Distribution of putative neurotransmitters in the neocortex

The treatment of late luteal phase dysphoric disorder

This mini-review provides a comprehensive discussion of the management of the late luteal phase dysphoric disorder (LLPDD). The various treatments will be described with particular attention to their efficacy and the nature of side effects. These include: psychoactive drugs (lithium, anxiolytics, antidepressants), nutritional agents (L-tryptophan, Vitamin B6, prostaglandins precursors and inhibitors), dopamine agonists, diuretics, antihypertensives, hormonal interventions (gonadotrophin releasing hormone analogues, oestradiol, tamoxifen, progesterone, danazol, and oral contraceptives). Less attention has been given to non-pharmacologic approaches such as diet, exercise and psychotherapy. The availability of an operational definition of LLPDD in the DSM-III-R and the improvement in research methodology has provided a clearer direction for clinical management and for future investigations.

Excitatory amino acid transmitters and their receptors in neural circuits of the cerebral neocortex

In 1954, L-glutamate (Glu) and L-aspartate (Asp) were first suggested as being excitatory synaptic transmitters in the cerebral cortex. Since then, evidence has mounted steadily in favor of the view that Glu and Asp are major excitatory transmitters in the neocortex. Many of the experimental studies which reported how Glu/Asp came to satisfy the criteria for transmitters in the neocortex are reviewed here, according to the methods employed. Since the question of which particular synaptic sites in cortical neural circuits Glu/Asp operate as excitatory transmitters has not previously been reviewed, particular attention is given to efferent, afferent and intrinsic neural circuits of the visual and somatosensory cortices, where circuitry is relatively clearly delineated. Recent studies using chemical assays of released amino acids, high-affinity uptake mechanisms of Glu/Asp from nerve terminals, the direct micro-iontophoretic administration of Glu/Asp antagonists, and immunocytochemical techniques have demonstrated that almost all corticofugal efferent projections employ Glu/Asp as excitatory synaptic transmitters. Evidence indicating that thalamocortical afferent projections, including geniculocortical projections and some intrinsic connections are glutamatergic, is also reviewed. Thus, the results highlighted here indicate that the main framework of neocortical circuitry is operated by Glu/Asp. Pharmacological studies indicate that synaptic receptors for Glu/Asp can be classified into a few subtypes, including N-methyl-D-aspartate (NMDA) and quisqualate/kainate (non-NMDA) types. Some evidence indicating the sites of operation of NMDA and non-NMDA receptors in neocortical circuitry is reviewed, and the distinct, functional significance of these two types of Glu/Asp receptors in information processing in the neocortex is proposed.

Distribution of choline acetyltransferase and acetylcholinesterase in the vocal motor system of zebra finches

The distribution of choline acetyltransferase immunoreactivity (ChAT-IR) was surveyed in the vocal motor system of adult male and female zebra finches and was compared with the pattern of histochemical acetylcholinesterase (AChE-His). In the vocal motor system the most prominent accumulation of ChAT-IR somata was found in lobus parolfactorius (LPO) including Area X. Immunoreactive neuropil was found to be concentrated in pericellular networks of fibers in male's Area X while the corresponding area in females could not be demarcated within the LPO. The density of ChAT-IR fiber networks was much higher in LPO, paleostriatum augmentatum and in a shelf region around nucleus robustus archistriatalis (RA) than in neostriatal and hyperstriatal parts of the telencephalon. AChE positive neurons and neuropil were observed in all ChAT-IR regions and, in addition, in the vocal motor nuclei nucleus hyperstriatum ventrale pars caudalis (HVc), nucleus magnocellularis in the anterior neostriatum (MAN), nucleus interfacialis (NIF) and RA. However, none of the latter nuclei contained ChAT-IR cell bodies. They were characterized by rare ChAT-IR neuropil. MAN and RA exhibited shelf regions with a higher degree of stained fibers. The discrepancy between the localization of AChE-His and ChAT-IR can hardly be explained by different classes of ChAT isoenzymes in neurons within the basal forebrain and the neostriatal, hyperstriatal and archistriatal vocal control nuclei not detected by our antibody. On the other hand, vocal control centers while receiving cholinergic inputs, might - except for Area X - not possess cholinergic efferent projections within the telencephalon.

Excitatory transmitter amino acid-containing neurons in the rat visual cortex: a light and electron microscopic immunocytochemical study

The distribution and morphology of neurons labelled with antisera to glutamate or aspartate were examined, at the light and electron microscope levels, in the rat visual cortex. Using widely accepted light microscopic features as well as well-established nuclear, cytoplasmic, and synaptic criteria, we noted that glutamate-immunoreactive neurons were pyramidal cells distributed in layers II-VI, with an increased concentration in layers II and III. Aspartate immunoreactivity was localized chiefly to pyramidal neurons in layers II-VI. However, approximately 10% of immunolabeled cells were nonpyramidal neurons scattered throughout the cortex. Cell-body measurements revealed that, for both groups of neurons, layer V contained the largest labelled neurons, whereas layers IV and VI contained the smallest. Furthermore, in every layer, aspartate-stained neurons were larger than glutamate-positive cells. Finally, glutamate- and aspartate-labelled axon terminals formed asymmetrical synapses, which are presumably excitatory in nature, primarily with dendritic spines. These findings, together with recent detailed studies of the projections of glutamate- and aspartate-labelled cortical neurons, may provide essential background information for studies aimed to elucidate the function(s) of excitatory amino acids in the cortex and their role in pathological conditions.

Characterization of acute N-ethyl-3,4-methylenedioxyamphetamine (MDE) action on the central serotonergic system

The effect of N-ethyl-3,4-methylenedioxyamphetamine (MDE) on the central serotonergic system was studied. Within 1 hr after administration of MDE (10 mg/kg), the concentration of 5-hydroxytryptamine (5-HT) and the activity of tryptophan hydroxylase (TPH) had declined significantly in the hippocampus but returned to control within 12 hr. Hippocampal 5-hydroxyindoleacetic acid (5-HIAA) content decreased within 2 hr, rebounded to 22% above control by 12 hr, and returned to control by 24 hr. Blockade of the 5-HT uptake carrier with fluoxetine (10 mg/kg) prevented or attenuated the MDE-induced changes in 5-HT content and TPH activity, except for neostriatal TPH activity which remained unresponsive to the fluoxetine treatment. The MDE-induced decline in TPH activity could be reversed by incubating the TPH preparation with dithiothreitol and Fe2+ under nitrogen for 24 hr. This suggests that the loss in TPH activity induced by MDE results from an alteration of the oxidation-reduction state of a sulfhydryl group located on the enzyme. The inhibition of monoamine oxidase (MAO) by the administration of pargyline (75 mg/kg) failed to protect the neostriatal TPH activity from the MDE-induced decline while potentiating the MDE-induced decrease in cortical TPH activity. This suggests that H2O2 generated by MAO in vivo is not responsible for oxidation of the sulfhydryl site located on TPH during the MDE treatment.

Brainstem auditory evoked potentials in patients with multi-infarct dementia and dementia of the Alzheimer type

Brainstem auditory evoked potentials (BAEPs) were recorded in 25 patients with multi-infarct dementia (MID) (mean age 71.2 years), 16 patients with dementia of the Alzheimer type (DAT) (mean age 70.6 years), and 34 normal subjects (mean age 69.1 years). Both MID and DAT patients showed significant prolonged interpeak latencies between waves I and V (I-V IPLs) compared to normal subjects (p less than .001 and p less than .01, respectively). In patients with MID, both I-III IPLs and III-V IPLs were significantly longer than those of normal subjects (p less than .01 and p less than .01 respectively). On the other hand, only III-V IPLs were significantly prolonged in patients with DAT (p less than .01). There were no significant differences between MID and DAT with regard to any of the IPLs. Present results suggest that the brainstem lesions are located in the auditory pathways in patients with MID and DAT. However, with BAEP measurements, we were not able to discriminate between patients with MID and DAT.

