Quantitative stereological evaluation of the gracile and cuneate nuclei and their projection neurons in the rat

Stereological methods were employed to estimate the volume and neuron numbers of the rat dorsal column nuclei (DCN). These methods were applied to Nissl-stained sections from control animals and cases that received injections of horseradish peroxidase in the thalamus, the cerebellum, or the spinal cord. Additional cases received combinations of fluorescent tracers in the same structures, to examine whether some of the retrogradely labeled neurons sent collaterals to different targets. The mean volume of the DCN is 0.81 mm(3) (range 0.65-1.10 mm(3)), of which 3%, 39%, and 59% correspond, respectively, to the nucleus of Bischoff (Bi), the gracile (Gr), and the cuneate (Cu) nuclei. Within Cu, the middle division (CuM) is the largest (42%), followed by the rostral (CuR; 36%) and caudal (CuC; 22%) divisions. The mean total number of neurons in the DCN is 16,000 (range 12,400-19,500), of which 2.4%, 34.0% and 63.6% correspond, respectively, to Bi, Gr, and Cu. Within Cu, CuM contains 48% of all neurons, and 27% correspond to CuR and 25% to CuC. Interanimal variability is moderate for the whole DCN and Cu but increases when individual nuclei are considered. About 80% of DCN neurons project to the thalamus, 3% to the spinal cord, and 7% to the cerebellum. Thalamic-projecting cells are more numerous in CuM and Gr (83%), and relatively less common in Bi and CuC (72-74%). Most of the DCN neurons projecting to the spinal cord appear in CuC and CuM. Two-thirds of the neurons projecting to the cerebellum are located in CuR, 20% in CuM, and 15% in Gr. A small fraction of neurons projects simultaneously to spinal cord and thalamus.     

Distribution of GABAergic neurons and terminals in the auditory system of the barn owl

Antisera to GAD (glutamic acid decarboxylase) and GABA were used to determine the distribution of GABAergic cells and terminals in the brainstem and midbrain auditory nuclei of the barn owl. The owl processes time and intensity components of the auditory signal in separate pathways, and each pathway has a distinctive pattern of GAD- and GABA-like immunoreactivity. In the time pathway, all the cells of the cochlear nucleus magnocellularis and nucleus laminaris receive perisomatic GABAergic terminals, and small numbers of GABAergic neurons surround both nuclei. The ventral nucleus of the lateral lemniscus (anterior division) contains both immunoreactive terminals and some GABAergic neurons. In the intensity pathway, dense immunoreactive terminals are distributed throughout the cochlear nucleus angularis, which also contains a small number of GABAergic neurons. The superior olive contains two GABAergic cell types and immunoreactive terminals distributed throughout the neuropil. All the neurons of the nucleus of the lateral lemniscus (ventral part) appear to be GABAergic, and this nucleus also contains a moderate number of immunoreactive terminals. Immunoreactive terminals are distributed throughout the neuropil of the ventral nucleus of the lateral lemniscus (posterior division), whereas multipolar and small fusiform GABAergic neurons predominate in the dorsal regions of the nucleus. The time and intensity pathways combine in the inferior colliculus. The central nucleus of the inferior colliculus contains a larger number of fusiform and stellate GABAergic neurons and a dense plexus of immunoreactive terminals, whereas the external nucleus contains slightly fewer immunoreactive cells and terminals. The superficial nucleus contains dense, fine immunoreactive terminals and a small number of GABAergic neurons.     

Glutamic acid decarboxylase-like immunoreactivity in brainstem auditory nuclei of the rat

The distribution of GABA-producing neurons in the brainstem auditory nuclei of the rat was investigated immunohistochemically by using an antibody to glutamic acid decarboxylase (GAD). In the cochlear nuclei, GAD immunoreactive neurons are present only in the superficial granular and molecular layers, whereas terminals are found in all subdivisions of the nuclei and are particularly dense surrounding large spherical cells and one type of stellate cell. In the superior olivary complex, GAD immunoreactive neurons are located in the lateral olivary nucleus and throughout the periolivary region. Immunoreactive terminals are distributed along dendrites of principal cells of the medial and lateral olivary nuclei and are clustered around somata of globular neurons of the nucleus of the trapezoid body. An extremely dense band of immunoreactive somata and terminals is present along the ventral edge of the olivary complex. The ventral, intermediate, and dorsal nuclei of the lateral lemniscus contain small fusiform GAD-immunoreactive neurons and a moderately dense plexus of immunoreactive terminals. The inferior colliculus contains a large population of GAD-immunoreactive perikarya and an extremely dense accumulation of immunoreactive terminals in the central, dorsomedial, and external nuclei. These observations indicate that GABA systems are involved in function at all levels of the brainstem auditory pathway.     

