Pretectal jerk neuron activity during saccadic eye movements and visual stimulations in the cat

Summary The activity of jerk neurons was recorded extracellularly in the pretectum of the awake cat. The characteristic response of jerk neurons was a short, high-frequency burst that occurred after fast movements (jerks) of a large, structured visual stimulus, during saccadic eye movements in the light, and after on or off visual stimulation. Mean burst latency to pure visual jerks was 50 ms, whereas it was 30 ms to saccadic eye movements. Bursts were found to be stereotyped; the highest discharge rate was always at burst onset. Jerk neurons were not selective for stimulus parameters (such as movement amplitude or direction) except that in some neurons a weak correlation between stimulus velocity and discharge frequency was found. During saccades in the dark, clear bursts were only rarely found. In about half of the neurons, however, there was a slight but significant increase in the number of spikes above spontaneous frequency. Visual receptive fields were very large (46° horizontal and 35° vertical extent, on average). Nevertheless, the pretectal jerk neurons showed a rough retinotopic order, which was in accordance with the published retinotopy of the pretectum. Jerk neurons were found throughout the whole superficial pretectum, but preferentially in an area that corresponds to the nucleus of the optic tract (NOT) and the nucleus pretectalis posterior (NPP). Saccades were elicited by electrical stimulations at the sites where jerk neurons were recorded. The direction of the elicited saccades depended strongly on the pretectal stimulation site. A possible role of the jerk neurons as a visuomotor relay to elicit saccades or to modulate perception and attention is discussed.     

The development of spatial resolving power of lateral geniculate neurones in kittens

Summary The spatial resolving power and receptive field properties of sustained cells in layers A and A1 of the lateral geniculate nucleus (LGN), which received inputs from the area centralis of the retina in kittens of 3–16 weeks of age had been studied. The basic concentric organisation of receptive fields of sustained LGN cells receiving inputs from the area centralis appeared to be already laid out at 3 weeks in kittens. Spatial resolving power of the cells determined using the highest spatial frequency of a sinusoidal grating resolved by cells as a measure of cellular visual acuity, however, developed gradually to the level of adult LGN cells during the sensitive period (3–12 weeks). Although this development occurred alongside the process of maturation of ocular alignment and the refractive state of the eyes, following the clearing of the embryonic vasculature of the ocular media from the 4th week onward, it depended on the enhancement of distinct inhibitory surround mechanisms taking place during the 6th–11th week. The course of development of spatial resolution of sustained LGN cells receiving inputs from the area centralis of the retina runs parallel with the developmental curve of visual acuity in kittens obtained by visually evoked responses or by behavioural techniques by previous workers. The neural mechanisms which subserve high visual acuity are therefore already determined at the LGN before the inputs of the two eyes are mixed at the visual cortex.     

Glutamic acid decarboxylase immunoreactive large neuron types in the granular layer of the human cerebellar cortex

Non-traditional large neurons of the granular layer of the cerebellar cortex include all its large neuronal types, except the Golgi neuron, which is instead one of the five classic types of corticocerebellar neurons. The morphological, chemical and functional characteristics of the non-traditional large neurons have not been entirely ascertained. The aim of this study was to ascertain whether morphological evidence can be provided of GABA synthesis within the non-traditional large neurons of the human cerebellar cortex by means of immunocytochemistry for glutamic acid decarboxylase (GAD). Fragments of postmortem cerebellar cortex of various lobules from the hemispheres and vermis were studied. Immunoreactions revealed large neurons distributed throughout the granular layer in all lobules examined. They were discriminated by analyzing the morphological features of their bodies and processes and were identified as Golgi neurons and as some non-traditional types, such as the candelabrum, Lugaro and synarmotic neurons. In addition, immunoreactive large neurons, with their bodies and processes closely adjacent to microvessels, were observed throughout the layer: these perivascular neurons could represent a new type of non-traditional neuron of the cerebellar cortex. This study supplies the first indication that in the human cerebellar cortex some types of non-traditional large neurons are GAD-immunoreactive, in addition to those neurons already known to be GABAergic (i.e., stellate, basket, Purkinje and Golgi neurons). These morphological data further point out possible functional roles for GABA as a neurotransmitter/neuromodulator in intrinsic, associative and projective circuits of the cerebellar cortex.To our Master, Professor Rodolfo Amprino, with our great admiration, gratefulness and affection, on the occasion of his ninety-second birthday     