Light and electron microscopic immunocytochemical analysis of the dopamine innervation of the rat visual cortex

The dopaminergic innervation of the rat primary (area 17) and secondary (areas 18 and 18a) visual cortical areas was examined immunocytochemically using an antiserum directed against dopamine. This innervation was characterized by the differential density of the respective afferents within individual visual areas. Area 18, especially its rostral part, was observed to receive a considerable amount of dopaminergic axons, whereas areas 17 and 18a were sparsely innervated. The innervation of all layers of area 18 seemed to consist to a considerable extent of axonal branches of radial fibres ascending from layer VI to layer I. At the ultrastructural level, dopamine profiles were found to display similar characteristics in all visual areas. Dopamine labelled axon-terminals and axonal varicosities, examined in single and serial ultrathin sections, were seen to form primarily asymmetrical synaptic contacts with dendritic profiles. These observations suggest a 'specific' innervation of cytoarchitectonically distinct cortical regions by dopaminergic axons.

Amino acid profiles in Long-Evans rat superior colliculus, visual cortex, and inferior colliculus

An ultrasensitive triple-column ion-exchange/fluorometric method was utilized to measure the levels of over 30 amino acids and related primary amino compounds in Long-Evans rat superior colliculus (SC), visual cortex (VC) and inferior colliculus (IC). Comparison of levels of amino compounds revealed distinctly different profiles for each region. Major constituents were the neurotransmitters and related compounds glutamate, glutamine, GABA, taurine, aspartate and glycine. Glutathione levels were also relatively high in all three regions. SC exhibited a significantly higher level of GABA and beta-alanine compared to both VC and IC. VC had significantly higher levels of glutamate and taurine. VC exhibited the lowest level of glycine and IC the highest. A time-course experiment using SC documented that levels of eleven of thirty-four compounds, including GABA, were subject to significant postmortem alteration in vitro. SC GABA stability experiments indicated that significant in vitro increases of free GABA levels between 1 and 4 min postmortem were associated with equimolar decreases of conjugated GABA levels.

Physiological, morphological, and cytochemical characteristics of a layer 1 neuron in cat striate cortex

We have recorded from a small neuron in layer 1 of the striate visual cortex in a 34-day-old kitten. It had a simple, orientation-selective receptive field that was nondirectional and showed length summation. The neuron was injected intracellularly with horseradish peroxidase. Computer-aided reconstruction revealed that it had a dense axonal plexus confined to layer 1, elongated in the anteroposterior dimension. By means of an antibody directed against a GABA-like antigen, and postembedding immunocytohemistry, the neuron was found to be strongly immunoreactive. The main input to soma and dendrites of the neuron was from synapses that were not GABA-L-immunoreactive, and probably originated from pyramidal cells. The axon of the cell formed synapses on dendritic shafts and spines, whose most likely sources were the apical tufts of pyramidal cell dendrites. These data suggest that such neurons may be involved in local circuits that contribute to the formation of pyramidal cell receptive fields.

Selective labeling of visual corpus callosum connections with aspartate in cat and rat

Tritiated neurotransmitter candidates were unilaterally injected in visual cortical regions with abundant corpus callosum connections. D-aspartate (Asp) or gamma-aminobutyric acid (GABA) was injected along the area 17/18 border in cat, and the area 17/18a and 17/18b borders in rat. Retrograde Asp label was found contralaterally in supragranular and infragranular laminae in areas 17, 18, 19, PMLS, and PLLS in cat, and in areas 29, 18b, 17, and 18a in rat. No contralateral GABA label was found in cat or rat. Thus, the cat and rat corpus callosum may use Asp or a related substance as a neurotransmitter.

Biochemical mapping of cholecystokinin-, substance P-, [Met]enkephalin-, [Leu]enkephalin- and dynorphin A (1-8)-like immunoreactivities in the human cerebral cortex

The distribution of immunoreactive cholecystokinin, substance P, [Met]enkephalin, [Leu]-enkephalin and dynorphin was determined in the cerebral cortex of the human brain post mortem. Peptide radioimmunoassays in three selected zones of the cortical gray mantle (frontal, temporal, occipital) revealed significant regional differences, prompting to the development of a new dissection procedure for the complete mapping of peptide-like materials throughout the entire cerebral cortex. For this purpose, frozen cerebral hemispheres were cut rostrocaudally in 21 verticofrontal serial sections, from which the cortical gray matter was divided into 4-5 distinct zones. The peptides could be measured in each of the 93 dissected pieces of tissue, but their distribution was uneven. The most abundant was cholecystokinin, particularly in the anterior part of the frontal lobe and in the temporal cortex, where its levels reached 0.5 ng/mg of tissue. The regional distribution of cholecystokinin resembled that of substance P with a decreasing gradient from the frontal to the occipital pole, but absolute levels of substance P were hardly one tenth of cholecystokinin levels. The mean concentrations of the three opioid peptides were even less than those of substance P, and their regional distributions were markedly different. [Met]Enkephalin was concentrated in the occipital cortex, and [Leu]enkephalin in the temporal cortex. Dynorphin was the least abundant, even in the temporal cortex where the highest levels were found. The widespread and heterogeneous distribution of these peptides strongly suggests that each of them exerts specific functions in the human cerebral cortex.

Effects of dopaminergic and serotonergic receptor blockade on neurochemical changes induced by acute administration of methamphetamine and 3,4-methylenedioxymethamphetamine

As dopamine (DA) causes neurochemical changes in the central serotonergic system after an acute injection of methamphetamine, the present study examined the possibility that this response is mediated through dopaminergic receptors. Pretreatment with the DA receptor antagonist, haloperidol, failed to prevent the decreases in the activity of tryptophan hydroxylase and the concentration of serotonin (5-HT) in the frontal cortex, hippocampus and neostriatum 1 hr after a single administration of methamphetamine. Because methamphetamine is also a potent releaser of 5-HT, the possibility that 5-HT receptors mediate the effects of methamphetamine was evaluated. Pretreatment with methiothepin an antagonist of both DA and 5-HT receptors, failed to prevent the decline in activity of tryptophan hydroxylase but did attenuate the decreases in concentrations of 5-HT measured in the frontal cortex and hippocampus. This attenuation is not mediated through 5-HT2 receptors, as ritanserin failed to interfere with the changes induced by methamphetamine. In addition, DA or 5-HT receptors were apparently not involved in the changes in activity of tryptophan hydroxylase and concentrations of 5-HT induced by another analogue of amphetamine, 3,4-methylenedioxymethamphetamine (MDMA). This study suggests different mechanisms are responsible for the acute and long-term changes observed in the central serotonergic system following a single or multiple doses of methamphetamine.

Peptides and self-stimulation of the medial prefrontal cortex in the rat: effects of intracerebral microinjections of substance P and cholecystokinin

The effects of intracerebral microinjections of substance P and cholecystokinin on self-stimulation of the medial prefrontal cortex of the rat were studied. Intracerebroventricular administration of substance P at doses of 2.5, 5, 10 and 20 micrograms produced a dose-related decrease in self-stimulation of the medial prefrontal cortex; spontaneous motor activity, measured as a control, was not affected. Unilateral microinjections into the medial prefrontal cortex of substance P at doses of 10 and 20 micrograms produced a decrease of self-stimulation of the ipsilateral side, but self-stimulation of the contralateral cortex, used as a control, was not affected. On the contrary, cholecystokinin in both intracerebroventricular administration at doses of 100, 200 and 400 ng, or intracortical microinjections into the medial prefrontal cortex at doses of 200, 400 and 800 ng, had no effect on self-stimulation of this cortical area. These results suggest that substance P, but not cholecystokinin, could be part of the neurochemical substrate underlying self-stimulation of the medial prefrontal cortex in the rat.

