Projections of substance P containing neurons from neostriatum to substantia nigra

Comparison of the substance P- and dynorphin-containing projections to the substantia nigra: a radioimmunocytochemical and biochemical study

A series of knife cuts were made in the striatonigral pathway and changes in dynorphin B (Dyn) and substance P (SP) input to the substantia nigra were examined using radiolabeled antibodies and radioimmunoassay (RIA). Cryostat cut sections were incubated with primary antibody followed by a secondary antibody labeled with 125I. Apposition of the radiolabeled sections to LKB Ultrofilm generated an image that was qualified by computerized optical densitometry. The striatonigral system served as a model system for comparing the quantitative capabilities of radioimmunocytochemistry with RIA. The results indicated a strong correlation between optical densitometry measurements and RIA for both Dyn (r = 0.97) and SP (r = 0.98) antisera. This suggests that radioimmunocytochemistry may be used for quantitative, as well as, qualitative descriptions of the distribution of tissue antigens. Knife cuts separating the rostral caudate putamen from the substantia nigra resulted in less than 40% depletion of dynorphin and substance P in the nigra pars reticulata, leaving the levels of both peptides relatively unchanged in the pars lateralis. More caudal knife cuts resulted in progressively greater depletions of both peptides in the pars reticulata and pars lateralis.

Peptidase-containing neurons in rat striatum

The effects of surgical lesions on peptidase activity have been studied in the striatonigral system of the rat brain. Knife cuts separating the anterior part of the caudate putamen from the globus pallidus resulted in a decrease in the activity of angiotensin-converting enzyme and alanyl aminopeptidase in both the globus pallidus and substantia nigra. The activity of nigral prolyl endopeptidase and leucyl aminopeptidase was also decreased. An increase in dipeptidyl aminopeptidase and arginyl endopeptidase activity was observed in both the caudate putamen and globus pallidus. These results suggest that the striatal neurons containing angiotensin-converting enzyme or alanyl aminopeptidase project to both the globus pallidus and substantia nigra, and the neurons containing prolyl endopeptidase and/or leucyl aminopeptidase project to the substantia nigra. Dipeptidyl aminopeptidase and arginyl endopeptidase are probably associated with glial function.

Substance K excites dopaminergic and non-dopaminergic neurons in rat substantia nigra

Substance K (SK) is a newly discovered neuropeptide which is a member of the tachykinin family that includes substance P (SP). As it is present in high concentrations in substantia nigra, we have investigated the electrophysiological activity of SK microiontophoresed onto single neuronal units in this region. SK microiontophoresed onto single units in the substantia nigra caused excitation of approximately 50% of both dopaminergic and non-dopaminergic neurons. This relatively high proportion of responsivity correlates with the reported high density of SK receptors in the substantia nigra.

Disinhibition as a basic process in the expression of striatal functions. I. The striato-nigral influence on tecto-spinal/tecto-diencephalic neurons

The striato-nigro-collicular pathway is one of the neuronal circuits through which basal ganglia can influence ocular and cephalic motricity. Through this pathway striatal signals are conveyed to a major collicular efferent system i.e. the tecto-spinal/tecto-diencephalic neurons (TSD). A striking particularity of the striato-nigro-collicular connection is to present an assemblage of two successive GABAergic inhibitory links. To analyze how striatal information is expressed through this double inhibitory system we made use of concomitant unitary recordings of substantia nigra pars reticulata (SNR) and TSD activity while nigral and/or striatal activity was changed by local applications of pharmacological agents. We observed (1) that an intranigral application of GABA which transiently abolishes the tonic discharge of SNR cells, causes the TSD cells to discharge vigorously. During this period of increased excitability the responsiveness of TSD cells to somatosensory input is significantly enhanced; (2) that an intrastriatal injection of glutamate which silences the nigro-collicular cells, causes the TSD cells to discharge. This striatally induced tectal firing being sensitive to intranigral application of a GABA antagonist (bicuculline), led us to the conclusion that striatum exerts a facilitatory influence on TSD cells by releasing these neurons from the tonic inhibitory nigral influence. The functional implication of such a mechanism is discussed in the light of the current knowledge on the involvement of basal ganglia in eye/head orienting movements.

