Golgi-like immunoperoxidase staining of hypothalamic magnocellular neurons that contain vasopressin, oxytocin or neurophysin in the rat

Characterization of neurochemical phenotypes in cultured hypothalamic neurons with immunohistochemistry and in situ hybridization

The expression of neurochemical phenotypes was studied in long-term cultures of dissociated embryonic neurons from rat hypothalamus. With time in culture, these neurons establish a complex dendritic and axonal network, as indicated by staining with antibodies against microtubulin-associated protein (MAP2) and neurofilaments (SMI32 and SMI33) as well as GABA and glutamate decarboxylase mRNA immunoreactivity. Neurons expressing neuropeptide Y (NPY) mRNA and NPY peptide and opioid-like peptides as well as vasopressin were observed. Further, weakly acetylcholinesterase- and NADPH diaphorase (nitric-oxide synthase)-labelled neurons were present. In conclusion, the neurochemical phenotypes reported for hypothalamic neurons in vivo can be observed in these cultures. This indicates that the culture conditions allow morphological and molecular differentiation. These findings support the view that long-term hypothalamic cultures provide a valuable model for studying mechanisms of neurosecretion in hypothalamic networks.

Oxytocin neuron activation and Fos expression: a quantitative immunocytochemical analysis of the effect of lactation, parturition, osmotic and cardiovascular stimulation

As c-fos expression is generally thought to be linked to neuronal activation, we compared Fos immunoreactivity in identified oxytocinergic and vasopressinergic neurons of female rats under various conditions known to elicit particular patterns of electrophysiological and secretory activity in these neurons. In suckled lactating animals, Fos immunoreactivity was visible only in rare oxytocinergic and vasopressinergic neurons of the paraventricular and supraoptic nuclei, even after interruption of suckling for 18-72 h. On the other hand, many Fos-positive cells were visible in the nuclei of parturient rats; they involved about 25% of supraoptic oxytocinergic elements. Even more Fos-positive elements were visible in the nuclei of lactating rats that had also undergone 24 h water deprivation or haemorrhage. This involved about 75% vasopressinergic neurons and 25% oxytocinergic neurons of the supraoptic nucleus. Fos immunoreactivity was particularly conspicuous in oxytocin neurons of the anterior commissural nucleus after haemorrhage. After water deprivation or haemorrhage, Fos-positive oxytocinergic neurons in the supraoptic nucleus were significantly more numerous in virgin rats than in lactating rats. Our observations show that suckling, although a most potent stimulus for oxytocin neuron activation and oxytocin release, is inefficient in inducing Fos synthesis in magnocellular neurons, even after a period of interruption. On the other hand, parturition, water deprivation and haemorrhage were more potent stimuli for both neurosecretory systems. However, under each type of stimulation, only part of the neuronal populations within each nucleus were Fos-positive, suggesting that different stimulus-specific pathways are involved in these regulations. In so far as electrical activity is one possible mechanism for c-fos expression, comparison of the patterns of c-fos activation with the known electrophysiological behaviour of hypothalamic magnocellular neurons suggests that Fos synthesis in these neurons is linked to the number of action potentials generated over a period of time, more than to the pattern of electrical activity, whatever the physiological impact of this pattern. Furthermore, within a group of neurons, the heterogeneity of the response in terms of Fos synthesis may be correlated to the variability of the electrophysiological response within this group.

Properties of supraoptic magnocellular neurones isolated from the adult rat

1. Magnocellular neurosecretory cells (MNCs) were isolated from the supraoptic nucleus of adult Long-Evans rats using an enzymatic procedure. Immunocytochemical staining with antibodies against vasopressin and oxytocin revealed that MNCs can be identified by size. The membrane properties of these cells were examined at 32-34 degrees C using intracellular recording methods. 2. Isolated MNCs displayed a mean (+/- S.E.M.; n = 109) resting membrane potential of -64.1 +/- 1.0 mV, an input resistance of 571 +/- 34 M omega, and a time constant of 8.7 +/- 0.4 ms. Measurements of specific resistivity and input capacitance revealed that the soma of these cells accounts for a mere 20% of their total somato-dendritic membrane in situ. 3. Voltage-current relations measured near -60 mV were linear negative to spike threshold. From more hyperpolarized membrane potentials, voltage responses to depolarizing current steps displayed transient outward rectification and delayed impulse discharge. 4. Action potentials (76.6 +/- 0.9 mV) triggered from an apparent threshold of -59.3 +/- 0.1 mV broadened progressively at the onset of spontaneous or current-evoked spike trains. Steady-state spike duration increased as a logarithmic function of firing frequency with a maximum near 25 Hz. These effects were abolished in Ca(2+)-free solutions. 5. In all cells, evoked spike trains were followed by a prolonged Ca(2+)-sensitive after-hyperpolarization. In contrast, only a small proportion (16%) of MNCs displayed spontaneous bursting activity or depolarizing after-potentials following brief current-evoked bursts. 6. Isolated MNCs responded to amino acids (glutamate and GABA) and to the neuropeptide cholecystokinin, indicating that receptors for these neurotransmitters are expressed postsynaptically by MNCs and are retained following dissociation. 7. Increasing the osmolality of the superfusing solution by 5-30 mosmol kg-1 caused a membrane depolarization associated with a decrease of input resistance and accelerated spontaneous spike discharge in each of thirty-six MNCs tested. Current-clamp analysis suggested that these responses resulted from the activation of a cationic conductance. Excitatory effects of hyperosmolality were not observed in non-magnocellular neurones (n = 6).

Radial glia-like cells in the supraoptic nucleus of the adult rat

Conventional light and confocal microscopy of thick vibratome sections of the hypothalamus of adult male and female rats immunostained for the astrocytic marker glial fibrillary acidic protein (GFAP) revealed that the supraoptic nucleus (SON) contains two morphologically distinct types of astrocytes. One has a stellate form, similar to that of most astrocytes in the adult CNS. The other has a morphology reminiscent of radial glia in the developing CNS: from their cell bodies, located along the ventral glia lamina (VGL), arise one long thick process that spans the SON in the coronal plane, several horizontally-oriented processes that form a dense network in the VGL, and a short process oriented towards the pia. The latter astrocytes are immunoreactive for vimentin, an intermediate filament protein of immature glial cells and a marker for radial glia. The stellate astrocytes showed no vimentin immunoreactivity. The functional significance of each type of supraoptic astrocyte is at present unknown but the presence of radial glia-like cells in this hypothalamic region suggests that the SON retains a certain degree of immaturity during adulthood, that may be linked to its well known capacity to undergo neuronal-glial plasticity under physiological and experimental stimulation.

Relationship of vasopressin with NADPH-diaphorase in the hypothalamo-neurohypophysial system

The relative anatomical distributions of vasopressin and the nitric oxide synthase, nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) were examined in the hypothalamo-neurohypophysial system using immunocytochemical and histochemical techniques. Double-labeled neurons were localized predominately to rostral aspects of the hypothalamo-neurohypophysial system. Only scattered double-labeled cells were found throughout the subdivisions of the supraoptic and paraventricular nuclei. Because previous investigations suggest that nitric oxide may play a critical role in neurotransmission and reductions in NADPH-d have been reported in the neural lobe of salt-loaded animals, the present report of its coexistence with the antidiuretic hormone vasopressin in the hypothalamo-neurohypophysial system further supports a role for these neuroactive substances in mechanisms modulating fluid homeostasis.

Vasopressin- and oxytocin-immunoreactive hypothalamic neurones of inbred polydipsic mice

In the late 1950s the inbred polydipsic mice, STR/N, was discovered. The early studies indicated that the extreme polydipsia was not due to a lack of vasopressin but probably due to innate thirst of unknown origin. Because the recent investigation has revealed the presence of some functional abnormality in the brain of the STR/N mouse, we now investigated, using immunohistochemical techniques, distribution of vasopressin (AVP)- and oxytocin (OXT)-containing neurones in the hypothalamus of polydipsic strain of mouse and compared with that of the control. The pattern of distribution of AVP- and OXT-immunoreactive neurones in the paraventricular (PV), supraoptic (SO), and suprachiasmatic nuclei (SCN) of the STR/N polydipsic mouse was similar to that of the control, but the number of AVP-immunoreactive neurones was more numerous in the PVN and SON and less in the SCN in the polydipsic mouse than in the control. In addition, a discrete group of AVP- and OXT-containing neurones that was not clearly seen in the control was discovered in the STR/N. These results implicate that abnormal distribution in the brain AVP and OXT contribute to the mechanism responsible for the polydipsia shown by the strain STR/N.

