Visual response properties of striate cortical neurons projecting to area MT in macaque monkeys

We have previously shown that some neurons in extrastriate area MT are capable of signaling the global motion of complex patterns; neurons randomly sampled from V1, on the other hand, respond only to the motion of individual oriented components. Because only a small fraction of V1 neurons projects to MT, we wished to establish the processing hierarchy more precisely by studying the properties of those neurons projecting to MT, identified by antidromic responses to electrical stimulation of MT. The neurons that project from V1 to MT were directionally selective and, like other V1 neurons, responded only to the motion of the components of complex patterns. The projection neurons were predominantly "special complex," responsive to a broad range of spatial and temporal frequencies, and sensitive to very low stimulus contrasts. The projection neurons thus comprise a homogeneous and highly specialized subset of V1 neurons, consistent with the notion that V1 acts as clearing house of basic visual measurements, distributing information appropriately to higher cortical areas for specialized analysis.     

The laminar organization of the afferent connections of the cortical column in field 17 in the cat

The laminar structure of the cortical column connections in area 17 of the cat was studied using the microiontophoretic injection of the horseradish peroxidase. Following the enzyme injection in one column at different depths below the cortical surface the identification of morphological types of labelled neurons and the estimation of their localization were performed. When enzyme has been delivered in the whole depth of the column pyramidal neurons labelled were found in upper (I/III) and lower (V/VI) layers (ratio II;I). When the depth of enzyme injection exceeded the cortex width the cells in layer IV were labelled as well. The ratio between the quantity of cells labelled in upper and lower layers was preserved. (II; I). After the enzyme injection in the upper part of the column labelled cells were found mainly in the upper layers. It is concluded that the neurons of the column of have extensive (up to 5 mm), predominantly horizontal afferent connections with the cells in upper and lower layers while the connections with neurons in layer IV are local and do not extend beyond 0.5 mm.     

Re-examination of topographic distribution of thalamic neurons projecting to the caudate nucleus. A retrograde labeling study in the cat

This article aims to identify and describe the ethical dilemmas that are involved in the care of patients with incurable cancer. The data were collected in semistructured focused interviews with 32 patients, 13 nurses and 13 doctors from two central hospitals and four community health centres. The interviews were tape-recorded and transcribed verbatim. Interpretation was based on the method of content analysis. Ethical dilemmas occurred at the time of diagnosis, in connection with telling the truth, in providing information, in the treatment of pain, and in decision-making situations concerning active treatment. Dilemmas of active treatment concerned chemotherapy, intravenous infusions, blood transfusions and antibiotics. There were also problems in relationships between nursing staff and next of kin, as well as a lack of co-operation between nurses and doctors.     

Horizontal projections of area 17 in Cebus monkeys: metric features, and modular and laminar distribution

Metric features and modular and laminar distributions of intrinsic projections of area 17 were studied in Cebus apella. Anterogradely and retrogradely labeled cell appendages were obtained using both saturated pellets and iontophoretic injections of biocytin into the operculum. Laminar and modular distributions of the labeled processes were analyzed using Nissl counterstaining, and/or cytochrome oxidase and/or NADPH-diaphorase histochemistry. We distinguished three labeled cell types: pyramidal, star pyramidal and stellate cells located in supragranular cortical layers (principally in layers IIIa, IIIb alpha, IIIb beta and IIIc). Three distinct axon terminal morphologies were found, i.e., Ia, Ib and II located in granular and supragranular layers. Both complete and partial segregation of group I axon terminals relative to the limits of the blobs of V1 were found. The results are compatible with recent evidence of incomplete segregation of visual information flow in V1 of Old and New World primates.     

Response of cat cortical neurons to position and movement of the femur

The contribution of joint afferents to the response of cortical neurons in area 3a to mechanical stimulation of the contralateral hindlimb was evaluated in cats anesthetized with sodium pentobarbital and paralyzed with pancuronium bromide. The hindlimb projection to the pericruciate cortex was established by recording the evoked potentials to electrical stimulation of the sciatic nerve and some of its branches, the bicepssemitendinosus and the quadratus femoris. Out of 169 neurons, 63 responded exclusively to cutaneous stimuli (superficial), whereas the others could be activated by local pressure of hindlimb muscles and/or by joint rotation (deep). Deep neurons were classified as slowly adapting (SA) or rapidly adapting (RA) units. In the neurons responding exclusively to joint rotation, the site of the receptive field could not be identified with certainty. In 13 deep neurons, their firing was affected by rotation of multiple joints of the contralateral hindlimb. In an attempt to identify the source of activation of cortical neurons, partial denervations and muscle disconnections were performed in five animals to isolate and stimulate the hip capsule. In these preparations, in 14 of 15 cortical neurons the source of activation was localized in the periarticular muscles, with no response to mechanical stimulation of the joint capsule. Only one neuron (SA) could be selectively excited by punctate pressure on the hip capsule. Our results suggest that in neurons of area 3a of the cat, the information about the position of the femur relies mainly on muscle afferents.     