Functional organization of inferior area 6 in the macaque monkey

Summary The functional properties of neurons located in the rostral part of inferior area 6 were studied in awake, partially restrained macaque monkeys. The most interesting property of these neurons was that their firing correlated with specific goal-related motor acts rather than with single movements made by the animal. Using the motor acts as the classification criterion we subdivided the neurons into six classes, four related to distal motor acts and two related to proximal motor acts. The distal classes are: Grasping-with-the-hand-and-the-mouth neurons, Grasping-with-the-hand neurons, Holding neurons and Tearing neurons. The proximal classes are: Reaching neurons and Bringing-to-the-mouth-or-to-the-body neurons. The vast majority of the cells belonged to the distal classes. A particularly interesting aspect of distal class neurons was that the discharge of many of them depended on the way in which the hand was shaped during the motor act. Three main groups of neurons were distinguished: Precision grip neurons, Finger prehension neurons, Whole hand prehension neurons. Almost the totality of neurons fired during motor acts performed with either hand. About 50% of the recorded neurons responded to somatosensory stimuli and about 20% to visual stimuli. Visual neurons were more difficult to trigger than the corresponding neurons located in the caudal part of inferior area 6 (area F4). They required motivationally meaningful stimuli and for some of them the size of the stimulus was also critical. In the case of distal neurons there was a relationship between the type of prehension coded by the cells and the size of the stimulus effective in triggering the neurons. It is proposed that the different classes of neurons form a vocabulary of motor acts and that this vocabulary can be accessed by somatosensory and visual stimuli.     

Binocular interactions and disparity coding in area 21a of cat extrastriate visual cortex

We have examined, using both qualitative and quantitative techniques, binocular interactions of extracellularly recorded single neurons in the extrastriate cortical area 21a of anaesthetized and paralysed cats. Consistent with previous reports we have found that: (a) all area 21a neurons were orientation-selective, with about 65% of them preferring orientations within 30° of the vertical; and (b) over 75% of area 21a cells could be activated through either eye. Furthermore, a significant minority (4 cells; about 10%) of a subpopulation of 39 neurons in which binocular interactions were examined quantitatively, were obligatory binocular neurons, that is, they responded very weakly, if at all, to the monocular stimuli presented through either eye but responded vigorously to simultaneous stimulation through both eyes. Almost 70% (27/39) of neurons tested quantitatively for binocular interaction have shown significant modulation (over 50%) of their peak responses in relation to binocular positional retinal disparities. The majority of neurons sensitive to binocular positional disparities resembled either tuned excitatory (22 cells; 56.5% of the sample) or tuned inhibitory (2 cells; 5% of our sample) cells. In particular, they gave, respectively, maximal or minimal responses to optimally oriented, moving photic stimuli when the receptive fields plotted through each eye completely or partially overlapped. Although neurons recorded in area 21a have relatively large receptive fields (mean width 3.3±1.1°; range 2.0–5.6°), the mean width of the disparity tuning curve (2.8±1.0°; range 1.3–4.8°) for our sample of area 21a neurons was similar to those of neurons with significantly smaller receptive fields, recorded in areas 17 and 18 of cat's primary visual cortex. We conclude that area 21a of the cat, like areas 17 and 18 of primary visual cortex, is likely to play an important role in binocular depth discrimination and might constitute a higher order area for stereoscopic binocular vision.     

Transcranial magnetic stimulation to right parietal cortex modifies the attentional blink

The attentional blink (AB) reflects a limitation in the ability to identify multiple items in a stream of rapidly presented information. Repetitive transcranial magnetic stimulation (rTMS), applied to a site over the right posterior parietal cortex, reduced the magnitude of the AB to visual stimuli, whilst no effect of rTMS was found when stimulation took place at a control site. The data confirm that the posterior parietal cortex may play a critical role in temporal as well as spatial aspects of visual attention.     