Types and distribution of glutamic acid decarboxylase (GAD)-immunoreactive neurons in mouse motor cortex

Neuronal structures in mouse motor cortex that contain gamma-aminobutyric acid (GABA), were identified by an immunocytochemical method, using an antiserum to glutamic acid decarboxylase (GAD). GAD-positive cell bodies occurred in all layers of the motor cortex, but were more concentrated in layers III and VI. GAD-positive puncta, presumably axon terminals, were also distributed throughout the cortical layers; a high density of puncta occurred in layer III, whereas a somewhat lower density characterized layer VI. Based on the shapes of their somata and dendritic trees we concluded that all GAD-positive cells were of the non-pyramidal type.

Immunocytochemical localization of glutamate decarboxylase in the rat basolateral amygdaloid nucleus, with special reference to GABAergic innervation of amygdalostriatal projection neurons

Glutamate decarboxylase (GAD) immunohistochemistry was employed at the light and electron microscopic levels to localize GABAergic structures in the basolateral amygdaloid nucleus (BL). The GAD-immunoreactive (GAD-IR) staining pattern consisted of punctate structures and a morphologically diverse group of GAD-IR neurons. At the electron microscopic level many of these punctate structures were found to make symmetrical synaptic contacts with cell bodies as well as distal parts of unlabeled, presumably projection and nonprojection, neurons. In addition, GAD-immunoreactive neurons were identified in the BL, and they had the ultrastructural characteristics of local circuit or intrinsic neurons and were not retrogradely labeled with HRP following ventral striatal injections. Some of these GAD-immunoreactive neurons were contacted by GABAergic boutons, forming symmetrical synaptic contacts. GABAergic innervation of amygdaloid projection neurons in the BL was identified by combining GAD immunohistochemistry with Golgi impregnation and retrograde tracing of horseradish peroxidase (HRP) following injections of the tracer in the olfactory-tubercle-related parts of the ventral striatum. Amygdalostriatal projection neurons in the BL were observed to be in continuity with neurons in the piriform cortex which project to the ventral striatum. The results provide direct evidence for the presence of GAD-IR boutons in the BL making synaptic contacts with identified amygdalostriatal projection neurons. The present study provides direct anatomical evidence for the physiological observation that GABA exhibits a powerful regulation of the amygdaloid projection neurons in the BL and lends further support to the concept of a corticallike functional organization of the basolateral amygdala.

Neuronal and endothelial sites of acetylcholine synthesis and release associated with microvessels in rat cerebral cortex: ultrastructural and neurochemical studies

We sought to establish what proportion of the cholinergic innervation of the cerebral cortex (CX) is associated with intraparenchymal blood vessels by using immunocytochemical and neurochemical techniques, and whether [3H]acetylcholine ([3H]ACh) is synthesized and released by elements associated with cortical microvessels (MV). MVs and, for comparison, tissue homogenates were prepared using sucrose gradient/differential ultracentrifugation methods. Efficacy of the separation technique was indicated by the activity of gamma-glutamyltranspeptidase (up to 29.2-fold enrichment), an endothelial cell marker enzyme, in the MV fraction and microscopy. The size of isolated microvessels ranged from 5 to 40 micron (o.d.) with 67.7% of the vessels less than 10 micron and 32.2% between 11 and 40 micron (690 vessels measured from 4 animals). By electron microscopy immunoreactive choline acetyltransferase (ChAT), the biosynthetic enzyme for ACh, was localized to: (a) axons and axon terminals opposed to the basal laminae of capillaries and small arterioles, and (b) capillary endothelial cells. ChAT-labeled elements associated with MVs were most prominent in layers I, III and V of the CX consistent with the local pattern of cholinergic innervation. The absolute amount of ACh synthesized (pmol Ach/100 mg wet wt.) by elements associated with cortical MVs was relatively small (2.3% total cortical homogenate activity). Inhibition of MV ChAT activity to 5% of control by the specific ChAT inhibitor, 4-naphthylvinylpyridine, and HPLC analysis of the product, indicated that authentic ACh was measured. Other tissues similarly synthesized small amounts of ACh relative to the CX, caudate nucleus (CN, 2.4%), cerebellum (CRB, 1.4%) and liver (LIV, 3.9%). Consistent with the known extent of the cholinergic innervation of the tissues examined, the rank order of ChAT associated for both MVs and homogenate were: CN greater than CX much greater than CRB greater than LIV. However, based on the specific activities of ChAT, cortical MVs have the remarkable capacity to synthesize ACh at rates 95% greater than cortical (S1 fraction) homogenate (59.0 +/- 3.5 nmol/mg protein/40 min; n = 7), which is enriched in nerve terminals. Except for LV (+11%), other tissues also had remarkably high ChAT activity in MV (% above corresponding homogenate; P less than 0.05, n = 5): CN (+269) and CRB (+313). Release of [3H]ACh from MVs and, for comparison, nerve terminals were graded to K+ depolarization stimulus (5-55 mM), maximal with 55 mM K+ and Ca2+ dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Specific effects of punishment on biogenic monoamine turnover in discrete rat brain regions

Specific effects of punishment on the turnover rates of norepinephrine, dopamine and serotonin (5-HT) in brain regions were investigated in rats exposed to punishment. Two yoked controls were also used in an attempt to separate the non-specific effects of response rate, reinforcement density and direct effects of punisher (foot shock). Punished and unpunished littermate rats had similar response rates, and the reinforcement density was almost identical for both groups. A third group (yoked-shock rats) received food and shock independent of responding whenever these were given to the punished rats. When compared to the unpunished rats, changes in the monoamine turnover rates resulting from the punishment were similar to the effects of yoked-shock with respect to the direction of action in most cases (13 out of 17 changes). These changes may be related to non-specific effects of the shock. Four changes by the punishment were determined to be specific effects of the punishment since the yoked-shock had no effect or changed the turnover to the opposite direction. Among these, increase in 5-HT turnover rate in the frontal cortex (greater than 7-fold) was the largest change. These results and reported effects of drugs which act on serotonergic systems on the punished behavior suggest that the increase in 5-HT neuronal activity in the frontal cortex is involved in the behavioral suppression induced by the punishment.

Methylmercury-induced movement and postural disorders in developing rat: loss of somatostatin-immunoreactive interneurons in the striatum

Tissue concentrations of the neuropeptide somatostatin and the specific activities of glutamic acid decarboxylase (GAD) were measured in several regions of the central nervous system in young rats, following chronic postnatal administration of methylmercuric chloride. By the beginning of the fourth postnatal week, these animals exhibited clinical signs of a mixed spastic/dyskinetic syndrome with visual deficits. At the onset of neurological impairment, a significant decrease in GAD activity was detected in the occipital cortex (48-49%) and striatum (45-50%) when compared to either normal or weight-matched controls. At one subclinical stage of toxicity, decreased GAD activity was detected only in the occipital cortex (29-30%). Tissue levels of somatostatin did not change significantly in the occipital cortex of methylmercury-treated animals at any stage of the experiment. However, somatostatin levels in the striatum were significantly reduced at the onset of neurological impairment (55-57%) and at one subclinical stage of toxicity (49-54%). Immunohistochemistry for somatostatin- and neuropeptide Y-immunoreactive neurons confirmed a marked loss of cells in the dorsolateral region of the striatum with atrophy of the surviving neurons. In the cerebral cortex of methylmercury-treated animals the morphology and distribution of somatostatin-positive neurons appeared normal. In view of the reported co-localization of GAD and somatostatin in some non-pyramidal neurons of the cerebral cortex, these results indicate that methylmercury-induced lesions of the developing cerebral cortex involve a subpopulation of GABAergic neurons which are not co-localized with somatostatin. In the striatum, where GAD and somatostatin are not co-localized within the same neurons, methylmercury-induced lesions involve both GABAergic and somatostatin-positive neurons.