Vestibular nucleus neurons, projecting to the "gastric" area of the solitary tract nucleus

OBJECTIVES: To describe the natural recovery of visuospatial neglect in stroke patients and the distribution of errors made on cancellation tests using a standardised neuropsychological test battery. METHOD: A prospective study of acute (< seven days) patients with right hemispheric stroke. Patients identified with visuospatial neglect were followed up for three months with monthly clinical and neuropsychological testing RESULTS: There were 66 patients with acute right hemispheric stroke assessed of whom 27 (40.9%) had evidence of visuospatial neglect. Patients with neglect, on admission, had a mean behavioural inattention test (BIT) score of 56.3, range 10-126 (normal>129). Three of the subtests identified errors being made in both the right and left hemispaces. During follow up, recovery occurred across both hemispaces, maximal in the right hemispace. Recovery from visuospatial neglect was associated with improvement in function as assessed by the Barthel score. At the end of the study period only six (31.5%) patients had persisting evidence of neglect. On admission the best predictor of recovery of visuospatial neglect was the line cancellation test (Spearman's rank correlation r=-0.4217, p=0.028). CONCLUSION: The demonstration of errors in both hemispaces has implications for the theory that neglect is a lateralised attentional problem and is important to recognise in planning the rehabilitation of stroke patients.     

Morphology and laminar distribution of nonpyramidal neurons in the auditory cortex of the rabbit

A study of the morphology and laminar distribution of nonpyramidal neurons in Golgi-Nissl preparations of electrophysiologically verified auditory cortex was carried out in the adult rabbit. Nonpyramidal neurons were located primarily within laminae I-IV and were only infrequently seen in lamina V and VI. In lamina I, four nonpyramidal cell types were observed: (1) small, spine-free horizontal neurons, (2) small, sparsely spined multipolar neurons with radiate dendrites, (3) large, multipolar neurons with fusiform somata and vertically aligned, sparsely spined dendrites, and (4) small, spine-free neurogliform neurons. The horizontal and small multipolar neurons had tangentially running axons confined to lamina I. The large, fusiform cells had descending axons which arborized in lamina II and occasionally reached lamina III. In lamina II and the upper part of lamina III, seven nonpyramidal cell types were observed: (1) spine-free bipolar neurons with vertically aligned dendrites and axonal arbors; (2) large, (3) medium, and (4) small, spine-free and sparsely spined multipolar neurons, all with locally ramifying axons; (5) pear-shaped cells with highly oriented dendrites which branched toward the pial surface and vertically arborizing axons; (6) multipolar cells with tangentially and vertically oriented dendrites and ascending axons which entered lamina I, and (7) tufted cells with local axons. Three types of nonpyramidal cells were observed in lamina IV and the lower part of lamina III: (1) large, multipolar cells with radiate, spine-free dendrites and stout axons which arborized locally, (2) spiny multipolar cells with vertically aligned dendrites and ascending axons which arborized in lamina II and III via long horizontal collaterals, and (3) spine-free bipolar cells with vertical dendrites and axons which arborized in a narrow vertical column adjacent to the dendrites. Nonpyramidal neurons in lamina V and VI were primarily multipolar cells with sparsely spined and spine-free dendrites. A comparison of these data with those of other species indicates that the neuronal organization of the rabbit auditory cortex is similar to that of the sensory cortex of the rodent but is strikingly different from that of carnivores and primates.     