Local projections of GABAergic neurons in the dentate gyrus and CA1 region in the rat hippocampal formation

Using retrograde transport of wheat germ agglutinin conjugated colloidal gold (WGA-gold) combined with immunoreactivity for glutamate decarboxylase (GAD), a specific synthesizing enzyme for γ-aminobutyric acid (GABA), local projections of GABAergic neurons in the dentate gyrus and CAI were examined. In the hilus of the dentate gyrus, it was found that GABAergic neurons in the granule cell layer projected to the ipsilateral upper leaf of the molecular layer, with a mediolateral extension of more than 1.2 mm and a rostrocaudal extension of over 0.8 mm. Non-GABAergic neurons in nearly the entire hilar area were found to project to the ipsilateral upper leaf of the molecular layer. In the dorsal CAI region, GABAergic neurons in the stratum pyramidale and radiatum converged onto the ipsilateral stratum pyramidal/oriens, with a mediolateral extension of over 1 mm and a rostrocaudal extension of over 0.7 mm. These results provide direct evidence that in both the dentate gyrus and CAI, GABAergic interneurons from a fairly large field converge onto a very small target area. This suggests that the output signals from GABAergic neurons in the dentate gyrus and CAI, and non-GABAergic neurons in the dentate gyrus, may propagate beyond the anatomical limits contained in conventional slice preparations of the hippocampal formation.     

Co-localization of enkephalin and TRH in perifornical neurons of the rat hypothalamus that project to the lateral septum

Neurons of the lateral septal nucleus are surrounded by terminals immunoreactive for thyrotropin-releasing hormone (TRH) and enkephalin (Enk). Retrograde labeling from the lateral septum in combination with immunocytochemical analyses for Enk and TRH in colchicine-treated rats has revealed that nearly all Enk- (and TRH-) containing perifornical neurons project to the lateral septum. Immunostaining of adjacent, thin paraffin sections for either TRH or Enk and double staining of thick vibratome sections for the two peptides have shown that TRH and Enk immunoreactivities co-exist within the same neurons in the perifornical region of the hypothalamus.     

GABAergic neurons in the rat pontomesencephalic tegmentum: Codistribution with cholinergic and other tegmental neurons projecting to the posterior lateral hypothalamus

The present study was undertaken to determine the frequency and distribution of GABAergic neurons within the rat pontomesencephalic tegmentum and the relationship of GABAergic cells to cholinergic and other tegmental neurons projecting to the hypothalamus. In sections immunostained for glutamic acid decarboxylase (GAD), large numbers of small GAD-positive neurons (～50,000 cells) were distributed through the tegmentum and associated with a high density of GAD-positive varicosities surrounding both GAD-positive and GAD-negative cells. Through the reticular formation, ventral tegmentum, raphe nuclei, and dorsal tegineritum, GAD-positive cells were codistributed with larger cells, which included neurons immunostained on adjacent sections for glutamate, tyrosine hydroxylase (TH), serotonin, or choline acetyltransferase (ChAT). In sections dual-immunostained for GAD and ChAT, GABAergic neurons were seen to be intermingled with less numerous cholinergic cells (～2,600 GAD+ to ～ 1,400 ChAT+ cells in the laterodorsal tegmental nucleus, LDTg). Retrograde transport of cholera toxin (CT) was examined from the posterior lateral hypothalamus, where a major population of cortically projecting neurons are located. A small number of GABAergic cells were retrogradely labeled, representing a small percentage of all the GABAergic neurons (～1%) and of all the hypothalamically projecting neurons (～6%) in the tegmentum. The double-labeled GAD+/CT+ cells were commonly found ipsilaterally within (1) the deep mesencephalic reticular field, codistributed with putative glutamatergic projection neurons; (2) the ventral tegmental area, substantia nigra coinpacta, and retrorubral field, codistributed with dopaminergic projection neurons; (3) dorsal raphe, codistributed with serotonergic projection neurons; and (4) laterodorsal and pedunculopontine tegmental nuclei, codistributed with and in similar proportion to cholinergic projection cells (20–30% in LDTg). Acting as both projection and local neurons, the pontomesencephalic GABAergic cells would have the capacity to modulate the influence of the “ascending reticular activating system” and its chemically specific constituents upon cortical activation. © 1995 Wiley-Liss, Inc.     