Immunocytochemical detection of GABAergic nerve cells in the human temporal cortex using a direct gamma-aminobutyric acid antiserum

Recently, an immunocytochemical method using glutaraldehyde fixation and an antiserum developed against a GABA--glutaraldehyde--protein conjugate has permitted direct visualization of GABAergic structures in the brains of perfused animals. This paper reports a successful use of this technique on human temporal cortex fixed by immersion. The cerebral tissue was obtained from patients operated for focal epilepsy. GABA-positive somata, fibres and terminals are observed in all layers of the temporal cortex. Terminals are particularly abundant in the superficial portion of layer I and in layers II, III and IV. Dense plexuses of fibres are located in layers II, III, IV and VI and in the underlying white matter. Somata are found in all cortical layers and in the underlying white matter; they are round, oval, fusiform or triangular and exhibit a multipolar, bitufted or bipolar dendritic pattern. This technique for the visualization of GABAergic structures in the human brain may allow a better understanding of the pathogeny of epilepsy in which the GABAergic transmission has been implicated.

A comparison of the localization of choline acetyltransferase and glutamate decarboxylase immunoreactivity in rat cerebral cortex

The neurotransmitter-synthesizing enzymes choline acetyltransferase and glutamate decarboxylase were localized immunocytochemically at the light microscopic level. Their respective laminar distributions were compared in 17 different cytoarchitectural areas, comprising limbic and neocortical regions of rat cerebral cortex. The immunoreactive intensities within these areas were measured with an image analysis system and dark-field optics. Choline acetyltransferase and glutamate decarboxylase immunoreactivity displayed distinctive distribution patterns throughout the cerebrum. In general, limbic cortex showed greater intensity of both choline acetyltransferase and glutamate decarboxylase immunoreactivity than neocortex. For example, choline acetyltransferase immunoreactivity in pyriform and retrosplenial cortex was 54% and 29% greater, respectively, than in neocortex, and glutamate decarboxylase immunoreactivity in the same cortical areas was 5% and 17% greater, respectively. In addition to these regional differences, the marked variations of choline acetyltransferase and glutamate decarboxylase immunostaining were characterized as either coincidental or complementary when comparing their laminar distributions. The laminar pattern and relative intensities of choline acetyltransferase and glutamate decarboxylase immunostaining were coincident in some layers of all cortical regions. For example, both choline acetyltransferase and glutamate decarboxylase immunoreactive intensities were high in cellular layers II and IV of the entorhinal cortex. In contrast, examples of complementary choline acetyltransferase and glutamate decarboxylase immunoreactive patterns were observed in retrosplenial cortex and neocortex. In neocortex, layers III and part of V were intensely glutamate decarboxylase-positive, whereas these same layers were less intensely choline acetyltransferase immunoreactive than the intervening layer IV and upper part of V. Quantitatively, choline acetyltransferase immunoreactivity in layers IV and upper V was 27-37% greater than adjacent layers II and deep V. The glutamate decarboxylase immunostaining pattern was complementary in that layer IV was 19-23% less intensely stained than adjacent layers III and V. Our results demonstrate that terminals immunoreactive for choline acetyltransferase and glutamate decarboxylase, and presumably the synaptic terminals that respectively use acetylcholine or gamma-aminobutyric acid as their neurotransmitters, are distributed in distinct laminar patterns that are strategically situated for modulating either afferent information in the case of cholinergic terminals or efferent transmission for GABAergic endings.(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo analysis of cortical amino acid neurotransmitters collected in the rat by a new double lumen push-pull catheter system

The release of both endogenous and newly synthesized amino acid neurotransmitters was examined simultaneously in different areas of the cerebral cortex in the freely moving rat. An array of push-pull guide tubes was implanted permanently to rest above the frontal, parietal, temporal and occipital areas of the cortex of each rat. Then a new double-lumen catheter system, specially adapted for localized push-pull perfusion of the conscious animal, was used to perfuse an artificial cerebrospinal fluid at each cortical site. For the new synthesis experiments, 0.5 microCi of [14C]glucose in a volume of 2.0 microliter was first microinjected into the perfusion site as a precursor to label amino acids. After the site was perfused at a rate of 12.0 microliter/min, each of the samples was assayed by two-dimensional thin-layer chromatography. In a second analysis, the content of six endogenous amino acids present in unlabeled samples of push-pull perfusate was quantified by high-performance liquid chromatography analysis with electrochemical detection. The results showed a notable homogeneity among each of the four cortical areas in the content of four of the six amino acids examined. Endogenous glutamine exhibited the highest proportional content in the cortical perfusates, whereas glutamic acid was proportionally higher in terms of new synthesis. An anatomical analysis revealed that the level of endogenous glutamic acid in the frontal area was significantly lower than that found in the occipital or temporal regions of the rat's cortex. An opposite result was obtained when the proportional synthesis of glutamic acid from [14C] glucose was compared in different cortical regions in that a statistically higher release occurred in the frontal than in the occipital cortex.

Responses of neurons in somatosensory cortical area II of cats to high-frequency vibratory stimuli during iontophoresis of a GABA antagonist and glutamate

Areas in the second somatic sensory cortex (SII) of cats that responded vigorously to low-amplitude, high-frequency vibratory stimulation were mapped with respect to the surrounding somatotopic organization. Neurons with these properties were found in the posterior and medial parts of the distal forelimb zone and were judged as receiving input from Pacinian mechanoreceptors. The responses of these neurons to sinusoidal vibrotactile stimulation were studied during iontophoretic administration of glutamate or bicuculline methiodide (BMI) to determine if the temporal fidelity of these cortical neurons was controlled by inhibitory circuits that used gamma-aminobutyric acid (GABA) as a neurotransmitter. The data from 19 Pacinian-sensitive neurons were analyzed for changes in the mean firing rate, the percentage of entrainment, and the pattern of periodicity as revealed by autocorrelograms and interval histograms. Iontophoresis of BMI or glutamate caused significant increases in mean firing rates during low- and high-frequency vibratory stimulation. The pattern of increased activity produced by BMI was characterized by a small, yet significant, reduction in the percentage of entrainment, whereas glutamate caused smaller and fewer significant changes in this measure. Analysis of autocorrelation and interval histograms suggested that BMI increased the probability of firing on consecutive stimulus cycles in small segments of the stimulus duration.

Effects of N-ethyl-3,4-methylenedioxyamphetamine (MDE) on central serotonergic and dopaminergic systems of the rat

The influence of N-ethyl-3,4-methylenedioxyamphetamine (MDE) on the central serotonergic and dopaminergic systems of the rat after a single or multiple injections was studied. MDE (10 mg/kg) produced a significant decrease in the concentration of 5-hydroxytryptamine (5-HT) 1 hr later in the frontal cortex and the hippocampus without affecting the concentration of 5-hydroxyindoleacetic acid (5-HIAA) or tryptophan hydroxylase (TPH) activity. Hypothalamic and neostriatal concentrations of 5-HT, 5-HIAA, dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) remained unaffected, as well as the neostriatal TPH and tyrosine hydroxylase (TH) activities. However, 3 hr after the MDE injection, the serotonergic variables including TPH activity were decreased in most of the brain areas examined. The dopaminergic system remained unaffected, except for a significant reduction in neostriatal DOPAC concentrations. The changes in transmitter concentrations after a single injection were dose dependent; the maximum depletion in TPH activity was reached with a 10 mg/kg dose. The administration of multiple doses of MDE caused greater decreases in TPH activity and 5-HT concentrations 3 hr after the treatment than did a single injection; in addition, a partial recovery from multiple administrations occurred by 18 hr. The effects of MDE on DA and its metabolites were transient, and neostriatal TH activity was not altered. This study demonstrates that MDE primarily affects the central serotonergic system, as reported for its congeners 3,4-methylenedioxyamphetamine and 3,4-methylenedioxymethamphetamine. It does, however, produce less neurotoxicity as judged by its lower potency on the dopaminergic and the serotonergic systems as well as the recovery occurring in these systems.