Opposing effects of striatonigral feedback pathways on midbrain dopamine cell activity

The existence of a striatonigral GABAergic pathway has been well established both anatomically and biochemically. During intracellular recording from identified DA neurons in vivo, stimulation of the striatum (100 microA, 50 microseconds pulses) elicits an inhibitory postsynaptic potential (IPSP) and a rebound depolarization. The IPSP is a short latency (1.8-2.2 ms) conductance increase to chloride, since: the reversal potential is near the chloride reversal potential reported for other cells (-68 mV); intracellular chloride injection progressively reverses the IPSP into a depolarization with a similar time course; and the response of DA cells to systemic injection of the chloride channel blocker, picrotoxin, also exhibits a similar reversal potential. In contrast, during extracellular recording, stimulation of the striatum at low levels of intensity (e.g. 20 microA at 10 Hz) increases the firing rate of DA cells. Stimulation of the striatum will, in addition, elicit IPSPs in a subclass of substantia nigra zona reticulata neurons at the same latency as the IPSPs triggered in DA cells. These IPSPs also reverse with intracellular chloride injection. However, their amplitude is larger and their duration longer than observed in DA cells, and there is no depolarizing rebound. The late component of the IPSP in the zona reticulata neurons corresponds temporally to the rebound depolarization seen in DA cells in response to striatal stimulation. In addition, when recorded extracellularly, striatal stimulation will inhibit the firing of this class of zona reticulata interneurons at the same stimulation parameters that will excite DA cells. These data suggest that striatal cells may send branched fast-conducting GABAergic projections to zona reticulata cells and DA cells. Furthermore, low levels of striatal stimulation can excite DA cells by preferentially inhibiting interneurons in the zona reticulata which are more sensitive to the inhibitory effects of GABA than are DA neurons.

Striatonigral and pallidonigral pathways studied by a combination of retrograde horseradish peroxidase tracing and a pharmacohistochemical method for gamma-aminobutyric acid transaminase

The pharmacohistochemical neuronal staining method for gamma-aminobutyric transaminase (GABA-T) combined with retrograde horseradish peroxidase (HRP) staining was used to define more precisely the descending striatonigral and pallidonigral pathways. Previous studies have established that GABA-T intensive cells in the basal ganglia and other structures correspond with reported glutamic acid decarboxylase (GAD)-containing cells and are therefore presumed to use GABA as their neurotransmitter. Following injection of HRP into the substantia nigra, many HRP-labeled cells were detected in the caudate-putamen and globus pallidus. Two separate groups of cells were doubly labeled for GABA-T and HRP and seemed to represent two distinct GABA-T-rich descending pathways to the substantia nigra. One component came from medium-sized cells in the lateral aspect of the globus pallidus. It represented a majority of all descending cells from that nucleus. The other came from the lateral aspect of the caudate-putamen and represented only a minority of descending cells from that structure. These data suggest that the majority of striatonigral fibers are non-GABA containing while the majority of pallidonigral fibers are GABA-containing. The precise location of the GABA-T intensive cells making up these two pathways helps to explain much confusing data in the literature on the source of descending GABA fibers to the substantia nigra.

Immunohistochemical demonstration of differential substance P-, met-enkephalin-, and glutamic-acid-decarboxylase-containing cell body and axon distributions in the corpus striatum of the cat

The immunohistochemical localization of neuronal cell bodies and axons reactive for substance P (SP) and methionine-enkephalin (ME) was investigated in the corpus striatum of the adult cat brain and compared with that of glutamate decarboxylase (GAD), synthetic enzyme for gamma-aminobutyric acid. Striatal cell bodies reactive for ME could be identified only in colchicine treated cats, are medium size, ovoid striatal cells, and are found in large numbers in a more or less even distribution throughout the caudate nucleus, putamen, and nucleus accumbens. The striatal region most densely occupied by ME-immunoreactive cells is the ventral and central part of the caudate head. Modest numbers of larger ME-reactive neurons are dispersed throughout the entopeduncular nucleus and the pars reticulata of the substantia nigra. Striatal cells of medium size reactive for SP could be identified, with or without colchicine, in largest numbers in the medial half of the caudal three-fourths of the putamen and in clusters of irregular size and shape in the head of the caudate nucleus. Cells reactive for SP are also common in layer II and the islands of Calleja of the olfactory tubercle. We could not reliably visualize GAD-positive cell bodies in the striatum, even with colchicine treatment; however, they could be seen readily in all pallidal structures such as the globus pallidus, ventral pallidum, entopeduncular nucleus, and substantia nigra. Axons reactive for ME are found mainly in the globus pallidus where they form a dense and even network throughout the nucleus. The globus pallidus is almost devoid of SP reactivity except near its extreme caudal pole. Conversely, SP-immunoreactive axons form dense meshworks in the entopeduncular nucleus and substantia nigra where ME immunoreactivity is minimal. Fewer, but still ample numbers, of SP-reactive axons are present also in the ventral tegmental and retrorubral areas of the midbrain tegmentum and in the ventral pallidum of the basal forebrain, but only sparse ME-reactive axons are present in these areas. This differential distribution of SP- and ME-containing axons in the pallidal and nigral structures stands in contrast to the relatively homogeneous and dense distribution of GAD-containing axons throughout the dorsal and ventral pallidum, entopeduncular nucleus, and substantia nigra.(ABSTRACT TRUNCATED AT 400 WORDS)