In vivo intracellular recordings of medial septal and diagonal band of Broca neurons: relationships with theta rhythm

Transmembrane potentials from medial septal and diagonal band of Broca (MS-DBB) neurons and hippocampal field activity were recorded in curarized and urethanized rats. MS-DBB cells were studied during large amplitude irregular activity and during hippocampal rhythm, elicited by either sensory (i.e. stroking the fur on the animal's back) or electrical stimulation of the reticularis pontis oralis nucleus (RPO). Three types of cells were described according to their firing pattern and the characteristics of their intracellular rhythm. Type A neurons displayed continuous rhythmic oscillations in the membrane potential (Vm) of approximately 17 mV. These oscillations generated rhythmic high-frequency spike trains which were phase-locked with hippocampal rhythm. Type A cells revealed intracellular rhythm even in the absence of hippocampal rhythm, suggesting that the activity of this type of cell was the most important in hippocampal genesis. Type B cells were characterized by marked postspike afterhyperpolarization and intracellular oscillations of smaller amplitude than in type A cells. Type C cells revealed a post-spike afterdepolarization and a lower amplitude, intracellular rhythm only in the presence of hippocampal rhythm. Type C neurons could fire slow spikes at depolarizing (46% of cells) or hyperpolarizing (15% of cells) Vms. Type B and C cells were intracellularly stained with Lucifer yellow. Although type B and C neurons revealed dissimilar electrophysiological properties, they had comparable morphological shapes. RPO electrical stimulation generated hippocampal rhythm and intracellular rhythm in types A and B cells but not in type C cells, and increased the spike rate in type C neurons. Electrical stimulation of the fornix only evoked synaptic responses in type B and C neurons, with antidromic responses being elicited in 12% of type C cells. These results indicate that probably most of the type A rhythmic cells did not receive direct hippocampal feedback and that at least some type C cells were projecting neurons. The present findings demonstrate that rhythm oscillations in the Vm of MS-DBB neurons elicit different rhythmic discharge patterns.     

Viewing-distance invariance of movement detection

Summary Since visual movement information is often presented in electronic displays or films it is amazing that there is a paucity of research on the influence of viewing distance on motion detection in cinematograms. We report a relatively high degree of detection constancy with changing viewing distance for coherent motion in random-pixel cinematograms. A constant performance irrespective of viewing-distance is called distance-invariance and for motion detection it proves to hold reasonably well for a relatively wide range of viewing distances both for foveal and eccentric vision. The limits of this viewing-distance invariance are explored as a function of screen velocity. Detection performance is quantified by a theshold signal-to-noise-ratio (SNR-) value, S, which is determined as a function of velocity for a range of viewing distances from 53 to 13476 mm for foveal vision and from 60 to 1925 mm at 24° eccentricity on the nasal horizontal meridian of the right eye's retina. The data can be explained, at least qualitatively, by a model in which a spatial-resolution stack has a stack of velocity-tuned motion detectors at every resolution layer. Such a stack-of-stacks model is in line with proposals for contrast-detection stack-models, but it suggests that the usual hypothesis that motion perception is based on the activity of two separate systems, the short-range and the long-range system, might be superfluous. This two-systems distinction was largely based on the different performance found for moving random dot patterns and moving form-defined stimuli. A moving random pixel array viewed at very close range (e.g. 6 cm) presents the subject with relatively large almost square blobs, which are less dissimilar from the phi-stimuli used in classic motion perception studies than random dot stimuli at the usual medium to large viewing distances. It leads to maximum displacement threshold (D_m-) values that are not untypical of the long-range system, but by gradually increasing the viewing-distance and thus decreasing the pixel-size a continuous change is found from typical long-range to typical short-range values of D_m. The two-systems distinction for motion detection appears to refer to the stimulus rather than to the visual system: The motion-detection system might be forced into a local or a global mode of operation by the choice of stimulus.     

Lability in the responses of cells in the auditory cortex of squirrel monkeys to species-specific vocalizations

Summary The activity of 28 cells located mainly in the secondary auditory cortex (A II) of awake squirrel-monkeys, was extracellularly recorded for periods of up to 6 h. Seven different species-specific vocalizations, which were repeatedly presented to the monkey, were used as auditory stimuli. Twenty-six cells responded, at least once, to one or more vocalizations; 22 cells revealed some change in their response (pattern or strength) to at least one vocalization (change in response). Twenty-one cells exhibited a change in the number and/or type of vocalization to which they responded during the recording period (change in selectivity). At some time during the recording period all the responding cells exhibited a change in response and/or a change in selectivity (change in responsiveness). A change in response of a cell to a vocalization did not necessarily exclude a change in selectivity, associated with the same vocalization, later in time and vice-versa. A change in responsiveness to one vocalization was not necessarily correlated with changes in responsiveness to other vocalizations.     