Analysis of peptide histidine-isoleucine/vasoactive intestinal polypeptide-immunoreactive neurons in the central nervous system with special reference to their relation to corticotropin releasing factor- and enkephalin-like immunoreactivities in the paraventricular hypothalamic nucleus

The distribution of peptide histidine-isoleucine (PHI) and vasoactive intestinal polypeptide (VIP), two peptides derived from the same precursor molecule, was analysed with immunohistochemistry in the central nervous system of the rat, and to a limited extent in some other species including sheep, monkey and man. Special attention was focused on possible cross-reactivity between PHI antisera and corticotropin releasing factor in parvocellular neurons in the hypothalamic paraventricular nucleus projecting to the external layer of the median eminence. (1) Characterization of the PHI and VIP antisera revealed that they recognized different sequences of the peptide molecules. One of the PHI antisera (PHI-N), although mainly N-terminally directed, also probably contained an antibody population directed against the C-terminal amino acid in PHI which is an amidated isoleucine. Rat and human corticotropin releasing factor but not ovine also have an amidated isoleucine in C-terminal position. (2) PHI- and VIP-like immunoreactivity were found with parallel and overlapping distribution in all areas investigated in the rat central nervous system. In many cases coexistence of the two immunoreactivities could be directly demonstrated. PHI neurons were found in some areas so far not know to contain PHI/VIP neurons, including the dorsal septum, the septofimbrial nucleus, the stria terminalis and lamina V of the spinal cord. (3) Using an antiserum directed against the amino acid sequence 111-122 of the VIP/PHI precursor, immunoreactive cell bodies were seen in some areas containing VIP and PHI neurons. PHI- and VIP-like immunoreactivity were expressed in parallel in increasing amounts in the superficial laminae of the dorsal horn after transection of the sciatic nerve [G. P. McGregor et al. (1984) Neuroscience 13, 207-216; S. A. S. Shehab and M. E. Atkinson (1984) J. Anat. 139, 725; S. A. S. Shehab and M. E. Atkinson (1986) Expl Brain Res. 62, 422-430]. (5) The PHI-N antiserum stains large numbers of immunoreactive cells in the parvocellular part of the paraventricular nucleus and these cells are mostly identical with corticotropin releasing factor-positive neurons. Absorption experiments suggested that this PHI-N-like immunoreactivity to a large extent represented cross-reactivity with rat CRF and that earlier demonstration of many PHI-positive neurons in the paraventricular nucleus probably represents an artefact as proposed by F. Berkenbosch et al. (Neuroendocrinology 44, 338-346). However, some cells did, in fact, contain VIP- as well as PHI-like immunoreactivity as was shown with antisera not cross-reacting with corticotropin releasing factor.(ABSTRACT TRUNCATED AT 400 WORDS)

Monoamines and metabolites in cortex and subcortical structures: normal regional distribution and the effects of thiamine deficiency in the rat

The present study measured the concentration of monoamines, metabolites and estimates of turnover rate in eighteen separate brain regions from controls and a rat model of Korsakoff's disease induced by a two week bout of pyrithiamine and thiamine deficient diet (PTD). A behaviorally tested control (n = 12) and PTD (n = 17) group, and a non-behaviorally tested PTD group (n = 8) were sacrificed 7 months after recovery from treatment. The brains were dissected into nine cortical areas and nine subcortical regions. In behaviorally tested PTD animals, a significant reduction of NE was observed in entorhinal cortex. Diminished norepinephrine (NE) concentration was also observed in entorhinal, hippocampal, septal and olfactory areas of the non-behaviorally tested PTD group. Serotonin and 5-hydroxyindoleacetic acid (5-HIAA) levels were increased in several brain areas, particularly midbrain-thalamus, striatum, of both groups of recovered PTD animals. These findings are discussed with respect to results and hypotheses presented in our previous study of this animal model. Significant differences in monoamine, metabolite and turnover estimates were also observed among cortical areas of the control animals. Entorhinal cortex contained the highest concentration of NE and 5-hydroxytryptamine (5-HT), while DA was highest in somatosensory cortex. The distribution of 5-HT and 5-HIAA were more homogeneous and displayed a rostral-caudal decline in concentration.

D-[3H]aspartate retrograde labelling of callosal and association neurones of somatosensory areas I and II of cats

Experiments were carried out on cats to ascertain whether corticocortical neurones of somatosensory areas I (SI) and II (SII) could be labelled by retrograde axonal transport of D-[3H]aspartate (D-[3H]Asp). This tritiated enantiomer of the amino acid aspartate is (1) taken up selectively by axon terminals of neurones releasing aspartate and/or glutamate as excitatory neurotransmitter, (2) retrogradely transported and accumulated in perikarya, (3) not metabolized, and (4) visualized by autoradiography. A solution of D-[3H]Asp was injected in eight cats in the trunk and forelimb zones of SI (two cats) or in the forelimb zone of SII (six cats). In order to compare the labelling patterns obtained with D-[3H]Asp with those resulting after injection of a nonselective neuronal tracer, horseradish peroxidase (HRP) was delivered mixed with the radioactive tracer in seven of the eight cats. Furthermore, six additional animals received HRP injections in SI (three cats; trunk and forelimb zones) or SII (three cats; forelimb zone). D-[3H]Asp retrograde labelling of perikarya was absent from the ipsilateral thalamus of all cats injected with the radioactive tracer but a dense terminal plexus of anterogradely labelled corticothalamic fibres from SI and SII was observed, overlapping the distribution area of thalamocortical neurones retrogradely labelled with HRP from the same areas. D-[3H]Asp-labelled neurones were present in ipsilateral SII (SII-SI association neurones) in cats injected in SI. In these animals a bundle of radioactive fibres was observed in the rostral portion of the corpus callosum entering the contralateral hemisphere. There, neurones retrogradely labelled with silver grains were present in SI (SI-SI callosal neurones). Association and callosal neurones labelled from SI showed a topographical distribution similar to that of neurones retrogradely labelled with HRP. The laminar patterns of corticocortical neurones labelled with D-[3H]Asp or with HRP were also similar, with one exception. In the inner half of layer II, SII-SI association neurones and SI-SI callosal neurones labelled with the radioactive marker were much less numerous than those labelled with HRP. In cats injected in SII, D-[3H]Asp retrogradely labelled cells were present in ipsilateral SI (SI-SII association neurones). Their topographical and laminar distribution overlapped that of neurones labelled with HRP but, as in cats injected in SI, association neurones labelled with silver grains were unusually rare in the inner layer III.(ABSTRACT TRUNCATED AT 400 WORDS)

GABA immunoreactive neurons in rat visual cortex

An antiserum to gamma-aminobutyric acid (GABA) was used in a light and electron microscopic immunocytochemical study to determine the morphology and distribution of GABA-containing neurons in the rat visual cortex and to ascertain whether all classes of nonpyramidal neurons in this cortex are GABAergic. The visual cortex used for light microscopy was prepared in such a way that the antibody penetrated completely through tissue sections, and in these sections large numbers of GABA immunoreactive neurons were apparent. The labeled neurons could be identified as being either multipolar, bitufted, bipolar, or horizontal neurons. In layers II through VIa, GABA immunostained cells were distributed uniformly and accounted for approximately 15% of all neurons, but in layer I all neurons appeared to be immunostained. Electron microscopy of GABA immunostained visual cortex prepared to ensure good fine structural preservation confirmed the presence in layers II through VIa of numerous immunoreactive bipolar neurons, both small and large varieties, as well as multipolar and bitufted neurons. Additionally, electron microscopy reveals that astrocytes are frequently GABA immunoreactive. From a correlated light and electron microscopic evaluation of neurons in GABA immunostained visual cortex, it was possible to confirm which kinds of neurons are GABAergic and what proportion of the neuronal population they represent. Thus, from an analysis of some 950 neurons, it was found that pyramidal neurons were never immunoreactive and that except for 20% of the bipolar cell population, all examples of other types of nonpyramidal neurons encountered in this material were GABA immunoreactive.

The laminar distribution of glutamate decarboxylase and choline acetyltransferase in the adult and developing visual cortex of the rat

The activities of choline acetyltransferase and glutamate decarboxylase were measured in individual layers of the adult and developing rat visual cortex. In the adult, the level of choline acetyltransferase activity was highest in layer V followed by layers I, II & III, IV and VI. These measurements are in complete agreement with recent immunohistochemical observations in the same cortical area. Glutamate decarboxylase activity was highest in layer IV and declined significantly in the more superficial and deeper layers. The activities of both enzymes were low during the first postnatal week but increased dramatically between days 8 and 18. Choline acetyltransferase activity in all layers demonstrated a more gradual rise to adult levels from day 18 onward, while glutamate decarboxylase activity reached adult levels by day 24 in all layers, except layer IV, which showed a continuous increase to adulthood. The functional role of the differences in the laminar distribution of these enzymes remains unknown.