Stimulus dependence of orientation and direction sensitivity of cat LGNd relay cells without cortical inputs: a comparison with area 17 cells

The cortical contribution to the orientation and direction sensitivity of LGNd relay cells was investigated by recording the responses of relay cells to drifting sinusoidal gratings of varying spatial frequencies, moving bars, and moving spots in cats in which the visual cortex (areas 17, 18, 19, and LS) was ablated. For comparison, the spatial-frequency dependence of orientation and direction tuning of striate cortical cells was investigated employing the same quantitative techniques used to test LGNd cells. There are no significant differences in the orientation and direction tuning to relay cells in the LGNd of normal and decorticate cats. The orientation and direction sensitivities of cortical cells are dependent on stimulus parameters in a fashion qualitatively similar to that of LGNd cells. The differences in the spatial-frequency bandwidths of LGNd cells and cortical cells may explain many of their differences in orientation and direction tuning. Although factors beyond narrowness of spatial-frequency tuning must exist to account for the much stronger orientation and direction preferences of cells in area 17 when compared to LGNd cells, the evidence suggests that the orientation and direction biases present in the afferents to the visual cortex may contribute to the orientation and direction selectivities found in cortical cells.     

Respiratory responses to tracheobronchial stimulation during sleep and wakefulness in the adult cat

The response to tracheal stimulation (50 microliters of tap water) during wakefulness, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep was investigated in adult cats. In wakefulness, repetitive coughing occurred on 80% of the trials. In NREM and REM sleep, the most frequent response (approximately 69% and 58% of the trials, respectively) was arousal, followed by coughing. Apneas occurred following the stimulus and before arousal in 11% and 24% of the trials in NREM and REM sleep, respectively. In NREM sleep, the tracheal stimulus sometimes evoked expiratory efforts following a normal inspiratory effort (11% of the trials). These were much weaker than the expiratory efforts during coughing in wakefulness. In REM sleep, stimulation in 11% of the trials elicited increased inspiratory efforts. Although these may have been diminutive preparatory inspirations for coughing, they were much smaller than preparatory inspirations associated with coughing in wakefulness, and they were never followed by active expiratory efforts. Arousal from either NREM or REM sleep in response to tracheal stimulation was sometimes associated with an augmented breath. This response, which is common upon spontaneous arousal, may lead to deeper aspiration of the tracheal fluid. We conclude that in cats coughing requires wakefulness and that airway stimuli in sleep cause a variety of respiratory responses, some of which may be maladaptive.     

Extrastriate feedback to primary visual cortex in primates: a quantitative analysis of connectivity

Knowledge-based or top-down influences on primary visual cortex (area V1) are believed to originate from information conveyed by extrastriate feedback axon connections. Understanding how this information is communicated to area V1 neurons relies in part on elucidating the quantitative as well as the qualitative nature of extrastriate pathway connectivity. A quantitative analysis of the connectivity based on anatomical data regarding the feedback pathway from extrastriate area V2 to area V1 in macaque monkey suggests (i) a total of around ten million or more area V2 axons project to area V1; (ii) the mean number of synaptic inputs from area V2 per upper-layer pyramidal cell in area V1 is less than 6% of all excitatory inputs; and (iii) the mean degree of convergence of area V2 afferents may be high, perhaps more than 100 afferent axons per cell. These results are consistent with empirical observations of the density of radial myelinated axons present in the upper layers in macaque area V1 and the proportion of excitatory extrastriate feedback synaptic inputs onto upper-layer neurons in rat visual cortex. Thus, in primate area V1, extrastriate feedback synapses onto upper-layer cells may, like geniculocortical afferent synapses onto layer IVC neurons, form only a small percentage of the total excitatory synaptic input.     

Comparison of the distribution and somatodendritic morphology of tectotectal neurons in the cat and monkey

The presence of a commissure connecting the two superior colliculi suggests they do not act independently, but the function of the tectotectal connection has never been firmly identified. To develop a better understanding of this commissural system, the present study determined the distribution and morphology of tectotectal neurons in the cat and macaque monkey, two animals with well-studied, but different orienting strategies. First, we compared the distribution of tectotectal cells retrogradely labeled following WGA-HRP injections into the contralateral superior colliculus. In monkeys, labeled tectotectal cells were found in all layers, but were concentrated in the intermediate gray layer (75%), particularly dorsally, and the adjacent optic layer (12%). Tectotectal cells were distributed throughout nearly the entire rostrocaudal extent of the colliculus. In cats, tectotectal cells were found in all the layers beneath the superficial gray, but the intermediate gray layer contained the greatest concentration (56%). Labeled cells were almost exclusively located in the rostral half of the cat superior colliculus, in contrast to the monkey distribution. In the context of the representation of visuomotor space in the colliculus, the distribution of monkey and cat tectotectal cells suggests a correspondence with oculomotor range. So these neurons may be involved in directing orienting movements performed within the oculomotor range. The somatodendritic morphology of tectotectal cells in these two species was revealed by homogeneous retrograde labeling from injections of biocytin or biotinylated dextran amine into the contralateral colliculus. The cell classes contributing to this pathway are fairly consistent across the two species. A variety of neuronal morphologies were observed, so there is no single tectotectal cell type. Instead, cell types similar to those found in each layer, excepting the largest neurons, were present among tectotectal cells. This suggests that a sample of each layer's output is sent to the contralateral colliculus.     

