Supramammillary Nucleus Research Articles

Dual projection from the medial septum to the supramammillary nucleus in the rat

The supramammillary nucleus, collecting information about the physiological state of the animal, innervates medial septal neurons that are involved in the generation of hippocampal theta activity. Here we demonstrate that septal neurons located in an area bordering the medial and lateral septal nucleus project back to the supramammillary nucleus, and most of these cells contain calretinin, calbindin or both. GABA-immunoreactive boutons of these neurons (60%) form symmetrical synapses, whereas the remaining GABA-negative terminals form asymmetrical synapses (40%) with their supramammillary targets. We hypothesize that the septosupramammillary feedback, because of the specific location of its parent cells, carries information about the activity of theta generator cells in the medial septum and supramammillary nucleus, as well as about the resulting theta activity in the hippocampus.

Altered c- fos expression in autonomic regulatory centers of genetically obese ( ob/ob) mouse brain

This study examined c- fos-like immunoreactivity (FLI) in the brain of obese ( ob/ob) and lean (+/+) mice during states of satiety and hunger. The results demonstrated that there is an altered neural activity primarily in the hypothalamus of the obese mouse brain. Most interestingly, only obese mice had an increased FLI in the dorsomedial and supramammillary nuclei. Conversely, only lean mice showed increase in FLI in the medial part of perifornical nucleus following food deprivation for 24 h.

Infant cold exposure changes Fos expression to acute cold stimulation in adult hypothalamic brain regions

It is known that cold exposure as an infant results in a permanent cold tolerance which is accompanied by a reduced rate of colonic temperature decline and increased metabolic heat production to cold stimulation. The present study was aimed to elucidate the central mechanism of cold tolerance of adult rats with cold exposure as infants. Newborn infants were exposed to cold ambient (4°C) daily for 2 weeks, and when they were 15-weeks old, Fos expression to acute cold stimulation (10°C) in whole brain regions was investigated using quantitative immunohistochemistry. Acute cold stimulation induced a significant increase of Fos-positive neurons in many nuclei of whole brain areas in adult rats both with and without cold exposure as infants. However, the number of Fos-positive neurons was significantly less in the rats with cold exposure than without cold exposure as infants, particularly in the hypothalamic nuclei such as the lateral septal nucleus (LS), preoptic area (POA), parvocellular paraventricular nucleus (pPVN), ventromedial hypothalamic nucleus (VMH) and supramammillary nucleus (SuM). However, there was no significant difference in the number of Fos-positive neurons in the extra-hypothalamic regions between the rats with and without cold exposure as infants. These results suggest that the central mechanism of cold tolerance with cold exposure as infants is due to metabolic changes of the hypothalamic brain regions.

A new visceral nociceptive pathway in the dorsal column: Anatomical and functional studies of pancreatic pain including the effects of limited dorsal column lesions in rats

Novel neuronal pathways carrying visceral nociceptive information through the dorsal column of the spinal cord have recently been described by our group. The clinical importance of these pathways is suggested by the effectiveness of a midline dorsal column lesion in the relief of pelvic visceral pain in cancer patients. Aims: To describe the neuronal pathways mediating pain from the pancreas and to study the effectiveness of dorsal myelotomy for the relief of pancreatic pain. Methods: Neuronal tract mapping was done after small iontophoretic injections of Phaseolus vulgaris-leucoagglutinin (PHAL, 2.5% in phosphate buffer; pH 8.0) around the central canal at 1'7 or S1 spinal segments. Acute pancreatitis was induced by glyoxydecholic acid (GDOC) injection into the pancreatic duct followed by six hourly intraperitoneal injections of caerulean (72mg total). Dorsal myelotomy was performed either at the C1 or T10 level. The above procedures were done in anesthetized rats. Body weight and behavior (locomotion, exploratory and grooming) was monitored. Results: The ascending neuronal projections from the T7 or S1 spinal cord regions ascend near the dorsal intermediate and dorsal midline septi of the dorsal column, respectively. These pathways terminated primarily in the cuneate and gracile nuclei, respectively, in the caudal medulla. Some terminal fibers were found throughout the brainstem primarily in midline structures such as the pontine reticular formation, periaqueductal gray, and the medial portions of the thalamus and hypothalamus. Limbic structures, including the supramammillary nucleus, the nucleus basaiis of Meynert, and the zona incerta also contained axonal terminals. Assessment of exploratory behavior in animals with acute pancreatitis revealed a significant decrease from controls. Normal rearing activity returned in animals after dorsal column lesions including the area near the dorsal intermediate septum. The long-term effects of dorsal myelotomy involving each of these dorsal column pathways was examined. Body weight and behavioral activity in animals with dorsal column lesions were not affected significantly at any time point through 30 weeks. Condnsions: These data demonstrate that pancreatic pain is transmitted via a dorsal column pathway. Further, a dorsal intermediate septum myelotomy may provide long term relief of such pain and is well tolerated. This research was made possible by full grant support from NIH NS 11255.