Comparative localization of corticotropin and corticotropin releasing factor-like peptides in the brain and hypophysis of a primitive vertebrate, the sturgeon Acipenser ruthenus L

The sturgeon is a primitive actinopterigian fish that, unlike modern teleosts, possess a portal vascular system that connects a true median eminence with the anterior pituitary as in mammals. The occurrence and localization of corticotropin and corticotropin releasing factor-like immunoreactivies were examined in the brain of the sturgeon (Acipenser ruthenus L.) by immunocytochemistry with antisera raised against synthetic non-conjugated human corticotropin, and rat/human corticotropin releasing factor. In the hypothalamus, corticotropin-immunoreactive parvicellular perikarya were found in the infundibular nucleus and in dendritic projections to the infundibular recess. In addition, ependymofugal corticotropin-immunoreactive fibres were found to terminate in the ventral hypothalamus. Corticotropin releasing factor-immunoreactive neurons were found in the rostral portion of the ventral hypothalamus (tuberal nucleus), and in the vicinity of the rostral aspect of the lateral recess. These cells projected to the dorsal hypothalamus, the ventral hypothalamus, the median eminence, the anterior and posterior telencephalon, the tegmentum mesencephali, and the pars nervosa of the pituitary. An affinity-purified UI antiserum failed to stain the sturgeon hypothalamus. Corticotrophs in the rostral pars distalis of the pituitary were also corticotropin-immunoreactive. In the neurointermediate lobe, only about 50% of cells of the pars intermedia appeared to be corticotropin-positive, the rest appeared unstained. These results suggest that the presence of corticotropin-like and corticotropin releasing factor-like peptides in the brain is a relatively early event in vertebrate evolution, already occurring in Chondrostean/Actinopterigian fishes, as exemplified by A. ruthenus. The close spatial relationship between corticotropin releasing factor immunoreactivity and corticotropin immunoreactivity in the ventral hypothalamus of A. ruthenus supports a possible interaction between the two systems in that area of the sturgeon brain. The pars intermedia might be an important site for corticotropin synthesis, even though the possibility cannot be excluded that the antiserum was recognizing the proopiomelanocortin molecule. The occurrence of corticotropin releasing factor immunoreactivity in the region of median eminence/pars intermedia of the sturgeon suggests that the sturgeon corticotropin releasing factor might regulate the adenohypophyseal release of proopiomelanocortin products in the same manner as in other vertebrates. The presence of extrahypothalamic corticotropin releasing factor-immunoreactive projections suggests further neuromodulatory functions for this peptide in A. ruthenus.

Localization of vasopressin-like immunoreactivity in the CNS of Aplysia californica

Chromatographic and immunological evidence indicates that a vasopressin-like peptide might be present in the CNS of Aplysia californica, and that this peptide may be involved in modulating the behaviour of the gill. Immunocytochemical techniques using antisera raised against various vasopressin-like peptides were used to localize the sites containing these peptides in the CNS of Aplysia. Vasopressin-like immunoreactivity was found to be restricted to one single neuron in the abdominal ganglion and two small neurons located bilaterally in each pedal ganglion. Immunoreactive fibres were present in the neuropile of the abdominal, pedal, pleural and cerebral ganglia, but not in the buccal ganglion. The identification of these neurons provides a morphological localization for vasopressin-like substances detected previously in CNS extracts of Aplysia californica. In addition, the possibility of electrophysiological studies involving the immunoreactive neurons identified in the present paper will allow a more direct approach to study the physiological role of vasopressin-like peptides in Aplysia.

Distribution and coexistence of urotensin I and urotensin II peptides in the cerebral ganglia of Aplysia californica

Urotensin I (UI) and urotensin II (UII) were demonstrated in the cerebral ganglia of Aplysia californica by applying immunocytochemical and radioimmunoassay procedures. Sequential analysis of adjacent sections of the cerebral ganglia of Aplysia demonstrated that the UI-immunoreactive (UI-IR) neurons of the F cluster of the cerebral ganglia also contained UII immunoreactivity (UII-IR). Both UI-IR and UII-IR were also observed in a cuff-like arrangement of fibers surrounding the proximal portion of the supralabial nerve, as well as in a few fibers in the anterior tentacular nerves. The UI-IR perikarya of the cerebral ganglia appeared to project to the entire CNS of Aplysia, but the UII-IR fibers appeared only in the neuropile and commissure of the cerebral ganglia. The UI-IR staining was abolished by previous immunoabsorption of the UI antiserum with sucker (Catastomus commersoni) UI, but not with ovine corticotropin-releasing factor (CRF), rat/human CRF, or goby (Gillichthys mirabilis) UII. Immunostaining with UII antiserum was quenched by goby UII, but not by sucker UII-A, UII-B, UII-A(6-12), or carp (Cyprinus carpio) UII-alpha and UII-gamma. The UII staining was not abolished by UI or somatostatin. The F cluster was not stained when a somatostatin antiserum was applied. Radioimmunoassay of dilutions of cerebral ganglia extract, using UII antiserum, revealed a parallel displacement curve to synthetic goby UII.(ABSTRACT TRUNCATED AT 250 WORDS)

Third ventricular subependymal oxytocin-like immunoreactive neuronal plexus in the rat

In a previous retrograde tracing study, a dense subependymal neuronal plexus was found along the anterior ventral third ventricle that projects to the posterior pituitary. In the work reported here, the oxytocin-like immunoreactive neurons of this plexus were studied in detail. It has a population of about 650 cells with a great wealth of dendrites. The neurons are of magnocellular neurosecretory type with long straight dendrites running parallel to the ependyma. The plexus is composed of a dorsal and a ventral part. The dorsal part consists of about 75% of the whole population and is most dense at the levels of the anterior and medial magnocellular paraventricular nuclei. Their dendrites appear vacuous in immunohistochemically stained sections and have a tendency to form fascicles. The ventral part is more sparse. The dendrites of the subependymal plexus are well organized so the anteriorly located ones tend to be directed rostrally and the posteriorly ones caudally. The functional significance of the plexus is discussed.

Distribution and dendritic features of three groups of rat olivocochlear neurons. A study with two retrograde cholera toxin tracers

Cholera toxin B subunit conjugated to horseradish peroxidase, and unconjugated cholera toxin B subunit are useful tools for retrograde tract tracing. Unilateral injection of either cholera toxin preparation into the cochlea results in excellent labeling of olivocochlear neurons, as judged by the Golgi-like filling of cell bodies, dendrites, and even axons. By this approach, we have studied the light microscopic cytology and topographic distribution of olivocochlear neurons and counted their numbers in Sprague-Dawley rats. The olivocochlear system of rats can be divided into three subgroups. The lateral olivocochlear system, composed of small cells located exclusively within the ipsilateral lateral superior olive (relative to the test cochlea), and a medial olivocochlear system, composed of large cells bilaterally dispersed within the ventral nucleus of the trapezoid body, conformed to previous topographic descriptions. A third subgroup of approximately 110 large cells, herein termed shell neurons, was labeled by both tracers, but was not well recognized in previous studies. Shell neurons and their dendrites surround the ipsilateral, and to a much lesser extent the contralateral, lateral superior olive. Lateral olivocochlear neurons do not project their dendrites outside the gray matter of the lateral superior olive, while dendrites belonging to shell neurons penetrate into that nucleus as well as into other auditory brain stem nuclei and the surrounding reticular formation. Medial olivocochlear neurons usually project dendrites ventrally into the trapezoid body and are always excluded from the lateral superior olive.

Widespread release of peptides in the central nervous system: quantitation of tannic acid-captured exocytoses

Tannic acid methods have been applied to capture the exocytosis of peptide-containing granules from peptidergic neurons. The captured exocytoses have been quantitated to assess the proportion and amount of peptide released at different parts of the neuronal membrane. Examination of hypothalamic synaptic boutons shows that only about one-half of the peptidergic vesicles is exocytosed into the synaptic cleft and also that exocytosis also occurs from undilated peptidergic axons. Study of the magnocellular neurosecretory system reveals that all parts of their extensive terminal arborization appear to be equally capable to exocytose peptide. Only about one-half of their peptide is released from their nerve endings, which about the capillaries. The remainder is released much deeper in the lobules of secretory tissue where its principal target(s) could be the pituicytes and/or neurosecretory axons. Dendrites of magnocellular neurons are also capable of releasing peptide by exocytosis and dendrites could release sufficient oxytocin and vasopressin to account for the peptide known to be released into the hypothalamus. We conclude that peptidergic neurons release substantial amounts of peptides from all of their processes and that this must be taken into account when considering what functions those peptides might serve.

Co-cultures of inferior olive and cerebellum: electrophysiological evidence for multiple innervation of Purkinje cells by olivary axons

Slices of inferior olive (IO) and cerebellum were co-cultured for several weeks by means of the roller tube technique. Recordings were carried out intracellularly from Purkinje cells (PCs) which were identified morphologically by intracellular injection of the fluorescent dye Lucifer yellow, or by immunohistochemical stainings with antibodies raised against the 28 kD Ca(2+)-binding protein calbindin. Following stimulation of olivary tissue, an all-or-none full complex spike response was recorded in some PCs consisting of a fast rising spike followed by a depolarizing potential. In other PCs, graded stimulation of the olivary explant induced synaptic potentials which were characterized by step-wise variation in their amplitude and resembled the ones occurring spontaneously. In contrast, only smoothly graded synaptic potentials were observed in cerebellar mono-cultures. These results indicate that some of the PCs in olivo-cerebellar co-cultures are innervated by several olivary neurons.