Corticotropin-releasing factor in the dorsal raphe nucleus regulates activity of lateral septal neurons

Corticotropin-releasing factor (CRF) has substantial effects on brain serotonergic activity, especially in limbic structures related to stress and anxiety. For example, relatively low doses of CRF administered into the dorsal raphe nucleus (DRN) decrease DRN unit activity and serotonin release in the lateral septum (LS), a limbic target of the DRN. In contrast, higher doses of CRF tend to be excitatory on both endpoints. The present experiment sought to establish the functional connection between CRF effects in the DRN and the ultimate effect on activity in the LS as a terminal region. We recorded the effects of CRF (3, 10, 30 and 100 ng in 100 nl of artificial cerebrospinal fluid) administered into the DRN upon LS unit activity. In general, the lower doses of CRF (3 and 10 ng) had a facilitatory effect on LS unit activity, peaking at about 15–20 min post-injection. The higher doses had a more complex effect with an early suppression of unit responding maximizing at about 5 min followed by a facilitatory rebound, especially at the 100 ng dose, maximizing at about 20 min. Taken with previous studies demonstrating an inhibitory effect of 5-HT on neuronal activity in LS, the findings suggest that CRF regulation of the DRN is translated to changes in LS activity. This effect may underlie certain coping behaviors in response to stress.     

GABA-synthesizing neurons in the medulla: their relationship to serotonin-containing and spinally projecting neurons in the rat.

GABA-synthesizing neurons were identified in the medulla of the rat by peroxidase-antiperoxidase (PAP) immunohistochemistry for glutamic acid decarboxylase (GAD). Using diaminobenzidine (DAB) either alone or intensified with silver, a relatively large number of GAD-immunoreactive neurons were evident within the reticular formation, raphe nuclei and vestibular nuclei. In all these areas, profuse GAD-immunoreactive varicosities appeared to contact the soma and dendrites of both non-GABA and GABA neurons. These observations suggest that GABA neurons may act as interneurons or local projection neurons within the medulla and accordingly exert a potent inhibitory and/or disinhibitory control on bulbar projection neurons. Within the ventral reticular formation (pars alpha and ventralis of the gigantocellular reticular field) and raphe magnus, large numbers of prominent GAD-immunoreactive neurons resembled in size and morphology and overlapped in distribution the serotonin-immunoreactive neurons of the same regions. However, by sequential double immunostaining utilizing DAB as a chromogen for serotonin (5-HT) and benzidine dihydrochloride (BDHC) for GAD, it was found that GAD-containing neurons were distinct from 5-HT-containing neurons. Following injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the upper cervical spinal cord and combined processing for WGA-HRP (using tetramethylbenzidine [TMB] with cobalt) and immunohistochemistry (with DAB), a contingent of spinally projecting neurons were found to contain GAD. The GAD-immunoreactive reticulo- and raphe-spinal neurons were most frequent within the pars alpha and ventralis of the gigantocellular reticular fields and the raphe magnus, where they were approximately equal in number to the coexistent, but distinct 5-HT spinally projecting neurons. GABA neurons of the medulla may thus contribute directly to the bulbar inhibitory influence upon spinal sensory and motor systems.     

GABAergic neurons and axon terminals in the brainstem auditory nuclei of the gerbil

The anatomical localization of glutamic acid decarboxylase (GAD), the synthesizing enzyme for GABA, was analyzed in the brainstem auditory nuclei of the adult gerbil. GAD-positive terminals and somata were present in the cochlear nucleus, superior olivary complex, lateral lemniscus, and inferior colliculus in varying concentrations and patterns. One of the highest densities of GAD-positive terminals is found in the superficial layers of the dorsal cochlear nucleus (DCN), whereas the ventral cochlear nucleus (VCN) has somewhat fewer terminals that are arranged in pericellular plexuses. GAD-positive neurons occur mainly in the superficial and fusiform layers of the DCN and are scattered throughout the VCN. Within the superior olivary complex, the highest concentration of immunoreactive terminals and neurons occurs in the ventral and lateral nuclei of the trapezoid body. In contrast, the medial nucleus of the trapezoid body and the medial superior olive contain fewer GAD-positive puncta and probably no immunoreactive somata. The lateral superior olive and superior periolivary nucleus contain a few immunoreactive puncta but a large number of immunoreactive somata. In the midbrain, the nuclei of the lateral lemniscus contain a moderate number of GAD-positive puncta and a large number of different types of GAD-positive neurons. The inferior colliculus also contains a heterogeneous population of labeled somata, most of which are multipolar neurons. In addition, a high concentration of immunoreactive puncta occurs in this region. These data demonstrate a diverse distribution of GAD-positive neurons and puncta throughout the brainstem auditory nuclei and suggest that GABA might be an important neurotransmitter in the processing of auditory information.     

