgroups of the magnocellular part of the nucleus are found 300-400 mu from the caudal pole. A lateral horn of small and medium size neurons with the addition of a few large neurons extends from the lateral part of the nucleus 500-700 mu from the caudal pole. Golgi preparations of the red nucleus were examined in three planes of section. Giant and large neurons display short spines on the soma and also, along the entire length of the dendrites. Inaddition, more elongate spinous processes are seen on these dendrites and are frequently aggregated into tufts at loci on the dendrites or at their terminations. The dendrites of these neurons radiate in all directions from the soma but remain within the confines of the nucleus. Medium size neurons demonstrate radially arranged dendrites. Sparsely positioned spines are seen along the length of the dendrites but are absent on the soma. A number of such neurons demonstrate tufts of elongate spines on their dendrites. The dendrites of small neurons branch infrequently and remain within the confines of the nucleus. A few dendritic but no somatic spines are seen in association with these neurons.

Effect of methscopolamine, physostigmine, and neostigmine on neuron activity in the midbrain, the hippocampus, and the hypothalamus in the behaving rat

The effect of systemic injection of physostigmine (0.1 mg/kg) on spontaneous and evoked neuronal activity and on behavior has been examined in the freely moving rat. There was a decrease in the frequency of firing of hippocampal neurons in a large majority of cases. There was a smaller but significant decrease in the frequency of firing of midbrain neurons, although in a few cases increases were observed. There were either no changes or small increases in the frequency of discharge of hypothalamic neurons. Parkinsonian-type tremors recorded as increases in movements were observed in all animals after methscopolamine, physostigmine, and neostigmine. Decreases in the rate of neuronal discharges in the hippocampus and the midbrain occurred after methscopolamine; increases were observed in the hypothalamus. Neostigmine caused large increases in behavior, but no increases in the frequency of discharge of neurons. The results show that the hippocampus contains a large number of neurons whose rate of firing was modified by cholinergic agents which cross the blood-brain barrier; the midbrain contains a smaller number of such neurons, whereas the hypothalamus contains neurons responsive to cholinergic agents acting at the periphery.