Release of oxytocin into blood and into cerebrospinal fluid induced by naloxone in anaesthetized morphine-dependent rats: the role of the paraventricular nucleus

Abstract Opioid actions on oxytocin secretion into blood and cerebrospinal fluid (CSF) were investigated in urethane-anaesthetized female rats after intracerebroventricular (icv) infusion of morphine sulphate or vehicle for 5 days. Serial femoral arterial blood samples and cisterna magna CSF samples were collected for radioimmunoassay. Naloxone was given to assess endogenous opioid tone in icv vehicle-infused rats and to precipitate withdrawal in morphine-dependent animals. Initial plasma oxytocin concentration was not affected by icv morphine infusion. In control rats receiving icv vehicle, naloxone increased plasma oxytocin 11-fold within 5 min, and in icv morphine-infused rats, naloxone increased plasma oxytocin 80-fold within 5 min. In both groups, 90 min after naloxone plasma oxytocin was still 5 and 10 times, respectively, the initial concentration. Without naloxone, neither plasma nor CSF oxytocin concentration changed significantly with time (up to 90 min) in either icv treatment group. In the icv vehicle group, there was a 2-fold increase in CSF oxytocin 90 min after naloxone. In the icv morphine-infused group, CSF oxytocin was increased 5-fold 40 min after naloxone. In another group of icv morphine-infused rats, intravenous infusion of oxytocin to achieve plasma levels similar to those seen after naloxone, did not significantly increase CSF oxytocin. In a further group of icv morphine-infused rats, [(3)H]oxytocin was infused intravenously immediately after naloxone was given; in these rats oxytocin transfer from blood to CSF could account at most for only 20% of the increase in CSF oxytocin after naloxone. A further group of rats underwent bilateral microknife ablation of the paraventricular nuclei (PVN) 9 days before icv vehicle or morphine infusions were started; blood and CSF samples were collected under urethane anaesthesia. Initial concentrations of oxytocin in CSF and in plasma were similar in both groups with PVN ablation. In all PVN-lesioned rats initial plasma concentrations of oxytocin were undetectable (<5 pg/ml) and thus less than in intact rats. In contrast, initial levels of oxytocin in CSF were 8-fold greater in PVN-lesioned rats than in intact animals. Naloxone increased plasma oxytocin concentration in the icv vehicle group at least 10-fold within 30 min and in the icv morphine group at least 100-fold within 5 min. CSF oxytocin in the icv vehicle group was not altered by naloxone, but in the icv morphine group CSF oxytocin was increased 5-fold 40 min after naloxone. There were no consistent differences between the icv vehicle- and icv morphine-treated groups in the initial plasma levels of vasopressin, growth hormone and adrenocorticotrophin; PVN ablation did not affect adrenocorticotrophin levels. After naloxone growth hormone levels did not change, vasopressin concentration rose moderately only after 90 min and only in the icv vehicle-treated group, and adrenocorticotrophin concentrations decreased with time whether or not naloxone was given. The results imply an endogenous opioid tone on neurons releasing oxytocin into CSF, and morphine-dependence of these neurons. Furthermore, in PVN-lesioned rats, magnocellular supraoptic neurons could be a source of oxytocin release into CSF.

Urotensin I-like immunoreactivity in the central nervous system of Aplysia californica

In the present study the occurrence and localization of urotensin I (UI, a corticotropin releasing factor-like peptide) in the CNS of Aplysia californica were investigated by immunocytochemistry and radioimmunoassay. The RIA cross-reactivity pattern indicated that the UI antiserum used recognized an epitope in the C-terminal region of the UI, but it did not cross-react with mammalian corticotropin-releasing factor (CRF) and partially recognized sauvagine (SVG, a frog CRF-like peptide). The use of CRF-specific and sauvagine-specific antisera failed to give positive immunostaining. The application of UI antiserum (which does not cross-react with CRF in RIA) gave a positive staining, which was blocked by synthetic sucker (Catostomus commersoni) UI, but not by rat/human CRF (10 microM). On the basis of immunostaining and RIA parallel to fish UI displacement curves of cerebral ganglia extracts, the unknown UI/CRF-like substance in the Aplysia ganglia is likely to have greater homology with sucker UI than with the known CRF peptides. Urotensin I-immunoreactive (UI-ir) neurons were seen mainly in the F neuron clusters, located in the midline and rostrodorsal portion of the cerebral ganglia. Few UI-ir neurons were also found in the C and D neuron clusters of the cerebral ganglia, as well as in the left pleural and abdominal ganglia. In addition, numerous fine and coarse, and beaded UI-ir fibers were found in the cerebral commissure. UI-ir fibers were also seen in the neuropile of the buccal, pedal and pleural ganglia, and abdominal ganglion. A cuff-like arrangement of UI-ir fibers was seen in the supralabial nerves.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxytocin in the bed nucleus of the stria terminalis and lateral septum facilitates bursting of hypothalamic oxytocin neurons in suckled rats

Abstract Several regions of the forebrain possess high densities of oxytocin (OT)-binding sites including the bed nucleus of the stria terminalis (BST) and lateral septum (LS). In order to examine whether these regions participate in the central facilitation of the milk ejection reflex by OT, microinjections of OT (1 ng in 100 nl containing Janus Green dye) were made into the BST (13 tests) or LS (9 tests) of anaesthetized, suckled rats, while recording the electrical activity of OT neurons in the contralateral supraoptic nucleus. Histological localization of injection sites using Janus Green demonstrated that all BST injections were close to the anterior commissure, and LS injections were all located in the ventral division of the LS. Film autoradiographic visualization of OT-binding sites (in 7 tests using [(125)I]OT antagonist) confirmed that the BST and LS injections were located within regions of high OT binding. Injections into both regions facilitated the milk ejection reflex by increasing either the frequency and/or amplitude of OT neuron bursts, or by triggering bursts in animals that previously had shown no milk ejection responses; the mean number of milk ejections in the 30 min before and after injection increasing from 1.6.0.5 to 3.6.0.5 for BST and from 1.5.0.6 to 3.9.0.4 for LS. The OT microinjections had a more variable effect on background activity of OT neurons, increasing firing in some cases and not in others. This facilitatory effect was similar to that induced by microinjections into the lateral ventricle, but was smaller and delayed compared to that induced by injection into the third ventricle (9 tests), possibly due to unilateral activation of target sites. The facilitatory effect was unlikely to have been due to diffusion of OT into the ventricle, since injections into control sites (striatum and thalamus) at similar distances from the ventricle (9 tests) had no facilitatory effect (number of bursts during 30 min before and after injection; 2.2.0.5 and 1.8.0.5, respectively). These data suggest that limbic structures (BST and LS) participate in the action of central OT on the pattern of milk ejections in the suckled rat.

Responses to excitatory amino acids of Purkinje cells' and neurones of the deep nuclei in cerebellar slice cultures

1. The actions of the endogenous excitatory amino acids (EAAS) glutamate (Glu), aspartate (Asp) and homocysteate (HCA) on Purkinje cells and neurones of the deep nuclei in cerebellar slice cultures were investigated using intracellular recordings in the single-electrode voltage-clamp mode and the whole-cell configuration of the patch-clamp technique. 2. Purkinje cells and neurones of deep cerebellar nuclei were identified according to their localization in the living cultures, their morphology as revealed by intracellular injections of Lucifer Yellow and their immunoreactivity to antibodies to the 28 kDa Ca2(+)-binding protein. 3. When Purkinje cells were voltage-clamped near their resting membrane potential in a TTX-containing salt solution, Glu, Asp and HCA induced inward currents which were abolished by 6-cyano-7-nitroxaline-2,3-dione (CNQX), a selective antagonist of the non-N-methyl-D-aspartate (NMDA) subtype of EAA receptors. The selective antagonist of NMDA receptors, D-(-)-2-amino-5-phosphonovaleric acid (D-APV), was ineffective in blocking the responses induced by these three amino acids. NMDA, even at high concentrations and in magnesium-free bathing solution, had no detectable effect on membrane properties of Purkinje cells grown in culture during 11-34 days. 4. In magnesium-containing saline, the amplitude of the responses induced by Glu, Asp and HCA was a linear function of the membrane potential. 5. In contrast, neurones of the deep cerebellar nuclei were responsive to NMDA and the inward currents induced by Glu, Asp and HCA were partially blocked both by CNQX and by D-APV. 6. In magnesium-containing saline, the amplitude of the currents induced by NMDA as well as by the three endogenous EAAs decreased at hyperpolarizing holding potentials whereas the current-voltage relation of the responses induced by quisqualate (QA) was strictly linear. 7. It is concluded that Purkinje cells in cerebellar slice cultures do not express NMDA receptors and that excitation of these neurones by the endogenous amino acids Glu, Asp and HCA is mediated exclusively through the activation of non-NMDA receptors. In the same preparation, neurones of the deep cerebellar nuclei possess NMDA and non-NMDA receptors which can be both activated by the three endogenous excitatory amino acids.

Efferent connections of the A1 noradrenergic cell group: a DBH immunohistochemical and PHA-L anterograde tracing study

Immunohistochemical localization of the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) was employed to reveal the anatomical organization of the A1 noradrenergic cell group in the caudal ventrolateral medulla oblongata of the rat. Subsequently, the supraspinal efferent axonal projections of A1 were investigated with a view to elucidating the anatomical substrates underlying its postulated function in central fluid and cardiovascular homeostasis. Within the caudal medulla, DBH-positive/PNMT-negative (noradrenergic) neurons were observed extending bilaterally through the ventrolateral medullary reticular formation from upper cervical spinal cord levels to the level of the area postrema. At the rostral pole of A1, its neurons intermingled with PNMT-immunoreactive perikarya of the more rostrally situated C1 adrenergic cell group. Discrete injections of the anterogradely transported plant lectin Phaseolus vulgaris leucoagglutinin (PHA-L) into A1 resulted in terminal labeling in a number of presumptive efferent target sites including the nucleus of the solitary tract, rostral ventrolateral medulla, dorsal parabrachial nucleus, Kolliker-Fuse nucleus, central grey, dorsomedial nucleus of the hypothalamus, perifornical region, zona incerta, lateral hypothalamus, paraventricular nucleus of the hypothalamus, supraoptic nucleus, bed nucleus of the stria terminalis, and organum vasculosum of the lamina terminalis. Tissue sections adjacent to those reacted for PHA-L were processed immunohistochemically for DBH to determine if anterogradely labeled terminals were localized in regions that demonstrated appropriate immunoreactivity. The majority of regions in which PHA-L terminal labeling was present also exhibited moderate to intense DBH activity. These experiments provide neuroanatomical evidence for direct efferent pathways from the A1 noradrenergic cell group to a number of supraspinal sites that have been reliably implicated in the neural circuitry underlying the central regulation of fluid and cardiovascular homeostasis. Furthermore, the results suggest a selective anatomical interrelation between A1 and sites in the basal forebrain and hypothalamus in which vasopressinergic neurons have been previously demonstrated. It is postulated that the noradrenergic A1 projections observed in this investigation represent the morphological substrate through which A1 exerts a significant influence on cardiovascular regulatory mechanisms.