Relative contributions of thalamic reticular nucleus neurons and intrinsic interneurons to inhibition of thalamic neurons projecting to the motor cortex

1. Intracellular responses to stimulation of the cerebral cortex (Cx) and cerebellum were analyzed in thalamocortical neurons (TCNs) in the ventroanterior-ventrolateral (VA-VL) complex of the thalamus and neurons in the thalamic reticular nuclei (RNs) of anesthetized cats, and the contribution of reticular nucleus neurons (RNNs) and thalamic interneurons (TINs) to cerebral and cerebellar inhibition of TCNs was determined. 2. Single TCNs projecting to area 4 or 6 received convergent monosynaptic excitatory and disynaptic inhibitory inputs from both the dentate nucleus (DN) and the interpositus nucleus (IN). These TCNs also received monosynaptic excitatory postsynaptic potentials (EPSPs) and disynaptic inhibitory postsynaptic potentials (IPSPs) from the pericruciate cortex (areas 4 and 6). Each TCN received the strongest excitatory and inhibitory inputs from the cortical area to which that TCN projected, and weaker inhibitory inputs from adjacent cortical areas. 3. RNNs were identified morphologically by intracellular injection of horseradish peroxidase (HRP). Stimulation of the brachium conjunctivum (BC) evoked disynaptic EPSPs with a long decay phase in RNNs in the anterior ventrolateral part of the RN. Single RNNs received convergent disynaptic excitatory inputs from both the DNA and the IN. Stimulation of the Cx produced monosynaptic long-lasting EPSPs with two different latencies in these RNNs: early EPSPs with latencies of 0.9-2.1 ms and late EPSPs with latencies of 1.8-3.5 ms. Collision experiments with BC- and Cx-evoked EPSPs in RNNs indicated that BC-evoked disynaptic EPSPs and Cx-evoked early EPSPs were produced by axon collaterals of TCNs to RNNs. The latencies of the Cx-evoked late EPSPs in RNNs were almost identical to those of Cx-evoked monosynaptic EPSPs in TCNs, indicating that corticothalamic neurons (CTNs) exert monosynaptic excitatory effects on RNNs and TCNs. 4. Stimulation of the Cx produced IPSPs in TCNs with short latencies of 1.8-2.7 ms and longer latencies of > or = 2.8 ms. The Cx-evoked early IPSPs with latencies of 1.8-2.7 ms were mediated by RNNs. The origin of Cx-evoked late IPSPs with latencies of > or = 2.8 ms in TCNs was twofold, Cx-induced early IPSPs in TCNs were facilitated by conditioning cortical stimulation that induced late IPSPs in the TCNs. The same conditioning cortical stimulation also facilitated BC-evoked disynaptic IPSPs. The time course of this facilitatation indicated that CTNs produce long-lasting excitation in TINs. These results indicated that Cx-evoked IPSPs with latencies of > 2.7 ms were mediated at least in part by RNNs and inhibitory TINs in the VA-VL complex.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dexterity in adult monkeys following early lesion of the motor cortical hand area: the role of cortex adjacent to the lesion

Infant monkeys were subjected to unilateral lesions of the motor cortex (mainly its hand representation). After maturation, they showed normal use of the contralateral hand for global grip movements. However, as compared with the ipsilateral hand, precision grip tasks requiring relatively independent finger movements were performed with less dexterity, particularly if adjustments of the wrist position were necessary. The purpose of this study was to investigate mechanisms which may be responsible for the rather well, although not complete, preservation of manipulative behaviour of these adult monkeys. To this end, the hand representations were mapped bilaterally with intracortical microstimulation in the mature monkeys, and the dexterity of both hands assessed quantitatively in a precision grip task. The behavioural effects of reversible inactivations of the primary (M1) and supplementary (SMA) motor cortical areas were then tested. The following were found. (i) The hand contralateral to the lesion exhibited subtle but significant dexterity deficits, as compared with the ipsilateral hand; the deficit was essentially for complex movements requiring dissociation of the thumb-index finger pinch from the other digits, involving also an arm rotation. (ii) Reversible inactivation of the M1 hand representation in the intact hemisphere dramatically impaired dexterity of the opposite hand without affecting the ipsilateral hand (contralateral to the early lesion). (iii) A relatively complete hand representation was found to occupy a new territory, medial to the old lesion. (iv) The role of this new displaced representation was crucial for the preserved dexterity of the opposite hand, as evidenced by its functional inactivation. In contrast, inactivation of both SMA cortices did not interfere with the manipulative behaviour. It is thus concluded that the preserved functional capacity of manipulations with the hand opposite the early lesion can be essentially attributed to a cortical reorganization around the old lesion. Under the present experimental conditions, contributions from either the SMA or the intact M1 appear not to be crucial.     