Methionine-enkephalin and substance P in the basal ganglia of normals, Parkinson patients, Huntington patients, and schizophrenics. A qualitative immunohistochemical study

The distribution of methionine-enkephalin (ME)-like and substance P (SP)-like immunoreactivity in the basal ganglia of untreated schizophrenics as compared with normal control cases, and untreated Huntington and Parkinson patients was studied using the unlabeled peroxidase-antiperoxidase (PAP) method. ME but not SP was reduced in the pallidum of one of six schizophrenics. The remaining five cases showed no differences to the controls. In contrast, no or only very faint homogeneously distributed ME and SP was found in any part of the basal ganglia in Huntington's disease. In Parkinson's disease, SP immunoreactivity was within normal range.

Retrograde transport of [3H]GABA in the striatotegmental system of the pigeon

The method of retrograde transport of gamma-aminobutyric acid (GABA) injected into the nigral complex of the pigeon was used to determine the transmitter-specificity of the striatotegmental projection system in this species. The results indicate that descending GABAergic projections are derived from the nucleus accumbens (Ac), ventral lobus parolfactorius (LPO) and the ventral paleostriatum (VP). In birds VP is considered comparable to the mammalian ventral pallidum/substantia innominata area. These results are interpreted in terms of the similarities and differences of striatal organization in birds, reptiles and mammals.

Tonically discharging putamen neurons exhibit set-dependent responses

Previous microelectrode recordings in the putamen of monkeys have revealed a class of tonically active neurons without apparent behavioral correlates. The present study shows that such neurons have responses to stimuli that trigger movement but that these responses disappear when motor responses to the stimuli are extinguished. The short latency of the responses (less than for other putamen neurons) suggests that they may play a role in linking conditioned stimuli and responses.

Distribution of substance P and enkephalin-like immunoreactivity in the substantia nigra of rat, cat and monkey

A comparative study of the distribution of substance P (SP) and enkephalin (ENK) immunoreactivity in the substantia nigra (SN) of the rat, cat and squirrel monkey (Saimiri sciureus) was undertaken by means of the indirect immunofluorescence technique. In the rat a dense neuronal network composed of fine fibers displaying SP immunoreactivity is uniformely distributed throughout the rostrocaudal extent of the substantia nigra pars reticulata (SNr) and in the ventral part of substantia nigra pars compacta (SNc). Some coarse SP-positive fibers also occur in SNc. In addition, ENK-immunoreactive fibers are scattered amongst SNc neurons but abound particularly in the caudolateral part of SNr. In cat innumerable fine SP-positive fibers are distributed in SNr according to a pattern similar to that found in rat. ENK-immunoreactive fine fibers are densely packed in the ventromedial part of SNr whereas coarse ENK fibers are scattered in both SNc and SNr but abound particularly in the caudolateral portion of SNr. In monkey fine SP and ENK-immunoreactive fibers occur in very large number in SNr. These two types of fibers are distributed according to a similar but strikingly complex and heterogeneous pattern. In addition, coarse fibers displaying either SP or ENK immunoreactivity are scattered amongst the SNc neurons in monkey. These findings reveal that SP immunoreactive fibers are present in large number and are distributed according to a somewhat similar pattern in rat, cat and monkey. In contrast, the number of ENK-positive fibers and the complexity of their organizational feature in SN increase strikingly from rodent to primate.

Substance P immunoreactivity in the post-mortem parkinsonian brain

The amount of substance P immunoreactivity (SPI) was measured by radioimmunoassay from the cerebral cortex, caudate nucleus, putamen, pallidum, substantia nigra, hypothalamus, nucleus accumbens, amygdala and hippocampus from autopsy brains. The whole material consisted of 42 parkinsonian patients and 31 controls. The amount of SPI was significantly decreased in the substantia nigra of the parkinsonian brain. There was also a significant decrease of SPI in the putamen of those parkinsonian patients, who had not received levoDOPA treatment. The levels of SPI in the other brain regions studied did not show any difference between parkinsonian patients and controls. The results obtained suggest that substance P (SP) may have a role in the pathophysiology of Parkinson's disease.