Direct immunoblotting from histological sections of brain onto nitrocellulose: evaluation with the protein neurophysin

A method for the isolation and localization of proteins and peptides from histological sections of rat and human brain by immunoblotting is described. For validation, the well-characterized protein neurophysin was electrophoretically transferred from formaldehyde-fixed or fresh tissue sections onto a nitrocellulose membrane. Neurophysin on the nitrocellulose membrane was detected by a specific antibody reaction. The antibody against neurophysin was visualized either by using secondary antibodies, conjugated with peroxidase or by protein A gold, followed by enhancement with silver. With this simple and fast method, neurophysin (or other proteins and peptides) can be identified on nitrocellulose membranes in areas that correspond to anatomically defined regions. Since the procedure combines the advantages of precise regional localization of polypeptides with the specificity of antibody-antigen reactions, the method may prove useful for rapid screening of the distribution of peptides or proteins in (brain) tissue.

Efferent projections from the lateral septal nucleus to the anterior hypothalamus in the rat: a study combining Phaseolus vulgaris-leucoagglutinin tracing with vasopressin immunocytochemistry

The tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected into the lateral septum of the rat at different rostrocaudal locations to study the efferent septal projections to the anterior hypothalamus. For spatial correlation of these septofugal elements with the vasopressinergic system a dual immunocytochemical technique was used (i) to demonstrate nerve fibers and their corresponding bouton-like structures labeled with the tracer, and (ii) to identify vasopressin in the same section. The hypothalamic paraventricular and supraoptic nuclei, the accessory hypothalamic magnocellular system, and the suprachiasmatic nucleus are recipients of PHA-L-labeled fibers from all parts of the lateral septum. Close appositions between (i) these axons and their varicosities, and (ii) vasopressin-immunoreactive perikarya and their processes, putatively indicating functional interrelationships, were observed in all these nuclear areas, especially in their neuropil formations.

The effect of anteroventral third ventricular lesions on the changes in cholecystokinin receptor density in the rat supraoptic nucleus following saline drinking

Abstract Autoradiography and computerized image analysis were used to study the density of Cholecystokinin binding sites in the supraoptic nucleus of sham-lesioned and anteroventral third ventricle (AV3V)-lesioned animals in which the magnocellular system had been activated by salt-loading with 2% saline for 48 h. Rats were maintained in metabolic cages for 5 to 7 days prior to a sham- or AV3V-lesioning procedure, and the ratio of sodium intake:urinary sodium output used as a measure of sodium excretion. Following the sham or lesion procedure half of the rats had their drinking water replaced with 2% saline and the other half were maintained on normal drinking water. Neurohypophysial hormone levels were measured by specific radioimmunoassay in trunk blood samples taken 48 h after the saline or water treatment. The AV3V-lesioned group of animals were characterized by an inability to excrete the excess sodium load and by a failure to increase secretion of both oxytocin and vasopressin into the general circulation in response to the salt-stimulus. Despite this inappropriate response, [(125) l]cholecystokinin octapeptide binding in the oxytocin-rich dorsal portion of the supraoptic nucleus was similarly elevated in both sham- and AV3V-lesioned rats following 2 days of saline treatment. These results suggest that the magnocellular oxytocin system is capable of responding to an osmotic stimulus even when the release of hormone has been severely impaired.

Emerging concepts of structure-function dynamics in adult brain: the hypothalamo-neurohypophysial system

As the first known of the mammalian brain's neuropeptide systems, the magnocellular hypothalamo-neurohypophysial system has become a model. A great deal is known about the stimulus conditions that activate or inactivate the elements of this system, as well as about many of the actions of its peptidergic outputs upon peripheral tissues. The well-characterized actions of two of its products, oxytocin and vasopressin, on mammary, uterine, kidney and vascular tissues have facilitated the integration of newly discovered, often initially puzzling, information into the existing body of knowledge of this important regulatory system. At the same time, new conceptions of the ways in which neuropeptidergic neurons, or groups of neurons, participate in information flow have emerged from studies of the hypothalamo-neurohypophysial system. Early views of the SON and PVN nuclei, the neurons of which make up approximately one-half of this system, did not even associate these interesting, darkly staining anterior hypothalamic cells with hormone secretion from the posterior pituitary. Secretion from this part of the pituitary, it was thought, was neurally evoked from the pituicytes that made the oxytocic and antidiuretic "principles" and then released them upon command. When these views were dispelled by the demonstration that the hormones released from the posterior pituitary were synthesized in the interesting cells of the hypothalamus, the era of mammalian central neural peptidergic systems was born. Progress in developing an ever more complete structural and functional picture of this system has been closely tied to advancements in technology, specifically in the areas of radioimmunoassay, immunocytochemistry, anatomical tracing methods at the light and electron microscopic levels, and sophisticated preparations for electrophysiological investigation. Through the judicious use of these techniques, much has been learned that has led to revision of the earlier held views of this system. In a larger context, much has been learned that is likely to be of general application in understanding the fundamental processes and principles by which the mammalian nervous system works.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide gene expression in hypothalamic magnocellular neurons of normal and hypophysectomized rats: a combined immunohistochemical and in situ hybridization study

Hypothalamic magnocellular neurons of the paraventricular and supraoptic nuclei contain several peptides and non-peptide putative neurotransmitters co-existing with vasopressin and oxytocin. However, the functional role of these substances is still unknown. In the present paper the temporal course of changes in the expression of vasopressin, oxytocin, galanin, cholecystokinin, dynorphin and tyrosine hydroxylase in magnocellular hypothalamic neurons of rats subjected to hypophysectomy was examined. Following different survival times the animals were processed either for immunohistochemistry with antibodies against the above mentioned peptides or for in situ hybridization with synthetic oligonucleotide probes complementary to the mRNAs encoding for the peptides. The results obtained showed a marked rise in vasopressin mRNA levels at two days followed by a decrease up to 36 days of survival. Oxytocin mRNA responded to the lesion with a transient decrease, with its lowest values between five and seven days. This was followed by a recovery which almost reached normal values at 36 days of survival. The results also showed a marked, transient activation of the synthetic pathway for galanin and cholecystokinin. The numbers of cells expressing these peptides were maximal between five and seven days, and the respective mRNA levels were significantly increased at these survival times. This was followed by a decrease in the amount of galanin- and cholecystokinin-like immunoreactivity as well as in the levels of their respective mRNAs. Dynorphin-like immunoreactivity showed a course similar to that of galanin and cholecystokinin in operated animals. However, the amounts of dynorphin mRNA were significantly increased at two days, but were followed by a reduction at five days and remained low throughout the different survival times tested. The experiments performed with the tyrosine hydroxylase antibodies and probe showed undetectable levels of the enzyme and its mRNA in normal and hypophysectomized animals. These results demonstrate that, in magnocellular hypothalamic neurons, expression of several peptides occur in differential ways after hypophysectomy. The possibility is discussed that these changes represent part of the mechanisms underlying the process of degeneration and regeneration known to occur in magnocellular hypothalamic neurons after hypophysectomy.

Localization of chemical messengers in magnocellular neurons of the hypothalamic supraoptic and paraventricular nuclei: an immunohistochemical study using experimental manipulations