Oxytocin innervation of spinal preganglionic neurons projecting to the superior cervical ganglion in the rat

The paraventricular nucleus of the hypothalamus is a major integrative nucleus for relaying information from the suprachiasmatic nucleus to the autonomic system. The precise pathway by which this information can influence autonomic functions, such as melatonin synthesis in the pineal gland, is not clear. In the present study, we used a retrograde tracer injected in the superior cervical ganglion to identify spinal preganglionic neurons. One of the main neurotransmitters present in descending projections of the paraventricular nucleus of the hypothalamus, oxytocin, was detected with immunocytochemistry to visualise possible contacts with the neurons located in the intermediolateral column of the spinal cord and projecting to the superior cervical ganglion. Although many appositions could be seen at the light-microscopic level, this abundance could not be confirmed at the electron-microscopic level. The implications of these observations for the overall timing message received by the spinal preganglionic neurons are discussed.     

Calcium channels in the GABAergic presynaptic nerve terminals projecting to meynert neurons of the rat

Effects of selective Ca2+ channel blockers on GABAergic inhibitory postsynaptic currents (IPSCs) were studied in the acutely dissociated rat nucleus basalis of Meynert (nBM) neurons attached with nerve endings, namely, the "synaptic bouton" preparation, and in the thin slices of nBM, using nystatin perforated and conventional whole-cell patch recording modes, respectively. In the synaptic bouton preparation, nicardipine (3 x 10(-6) M) and omega-conotoxin-MVIIC (3 x 10(-6) M) reduced the frequency of spontaneous postsynaptic currents by 37 and 22%, respectively, whereas omega-conotoxin-GVIA had no effect. After blockade of L- and P/Q-type Ca2+ channels, successive removal of Ca2+ from external solution had no significant effect on the residual spontaneous activities, indicating that N-, R-, and T-type Ca2+ channels are not involved in the spontaneous GABA release. Thapsigargin, but not ryanodine, increased the frequency of spontaneous IPSCs in both the synaptic bouton and slice preparations, suggesting the partial contribution of the intracellular Ca2+ storage site to the spontaneous GABA release. In contrast, omega-conotoxin-GVIA (3 x 10(-6) M) and omega-conotoxin-MVIIC (3 x 10(-6) M) suppressed the evoked IPSCs by 31 and 37%, respectively, but nicardipine produced no significant effect. The residual evoked currents were abolished in Ca2+-free external solution but not in the external solution containing 10(-5) M Ni2+, suggesting the involvement of N-, P/Q-, and R-type Ca2+ channels but not L- and T-type ones in the evoked IPSCs. Neither thapsigargin nor ryanodine had any significant effects on the evoked IPSCs. It was concluded that Ca2+ channel subtypes responsible for spontaneous transmitter release are different from those mediating the transmitter release evoked by nerve stimulation.     

Influence of the presentation of remote visual stimuli on visual responses of cat area 17 and lateral suprasylvian area

Single units were recorded extracellularly from area 17 and lateral suprasylvian area (LSSA) in curarized cats. Visual stimuli, usually a 10 degree black spot, were introduced abruptly in the visual field remote from the discharge area of a neuron's receptive field and moved at a speed of about 30 degrees/sec. The effect of these remote stimuli (S2) on the reponse to a restricted visual stimulus (S1) crossing the discharge area was studied. It was found that most units in area 17 were not affected by the presentation of remote stimuli, the remainder being either slightly facilitated or slightly inhibited. In contrast the LSSA neurons were usually inhibited by the presentation of S2: this effect was strong, was present in all classes of LSSA neurons and was independent of the relative directions of movement of S1 and S2. On the basis of these data and those previously obtained from the superior colliculus it is concluded that the way the extrageniculate centres respond to a stimulus abruptly introduced in the visual field is substantially different from that of the striate cortex. Only in the extrageniculate centres a new stimulus, besides exciting the neurons which correspond to the position of the stimulus in the field, concomitantly decreases the responses of neurons located in positions of the visual field remote from that stimulus. Possible behavioral implications of the findings are discussed.     