Effects of thyroid state on serotonin, 5-hydroxyindoleacetic acid and substance P contents in discrete brain nuclei of adult rats

The effects of chemical thyroidectomy produced by propylthiouracil treatment or hyperthyroidism produced by daily injections of thyroxine on the content of serotonin, its metabolite 5-hydroxyindoleacetic acid and of substance P in discrete brain nuclei of adult rats have been studied. Brain nuclei were removed by punches of frozen brain slices. The serotonin and 5-hydroxyindoleacetic acid contents were measured by high performance liquid chromatography with electrochemical detection while substance P was assayed by radioimmunoassay. The serotonin level was significantly increased in 11 nuclei of the hypothyroid and in 12 nuclei of the hyperthyroid rats. The 5-hydroxyindoleacetic acid levels were higher in 16 nuclei of the hypothyroid and 7 nuclei of the hyperthyroid animals. The state of the thyroid gland in adult rats also affected the substance P system but less consistently than the serotonin pathway. Thus, the substance P content in the brain of propylthiouracil-treated animals increased significantly in 4 nuclei while it decreased in the septum lateralis and the striae terminalis. Following the chronic thyroxine injections, the substance P level was increased in the nucleus caudatus putamen and the tractus diagonalis and was decreased in the area ventralis tegmenti. We previously reported that neonatal thyroidectomy caused a general increase of the substance P and serotonin contents in many brain nuclei of young rats. It appears that the effects of chemical thyroidectomy on mature and immature rat brain are different for the substance P system, suggesting that thyroxine plays an important role in the maturation of substance P-containing neurons.

Distribution and origin of bombesin, substance P and somatostatin in cat spinal cord

Bombesin (BN), substance P-(SP) and somatostatin (SRIF) were measured in individual laminae of the cervical, thoracic and lumbar (L) spinal cord of control cats, and in the L6 segment of cats receiving a spinal hemisection (L2) or deafferentation via dorsal rhizotomy at L6, 7, S1. The interlaminar distribution of BN, SP, and SRIF was remarkably similar. Highest concentrations were found in the superficial dorsal horn, and progressively less was found proceeding ventrally. Some intersegmental variations in peptide concentration within a single lamina were found. Dorsal rhizotomy caused a significant decline in BN, SP and SRIF in lamina I-III, therefore all three peptides appear to be contained in dorsal root ganglion cells. Evidence is presented for the existence of ascending BN and SP projections originating in lamina I-III and VII, for a descending SRIF pathway terminating in lamina VIII, and for an ascending BN path in lamina VIII. Dorsal root afferents to lamina VIII influence levels of BN, SP and SRIF.

Pia arachnoid contains substance P originating from trigeminal neurons

Immunoreactive substance P is present in measurable amounts in pia arachnoid from rat, cat, dog and calf. Levels of substance P in this tissue are comparable to those found in peripheral structures receiving innervation from dorsal root or trigeminal ganglia. Separation and measurement of bovine pia-arachnoid extract by reverse phase high performance liquid chromatography and radioimmunoassay reveals a single peak of activity with a retention time identical to that of substance P. Unilateral lesions of the trigeminal ganglia decrease substance P levels within cat pia arachnoid and accompanying blood vessels ipsilaterally by greater than 50%. These data indicate that most of the substance P surrounding pial blood vessels resides within afferent nerve fibres from trigeminal ganglion cells.

The basal ganglia in extrapyramidal dysfunction

The rapid advances in knowledge of basal ganglia circuitry and function in recent years have allowed the construction of a functional scheme to explain many facets of known pathologic states. The dichotomy of Parkinson's disease; akinesia with increased tone, and the mirror effects in Huntington's disease; hemiballismus and tardive dyskinesia, hyperkinesia with decreased tone are explained as due to two outputs of the system with an intervening inhibitory neuron which reverses the sign. The two outputs control different motor functions; pallidothalamic involved primarily with movements and nigrobrainstem involved primarily with muscle tone.

The islands of Calleja complex of rat basal forebrain. III. Histochemical evidence for a striatopallidal system