Indirect immunofluorescence histochemistry was used to investigate the distribution and extent of co-localization of chemical messengers in magnocellular neurons of the supraoptic and paraventricular nuclei. In order to increase the number of neurons immunoreactive to the antisera used, experimental manipulations were employed. The homozygous Brattleboro (diabetes insipidus) rat was also investigated. In untreated rats, only vasopressin- and oxytocin-like immunoreactivities could be observed. Colchicine treatment alone resulted in appearance of galanin-, dynorphin-, cholecystokinin-, [Leu]enkephalin- and thyrotropin-releasing hormone-positive cells. In hypophysectomized rats, all these markers, except tyrosine hydroxylase, showed substantial further increases. In addition, peptide histidine-isoleucine-immunoreactive cell bodies could now be seen. After salt-loading alone, tyrosine hydroxylase-like immunoreactivity was markedly increased, whereas vasopressin- and oxytocin-like immunoreactivity were very weak or undetectable. When salt-loaded rats received colchicine, corticotropin-releasing factor- and peptide histidine-isoleucine-like immunoreactivity in addition increased, whereas galanin- and dynorphin-like immunoreactivity markedly decreased. The Brattleboro rats resembled untreated rats, except their lack of vasopressin-like immunoreactivity, the marked increase in tyrosine hydroxylase-like immunoreactivity, and smaller increase in galanin- and dynorphin-like immunoreactivity. Addition of colchicine to Brattleboro rats resulted in some distinct further changes in that dynorphin-like immunoreactivity decreased in some neurons and that [Leu]enkephalin-, corticotropin-releasing factor- and peptide histidine-isoleucine-like immunoreactivity increased substantially. Several similarities could be observed between the salt-loaded and Brattleboro rats, with or without colchicine. However, a marked difference in immunoreactive [Leu]enkephalin levels was observed with no difference in dynorphin-like immunoreactivity, and opposite changes in galanin-like immunoreactivity. The results confirm the traditional view that hypothalamic magnocellular neurons in the supraoptic and paraventricular nuclei contain two separate cell populations, characterized by vasopressin and oxytocin, respectively, and that they contain additional messenger molecules in specific patterns. Vasopressin-containing neurons primarily express tyrosine hydroxylase, galanin, dynorphin, [Leu]enkephalin and peptide histidine-isoleucine, and to a minor extent cholecystokinin and thyrotropin-releasing hormone. Oxytocin-containing neurons mainly have cholecystokinin and corticotropin-releasing factor, and to a minor extent galanin, dynorphin, [Leu]enkephalin and thyrotropin-releasing hormone. Furthermore, our results detail individual co-existence situations among these putative messenger molecules. Thus, magnocellular neurons respond in a differential way to various stimuli and they store multiple bioactive substances in specific combinations.

Sodium and potassium conductances in somatic membranes of rat Purkinje cells from organotypic cerebellar cultures

1. The somatic voltage-gated conductances of Purkinje cells in organotypic cultures (Gähwiler, 1981) were studied using the outside-out patch recording configuration of the patch-clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). 2. When activated by step depolarizations, the tetrodotoxin-sensitive voltage-dependent Na+ current presented two distinct phases: an initial surge of inward current fluctuations which activates rapidly upon pulse onset and decays within 20-40 ms, and a later phase in which discrete bursts of single-channel activity are interspersed with silent periods. 3. Ensemble fluctuation analysis of the current fluctuations during the early phase of the Na+ current and measurements of single channels during both early and late phases indicate that a single type of Na+ channel can account for both phases of the Na+ current. This channel has an elementary current amplitude of -2 pA at -40 mV. This amplitude did not vary significantly between -60 and -20 mV. The mean open time depended on membrane potential, increasing by a factor of three between -60 and -20 mV. 4. The early component of the Na+ current activated at a threshold of -60 mV and reached its maximum amplitude at -20, mid-point for the activation curve being -40 mV. Times-to-peak current decreased with membrane potential, from 3.5 ms at -60 mV to 0.3 ms at 0 mV. The decay phase of the current presented two exponential components, with time constants of 1.5 and 10 ms at -40 mV. The steady-state inactivation curve had a mid-point at -75 mV. 5. The late component of the Na+ current was observed in the voltage range from -60 to -20 mV, with a maximum at -40 mV. Its maximum amplitude corresponded to approximately 1.7% of the peak amplitude of the early component. 6. Macroscopic potassium currents were observed upon step depolarizations above a threshold of -30 mV. The currents activated in a voltage-dependent fashion, times-to-peak decreasing with depolarization, and partially inactivated during 40 ms depolarizing steps. Peak current amplitudes at any given membrane potential were decreased by depolarizing the holding potential. The macroscopic properties of the K+ current varied from patch to patch. 7. Two types of single-channel K+ currents were observed during steady-state depolarizations. The unitary current amplitudes were 2.7 and 10.4 pA at 30 mV, corresponding to chord conductances of 28 and 90 pS respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution and morphometric characteristics of oxytocin- and vasopressin-immunoreactive neurons in the rabbit hypothalamus

The distribution, morphological features, and morphometric characteristics of cell bodies producing oxytocin (OT) and vasopressin (AVP) were studied in the rabbit hypothalamus by means of a conventional immunoperoxidase method. The aim of the present study was to determine the existence or not of a species-specific OT-cell group that might be involved in the dense OT innervation of the intermediate lobe in the leporidae. No OT-cell group clearly distinct from the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei was found, even in colchicine-treated animals. Most immunoreactive perikarya were found within these nuclei. In addition, small AVP neurons occurred in the suprachiasmatic nucleus. In the SON, the predominant, tightly packed AVP cells occupied the ventral part of the nucleus, whereas OT neurons were dorsolaterally located. The PVN presented a loose organization without any obvious subdivision. OT cells, which predominated, occupied the medial part of the nucleus. The PVN had a prominent rostral anterobasal extension composed mainly of OT cells. Laterally to the nucleus, numerous large AVP neurons, with few and smaller OT cells, dispersed along the neurosecretory tract without forming definite cell clusters. AVP cell bodies had a rough granular aspect contrasting with the smooth and fine one of OT cells. Spinelike processes were rarely observed on the perikarya, except on large scattered AVP neurons, but frequently covered the proximal dendrites of both types of neurons. Throughout the hypothalamus, OT neurons had definitely smaller mean somal areas and were more homogeneous in size than AVP cells.

Vasopressin-sensitive neurons in the lateral paraventricular nucleus area in a guinea pig slice preparation

The effects of vasopressin (VP) on hypothalamic neurons located in the region of the paraventricular nucleus (PVN) were analyzed using intracellular techniques in slices of guinea pig brains. Two different classes of neurons were electrophysiologically identified in the magnocellular lateral part of the PVN and in the adjacent area. In the former area, vasopressinergic neurons were identified according to their phasic activity and their endogenous properties. These neurons were not responsive to VP, applied through the perfusion medium or locally by pressure. On the other hand, nonmagnocellular neurons exhibiting low-threshold Ca2+ spikes (LTS) were recorded in the area adjacent to the lateral part of the PVN. LTS were deinactivated at hyperpolarized membrane levels and induced short bursts of action potentials. On these neurons, VP evoked depolarizations accompanied by increases in firing, without modification of membrane resistance. VP effects were not blocked by TTX, suggesting a postsynaptic action of the peptide. These data indicate that VP controls the firing pattern of LTS neurons and suggest that this action may involve collaterals of axons originating from neighbouring vasopressinergic neurons.

Paraventricular and supraoptic bursting oxytocin cells in rat are locally regulated by oxytocin and functionally related

1. Oxytocin was pressure injected through a glass micropipette into a supraoptic (SON) or paraventricular nucleus (PVN) while recording the electrical activities of oxytocin cells in a contralateral nucleus, to see whether oxytocin acts locally in the magnocellular nuclei to control their bursting activity and whether the oxytocin cells of the four magnocellular nuclei were functionally interconnected during suckling. To test the rapidity of these relations, similar intranuclear injections were realized with acetylcholine, known to rapidly increase the background activity of oxytocin cells. The effects of intranuclear injections of oxytocin and acetylcholine were tested before and after interhemisphere sections of various dimensions. 2. Injecting oxytocin (1 ng in 100 nl) into a magnocellular nucleus (5 times into the PVN and 15 times into the SON) facilitated the occurrence and increased the amplitude of bursts of the oxytocin cells in both the contralateral PVN and SON. This facilitatory effect was similar to that induced by intraventricular injection of the same dose of oxytocin, though slightly delayed and lower. 3. Injecting acetylcholine (0.6 microgram in 100 nl) into the SON (7 times) induced a rapid and sustained increase in the background activity of oxytocin cells in both the contralateral PVN (2 times) and SON (5 times) within the same delay (less than 15 s). This excitatory effect was similar to that induced by an intraventricular injection of 5 micrograms acetylcholine. The effects on bursting activity were not considered in this study. 4. Neither the injections of oxytocin or acetylcholine outside but near the magnocellular nuclei (200-500 microns), nor the intranuclear injection of 100-200 nl of cerebrospinal fluid-like medium, modified the background activity, the frequency and amplitude of bursts of the oxytocin cells in the nucleus contralateral to the injection site. 5. After interhemisphere sections most oxytocin cells were silent, bursts occurred in an erratic manner, and their amplitude was attenuated and irregular (more than the 20% variation normally recorded in non-operated rats). Moreover, the amplitudes of successive bursts of pair-recorded supraoptic-supraoptic (SO-SO) oxytocin cells, highly related in control conditions (correlation coefficient, r = 0.68 to 0.98) were no longer correlated after interhemisphere section (r = 0.24 to -0.61), but all bursts remained synchronized.(ABSTRACT TRUNCATED AT 400 WORDS)

Tyrosine hydroxylase-containing neurons in the supraoptic and paraventricular nuclei of the adult human

We have studied the distribution of tyrosine hydroxylase-containing neurons in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the adult human hypothalamus. Large numbers of these neurons were seen in these hypothalamic nuclei; approximately 40% of all the cells within the SON and PVN were immunoreactive for tyrosine hydroxylase (TH-ir). Most of these cells were magnocellular. Their distribution was compared to that of arginine-vasopressin-immunoreactive (AVP-ir) cells. In the SON a greater proportion of magnocellular TH-ir cells was found caudally compared to AVP-ir cells. In the PVN the magnocellular TH-ir cells were larger in mean diameter compared to AVP-ir cells. In double-immunofluorescence experiments some TH-ir cells contained oxytocin immunoreactivity but none contained AVP-ir. In the adult human a large number of PVN and SON magnocellular cells appear to synthesize a catecholamine. A subclass of these neurons also synthesize oxytocin but most cells are distinct from the classically described neurosecretory neurons.