Visual field projection columns and magnification factors in the lateral geniculate nucleus of the cat

Summary The precision of the projection of the visual field to the dorsal lateral geniculate nucleus (LGNd) of the cat was studied by plotting the receptive fields of single neurons recorded extra-cellularly in the nucleus. The concepts of a projection column and of random scatter in the location of receptive fields have been defined in relation to cells in the LGNd. A projection column contains 90% of all the cells in the LGNd that have receptive fields with a common visual direction, the central axis of the column being the projection line for the given visual direction. In the region of the LGNd devoted to central vision the columns have a circular cross section and are about 1 mm in diameter.The projections of adjacent areas of visual field (and hence of the retina) overlap extensively in the LGNd. In this study, the overlap of retinal afferents in the LGNd was measured in terms of the random scatter of receptive field positions for cells recorded in a given electrode penetration parallel to projection columns in the nucleus. The monocular receptive field scatter within a column in the LGNd is about of the same magnitude as both the monocular receptive field scatter within a cortical column and the binocular receptive field disparities of cortical units.The differential magnification of the visual field on the LGNd is a reflection of the ganglion cell density differences in the retina.     

An α-mating-type-specific mutation causing specific defect in sexual agglutinability in the yeast Saccharomyces cerevisiae

We have identified a recessive -mating-type-specific gene agl causing agglutinability defect without significant effects on other sexual activities. a cells carrying agl showed sexual agglutination with cells but cells carrying agl showed sexual agglutination with neither cells nor a cells. cells carrying agl produced pheromone and responded to a pheromone just like wild cells. cells carrying agl showed a little decreased but significant mating ability when tested on solid media or membrane filter. The agl mutant is different from any -specific ste mutants found so far in many sexual activities. The agl gene is recessive, and unlinked to the mating type locus. Biological significance of the mating type agglutinability is discussed based on the results obtained with the mutant.     

Diversity in receptive field properties of vertical neuronal arrays in the crown of the postcentral gyrus of the conscious monkey

Summary Single neuronal activity was recorded in the crown of the postcentral gyrus (areas 1 and 2) in 5 conscious monkeys. A total of 93 penetrations were made in the hand and finger region of 9 hemispheres and 827 neurons were isolated. The receptive field characteristics of neurons recorded along each of 88 penetrations which entered perpendicularly to the cortical surface were compared. The majority of neurons in this region were responsive to skin stimulation. In 54 penetrations, neurons related to different sensory submodalities were mixed. In 30, skin neurons predominated, and in 8, deep neurons, while in the remaining 16 penetrations neurons related to different submodalities were equally mixed. In 16 penetrations, neurons responded exclusively to stimulation of skin, hair or nails. In 9 penetrations, neurons were exclusively related to joint manipulation or other types of deep submodality. In 9 penetrations, unidentified neurons were in the majority. In each penetration, the receptive field positions varied considerably on the same finger or encompassed more than one finger. Although neurons of the same submodality, either skin or deep tended to be set in an array, the most adequate stimulus could vary among neurons of a given array. The variability in the receptive field positions or the most adequate stimuli remained constant irrespective of the angle of the electrode penetration in the cortex. The results are compatible with the idea that vertically arranged neuronal array receive inputs of multiple sources, both thalamacortical and corticocortical, so that interactions between different inputs can readilly occur.Supported by grants from the Japanese Ministry of Education     

Expression of GFRα-1, GFRα-2, and c-Ret mRNAs in rat adrenal gland

Glial cell line-derived neurotrophic factor (GDNF), an important factor for developing and lesioned pre- and postganglionic sympathetic neurons, and its congeners signal through a receptor complex consisting of the tyrosine kinase c-Ret and a lipid-anchored receptor (GFR-1-4). Using in situ hybridization we show now that the mRNA for GFR-2 is abundant in the adult rat adrenal medulla and its chromaffin cells. Coexpression of c-Ret and GFR-1 mRNA's is restricted to a scarce subpopulation of medullary sympathetic neurons. Both GFR-1 and GFR-2 mRNA's are associated with preganglionic nerve trunks in the adrenal cortex. It is conceivable therefore that GDNF and related factors may activate chromaffin and preganglionic Schwann cells through a GFR- receptor in absence of c-Ret.     