The characteristics of the islands of Calleja complex (ICC) in the basal forebrain of the rat were studied with immunohistochemistry, histofluorescence, acetylcholinesterase staining, India ink vascular perfusions, electron microscopy, and steroid autoradiography. The ICC contains clusters of granule cells and associated medium-sized and large cells in the surrounding neuropil of the olfactory tubercle and septum-nucleus accumbens interface. The ICCs were found to contain monoamine fibers (dopamine and norepinephrine), neuroactive peptide fibers (leu-enkephalin, met-enkephalin, substance P, cholecystokinin, luteinizing hormone-releasing hormone), acetylcholinesterase-containing somata and dendrites, and medium-sized and large cells that concentrate [3H] estradiol. The specific overlap and combination of putative neurotransmitters in separate compartments of the ICC suggest that these structures contain striatum- and pallidumlike components. Striatumlike regions are defined as the zone in the rim regions of the ICC and are innervated predominantly by dopamine and cholecystokinin inputs. Pallidumlike regions are defined as the synaptic zone near the medium-sized and large cells of the cap and core regions of the ICC and they are innervated predominantly by enkephalin, substance P, and gamma aminobutyric acid inputs. The morphology, connections, and neurotransmitter relationships of the ICC, therefore, resemble classical striatopallidal systems. The additional presence of substances involved in the reproductive neuroendocrine systems (luteinizing hormone-releasing hormone, estradiol-binding cells, especially in the medial ICC, suggest that some ICC are involved in an endocrine corticostriatopallidal system. These endocrine systems resemble other neocortically and allocortically originating corticostriatopallidal systems in terms of their cell types, connections, and neurotransmitter systems. A functional role for the ICC in extrapyramidal motor systems is proposed.

The functional role of the nucleus accumbens in the control of the substantia nigra: electrophysiological investigations in intact and striatum-globus pallidus lesioned rats

The effects of electrical stimulation of the nucleus accumbens on the activity of identified substantia nigra neurons were studied in intact and lesioned rats. The latter had both the caudate-putamen complex and globus pallidus destroyed by electrolytic lesions. In intact rats a total of 42 of 107 neurons (39.2%) responded to stimulation of the nucleus accumbens. Of the 107 neurons 32 (29.8%) were inhibited and 10 (9.4%) were excited. Pure short inhibitions, long latency inhibitions and excitations followed by inhibition were found in both parts of the substantia nigra. Pure long lasting inhibitions were determined on pars compacta cells only. In lesioned animals, in which the coactivation of striatal and/or cortical fibers traversing the accumbens region was avoided, the percentage of responsive neurons decreased to 20% (23/115). The predominant responses recorded in this situation were pure inhibitions of pars compacta cells (14/46) and long latency inhibitions of pars reticulata neurons (7/69). No pure excitation or excitation-inhibition sequence was recorded. In the two sets of experiments 5 cells were activated antidromically from the nucleus accumbens. The results provide electrophysiological evidence for an inhibitory pathway from the nucleus accumbens to the substantia nigra. The low percentage of responsive neurons, the lack of excitatory responses, the paucity of reciprocal connections and the different inhibitory effects on the two populations of nigral neurons demonstrate that the functional role of the nucleus accumbens in controlling the substantia nigra differs from that exerted by the striatum.

A theory of the functional organization of the neostriatum and the neostriatal control of voluntary movement

A theory of the intrinsic, functional organization of the neostriatum and the neostriatal control of voluntary movement is presented. The cell types of neostriatum are described in accordance with the classification scheme of Pasik, Pasik and DiFiglia (ref. 204) and their suspected neurotransmitters are identified. The functional relations between the afferent projections to neostriatum and the intrinsic elements of neostriatum are described. A division of the neostriatal efferents into two functional cell systems is conceived, in which one efferent system, the Spiny I cell matrix, is thought to be represented by a lateral inhibitory network comprised of the common Spiny I neurons which inhibit their targets, while another is termed the Spiny II cell cluster and consists of the far less numerous excitatory efferents of neostriatum (the Spiny II cells) and is represented by clusters of neurons, the members of each cluster consisting of one excitatory efferent neuron and three interneurons. The implications of this view for neostriatal input--output relations are discussed, and the theory is developed by reference to a variety of converging lines of empirical evidence, and is used to interpret the effects of various pharmacologic strategies which have been employed to achieve symptom management in disorders of voluntary movement. In the course of this review, there emerges an integrative theory of the principles governing the neostriatal control of voluntary movement.

The transsynaptic regulation of the septal-hippocampal cholinergic neurons

There is not yet a complete understanding of the functional interactions among various septal nuclei which regulate hippocampal function. Nevertheless, much has been learned histologically and biochemically about the major connections of the distinct areas of the septal complex and the chemical character of some of these pathways. The cholinergic septal-hippocampal pathway serves as a well defined link between these two important structures of the limbic system. Acetylcholine turnover rates in the hippocampus have been shown to increase or decrease proportionally to the activity of the cholinergic neurons originating in the septum. Moreover, these turnover rates have been shown to be modulated by intraseptal injections of agonists or antagonists of various neurotransmitters or neuromodulators which are stored in various cell groups located in the septum. By coupling this biochemical approach with techniques to study the receptor organization, greater detail concerning the transmitter and cotransmitter interactions among the various neuromodulators can be obtained.