Frequency Modulation of Hippocampal Theta by the Supramammillary Nucleus, and Other Hypothalamo–Hippocampal Interactions: Mechanisms and Functional Implications

KIRK, I.J. Frequency modulation of hippocampal theta by the supramammillary nucleus, and other hypothalamo-hippocampal interactions: mechanisms and functional implications. NEUROSCI BIOBEHAV REV 22(2), 291–302, 1998.—In this paper it is argued that theta-range hippocampal EEG activity, and in particular the specific frequency at which it occurs, is critical to hippocampal function. Results of the reviewed studies suggest that in particular circumstances (in the urethane anaesthetized animal and possibly during particular behavioral states), the frequency of hippocampal theta is primarily determined in the supramammillary nucleus (SuM). Rhythmic theta-frequency neuronal activity in the SuM is relayed to, and determines the frequency of theta activity in, the septum (and hence the hippocampus). It is also suggested that in general (e.g. freely moving, as opposed to anaesthetized animals, and in all but some specific behavioral states), other ascending pathways and mechanisms in addition to those from SuM are probably also involved in the modulation of theta frequency. The posterior hypothalamic nucleus (PH) probably acts in synergy with the SuM, but it is principally involved in the release and amplitude modulation of theta. Although descending input from the septo–hippocampal system to PH and SuM is not required for theta-related neuronal activity in these structures, we provide evidence for descending, rate-limiting influences from the septo–hippocampal system to both PH and SuM during theta. These descending systems are likely involved in the suppression of theta during non-theta (i.e. sharp-wave) hippocampal EEG. In contrast to the SuM and PH, theta-related neuronal activity in the medial mammillary nucleus (MM) is dependent on theta-frequency activity in, and descending from, the septo–hippocampal system. The MM it is argued, is involved in relaying theta-frequency activity around the limbic circuitry. A role for this re-entrant process is suggested.

Cholecystokinin Innervation of the Cerebral Cortex in a Reptile, the Lizard Psammodromus algirus

We used light and electron microscopic and immunohistochemical methods to map the distribution of cholecystokinin (CCK) in the cerebral cortex of a lizard, Psammodromus algirus. At light microscopy, the CCK immunoreactivity was limited to fibers and terminals densely innervating all cortical regions except for the lateral (pyriform) cortex which was very slightly immunostained. The CCK-positive terminals were almost restricted to the cell layers in every cortical region where they surrounded immunonegative cell bodies and proximal dendrites of neurons within the layer. No CCK-containing neurons were observed within the cerebral cortex. At the electron microscopic level, most positive structures were presynaptic boutons contacting cell bodies and proximal dendrites. All contacts appeared to form symmetric junctions. both the distribution and type of synaptic contacts of CCK fibers in the cerebral cortex of Psammodromus are very similar to the corresponding features in the hippocampus of mammals, although in this lizard the CCK cortical innervation, unlike that in mammals, is probably of extrinsic origin. Double HRP-retrograde labeling and CCK immunohistochemistry show that part of the CCK in the cerebral cortex of Psammodromus arises from the hypothalamic supramammillary nuclei.

Immunocytochemical localization of an imidazoline receptor protein in the central nervous system