Localization of vasopressin mRNA-containing neurones in the hypothalamus of the monkey

Neuronal perikarya containing vasopressin mRNA were detected in cryostat sections of cynomolgus monkey brains by using an in situ hybridization technique. The neurones were observed in hypothalamic regions (supraoptic nucleus, paraventricular nucleus, suprachiasmatic nucleus and accessory supraoptic nucleus). These findings are in agreement with previous reports using immunohistochemical methods.

Slice cultures of rat hypothalamus examined by immunohistochemical staining for neurohypophyseal peptides and GFAP

Organotypic cultures were prepared from slices of neonatal rat hypothalami and were immunohistochemically stained for the neurohypophyseal peptides vasopressin and oxytocin, their associated neurophysins, and for glial fibrillary acidic protein (GFAP). Both glial and neural elements survived and matured within the cultures, expressing cellular morphologies and retaining a topographic organization similar to that found in vivo. Neurones producing peptides were readily identified and such peptidergic neurones elaborated processes with an appearance characteristic of beaded axons. These presumptive axons grew in a selective and specific manner over certain regions in the slice cultures while avoiding other regions in a manner similar to that found in vivo. In cocultures of hypothalamus and neurointermediate lobe tissue, peptidergic axons found and grew over the neurointermediate lobe tissue and elaborated extensive terminal arborizations. Thus, it appears that at least some of the cues used for appropriate axonal guidance are maintained in these cultures. Organotypic cultures retain many in vivo characteristics as regards cellular morphology and cellular interactions, yet provide an in vitro environment useful for the study of morphology, physiology, cell biology and neurone-target interaction of hypothalamic neurones.

Thermal, osmotic and chemical modulation of neural activity in the paraventricular nucleus: in vitro studies

To investigate the functions of the paraventricular nucleus (PVN) which plays an important role as an integration site for the neuroendocrine and autonomic nervous systems, the firing activity of PVN neurons was recorded from hypothalamic slice preparations during thermal, osmotic and chemical stimulation. Neurons responded to environmental factors such as temperature and osmolarity and both warm-responsive and cold-responsive neurons were observed in the PVN. Some PVN neurons were also osmoresponsive and unlike neurons in the supraoptic nucleus, most osmoresponsive PVN neurons decreased their firing rate during hyperosmotic stimulation. One of the classical transmitters, noradrenaline, exerted excitatory effects on PVN neurons through alpha 1- and beta-receptors and inhibitory responses through alpha 2-receptors. Atrial natriuretic polypeptide exerted inhibitory effects on putative parvocellular PVN neurons but it had no effect on putative magnocellular PVN neurons. An endogenous sugar derivative, 2-deoxytetronic acid, thought to be an endogenous satiety factor, elicited inhibitory effects, supporting the possibility that the PVN also may be related to feeding behaviour. Arginine-vasopressin and oxytocin which are synthesised in the magnocellular neurosecretory cells excited PVN neurons, suggesting that the PVN may have short circuits modulating neural activity within the nucleus itself. We conclude that neurons in the PVN may receive multiple information and act as one of the important integrative sites in the brain.

The neurophysin-containing innervation of the forebrain of the mouse

The oxytocinergic and vasopressinergic innervation of the forebrain of normal mice was studied immunocytochemically by use of a set of mouse monoclonal anti-neurophysins applied to serial vibratome sections. The extensive hypothalamic and extra-hypothalamic location of these neuropeptides was revealed, with, or without colchicine pretreatment. Magnocellular perikarya immunoreactive for either oxytocin-neurophysin or vasopressin-neurophysin were concentrated mainly: in the anterior commissural nucleus; in various subdivisions of the paraventricular nucleus; in a profuse array in the periventricular region; in the supraoptic nucleus including its retrochiasmatic division; in various accessory nuclei; and as a number of cells scattered throughout the preoptic and hypothalamic regions. Extensive groups of parvocellular neurons, containing only vasopressin-neurophysin, were located in the suprachiasmatic nucleus including a ventromedial division, in the bed nucleus of the stria terminalis, and in the medial amygdaloid nucleus. Perikarya in the magnocellular nuclei were of generally similar size distribution and there was no evidence that distinct populations of magnocellular and parvicellular neurons, separable on the basis of size, had been labelled within these nuclei. Within the paraventricular nucleus, however, neurons in the posterior part were smaller than those located more anteriorly, and the cells containing oxytocin-neurophysin were slightly smaller than those containing vasopressin-neurophysin. Within the generally similar size distribution, magnocellular neurons of the anterior commissural nucleus were the largest. During processing, shrinkage of the tissue and immunolabeled cells had occurred. The immunocytochemical procedure delineated neuronal processes, in particular dendrites, very effectively. The dendrites were shown to project for far greater distances than is generally recognized, some were of a characteristic corkscrew-like morphology, and most were oriented in a well-defined pattern. Many dendrites of paraventricular neurons passed medially than caudally towards and then along the third ventricle. Most dendrites of supraoptic neurons, in particular those containing vasopressin-neurophysin, had an extensive anteroposterior course beneath the pia of the base of the brain. The axons containing oxytocin- and vasopressin-neurophysin were shown to take rather different paths from the paraventricular nucleus towards the median eminence.(ABSTRACT TRUNCATED AT 400 WORDS)

An immunochemical analysis of oxytocin and vasopressin prohormone processing in vivo

Antisera against partially processed, unamidated forms of AVP and OT were raised and characterized by radioimmunoassay and immunocytochemistry. These antibodies, and antibodies that recognize fully processed, amidated forms of AVP and OT, were used together with various fractionation methods to study the content of prohormones, partially processed and fully processed forms of AVP and OT in the hypothalamo-neurohypophysial system of adult and fetal (E21) rats. The levels of cleaved AVP and OT in the fetus were lower than those of the adult (1 to 3 orders of magnitude for brain and pituitary, respectively), and the detection of cleaved OT in brain and pituitary was delayed compared to that of AVP. Pro-AVP cleavage efficiency in the adult and the fetus was high (99 and 95% cleavage, respectively) resulting in formation of fully processed amidated forms of AVP, with no detectable partially processed peptides. Pro-OT processing in the adult was very similar (over 99% cleavage) resulting in formation of fully processed amidated OT. However, Pro-OT processing efficiency in the fetus was very low and incomplete, resulting in 40% unprocessed precursor and the accumulation of C-terminally extended unamidated intermediate forms (OT-Gly, OT-Gly-Lys, and OT-Gly-Lys-Arg).

Oxytocin predominantly excites putative oxytocin neurons in the rat supraoptic nucleus in vitro

To determine the oxytocin (OXT) sensitivity of neurons in the supraoptic nucleus (SON), extracellular recordings were made from the rat hypothalamic slice preparation. OXT added to the bathing medium (3 X 10(-7) M) excited 13 (93%) of 14 cells which fired continuously (average 4.9 +/- 0.7 spikes/s) and 26 (81%) of 32 cells which fired slowly and irregularly (average 1.4 +/- 0.4 spikes/s). By contrast, only 2 (8%) of 26 phasically firing neurons were excited and none of the SON cells tested were inhibited. The excitation was reversibly antagonized by a synthetic OXT analogue, 1-deamino-[2-(O-methyltyrosine), 4-valine, 8-D-arginine]vasopressin. The results suggest that OXT exerts predominantly excitatory effects in the SON and that putative OXT cells are more likely to be affected than putative vasopressin cells.

In situ hybridization of oxytocin messenger RNA: macroscopic distribution and quantitation in rat hypothalamic cell groups

Oxytocin mRNA was detected in the rat hypothalamus by in situ hybridization to a single stranded 35S-labelled DNA probe and the distribution of oxytocin mRNA-containing cell groups was studied at the macroscopic level. Specificity of hybridization was confirmed by comparison to vasopressin mRNA hybridization in parallel tissue sections. Cell groups containing oxytocin mRNA were confined to a set of hypothalamic cell groups, i.c. the supraoptic, paraventricular, anterior commissural nuclei, nucleus circularis and scattered hypothalamic islets. These cell groups displayed similar densities of autoradiographic signals indicating that the oxytocin gene is expressed at approximately the same average level at these various sites.