Distribution of substance P-like immunoreactivity in the lower brainstem of the human fetus: an immunohistochemical study

The regional distribution of substance P-like immunoreactive (SPI) structures in the lower brainstem of the human fetus was investigated using the indirect immunofluorescence technique. SPI cells were found in a number of areas including the inferior colliculus, central gray matter of the midbrain, n. laterodorsalis tegmenti, midbrain and medullary reticular formation, n. vestibularis inferior, and n. prepositus hypoglossi. An extensive network of SPI fibers of varying densities were identified throughout the lower brainstem.

Postnatal ontogeny of evoked neuronal responses in the substantia nigra of the cat

Single unit extracellular responses evoked by striatal, cortical, and somatosensory stimulation were recorded in substantia nigra (SN) neurons of kittens (1-70 days of postnatal age) and adult cats. Neuronal responses to stimulation of each site were obtained throughout postnatal development. However, 4 major developmental shifts in the response of neurons were found: (1) the responsiveness of neurons to orthodromic activation increased with age; (2) the signs of the initial responses of neurons to orthodromic activation increased with age; (2) the signs of the initial responses of neurons to caudate and cortical stimulation changed with age (excitatory and inhibitory responses in kittens vs almost entirely inhibitory responses in adults); (3) the the response latencies of neurons decreased with age; (4) nigral neurons that were activated antidromically by stimulation of nigrostriatal axons showed age-related decreases in refractory periods and increases in conduction velocities.

Experimental and immunohistochemical studies on the cerebellar substance P of the rat: localization, postnatal ontogeny and ways of entry to the cerebellum

With the indirect immunofluorescence technique, the localization (including the postnatal ontogeny) of substance P in the cerebellum, and the ways of entry of substance P-containing fibers into the cerebellum were explored. In the newborn rat cerebellum, dense fiber bands of axons with substance P-like immunoreactivity which can be traced to the lower brain stem are found. These fibers are also traceable to the developing granular cell layer. Two weeks after birth, however, substance P-containing structures seen in the cerebellum begin to decrease progressively and in the cerebellum of the adult rats, only a small amount of substance P-containing structures is observed. The present study established that substance P-containing fibers are mostly derived from extracerebellar substance P-containing cells and demonstrated the presence of three sites of entry of these substance P-containing fibers to the cerebellum, via (1) the inferior cerebellar peduncle, (2) the fasciculus uncinatus and (3) the middle cerebellar peduncle, respectively. Following deafferentation of the cerebellum, substance P-accumulating fibers are observed only ventral to the lesion (i.e. on the brain stem side), while in the cerebellum a remarkable decrease of substance P-containing fibers is seen and no substance P-accumulating fibers are found dorsal to the lesion (cerebellar side).

A study of the connections of nociceptive substantia nigra neurones

(i) Of 226 spontaneously active neurones recorded from the substantia nigra (SN) of rats anaesthetised with halothane, 112 (50%) were found to be nociceptive. (ii) Nociceptive neurones were located in both the zona compacta (ZC) and zona reticulata (ZR) compartments of the SN. (iii) Using the collision-test technique it has been shown that approximately equal proportions of nociceptive and non-nociceptive SN neurones project to the thalamus. The majority of nigrostriatal neurones were found to be non-nociceptive. In contrast striatonigral and amygdalonigral afferents are more likely to influence nociceptive than non-nociceptive SN neurones. (iv) Experiments were performed to determine whether nociceptive SN neurones were dopaminergic. Examination of spontaneous firing rate, action potential configuration and responses to systemically administered dopaminomimetic agents of histologically identified SN neurones did not allow a reliable distinction to be made between dopaminergic and non-dopaminergic neurones. It was therefore not possible to resolve this question.

Ontogeny of substance P-containing neuron system of the rat: immunohistochemical analysis--I. Forebrain and upper brain stem

The ontogeny of substance P-containing neuron system in the forebrain and upper brain stem of the rat was investigated by means of the indirect immunofluorescence technique. Substance P-positive structures first appeared in the primordium of the epithalamus and the area which surrounded the commissura posterior of the rat fetus corresponding to gestational day 14 (10-12 mm embryos). On and after gestational day 14, substance P-positive structures gradually made their appearance in various areas of the forebrain and upper brain stem. Substance P-positive structures thus continued to increase in number and in density during the fetus and perinatal stage and showed histochemically maximum content at the stage between postnatal days 5 and 15. After then, substance P-positive neurons tended to decrease in number as the rats grew, while substance P-positive fibers maintained in general their strong immunoreactivity even in the adult rats. The present study demonstrates that substance P-positive structures appear at a very early ontogenetical stage. This suggests that substance P might play an important role in the development of the forebrain and upper brain stem in addition to its neurotransmitter or neuromodulator functions.