Role of the dopaminergic nigrostriatal pathway in methamphetamine-induced depression of the neostriatal serotonergic system

The prevention of the decrease in neostriatal tryptophan hydroxylase (TPH) activity with a single dose of methamphetamine (MA) was attempted by lesioning the nigrostriatal dopaminergic projections with bilateral nigral injections of 6-hydroxydopamine (6-OHDA). The rats were injected with MA (10 mg/kg) 11 days later, and killed 3 h after the injection. The 6-OHDA lesions prevented the decrease of TPH activity in the neostriatum, while the decrease of enzyme activity was slightly attenuated in the hippocampus and unaffected in the frontal cortex. This study demonstrates: that the attenuation of TPH activity can be prevented in a selected brain area by destroying its dopaminergic afferents, and implicates central dopamine (DA), or its metabolite, in the decrease in central TPH activity observed after a single injection of MA.

Behavioural, biochemical and histochemical effects of different neurotoxic amino acids injected into nucleus basalis magnocellularis of rats

Lesions of the nucleus basalis magnocellularis in rats have been used to investigate functions of the extrinsic cortical cholinergic system which originates from these neurons. These lesions also produce extensive non-specific subcortical damage and associated regulatory and neurological impairments, causing doubt about the specificity of consequent functional impairments. Here, nucleus basalis magnocellularis lesions made with four different neurotoxic amino acids (kainic acid, ibotenic acid, N-methyl-D-aspartate, and quisqualic acid) have been compared. Quisqualic acid produced less subcortical damage and lesser neurological and regulatory impairments than the other toxins at doses that produced comparable cholinergic deafferentation of the neocortex, as assessed both histologically and biochemically. This suggests that these impairments are non-specific rather than specific consequences of cholinergic cell loss. The effects on learning a spatial navigation task were more ambiguous, suggesting the involvement of both cholinergic and non-cholinergic systems. Impairment of a passive shock avoidance task was as great following quisqualic acid as the other neurotoxins, which may suggest a more direct relationship specifically with the decline in cortical cholinergic activity. It is concluded that in the absence of availability of a specific cholinergic neurotoxin, quisqualic acid produces less non-specific neuroanatomical and neurological side effects than the more widely used toxins N-methyl-D-aspartate, kainic acid or ibotenic acid.

Glutamic acid decarboxylase- and peptide-immunoreactive neurons in cortex cerebri following development in isolation: evidence of homotypic and disturbed patterns in intraocular grafts

Fetal parietal cerebral cortex was transplanted to the anterior eye chamber of adult Sprague-Dawley rats. After two to three months the grafts, with or without colchicine treatment, were subjected to immunohistochemical analysis using antibodies against cholecystokinin (CCK), somatostatin (SOM), neuropeptide tyrosine (NPY), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI) and the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD). Cerebral cortex in situ of untreated and colchicine-treated rats was always analyzed in parallel. A dense plexus of CCK-immunoreactive fibers was distributed in all parts of the transplants, and after colchicine treatment a large number of CCK-positive cells was observed. These cells were markedly increased in number as compared to normal cortical tissue in colchicine-pretreated rats. The amount of NPY-immunoreactive cells was also markedly increased, whereas somatostatin-positive cells were found in numbers similar to those seen in cortex in situ. In the grafts only a few VIP- and PHI-positive fibers were seen with a few VIP-positive cell bodies, but no clearly discernible PHI-positive cells. A very dense plexus of GAD-positive fibers with an even distribution throughout the grafts was observed. Cortex in situ exhibited a lower density of GAD-immunoreactive fibers. Even after colchicine treatment the number of GAD-positive cells in the grafts was low. Using double-staining techniques, it was found that most of the few GAD-positive cells in the grafts were also NPY-positive, SOM-positive or, to a minor extent, CCK-positive. The present results demonstrate that several peptides and transmitter markers are expressed in cortical grafts in oculo, but marked differences in their expression can be observed in cortical tissue that has developed in isolation. Thus, the intraocular cortex graft, alone and in combination with other brain areas, should provide a useful model in which to study factors that regulate brain development.

Colocalization of gamma-aminobutyric acid and acetylcholinesterase in rodent cortical neurons

We have previously demonstrated that neurons of the rat cerebral cortex which stain positively for acetylcholinesterase are not likely to be cholinergic since they do not colocalize with choline acetyltransferase immunoreactivity [Levey, Rye, Wainer, Mufson and Mesulam (1984) Neuroscience 9, 9-22]. These noncholinergic acetylcholinesterase-positive cells were similar in morphology to cortical neurons which localize gamma-aminobutyric acid or glutamate decarboxylase immunoreactivity. In order to investigate the possibility that the two substances may be colocalized to the same cortical neurons, gamma-aminobutyric acid immunohistochemistry and acetylcholinesterase histochemistry were combined in single sections of rat cerebral cortex. We found that 18% of gamma-aminobutyric acid-immunoreactive cortical neurons are also acetylcholinesterase-positive, and about 36% of acetylcholinesterase-positive cells are gamma-aminobutyric acid-immunoreactive. Neurons which colocalized both substances were multipolar and bipolar neurons in cortical laminae II-VI and were observed in every cortical area examined. The possibility that gamma-aminobutyric acid-immunoreactive/acetylcholinesterase-positive cortical neurons may be postsynaptic targets of cholinergic afferents to the cerebral cortex is discussed.

Synaptic targets of HRP-filled layer III pyramidal cells in the cat striate cortex

There are numerous hypotheses for the role of the axon collaterals of pyramidal cells. Most hypotheses predict that pyramidal cells activate specific classes of postsynaptic cells. We have studied the postsynaptic targets of two layer III pyramidal cells, that were of special interest because of their clumped axon arborization near, and also 0.4-1.0 mm from the cell body, in register in both layers III and V. 191 terminations from four sites (layers III and V, both in the column of the cell and in distant clumps) were analysed by electron microscopy. Only one bouton contacted a cell body and that was immunoreactive for GABA. The major targets were dendritic spines (84 and 87%), and the remainder were dendritic shafts. Of these 13 were classed as pyramidal-like (P), 8 smooth cell-like (S) and three could not be classified. Four of five S types, but none of the seven P types tested were immunoreactive for GABA, supporting the fine structural classification. The putative inhibitory cells therefore formed not more than 5% of the postsynaptic targets, and their activation could only take place through the convergence of pyramidal cells onto a select population of GABA cells. The results show that the type of pyramidal cells with clumped axons studied here make contacts predominantly with other pyramidal cells. Thus the primary role of both the intra and intercolumnar collateral systems is the activation of other excitatory cells.