Distribution and morphology of vasopressin-, neurophysin II-, and oxytocin-immunoreactive cell bodies in the forebrain of the cat

Experiments were done to provide a detailed map of the location and a description of morphological characteristics of vasopressin (AVP-IR)-, neurophysin II (NII-IR)- and oxytocin (OXY-IR)-immunoreactive neuronal perikarya in the forebrain of the cat. In addition, the location of cells in the forebrain retrogradely labeled following injections of tracers into the neurohypophysis was determined. The distribution of AVP-IR and NII-IR was similar in all cases studied. Most of the cells containing AVP-IR and OXY-IR were observed in the hypothalamic paraventricular (PVH) and supraoptic (SON) nuclei. In addition, AVP-IR and OXY-IR cell bodies were found in the regions of the nucleus of the diagonal band of Broca, the dorsal chiasmatic nucleus, the anterior hypothalamic-preoptic area, the periventricular area, the nucleus circularis, the perifornical area of the lateral hypothalamus, the accessory SON, the area of the tuber cinereum (Tca), and the medial nucleus of the amygdala. The density of AVP-IR cells was greater than that of OXY-IR cells in these regions. Several forebrain areas were also observed to contain only AVP-IR perikarya: the suprachiasmatic nucleus (Sc), the bed nucleus of the stria terminalis, and the region of the substantia innominata and ventral globus pallidus (SI/GP). In addition, the dorsomedial nucleus of the hypothalamus only contained OXY-IR perikarya. Most of the cells immunoreactive to AVP were multipolar and had spinelike processes over their somata and proximal dendrites. In addition, the majority of cells in the PVH and SON were round or oval, whereas those outside these nuclei were fusiform or triangular. The mean somal area of AVP-IR cells in the region of the SI/GP was significantly (P less than 0.05) larger than that of AVP-IR cells in all other regions examined, whereas the mean somal area of Sc AVP-IR cells was significantly (P less than 0.05) smaller than that of all other groups of AVP-IR cells examined. Most OXY-IR cells were similar morphologically to those immunoreactive to AVP, except that OXY-IR cell bodies and their appendages did not have spinelike processes. In addition, OXY-IR perikarya were generally of uniform size. OXY-IR cells in the PVH and accessory SON were significantly (P less than 0.05) larger than AVP-IR cells in the same regions, but were not different from AVP-IR cells in the lateral hypothalamus and SON.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical stimulations of perifused magnocellular nuclei in vitro elicit Ca2+-dependent, tetrodotoxin-insensitive release of oxytocin and vasopressin

Isolated rat paraventricular (PVN) and supraoptic (SON) nuclei were perifused in vitro and oxytocin and vasopressin releases were measured by radioimmunoassay during rest and during electrical stimulation. Stimulations at a frequency of 10 Hz (10-s bursts, every 10 s for 5 min) and an intensity of 4 mA, induced significant hormone release only with long duration pulses (10 ms). Short pulses (1 ms) applied at various frequencies (10, 20, 40 or 80 Hz) and intensities (4, 5, 10 or 20 mA) had no effect. The electrically evoked release of both hormones was not affected by tetrodotoxin (TTX), a sodium channel blocker, but was blocked in low-calcium medium or in the presence of gallopamil hydrochloride (D-600), a calcium channel blocker. These results suggest that, following electrical stimulation, oxytocin and vasopressin are released locally within the magnocellular nuclei even when blocking action potentials. The possibility of dendritic release is discussed.

Do antidromic latency jumps indicate axonal branching in nigrostriatal and hypothalamo-neurohypophysial neurons?

Neurons in many brain regions exhibit discontinuous decreases in antidromic latency with small increases in stimulating current. We used an electrophysiological test requiring a single stimulating electrode to determine whether these 'latency jumps' are due to shifts in the site of spike initiation to the same or different axon branches. Latency jumps in response to stimulation of the striatal terminal fields of substantia nigra, pars compacta neurons represent spike initiation on different branches while those seen in paraventricular neurons with pituitary stalk stimulation usually reflect a change in site on a single branch.

Golgi-like immunostaining of pituicytes and tanycytes positive for glial fibrillary acidic protein in the neurohypophysis of the Mongolian gerbil (Meriones unguiculatus)

Glial cells that contain the glial fibrillary acidic protein (GFAP; the major protein constituent of glial filaments) were stained immunohistochemically in thick frozen sections of the neurohypophysis of the Mongolian gerbil (Meriones unguiculatus). The resulting Golgi-like images provided informations on cytological features and distributional patterns of tanycytes and pituicytes. In the proximal median eminence, numerous bundled processes of tanycytes were revealed. They emerged from the ependymal and sub-ependymal layer and mostly reached the brain surface. Several tanycytic processes extended into the anatomical neural stalk. In the whole neural lobe, a dense network of GFAP-immunoreactive pituicyte processes was visualized. Stained pituicytes were highly asymmetric and exhibited a great morphological variability. Immunopositive fibers which were encountered in the intermediate lobe might be derived from pituicytes. Electron-microscopically further evidence was obtained that GFAP-positive pituicytes correspond to filament-rich fibrous pituicytes at the ultrastructural level.

Immunocytochemically-stained vasopressin binding sites in rat brain. Ventricular application of vasopressin/Accurel in the Brattleboro rat

An immunocytochemical procedure was developed to localize binding sites for vasopressin (VP) in the brain of Brattleboro (di/di) rats after 2 weeks of continuous ventricular administration of the peptide. Accurel-polypropylene tubing loaded with 0.15, 1.5 or 15 micrograms vasopressin was implanted into the lateral ventricle. Subsequently, bound VP was detected immunocytochemically in 2 distinct patterns: in perineuronal structures and dots between cells, in the lateral septum (dorsorostral part), striatum, cingulate cortex, granular cells of the dentate gyrus of the hippocampus, pyramidal cells of CA1 and CA3 hippocampal areas and around cerebellar Purkinje cells. The high dose (15 micrograms) loaded implants revealed the most intense staining; in the cytoplasm of neuronal cell bodies in the lateral and medial septum, striatum, cingulate cortex, bed nucleus of the stria terminalis, organum vasculosum of the laminae terminalis and locus coeruleus. The most intense staining in cell bodies was observed in brains which had low-loaded implants (0.15-1.5 microgram). A variety of controls, proved that no aspecific uptake was involved in the present procedure. The distribution of VP binding sites was only partly coincident with known sites of VP fiber innervation, and largely agrees with data obtained by autoradiographic techniques for [3H]VP binding. The present immunocytochemical technique gave a higher resolution than the currently used autoradiographic techniques. The differences in pattern and intensity of staining due to increasing the dosage rate of the in vivo vasopressin treatment, might mean that the current procedure retains preferentially either low or high affinity populations of binding sites depending on the implanted dose.

Projections from the hypothalamus and its adjacent areas to the posterior pituitary in the rat

Cholera toxin conjugated horseradish peroxidase was injected into the posterior pituitary and its afferents traced in 21 albino rats. The neuronal processes as well as the perikarya were elaborately displayed. The principal and retrochiasmatic supraoptic nuclei and the magnocellular paraventricular subnuclei were densely labelled. The accessory cell groups or nuclei labelled included: the medial preoptic and anterior hypothalamic areas, the anterior and posterior fornical nuclei, the lateral hypothalamic area, the nucleus circularis and nucleus of the forebrain bundle and hitherto unknown or not fully appreciated retrochiasmatic area, the dorsal accessory groups in an area between the stria medullaris and fornix, on the one hand, and the stria terminalis and internal capsule, on the other, and a well developed subependymalperiventricular zone. The medial preoptic nucleus, subfornical organ and organ vasculosum laminae terminalis were also weakly stained. Dendrites of the magnocellular paraventricular nucleus have been said by some to be largely confined to the subnuclei in which they lie. Immunohistochemical studies have proved that they extended beyond their nuclear confinement. The present study has found much wider extension of their dendritic fields. In fact, dendrites of the magnocellular neurosecretory cells in general were long and had a certain degree of directional bias. Several sites projecting to the posterior pituitary were closely related to the cerebrospinal fluid. Namely, the subependymal neuronal plexuses along the third ventricle and beneath the interventricular foramen, and the subpial dendritic plexuses of the supraoptic and retrochiasmatic supraoptic nuclei. Neurons were seen to squeeze in-between the ependymal cells, bringing themselves very close to the cerebrospinal fluid. No direct cerebrospinal fluid-contacting elements, either cell bodies or processes, however, could be ascertained. It is proposed that these plexuses may monitor changes in the cerebrospinal fluid. Besides the principal neurohypophysial tract the posterior pituitary was found in the present study to receive its afferents via two accessory fasciculi, one coursing in the medial forebrain bundle and the other running along the lateral wall of the infundibular recess subependymally.

Paired recordings from supraoptic and paraventricular oxytocin cells in suckled rats: recruitment and synchronization

Oxytocin cells in the paraventricular (p.v.) and contralateral supraoptic (s.o.) nuclei were pair-recorded (with two micro-electrodes) in suckled rats after being anaesthetized with urethane (1.2 g/kg), to study the synchronization of their neurosecretory bursts, the importance of cell recruitment and their firing characteristics. The synchronization of paired bursts was determined by measuring the onset time-lag (time in milliseconds between the onset of two corresponding bursts) and the maximum firing time-lag (time in milliseconds between the two shortest interspike intervals for the corresponding bursts). For each cell, the characteristics studied were: the background activity and the frequency and amplitude (total number of spikes) of the neurosecretory bursts. All paired p.v.-s.o. cells recorded were activated simultaneously 12-18 s before each milk ejection. The onset of a burst could vary either way, up to 680 ms, in relation to the other (mean onset time-lag was 206 +/- 18 ms; n = 85) but the maximum activation periods fitted more closely, the mean maximum firing time-lag being 122 +/- 14 ms (n = 64). Both parameters varied randomly, in duration and order from one pair of cells to another, from one pair of bursts to another for successive bursts of a given pair of cells and independently, whether the cells were in the p.v. or the s.o. nucleus. However, in most cases, the neurosecretory burst with the highest amplitude began and reached its peak firing rate before the corresponding burst from the other cell. Cell recruitment was observed when the milk ejection reflex began, for both the p.v. and the s.o. cells. The bursts of the non-responsive cells developed progressively with the reflex, but, as soon as a cell was recruited, all its successive bursts were simultaneous with those of the first-recruited oxytocin cells. During a regular pattern of milk ejections, the mean background activity of sixty p.v. cells (3.1 +/- 0.2 spikes/s) was significantly higher than that of their s.o. counterparts (1.9 +/- 0.2 spikes/s). Nevertheless, the mean amplitude of the neurosecretory bursts of the sixty p.v. cells (49 +/- 3 spikes) did not differ significantly from that of their s.o. counterparts (55 +/- 4 spikes).(ABSTRACT TRUNCATED AT 400 WORDS)