Glutamate/aspartate and leu-enkephalin immunoreactivity in mammillothalamic projection neurons of the rat

We have used retrograde transport and immunohistochemistry to study glutamate, aspartate, and enkephalin-like immunoreactive pathways from the mammillary nuclei to the anterior nuclei of the thalamus. Injections of wheat germ agglutinin conjugated to horseradish peroxidase into the anterodorsal thalamic nucleus resulted in retrogradely labelled cell bodies in the lateral mammillary nucleus, bilaterally, whereas injections into the anteroventral thalamic nucleus resulted in retrogradely labelled neurons in the ipsilateral medial mammillary nucleus. In three parallel series of sections immunoreacted for glutamate, aspartate, and enkephalin, respectively, 50-60% of the retrogradely labelled cell bodies were also immunolabelled for glutamate, 50-60% for aspartate, and 40-50% for enkephalin. The enkephalin-immunoreactive neurons may coincide with or constitute a separate population from the glutamate/aspartate-containing neurons. These results are compatible with the possibility that mammillothalamic projection neurons may use glutamate and/or aspartate and enkephalin as neurotransmitters.     

Discharge properties of single neurons in the dorsal nucleus of the lateral lemniscus of the rat

The aim of the present study was to characterize the discharge properties of single neurons in the dorsal nucleus of the lateral lemniscus (DNLL) of the rat. In the absence of acoustic stimulation, two types of spontaneous discharge patterns were observed: units tended to fire in a bursting or in a nonbursting mode. The distribution of units in the DNLL based on spontaneous firing rate followed a rostrocaudal gradient: units with high spontaneous rates were most commonly located in the rostral part of the DNLL, whereas in the caudal part units had lower spontaneous discharge rates. The most common response pattern of DNLL units to 200 ms binaural noise bursts contained a prominent onset response followed by a lower but steady-state response and an inhibitory response in the early-off period. Thresholds of response to noise bursts were on average higher for DNLL units than for units recorded in the inferior colliculus under the same experimental conditions. The DNLL units were arranged according to a mediolateral sensitivity gradient with the lowest threshold units in the most lateral part of the nucleus. In the rat, as in other mammals, the most common DNLL binaural input type was an excitatory response to contralateral ear stimulation and inhibitory response to ipsilateral ear stimulation (EI type). Pure tone bursts were in general a more effective stimulus compared to noise bursts. Best frequency (BF) was established for 97 DNLL units and plotted according to their spatial location. The DNLL exhibits a loose tonotopic organization, where there is a concentric pattern with high BF units located in the most dorsal and ventral parts of the DNLL and lower BF units in the middle part of the nucleus.     

Distribution and intrinsic membrane properties of basal forebrain GABAergic and parvalbumin neurons in the mouse

The basal forebrain (BF) strongly regulates cortical activation, sleep homeostasis, and attention. Many BF neurons involved in these processes are GABAergic, including a subpopulation of projection neurons containing the calcium‐binding protein, parvalbumin (PV). However, technical difficulties in identification have prevented a precise mapping of the distribution of GABAergic and GABA/PV+ neurons in the mouse or a determination of their intrinsic membrane properties. Here we used mice expressing fluorescent proteins in GABAergic (GAD67‐GFP knock‐in mice) or PV+ neurons (PV‐Tomato mice) to study these neurons. Immunohistochemical staining for GABA in GAD67‐GFP mice confirmed that GFP selectively labeled BF GABAergic neurons. GFP+ neurons and fibers were distributed throughout the BF, with the highest density in the magnocellular preoptic area (MCPO). Immunohistochemistry for PV indicated that the majority of PV+ neurons in the BF were large (>20 μm) or medium‐sized (15–20 μm) GFP+ neurons. Most medium and large‐sized BF GFP+ neurons, including those retrogradely labeled from the neocortex, were fast‐firing and spontaneously active in vitro. They exhibited prominent hyperpolarization‐activated inward currents and subthreshold “spikelets,” suggestive of electrical coupling. PV+ neurons recorded in PV‐Tomato mice had similar properties but had significantly narrower action potentials and a higher maximal firing frequency. Another population of smaller GFP+ neurons had properties similar to striatal projection neurons. The fast firing and electrical coupling of BF GABA/PV+ neurons, together with their projections to cortical interneurons and the thalamic reticular nucleus, suggest a strong and synchronous control of the neocortical fast rhythms typical of wakefulness and REM sleep. J. Comp. Neurol., 521:1225–1250, 2013. © 2012 Wiley Periodicals, Inc.     