Spinal neurons mediate return of substance P following deafferentation of cat spinal cord

Deafferentation of the cat dorsal horn by complete unilateral lumbosacral dorsal rhizotomy produces a loss and subsequent partial recovery of substance P (SP) immunoreactivity as visualized by the peroxidase-antiperoxidase technique. The present experiments aimed to determine whether this return of SP represents a generalized response of all fiber systems afferent to the denervated segments or a more selective response of a specific spinal system. Although a contribution from other sources cannot be excluded by this qualitative immunocytochemical technique, several observations indicate that the return of SP staining depends on interneurons which contain SP immunoreactivity: (1) the amount of SP staining in the chronically deafferented dorsal horn deprived of extrinsic fiber systems is comparable to that seen after deafferentation alone; (2) SP-containing neurons are present within the lumbar segments; and (3) destruction of lumbar neurons by the intraspinal injection of kainic acid abolishes SP staining from the chronically deafferented dorsal horn. From these observations it would appear that the anatomical plasticity of SP-containing fibers in the deafferented dorsal horn is due to the response of a particular system rather than to a generalized response of all systems which terminate there.

Kainic acid-induced changes of serotonin and dopamine metabolism in the striatum and substantia nigra of the rat

Levels of the putative neurotransmitters serotonin (5-HT) and dopamine (DA) and their respective metabolites 5-hydroxyindoleacetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC) was determined in the rat striatum after unilateral intrastriatal injection of the convulsive neurotoxin kainic acid. Two days after intrastriatal kainic acid injection, levels of the 5-HT metabolite 5-HIAA were increased by abut 200% in the injected striatum and by about 150% in the contralateral striatum. An elevated striatal 5-HIAA content was still detectable 10 days after the kainate lesion, but approached normal values 10 weeks after the injection of the neurotoxin. Two days after the lesion, but not at the other time intervals, a moderate increase of 5-HIAA also occurred bilaterally in other brain areas such as the substantia nigra, frontal cortex and hypothalamus. Levels of 5-HT were decreased significantly in the injected striatum 2 days after the intrastriatal application of kainic acid and increased by about 40% after 10 weeks. The 5-HT concentration in the contralateral striatum or in the three other brain areas examined was unchanged at all time intervals. Levels of the DA metabolite DOPAC and DA turnover were increased in the lesioned striatum 2 days after kainic acid injection; concomitantly the DOPAC level was increased in the substantia nigra of the contralateral side. DOPAC levels of the contralateral striatum were unchanged or slightly reduced 2 days after the injection. Ten days as well as 10 weeks after the lesion there was a slightly increased DOPAC concentration in both striata. The levels of DA were not altered at any time interval after the injection of kainic acid.

A substance P projection to the hippocampus

Electrolytic lesions of the septal area in the rat resulted in a major decrease in the activity of choline acetyltransferase in the hippocampus, consistent with the interruption of the septo-hippocampal cholinergic pathway. These lesions also significantly decreased the levels of substance P in the hippocampus. It is suggested that a substance P projection to the hippocampus arises in or passes through the septal area.

Reduction in basal ganglia and substantia nigra substance P levels in Huntington's disease

Substance P (SP) levels were determined by radioimmunoassay (RIA) in several regions of post-mortem brain of controls and Huntington's disease (HD) patients. In controls, highest SP levels were found in basal ganglia, substantia nigra and hypothalamus. Nigral pars reticulata contained 3--4-fold higher levels than pars compacta. In HD, SP levels were reduced in all basal ganglia and substantia nigra. The reductions ranged from 48% in caudate nucleus to over 90% in nigral pars reticulata. There were no changes in SP levels in HD frontal cortex, thalamus or hypothalamus.

Neuropeptides in striato-nigral pathways

The existence of a neuronal pathway containing Leu-enkephalin and connecting the neostriatum with the globus pallidus has been confirmed combining immunohistochemistry with microinjections of neurotoxic agents (kainic acid, colchicine) and discrete knife lesions. The presence of substance P in nerve terminals of the substantia nigra was demonstrated by the application of a monoclonal antibody against this peptide. Electron microscopic studies revealed immunoreactive sites for substance P in nerve terminals establishing symmetric and asymmetric synapses, mainly over dendritic profiles. The possible peptide-containing neuronal pathways in the nigro-striatal system are discussed.