Differential sparing of depth perception, orienting, and optokinetic nystagmus after neonatal versus adult lesions of cortical areas 17, 18, and 19 in the cat.

Performance by cats with lesions of the visual cortex made in infancy or adulthood was examined on tasks of visually guided behavior that do not require specific training. Cats with lesions confined to areas 17, 18, and 19 made during the 1st postnatal week showed more sparing of function on a visual cliff, at orienting to targets suddenly appearing in the visual field, and at optokinetic nystagmus than did cats with equivalent damage incurred as adults. Cats with lesions that included areas 17, 18, 19 and most of the contiguous visual areas were severely impaired at all tasks whether the lesions were incurred neonatally or in adulthood. These findings suggest that sparing of vision after neonatal lesions of cortical areas 17, 18, and 19 is not confined to pattern learning tasks and that remaining lateral cortical visual areas are importantly involved in such sparing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Horizontal propagation of visual activity in the synaptic integration field of area 17 neurons

The receptive field of a visual neuron is classically defined as the region of space (or retina) where a visual stimulus evokes a change in its firing activity. At the cortical level, a challenging issue concerns the roles of feedforward, local recurrent, intracortical, and cortico-cortical feedback connectivity in receptive field properties. Intracellular recordings in cat area 17 showed that the visually evoked synaptic integration field extends over a much larger area than that established on the basis of spike activity. Synaptic depolarizing responses to stimuli flashed at increasing distances from the center of the receptive field decreased in strength, whereas their onset latency increased. These findings suggest that subthreshold responses in the unresponsive region surrounding the classical discharge field result from the integration of visual activation waves spread by slowly conducting horizontal axons within primary visual cortex.     

Ultrastructural and immunocytochemical characterization of neurons in the rat ventral cochlear nucleus projecting to the inferior colliculus

Medium to large-giant multipolar neurons in the rat ventral cochlear nucleus were retrograde labelled after injection of the tracer Wheat Germ Agglutinin conjugated to Horse Radish Peroxidase into the contralateral cochlear nucleus. Light microscopy immunocytochemistry showed that 42.45% of these retrograde labelled neurons, generally strongly labelled with the tracer, were markedly glycine immunopositive, and that 57.55%, usually weakly retrograde labelled neurons, were immunonegative or weakly positive for glycine. These commissural neurons were generally GABA negative and variably immunopositive for glutamate. About 1/3rd of the commissural neurons had variably developed a rough endoplasmic reticulum whilst axo-somatic boutons covered 20-40% of the cell body. These cells were recognized as multipolar neurons of type I. Most of them were weakly glycine positive or even negative and a few appeared glycinergic. A little less than the remaining 2/3rds of the whole commissural population in the postero-ventral cochlear nucleus presented a surface which was 65-85% covered with synaptic boutons, among which some also appeared labelled. These cells were recognized as multipolar neurons of type II. Many microtubules and neurofilaments were present, free ribosomes being more numerous around Nissl bodies with short cisternae. A few low retrograde labelled type II were weakly or non glycinergic. A small number of large to giant neurons type II, strongly retrograde labelled, appeared to be glycine positive, consistently GABA negative and variably glutamate positive. A very small proportion of retrograde labelled neurons appeared having the characteristics of globular bushy neurons. Their weak labelling, however, suggests that they project by collaterals or thin axons to the contralateral cochlear nucleus. Spherical bushy cells in the rat anteroventral cochlear nucleus lack the nuclear capping of rough endoplasmic reticulum observed in the cat, and none was labelled after injection into the contralateral cochlear nucleus. Globular and spherical neurons were variably glutamate positive but glycine and GABA negative. In conclusion, the present study suggests that commissural neurons include a small number of strongly labelled large to giant glycinergic and presumably inhibitory type II and, less frequently type I. A large group of less heavily labelled commissural neurons of type I and II contain low levels or no glycine, which is probably used for metabolic purposes rather than as a neurotransmitter. This suggests that these neurons are presumably excitatory.