Immunocytochemical localization of proenkephalin-derived peptides in the central nervous system of the rat

Most of the early studies on the immunohistochemical distribution of enkephalin pentapeptide-like immunoreactivity used antisera that stained both proenkephalin- and prodynorphin-containing neurons. The present study used the peroxidase-antiperoxidase method, thick Vibratome sections and antisera specific for the carboxyl termini of [Met]enkephalin, [Met]enkephalyl-Arg6-Phe7, [Met]enkephalyl-Arg6-Gly7-Leu8, and metorphamide and for BAM 22P in order to obtain a detailed description of the distribution of authentic proenkephalin-containing perikarya and nerve processes. The peroxidase-antiperoxidase reaction product was intensified by the selective deposition of silver crystals in order to display the morphology of proenkephalin-containing neurons with great fidelity. The results indicate that the magnocellular perikarya in the supraoptic and paraventricular nuclei contain prodynorphin rather than proenkephalin as had been suggested by earlier investigators. The coarse fibers in the internal zone of the median eminence and the granule cell-mossy fiber pathway in the hippocampus also contain prodynorphin rather than proenkephalin. The number of proenkephalin-containing perikarya and/or the density of proenkephalin-containing nerve terminals in several other areas of the brain, e.g. the substantia nigra, the central amygdaloid nucleus, the periaqueductal gray and the parabrachial nuclei, were overestimated by earlier investigators. The distribution of authentic proenkephalin-containing perikarya and nerve processes is, despite these errors, similar to the distribution of enkephalin pentapeptide-like immunoreactivity described by earlier investigators. Proenkephalin-containing perikarya were identified for the first time in the medial and lateral habenular nuclei of the adult rat. Antisera specific for [Met]enkephalin, [Met]enkephalyl-Arg6-Phe7, [Met]enkephalyl-Arg6-Gly7-Leu8 and BAM 22P stain perikarya and nerve terminals with a similar distribution. The metorphamide antiserum also stains the same perikarya and nerve terminals; however, it also stains magnocellular perikarya in the zona incerta and the lateral hypothalamus that are not stained by any of the other proenkephalin-specific antisera.

Serial reconstruction of Lucifer yellow-labeled supraoptic nucleus neurons in perfused rat hypothalamic explants

Intracellular recordings from supraoptic nucleus neurons in perfused explants of rat hypothalamus were followed by intracellular injections of the fluorescent dye, Lucifer yellow. Following fixation, 40 microns sections were processed for whole cell light-microscopic reconstruction in the horizontal or coronal plane. The somata of most supraoptic neurons were elongated (mean 25 X 13 microns) with 1-3 sparsely branched dendrites (length 30-725 microns) that displayed numerous spines. Most (95%) dendrites turned in the ventral direction to end in the glial lamina along the base of the nucleus. Each neuron had one axon: in 60% of cells, the axon arose from a dendritic profile and immediately assumed a varicose appearance; in the other 40% of cells, the axon appeared to arise directly from the soma and demonstrated in its initial 80-200 microns numerous spines and few varicosities, i.e. the morphological features of a dendrite. All axons coursed in a dorsomedial direction over the optic tract. At this point, most axons revealed smaller secondary processes 2-15 microns in length. Axons then turned ventrally towards the basal hypothalamus; some could be followed for up to 2100 microns from the cell somata. This approach to the light microscope morphology of supraoptic neurons provides a surprising array of detail on soma, dendrite and axon characteristics, while retaining the overall relationship between individual neurons and neighboring structures, including the boundaries of the nucleus itself.

Histaminergic axons in the neostriatum and cerebral cortex of the rat: a correlated light and electron microscopic immunocytochemical study using histidine decarboxylase as a marker

Histaminergic nerve fibers and their axonal varicosities in the neostriatum and cerebral cortex were light and electronmicroscopically examined by means of peroxidase-antiperoxidase immunocytochemistry with histidine decarboxylase (HDC) as a marker. A majority of HDC-like immunoreactive axonal varicosities observed in serial thin sections for electron microscopy exhibited no synaptic contacts in either the neostriatum or cerebral cortex. The remaining small proportion of immunoreactive axonal varicosities formed synaptic contacts with non-immunoreactive dendritic shafts and spines.

Excitation of neurones in the rat paraventricular nucleus in vitro by vasopressin and oxytocin

Extracellular recordings were made from ninety-seven spontaneously firing cells in the paraventricular nucleus (p.v.n.) of the rat hypothalamic slice preparation. The spontaneously firing cells tested fired at 0.1-8 spikes/s but the majority showed a slow irregular firing pattern. The average firing rate of all ninety-seven cells was 2.2 +/- 0.2 spikes/s (mean +/- S.E. of mean). Six cells showed a phasic firing pattern. Following bath application of arginine-vasopressin (AVP) 10(-7) M, sixty-four (66%) of ninety-seven p.v.n. cells showed excitatory responses and three (3%) cells inhibitory responses. Bath application of oxytocin (OXT) 10(-7) M excited thirty-nine (57%) of sixty-eight p.v.n. cells and inhibited two (3%) cells. Individual p.v.n. cells responded to application of both AVP and OXT, but the magnitude and threshold of the responses varied from cell to cell. Of the sixty-six cells tested with both peptides at 10(-7) M, sixteen showed similar responses to both and fifteen showed no response to either: twenty cells showed a greater response to AVP and fifteen a greater response to OXT. Of six phasic firing cells, two showed excitatory responses to AVP and all four cells tested did not show any response to OXT. The dose-dependence of the response to AVP and OXT was tested in six p.v.n. cells. There was a direct relationship between peptide concentration and increased firing rate. The threshold concentration of the peptides ranged from 10(-8) to 10(-10) M. The cells responsive to the peptides were not located in particular areas of the p.v.n. but were diffusely distributed throughout the nucleus. After blocking synaptic transmission with a low Ca2+ and high Mg2+ medium, all tested cells (AVP, n = 15; OXT, n = 14) which had responded to applications of AVP or OXT in normal medium still showed responses to the peptides, although the effect was less marked in half the cells. However, in the absence of synaptic transmission two cells showed unimpaired responses to one of the peptides but greatly depressed responses to the other. The V1-receptor antagonist [1-(beta-mercapto-, beta-cyclopentamethylenepropionic acid)], 8-D-arginine-vasopressin (d(CH2)5DAVP) or V1/V2-receptor antagonist [1-(beta-mercapto-, beta-cyclopentamethylenepropionic acid), 2-D-tyrosine,4-valine]arginine-vasopressin (d(CH2)5D-TyrVAVP) completely or partly blocked the AVP-induced responses, while the V2-receptor agonist 1-deamino-8-D-arginine-vasopressin (dDAVP) did not influence the spontaneous discharges of the cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Electron microscopic examination of the catecholaminergic innervation of neurophysin- or vasopressin-containing neurons in the rat hypothalamus

The ultrastructural relationships between neurophysin (NP)- or vasopressin (VP)-containing neurons and catecholamine terminals in the paraventricular nucleus and supraoptic nucleus of the rat were observed by means of a technique combining immunocytochemistry using NP I/II or VP antiserum with autoradiography after [3H]noradrenaline (NA) injection or 5-hydroxydopamine (5-OHDA) uptake. NP- or VP-like immunoreactive nerve cell bodies and fibers received synaptic contacts from a large number of immunonegative axon terminals. The presynaptic elements that innervate the neurosecretory neurons were studied. Axon terminals labeled with [3H]NA or 5-OHDA made synaptic contacts with NP- or VP-like immunoreactive nerve cell bodies and fibers. Furthermore, axodendritic and/or axo/axonic and axosomatic synapses occurred between the same NP- or VP-like immunoreactive neurons. These findings suggest that at least NA- and 5-OHDA-containing neurons play some important role in the control of neurosecretion in the NP- or VP-producing neurons of the rat hypothalamus and that the axon collaterals of NP- and VP-containing neurons make synaptic contacts with the same kind of neurons to form a recurrent collateral circuit.

Epidermal growth factor binding and receptor distribution in term human placenta

Human placenta has a large number of epidermal growth factor (EGF) receptors when measured either by [125I]iodoEGF binding or by protein yield after purification. To localize EGF receptors in situ in normal human term placenta, two different light microscopic methods were used. To detect unoccupied, accessible EGF binding sites on the extracellular surface of placental cells in intact blocks of tissue, samples were incubated with [125I]iodoEGF, sectioned and autoradiography performed. To detect the total pool of intracellular and extracellular EGF receptors, placental tissue was sectioned, treated with detergent, and then anti-EGF receptor antibody was localized by immunohistoperoxidase techniques. Both [125I]iodoEGF and anti-EGF receptor antibody methods showed that EGF receptors were primarily present on syncytiotrophoblast cells of placental villi. Smooth muscle cells of placental blood vessels also contained EGF receptors. Neither connective tissue cells within the core of terminal chorionic villi nor endothelium of fetal blood vessels had detectable [125I]iodoEGF binding or immunoreactive EGF receptors. Since the quantity of placental smooth muscle cells is only a small fraction compared to trophoblast cells, we conclude that syncytiotrophoblast cells are primarily responsible for the high levels of EGF receptors found in extracts prepared from human term placenta.