Elevation of substance P-like immunoreactivity in rat central nervous system by protease inhibitors

Several substance P-rich areas in rat CNS had increased levels of substance P-like immunoreactivity following the intraventricular injection of the protease inhibitors SQ 20881, SQ 14225, and leupeptin. There were significant differences in response patterns from region to region, possibly on account of an interaction of anatomical, biochemical, or physiological variables. Although the compound SQ 14225 appeared to be the most potent of the inhibitors examined, it had no apparent effect on CNS substance P-like immunoreactivity when administered peripherally.

Anterograde and transsynaptic degeneration 'en cascade' in basal ganglia induced by intrastriatal injection of kainic acid: an animal analogue of Huntington's disease

Damage of striatal neurons by kainic acid (KA) induces an anterograde and transsynaptic degeneration 'en cascade' in the globus pallidus (GP) and substantia nigra (SN). By causing only degeneration of projections arising from KA-sensitive striatal neurons while sparing the connections of KA-resistant striatal neurons, the lesion-induced alterations of the basal ganglia show a characteristic pattern which bears a close resemblance with the neuropathological changes occurring in Huntington's disease: (1) severe degeneration of small and medium-sized striatal neurons, of pallidal neurons and the neurons of the pars reticulata of the SN, and (2) sparing of large striatal neurons, 'peripallidal' (nucleus basalis) neurons and neurons of the pars compacta of the SN. The probable interconnections of both the degenerated and the spared neuronal groups are discussed with respect to the present concept of the neuronal organization and biochemical neuroanatomy of the basal ganglia.

Neurotransmitters contained in the efferents of the striatum

The transmitters contained in the efferent projections of the striatum were studied by producing two types of lesions: coronal hemitransections just anterior to the globus pallidus, and semi-circular knife cuts that isolated a considerable portion of the globus pallidus from the striatum to produce 'GP islands'. The levels of substance P and Met-enkephalin in the globus pallidus, entopeduncular nucleus and substantia nigra were measured after these lesions. For comparison, the effect of these lesions on glutamic acid decarboxylase (GAD) and choline acetyltransferase (CAT) in some of these projection areas of the striatum was assessed. Both lesions caused similar reductions in substance P levels in each of the three striatal projection areas. In contrast, hemitransections reduced Met-enkephalin levels only in the globus pallidus. Both lesions reduced pallidal and entopeduncular GAD activity while nigral GAD activity was reduced only by the hemitransections. CAT activity was reduced in the globus pallidus by both lesions but was unaltered in the entopeduncular nucleus. However, additional experiments ruled out the existence of a striato-pallidal cholinergic projection. GAD activity and Met-enkephalin levels were significantly increased in the striatum anterior to the lesions. In contrast, CAT activity and substance P levels did not change in this region. The results support and broaden emerging view of the organization of the neurons containing the various transmitter candidates of the efferent projections of the striatum.

Selective retrograde labeling indicating the transmitter of neuronal pathways

A number of tritiated transmitter related compounds-amino acids and biogenic amines-were injected into the rat caudoputamen or substantia nigra in order to test (1) for the occurence of autoradiographic perikaryal labeling, (2) for a selectivity of perikaryal labeling relating certain compounds to certain pathways, and (3) for the relation of perikaryal labeling to known transmitter specificitites of the systems involved. Perikaryal labeling was observed after injection of some but not all of the substances used and was best explained by retrograde labeling in pathways projecting to the injection sites. Six hours after injection of high concentrations of tritiated transmitter into the terminal area, perikaryal labeling was observed: (A) in substantial nigra compacta (A9), A10 (rostral) and A8 (all heavy), and in n. raphe dorsalis (light) after [3H]-dopamine and [3H]-norepinephrine injection into caudoputamen; (B) same pattern as in A, but heavy in n. raphe dorsalis after [3H]-serotonin injection into caudoputamen; perikaryal labeling absent in cortex and thalamus after injection of substances mentioned in A and B; (C) only in substantia nigra compacta (minimally) after [3H]-GABA injection into caudoputamen; (D) in cerebral cortex and thalamus but not in substantia nigra, A10, A8, nor in n. raphe dorsalis after injection of [3H]-D-aspartate into caudoputamen; (E) in the rat caudoputamen but not in n. raphe dorsalis after [3H]-GABA injection into substantia nigra; (F) in n. raphe dorsalis but not in caudoputamen after [3H]-serotonin into substantia nigra. These results indicated, indeed, a certain selectivity-partly related to transmitter specificity-for perikaryal labeling patterns. As a method, transmitter specific retrograde tracing could be useful in pathways with dopamine-, serotonin-, and GABA-mediated synaptic transmission.