Connections of the auditory brainstem in a songbird,Taeniopygia guttata. II. Projections of nucleus angularis and nucleus laminaris to the superior olive and lateral lemniscal nuclei

Auditory information is important for social and reproductive behaviors in birds generally, but is crucial for oscine species (songbirds), in particular because in these species auditory feedback ensures the learning and accurate maintenance of song. While there is considerable information on the auditory projections through the forebrain of songbirds, there is no information available for projections through the brainstem. At the latter levels the prevalent model of auditory processing in birds derives from an auditory specialist, the barn owl, which uses time and intensity parameters to compute the location of sounds in space, but whether the auditory brainstem of songbirds is similarly functionally organized is unknown. To examine the songbird auditory brainstem we charted the projections of the cochlear nuclei angularis (NA) and magnocellularis (NM) and the third‐order nucleus laminaris (NL) in zebra finches using standard tract‐tracing techniques. As in other avian species, the projections of NM were found to be confined to NL, and NL and NA provided the ascending projections. Here we report on differential projections of NA and NL to the torus semicircularis, known in birds as nucleus mesencephalicus lateralis, pars dorsalis (MLd), and in mammals as the central nucleus of the inferior colliculus (ICc). Unlike the case in nonsongbirds, the projections of NA and NL to MLd in the zebra finch showed substantial overlap, in agreement with the projections of the cochlear nuclei to the ICc in mammals. This organization could suggest that the “what” of auditory stimuli is as important as “where.” J. Comp. Neurol. 518:2109–2134, 2010. © 2010 Wiley‐Liss, Inc.     

Organization and synaptic interconnections of GABAergic and cholinergic elements in the rat amygdaloid nuclei: single- and double-immunolabeling studies

The aim of this study was to describe the localization of cholinergic and GABAergic neurons and terminals in the amygdaloid nuclei of the rat. Double immunolabeling was performed to study cholinergic-GABAergic synaptic interconnections. Cholinergic elements were labeled by using a monoclonal antibody to choline acetyltransferase (ChAT), the acetylcholine synthesizing enzyme. Antibodies against glutamate decarboxylase (GAD), the GABA- synthesizing enzyme, were employed to identify GABAergic perikarya and terminals. The tissue sites of the antibody bindings were detected by using either Sternberger's peroxidase-antiperoxidase (PAP) method or a biotinylated secondary antibody and avidinated ferritin. These two contrasting immunolabels allowed us to study GABAergic-cholinergic interconnections at the electron microscopic level. Our study revealed a characteristic distribution of GABAergic and cholinergic elements in the various amygdaloid nuclei: 1) Large, ChAT-immunopositive cells with heavily labeled dendrites were observed in the anterior amygdaloid area and in the lateral and medial zones of the central nucleus. These cells seem to constitute the intraamygdaloid extension of the magnocellular basal nucleus. Their dendrites invaded other amygdaloid nuclei, in particular the intercalated nuclei, the lateral olfactory tract nucleus, and the central zone of the central nucleus. These ChAT-immunoreactive dendrites formed synaptic contacts with GAD-positive terminals. GABAergic terminals probably thus exert an inhibitory amygdaloid influence onto cholinergic neurons of the magnocellular basal nucleus. 2) Two amygdaloid nuclei-the basal dorsal nucleus and the lateral olfactory tract nucleus-contained a dense network of ChAT-immunoreactive fibers and terminals, but they also contained numerous GAD-positive perikarya. Double-immunolabeling experiments revealed cholinergic terminals forming synaptic contacts on GAD-immunopositive cell bodies, dendritic shafts, and spines. 3) The central and medial nucleus seem to be the main target of GABAergic fibers to the amygdala. Both nuclei contained a dense plexus of GAD-immunoreactive terminals that may arise, at least in part, from the GABAergic neurons in the basal dorsal nucleus. Inhibition of the centromedial "excitatory" region through intraamygdaloid GABAergic connections may reduce excitatory amygdaloid influence onto hypothalamus and brainstem.     