Short-term adaptation of the cervico-ocular reflex

Inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. IOR is typically investigated using a cue-target design, in which subjects respond only to the second stimulus of a pair. In such tasks, the measurement of true IOR may be confounded by the effect of non-ocular response inhibition, because the participant must suppress any tendency to respond (e.g. key press) to the first stimulus. This confound may be eliminated using a target-target design, in which responses are made to both stimuli. We assessed the contribution of non-ocular response inhibition to visual IOR, measured in a cue-target task, by testing participants on both cue-target and target-target detection tasks, with identical timings and stimuli. Significant IOR was obtained in both tasks but, at a stimulus onset asynchrony (SOA) of 1,400 ms, IOR magnitude was significantly greater in the cue-target condition than in the target-target condition. However, at an SOA of 1,800 ms, there was no significant difference in the magnitude of IOR between the two tasks. Thus, a proportion of the total IOR effect observed in visual cue-target tasks can be attributed to non-ocular response inhibition, but this process appears to decay more rapidly than does true IOR, having dissipated by 1,800 ms following cue onset.     

Parietal cortex neurons of the monkey related to the visual guidance of hand movement

Summary A class of neurons specifically related to hand movements was studied in the posterior parietal cortex while the monkeys manipulated different types of objects. We examined the neuronal activity during manipulation of objects by the hand in the light and in the dark. Fiftyfive neurons were active during manipulation in the dark and were classified as hand-movement-related neurons. Of these, 38/55 (69%) cells were also influenced by the visual stimulus. Most of the hand-movement-related neurons were selective in the type of objects manipulated. Moreover, some of these cells were selective in the axis of orientation of the object. These results suggest that the hand-movement-related neurons of the parietal cortex are concerned with the visual guidance of the hand movement, especially in matching the pattern of movement with the spatial characteristics of the object to be manipulated.     

The Effects of Sodium Nitrite on Neocortical Neuron Activity during Performance of Defensive and Inhibitory Conditioned Reflexes

Administration of the NO-generating substance sodium nitrite to conscious non-immobilized rabbits at a dose of 11 mg/kg (s.c.) decreased the intensity and duration of the short-latency modality-specific components of the responses of neurons in the visual cortex (to flashes of light) and sensorimotor cortex (to pain reinforcement). Decreases in neuron activation in the visual cortex in response to flashes of light occurred independently of their biological significance, i.e., as the signal for a defensive reflex and on the background of conditioned inhibition. The long-latency activatory components of the response of sensorimotor and visual cortex neurons to pain reinforcement, the inhibitory pause in the responses of visual cortex neurons to flashes of light, and the disinhibitory effect of pain reinforcement showed smaller changes after sodium nitrite. The results obtained here support the suggestion that different neuromediators are involved in transmitting modality-specific and modality-non-specific influences to neocortical neurons during learning, and provide the basis for suggesting that sodium nitrite has a neurotropic action when given systemically.     

Immunohistochemical studies on S-100 cells in the anterior pituitary gland of Sprague Dawley rats and spontaneous dwarf rats

The S-100 cells in the pituitary glands of adult male Sprague Dawley rats (SDs) and spontaneous dwarf rats (SDRs) were immunohistochemically examined using anti-S-100 and anti-S-100 monoclonal antibodies. The immunoreactive cells against S-100 protein were divided into three subtypes on the basis of their immunore-activity against subunits of S-100 protein: S-100 dominant type (the -type cell), S-100 dominant type (the \-type cell) and immunoreactive against both S-100 and S-100 (the -type cell). In the SD, -type cells represented 26% of the total S-100 immunoreactive cells (S-100 cells) and were localized in the peripheral area of the ventral region of the pituitary gland. This type of cell was observed forming clusters, with more abundant cytoplasm than the -type cell. The proportion of -type cells was 53%. They were diffusely distributed throughout the gland, and their processes were thicker than those of the -type cell. In the SDR, the proportion of -type cells was 55%, and they were observed throughout the gland. In contrast, -type cells totalled 12% and were localized in small areas of the central and peripheral region of the gland. The proportion of -type cells was 21% in the SD and 33% in the SDR and they were observed forming small clusters in both animal groups. The proportion of -type cells compared with the total of S-100-immunoreactive cells was significantly higher (P < 0.05) in the SDR than in the SD, while the proportion of -type cells was markedly lower (P < 0.05).     