Neurotransmitters, pathways and circuits as the neural substrates of self-stimulation of the prefrontal cortex: facts and speculations

Through a multidisciplinary approach considerable progress has been made in understanding the neural substrates of self-stimulation (SS) of the medial prefrontal cortex (MPC). Thus, neuroanatomical studies have revealed that intrinsic neurones in the MPC seem to be the central elements responsible for initiating and maintaining this phenomenon in this area of the brain. Complementary to this central finding are the electrophysiological and neurohistological data reviewed here, showing that neurones in the MPC are directly activated and have monosynaptic feed-back connections with neurones located in areas which also support SS. These findings have given rise to the hypothesis that several single feed-back pathways or single circuits exist between points of SS in the MPC and points of SS in other areas of the brain. This hypothesis implies that SS in a particular area would depend not only on the intrinsic local activity induced by the electrical stimulation but on the functional and specific activity of other nuclei in the brain. The fact that lesions of single circuits, which are apparently involved in SS of the MPC such as the medial prefrontal cortex-ventrotegmental area-medial prefrontal cortex and medial prefrontal cortex-n. dorsomedialis of the thalamus-medial prefrontal cortex, do not produce a permanent decrease of SS, together with the finding that transynaptic connections seem to exist between MPC and other areas of the brain, suggests further that a complex rather than several single independent circuits could be at the neural basis of SS of the MPC. If that were the case, then SS of the MPC would not only depend upon local and single feed-back activity but upon specific functional feed-back activity among the nuclei, which in turn have single feed-back connections with the MPC (see the concept of 'complex circuit' outlined in the section of Behavioural studies). On the basis of this hypothesis no permanent changes should be expected after lesions of single pathways since physiological and even anatomical compensation could be reached through the rest of the undamaged circuit. That terminals containing specific neurotransmitters exist in layers of the PC where electrodes for SS are located has been reviewed in this paper. Some of these neurotransmitters have been suggested to be part of the local substrates activated by SS.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction of serotonin with somatosensory cortical neuronal responses to afferent synaptic inputs and putative neurotransmitters

The present study was conducted to investigate the action of serotonin (5-HT) on synaptic transmission within local circuits of the rat somatosensory cortex. Responses of single somatosensory cortical neurons to activation of excitatory and inhibitory synaptic pathways or iontophoretic application of putative neurotransmitters were examined before, during and after microiontophoresis of 5-HT. Monoamine-induced changes in neuronal responsiveness were quantitatively assessed by computer-based analysis of peri-event histograms. 5-HT typically exerted a differential inhibitory effect on neuronal firing, such that stimulus-induced responses were reduced relative to spontaneous discharge. In 16 of 24 (67%) of the cells tested, 5-HT depressed synaptically evoked excitation more than background firing such that "signal to noise" ratio was decreased. In some cases evoked spiking was reduced from control levels at doses of 5-HT subthreshold for producing direct depression of baseline firing rate. Cortical neuron excitatory responses to iontophoretically applied acetylcholine (8 of 13 cells) and glutamate (10 of 15 cells) were also reduced during microiontophoresis of 5-HT. A similar reduction in inhibitory efficacy was observed in 62% of the cases (10 of 16 cells) where 5-HT was interacted with GABA-induced depressant responses. Local administration of 5-HT also resulted in an antagonism of stimulus bound inhibition of firing (9 of 11 cells). These results are contrasted with previously observed facilitory effects of norepinephrine (NE) on cortical neuronal responsiveness to afferent synaptic inputs and putative transmitter agents. It is suggested that endogenously released 5-HT and NE may exert complementary modulatory-type actions on neuronal responsiveness as a means of regulating the transfer of sensory information through local cerebrocortical circuits.

Ultrastructural organization of choline-acetyltransferase-immunoreactive fibres innervating the neocortex from embryonic ventral forebrain grafts

Suspension grafts of foetal tissue rich in cholinergic neurones were transplanted into the frontoparietal cortex of rats that had previously undergone deafferentation of the extrinsic cholinergic innervation of the cortex by injection of ibotenic acid into the nucleus basalis magnocellularis. The cortical tissue containing the graft was processed for electron microscopic immunocytochemistry by using a monoclonal antibody to choline acetyltransferase (ChAT) in order to examine the contacts established between cholinergic fibres from the graft and the host neocortex. The density, distribution, and targets of this graft-host innervation were compared with those seen in the intact and deafferented cortex. ChAT-positive fibres in both grafted and control animals formed extensive synaptic connections with various cortical neural elements--those of graft origin being of similar morphology to those in the intact cortex. However, the distribution of postsynaptic cortical targets of the graft-derived ChAT-immunoreactive boutons was abnormal, such that a greater percentage of such terminals formed synaptic contacts with neuronal perikarya, especially layer V pyramidal neurones, than was seen in control brains. It is possible that the formation of new synaptic contacts between the embryonic graft and host frontoparietal cortex may, in part, be necessary for the restoration of functional activity that has been previously reported in these grafted animals.

Neurotransmitters in the cerebral cortex

This article surveys the conventional neurotransmitters and modulatory neuropeptides that are found in the cerebral cortex and attempts to place them into the perspective of both intracortical circuitry and cortical disease. The distribution of these substances is related, where possible, to particular types of cortical neuron or to afferent or efferent fibers. Their physiological actions, where known, on cortical neurons are surveyed, and their potential roles in disease states such as the dementias, epilepsy, and stroke are assessed. Conventional transmitters that occur in afferent fibers to the cortex from brain-stem and basal forebrain sites are: serotonin, noradrenaline, dopamine, and acetylcholine. All of these except dopamine are distributed to all cortical areas: dopamine is distributed to frontal and cingulate areas only. The transmitter in thalamic afferent systems is unknown. Gamma aminobutyric acid (GABA) is the transmitter used by the majority of cortical interneurons and has a profound effect upon the shaping of receptive field properties. The vast majority of the known cortical peptides are found in GABAergic neurons, and the possibility exists that they may act as trophic substances for other neurons. Levels of certain neuropeptides decline in cases of dementia of cortical origin. Acetylcholine is the only other known transmitter of cortical neurons. It, too, is contained in neurons that also contain a neuropeptide. The transmitter(s) used by excitatory cortical interneurons and by the efferent pyramidal cells is unknown, but it may be glutamate or aspartate. It is possible that excitotoxins released in anoxic disease of the cortex may produce damage by acting on receptors for these or related transmitter agents.

Reinforcing properties of cocaine in the medical prefrontal cortex: primary action on presynaptic dopaminergic terminals

The presynaptic mechanisms involved in the initiation of cocaine reinforcement were investigated using neurotoxin lesions. Rats were trained to intracranially self-administer cocaine (50 to 90 pmol) into the medial prefrontal cortex and after dose-effect analyses were completed, each rat received a unilateral 6-hydroxydopamine lesion (4 micrograms in 0.2 microliter) at the self-administration site. The lesion selectively decreased dopamine content in the medial prefrontal cortex (-45%) and decreased cocaine-maintained responding to vehicle levels. Lever-pressing could be reinstated by substituting dopamine (300 pmol) but not serotonin for cocaine. Dopamine self-administration was attenuated by including equimolar concentrations of the D2 dopaminergic antagonist sulpiride in the injectate. These results suggest that the initiation of reinforcing neuronal activity in the medial prefrontal cortex appears to result in part through the direct interaction of cocaine with presynaptic reuptake sites associated with dopaminergic nerve endings. The resulting increased synaptic concentration of the neurotransmitter may then interact with postsynaptic D2 binding sites to activate neuronal systems involved in the mediation of this reinforcement.

Distribution of glutamic acid decarboxylase-immunoreactive structures in the barrel region of mouse somatosensory cortex

Neuronal structures in the barrel region of the mouse primary somatosensory cortex containing gamma-aminobutyric acid (GABA) were identified by an immunocytochemical method, using an antiserum to glutamic acid decarboxylase (GAD), the rate-limiting enzyme in the synthesis of GABA. GAD-positive cell bodies were found in all layers of the barrel cortex, but were more concentrated in the upper portion of layer II/III, and in layers IV and VI. Puncta, presumably axon terminals, were also distributed throughout the cortical layers; a high density of puncta occurs in layer IV, whereas a somewhat lower density characterizes layer VI. Based on the shapes of their somata and the distribution of their dendrites it was determined that all GAD-positive cell bodies were of the non-pyramidal type.