GABAergic neurons of the laterodorsal and pedunculopontine tegmental nuclei of the cat express c-fos during carbachol-induced active sleep

The laterodorsal and pedunculopontine tegmental nuclei (LDT-PPT) are involved in the generation of active sleep (AS; also called REM or rapid eye movement sleep). Although the LDT-PPT are composed principally of cholinergic neurons that participate in the control of sleep and waking states, the function of the large number of GABAergic neurons that are also located in the LDT-PPT is unknown. Consequently, we sought to determine if these neurons are activated (as indicated by their c-fos expression) during active sleep induced by the microinjection of carbachol into the rostro-dorsal pons (AS-carbachol). Accordingly, immunocytochemical double-labeling techniques were used to identify GABA and Fos protein, as well as choline acetyltransferase (ChAT), in histological sections of the LDT-PPT. Compared to control awake cats, there was a larger number of GABAergic neurons that expressed c-fos during AS-carbachol (31.5±6.1 vs. 112±15.2, P<0.005). This increase in the number of GABA⁺Fos⁺ neurons occurred on the ipsilateral side relative to the injection site; there was a small decrease in GABA⁺Fos⁺ cells in the contralateral LDT-PPT. However, the LDT-PPT neurons that exhibited the largest increase in c-fos expression during AS-carbachol were neither GABA⁺ nor ChAT⁺ (47±22.5 vs. 228.7±14.0, P<0.0005). The number of cholinergic neurons that expressed c-fos during AS-carbachol was not significantly different compared to wakefulness. These data demonstrate that, during AS-carbachol, GABAergic as well as an unidentified population of neurons are activated in the LDT-PPT. We propose that these non-cholinergic LDT-PPT neurons may participate in the regulation of active sleep.     

GABA neurons in the superficial layers of the rat dorsal cochlear nucleus: light and electron microscopic immunocytochemistry

This article is an application of light and electron microscopic immunocytochemistry to the study of the neuronal circuit of the superficial layers in the rat dorsal cochlear nucleus (DCN). An antiserum against the intrinsic marker glutamate decarboxylase (GAD) is used to identify and map axon terminals and neurons that use gamma aminobutyric acid (GABA) as a neurotransmitter. It is demonstrated that layers 1 and 2 of the DCN contain a very high density of GABAergic boutons, matched only by the granule cell domains of the ventral cochlear nucleus, especially the superficial granule cell domain. These two layers also contain much higher concentrations of GABAergic cell bodies than all other magnocellular regions of the cochlear nuclear complex. Cartwheel and stellate neurons, and probably also Golgi cells, previously characterized in Golgi and electron microscopic investigations, appear immunostained and, therefore, are presumably inhibitory. The synaptic relations between parallel fibers, the axons of granule cells, and cartwheel and stellate neurons are confirmed. The present study also supports the conclusion that stellate cells are coupled to one another by gap junctions. Also scattered in layer 1 are large, GABAergic neurons that occur with irregular frequency and presumably represent displaced Purkinje cells, previously identified with a Purkinje-cell-specific marker. Granule neurons and pyramidal neurons remain unstained, even after topical injection of colchicine, which enhances immunostaining of the other glutamate-decarboxylase-positive cells, and therefore must use transmitters different from GABA. The possible analogies between the spiny cartwheel and the aspiny stellate cells of the DCN and the cerebellar Purkinje and stellate/basket cells are discussed in the light of data from Golgi, electron microscopy, and transmitter imunocytochemistry.     

Interrelations between lateral, dorsomedial and ventromedial hypothalamic nuclei in the rat. An HRP study

Afferents of the lateral (LH) and ventromedial (VMH) hypothalamic nuclei were studied with the horseradish peroxidase method. The aim was to investigate relations between these two centers presumed to be involved in the regulation of food intake. Special attempts were made to produce HRP injections limited to intranuclear dimensions, which was achieved by iontophoretic delivery of the tracer. The results indicate that LH and VMH do not maintain direct interconnections. Both nuclei, however, appear to have numerous afferents from the dorsomedial hypothalamic nucleus (DMH) in common, which led us to extend our analysis to the DMH. DMH injections of HRP resulted in retrograde labeling of somata in both LH and VMH, suggesting a reciprocal relationship of DMH with these latter nuclei. The possible significance of such a LH-DMH-VMH relationship in the food intake control circuitry is discussed. The other labeling of afferents resulting from HRP injections localized to LH, DMH and VMH is described and discussed as regards their morphological significance. A number of these connections confirm studies using anterograde transport techniques, but others have not been described before, including an extensive projection to the VMH from the mesencephalic perpendicular nucleus.