Responses of neurons in the inferior temporal cortex in short term and serial recognition memory tasks

Summary Gaffan and Weiskrantz (1980) and Mishkin (1982) have shown that lesions to the inferior temporal visual cortex can impair the performance of serial visual recognition memory tasks. In order to provide evidence on whether the inferior temporal visual cortex contains a mechanism which enables memory to span the intervening items in a serial recognition task, or whether the inferior temporal cortex is merely afferent to such recent memory mechanisms, we analysed the activity of single neurons in the inferior temporal visual cortex and the adjacent cortex in the superior temporal sulcus in both delayed match to sample and serial recognition memory tasks. In the serial recognition task, various numbers of stimuli intervened between the first and second presentations of a stimulus. A considerable proportion (64/264 or 26%) of visually responsive inferotemporal neurons showed a different response to the novel and familiar presentations of a stimulus in the serial recognition memory task, and often a corresponding difference in response between the sample and match presentations of a stimulus in the delayed match to sample task. For the majority of neurons this difference was not sustained across even one intervening stimulus in the serial recognition task, and no neurons bridged more than 2 intervening stimuli. These results show that neurons in the inferior temporal cortex have responses which would be useful for a short term visual memory for stimuli, but would not be useful in recency memory tasks in which more than one stimulus intervenes between the first and second presentations of a stimulus. In this investigation, neurons were recorded both in the cortex on the inferior temporal gyrus (commonly called inferior temporal visual cortex, and consisting of areas TE3,TE2 and TE1 of Seltzer and Pandya 1978), and in the cortex in the adjacent anterior part of the superior temporal sulcus, in which a number of different temporal cortical visual areas have now been described (see Baylis et al. 1986).     

Synergistic activation of rat supraoptic neurosecretory neurons by noxious and hypovolemic stimuli

Summary The effects of saphenous nerve stimulation on discharge activity of supraoptic neurosecretory (NS) cells were studied in anesthetized rats. Of 112 supraoptic neurosecretory cells, 62 exhibited a phasic discharge pattern. The nerve stimulation transiently excited 46 of these 62 phasic units, as well as 35 of the 50 remaining non-phasic units. No appreciable blood pressure change was noted using PSTHs with 1-ms resolution. Though the nerve stimulation also evoked a flexor reflex of the ipsilateral hind limb, blockage of the hind limb movement with gallamine did not alter the amplitude of the supraoptic cell excitation. The threshold of the nerve stimulation was higher for the excitation than for the flexor reflex. Effects of hypovolemic and hyperosmotic stimuli on discharge activity of phasic cells during saphenous nerve stimulation were studied to find a possible interaction between these stimuli. Hemorrhage potentiated the transient excitation evoked by the nerve stimulation in all of the 8 phasic cells tested, while no such effect was seen after an injection of hypertonic sodium chloride solution in the 7 phasic cells tested. These electrophysiological data suggest that hypovolemic and noxious stimuli potentiate VP secretion in a synergistic manner but that hyperosmotic and noxious stimuli do not.Supported by grants from the Ministry of Education, Science and Culture, Japan     

Nerve growth factor induced changes in the Golgi apparatus of PC-12 rat pheochromocytoma cells as studied by ligand endocytosis, cytochemical and morphometric methods

Summary Cells of the PC-12 rat pheochromocytoma cell line respond to nerve growth factor (NGF) by sprouting neurites and biochemically differentiating into sympathetic ganglion-like cells. NGF-stimulated (differentiated) and unstimulated (undifferentiated) cells were studied by cytochemical techniques for the localization of the enzymes acid phosphatase (ACPase) and thiamine pyrophosphatase (TPPase), and by a morphometric analysis of the distribution of endocytosed wheat-germ agglutinin labelled with horseradish peroxidase (WGA-HRP). Both cytochemical stains showed the enzymes to be distributed in lysosomes and certain cisternae of the Golgi apparatus in both NGF stimulated and unstimulated cells. ACPase was not confined to GERL (Golgi-endoplasmic reticulum-lysosome) as in certain other cells. The morphometric studies demonstrated that the reaction product of the internalized WGA-HRP occupied 4.7% of the cytoplasmic area in unstimulated cells and 4.5% in NGF-stimulated ones. Despite this similarity, the distribution of the WGA-HRP among the studied intracellular compartments in these two cell groups varied. In the NGF-stimulated cells 3.3% of the WGA-HRP reaction product was found in the innermost Golgi cisterna(e) while in unstimulated cells only 0.3% was seen in this compartment. Similarly, 4.3% of the WGA-HRP stain was found in small vesicles at the trans aspect of the Golgi apparatus in stimulated cells, when only 0.3% of the stain occupied this compartment in undifferentiated cells. The morphometric analysis also revealed that when the PC-12 cells were stimulated with NGF, the Golgi apparatus increased in area by approximately 70%. These findings are consistent with the hypothesis that NGF induced differentiation of PC-12 cells is coupled with enhanced endocytosis of WGA and probably of its receptor to the innermost Golgi cisterna(e) and the closely associated vesicles.