Somatostatin and cholecystokinin octapeptide differentially modulate the release of [3H]acetylcholine from caudate nucleus but not cerebral cortex: role of dopamine receptor activation

The effects of somatostatin (SOM) and cholecystokinin octapeptide (CCK-8) on basal and potassium-induced release of acetylcholine (ACh) were investigated in slices of rat caudate nucleus (CN) and, for comparison, cerebral cortex (CX). Potassium (5-55 mM) produced a concentration-dependent increase in the release of [3H]ACh in the presence of extracellular Ca2+. SOM (1 microM), CCK-8 (1 microM) and the dopamine (DA) receptor agonist, apomorphine (APO, 30 microM) inhibited the K+-induced (35 mM) release of [3H]ACh by 26-32% from CN, but did not affect ACh release from CX. Other peptides (1 microM), such as Met-enkephalin, vasoactive intestinal peptide, thyrotropin-releasing hormone and substance P, had no effect on release of [3H]ACh in CN or CX. Sulpiride (SULP), a dopamine receptor antagonist, prevented the effects of APO and SOM, but not CCK-8, to inhibit [3H]ACh release. The results indicate that: (1) SOM and CCK-8 inhibit the release of [3H]ACh in CN, but not CX; and (2) the inhibitory effect of SOM, but not CCK-8, on [3H]ACh release is mediated by dopaminergic mechanisms.

The laminar distributions and postnatal development of neurotransmitter and neuromodulator receptors in cat visual cortex

We review efforts to further understand the development and nature of sensory processing mechanisms in the cat visual cortex. In vitro autoradiographic and homogenate assay techniques have been employed to determine the laminar distribution and characteristics of various neurotransmitter and neuromodulator receptor populations during postnatal development. Each receptor population shows a distinct laminar-specific pattern of binding, which, in most cases, is age-dependent. Changes in receptor number and affinity are also observed during postnatal development. These findings indicate that major alterations in the basic chemical circuitry of cat visual cortex are a normal feature of postnatal maturation and may play a role in plasticity mechanisms.

Prenatal development of nucleus basalis complex and related fiber systems in man: a histochemical study

To provide parameters for study of the "cholinergic" innervation of a human fetal cerebrum, we have analyzed the prenatal development of histochemical reactivity in the nucleus basalis complex (a magnocellular complex known to contain a high concentration of cholinergic perikarya). Brains from fetuses and premature infants ranging between 8 and 35 weeks of gestation were frozen cut and processed by the thiocholine method for the demonstration of acetylcholinesterase activity. Since no consistent results were obtained with inhibitors on the material younger than 15 weeks, the histochemical reactivity for early stages was expressed as the total cholinesterase reactivity. The first sign of histochemical differentiation of the basal telencephalon is the appearance of a dark cholinesterase reactive "spot" situated between the developing lenticular nucleus and basal telencephalon surface as early as 9 weeks of gestation. The first cholinesterase reactive bundle connects this reactive area (nucleus basalis complex anlage) with the strongly reactive fiber system situated along the dorsal side of the optic tract. During the next "stage" (10.5 weeks), there is a significant increase in the size of the nucleus basalis complex and strongly cholinesterase reactive neuropil occupies the sublenticular, diagonal and septal areas. At this stage we have seen two new cholinesterase-reactive bundles: one well developed cholinesterase reactive fiber stratum approaching (but not penetrating) the neocortical anlage through the external capsule and another minute bundle running towards the medial limbic cortex through the precommissural septum. The supraoptic fiber system can be traced now to the pregeniculate area and the tegmentum. At 15 weeks, the first acetylcholinesterase reactive perikarya appear and the nucleus basalis complex anlage becomes segregated into several strongly reactive territories, corresponding in position to the medial septal, diagonal and basal nuclei as defined on adjacent Nissl stained sections. At this stage, fibers from the nucleus basalis complex enter the "white" matter of frontal, temporal, parietal and occipital parts of the cerebral hemisphere via the external capsule. Between 15 and 18 weeks, acetylcholinesterase fibers spread throughout the "white" matter of the cerebral hemisphere. In the next "stage" (18-22 weeks), strongly reactive fibers can be followed from the nucleus basalis below the putamen and through the external capsule to the transient, synapse-rich subplate zone of frontal, temporal, parietal and occipital cortices.(ABSTRACT TRUNCATED AT 400 WORDS)

The relationship between GABA immunoreactivity and labelling by local uptake of [3H]GABA in the striate cortex of monkey

An antiserum to GABA was used in the macaque monkey to determine whether neurons that accumulate exogenously applied [3H]GABA in vivo are also immunoreactive for GABA. Following the injection of [3H]GABA into different laminae of striate cortex in two untreated animals and in one animal treated with amino-oxyacetic acid, selective accumulation of the labelled amino acid was demonstrated in perikarya by autoradiography. Radiographically labelled neurons (n, 519) and their unlabelled neighbours were tested in consecutive 0.5 micron thick sections by immunocytochemistry for GABA immunoreactivity. Injection of [3H]GABA did not increase the number of neurons showing GABA immunoreactivity. On the contrary many of the cells that accumulated [3H]GABA were immunonegative. These neurons were mostly located in layers IVC and VA following [3H]GABA injection into layers II-III, and in layers upper III and II following injection into layers V and VI. A comparison of the position of these neurons with known local projection patterns in the striate cortex of monkey suggests that GABA-immunonegative neurons may nevertheless become labelled by [3H]GABA if most of their local axon terminals fall within the injection site. The interlaminar projection of GABA-immunopositive neurons, which probably contain endogenous GABA, could be deduced from the position of the [3H]GABA injection site that leads to their autoradiographic labelling. Although the present study confirmed our previous results on the interlaminar connections of neurons that accumulate [3H]GABA, it demonstrated that [3H]GABA labelling alone may not be a sufficient criterion to assess the GABAergic nature of neurons in the striate cortex of monkey.

Glutamic acid decarboxylase and somatostatin immunoreactivities in rat visual cortex

Antibodies to glutamic acid decarboxylase (GAD) and somatostatin (SS) were used to determine the laminar distribution and morphology of GAD- and SS-immunoreactive neurons and terminals in rat visual cortex. The present study demonstrates that GAD-immunoreactive neurons constitute several morphologically distinct subclasses of neurons in rat visual cortex. These subclasses of neurons can be distinguished by differences in soma size, soma shape, dendritic branching patterns, axonal arborizations, and location in the neuropil. GAD-immunoreactive neurons are found throughout all layers of visual cortex. They have nonpyramidal morphology and constitute roughly 15% of the total neuronal population. The laminar pattern of GAD-immunoreactive puncta is uneven, with a prominent band of terminals in layer IV. Numerous large GAD-positive puncta surround the somata and proximal dendrites of pyramidal cells in layers II, III, and V. SS-immunoreactive neurons constitute a less numerous and more restricted population of nonpyramidal neurons. Their somata are located mainly in layers II, III, V, and VI. Very few, if any, SS-immunoreactive neurons are found in layers I and IV. SS-immunoreactive terminals are arranged along vertical and diagonal collateral branches that have a beaded appearance. Finally, many neurons in the supra- and infragranular layers and in the white matter are immunoreactive to both glutamic acid decarboxylase and somatostatin. This coexistence of immunoreactivity to both GAD and SS may characterize a broad subclass of cortical nonpyramidal neurons.

Neuropeptides in cerebral cortex of macaque monkey (Macaca fuscata fuscata): regional distribution and ontogeny

The concentrations of vasoactive intestinal polypeptide, somatostatin and substance P were determined in various cerebral subdivisions of adult and foetal Japanese monkeys (Macaca fuscata fuscata) by specific radioimmunoassays. In adult tissues, the highest level of vasoactive intestinal polypeptide was found in the somatosensory cortex and the lowest level in the occipital cortex. A high level of somatostatin was found in the association cortex (prefrontal, parietal and temporal cortex); the lowest level was noted in the occipital cortex. Substance P was found to be high in prefrontal and temporal cortex. The highest levels of substance P and somatostatin were obtained in the amygdala. Between embryonic 4 and 5.5 months, concentrations of peptides increased dramatically, and in the adult, all neuropeptides in cortical subdivisions significantly decreased. By the gel filtration method, only one immunoreactivity which coeluted with substance P and vasoactive intestinal polypeptide was demonstrated in extracts of 4-, 5.5-month-old and adult monkey cerebral cortex. In contrast, somatostatin immunoreactivity eluted as 3 peaks. Almost 80% of the immunoreactivity co-eluted with synthetic somatostatin, regardless of the age of the tissue. The molecular weights of two larger molecules were determined to be 13 and 3 kdaltons.