Imidazoline (I) receptors have been implicated in the regulation of arterial blood pressure and behavior although their distribution in the central nervous system (CNS) remains in question. Presumptive I- receptor sites were detected in the rat central nervous system with a polyclonal antibody to an imidazoline receptor protein (IRP) with binding characteristics of the native receptor. IRP-like immunoreactivity (LI) was detected in neurons and glia by light and electron microscopy. Spinal cord: processes were heavily labeled in superficial laminae I and II of the dorsal horn, lateral-cervical and -spinal nuclei and sympathetic cell column. Medulla: label was concentrated in the area postrema, rostral, subpostremal and central subnuclei of nucleus tractus solitarii, spinal trigeminal nucleus caudalis, and inferior olivary subnuclei. Visceromotor neurons in the dorsal vagal and ambigual nuclei were surrounded by high concentrations of immunoreactive processes. In reticular formation, label was light, though predominant in the intermediate reticular zone and ventrolateral medulla. Pons: label was detected in the neuropil of the periventricular gray, concentrated in the dorsal– and external–lateral subnuclei of lateral parabrachial nucleus, and present intracellularly in the mesencephalic trigeminal nucleus. Midbrain: IRP-LI was most heavily concentrated in the interpeduncular nucleus, nuclei interfascicularis and rostral-linearis, the subcommissural organ, central gray, and in glia surrounding the cerebral aqueduct. Diencephalon: high densities were detected in the medial habenular nucleus, nucleus paraventricularis thalami, other midline-intralaminar thalamic nuclei, the supramammillary and mediobasal hypothalamic nuclei. In the median eminence, immunolabeled processes were restricted to the lamina interna and lateral subependymal zone. Telencephalon: IRP-LI was concentrated in the central amygdaloid nucleus, bed nucleus of stria terminalis and globus pallidus, followed by moderate labeling of the medial amygdaloid nucleus, amygdalostriatal zone and caudoputamen, the hilus of the dentate gyrus, and stratum lacunosum-moleculare of field CA 1 of Ammon's horn. The subfornical organ and organum vasculosum lamina terminalis were filled with diffuse granular immunoreactivity. Ultrastructural studies identified IRP-LI within glia and neurons including presynaptic processes. I-receptor(s) localize to a highly restricted network of neurons in the CNS and circumventricular regions lying outside of the blood-brain barrier. Putative imidazoline receptors have a unique distribution pattern, show partial overlap with α 2 adrenoreceptors and are heavily represented in sensory processing centers and the visceral nervous system.

O-113 - High-frequency stimulation of the supramammillary nucleus facilitates the induction of long-term potentiation in the dentate gyrus in vivo

O-113 - High-frequency stimulation of the supramammillary nucleus facilitates the induction of long-term potentiation in the dentate gyrus in vivo

The supramammillary nucleus innervates cholinergic and GABAergic neurons in the medial septum-diagonal band of Broca complex

In the present study, the connectivity between two subcortical nuclei involved in hippocampal theta activity, the supramammillary nucleus and the medial septum-diagonal band of Broca complex, was examined. Targets of the supramammillary afferents in the medial septum-diagonal band of Broca complex were identified by combining anterograde transport of Phaseolus vulgaris leucoagglutinin with immunostaining for putative postsynaptic neurons, i.e. for parvalbumin and choline acetyltransferase that are known to label the GABAergic and cholinergic neurons, respectively, of the medial septum-diagonal band of Broca complex. Double retrograde transport experiments using the tracers horseradish peroxidase and wheat germ agglutinin-conjugated colloidal gold were employed to identify supramammillary neurons that project both to the hippocampus and the medial septum-diagonal band of Broca complex. Phaseolus vulgaris leucoagglutinin injections into the supramammillary nucleus of the rat resulted in dense fibre and terminal labelling in the medial septum-diagonal band of Broca complex. Labelled terminals formed asymmetric synapses mainly on distal dendrites of medial septal neurons. Proximal dendrites and somata were rarely contacted. The supramammillary afferents showed no target selectivity for a particular cell type; they innervated both cholinergic and GABAergic cells. Occasionally, perisomatic, basket-like terminals of supramammillary origin were found around parvalbumin-containing neurons. Double-retrograde experiments revealed that at least 25% of the supramammillo-hippocampal cells also projected to the medial septum-diagonal band of Broca.These data suggest that the nucleus, known to modulate the hippocampal electrical activity directly by the supramammillo-hippocampal pathway, also has the potential for an indirect action via the innervation of both the GABAergic and cholinergic septohippocampal neurons. This dual modulation may originate, at least in part, from the same population of supramammillary neurons.

Type 2 interleukin-1 receptor mRNA is induced by kainic acid in the rat brain

The in situ hybridization technique was used to examine the expression of type 2 interleukin-1 receptor (IL-1R2) mRNA in the rat brain following the systemic injection of kainic acid at a convulsive dose. The expression of IL-1R2 mRNA was not detected in any brain regions of the saline-injected control rats. 8 h after the systemic injection of kainic acid, weak expression of IL-1R2 mRNA was observed in the dentate gyrus and basolateral amygdaloid nucleus. At 12 and 24 h after the injection of kainic acid, IL-1R2 mRNA was markedly induced in various brain regions including the CA1 and CA3 fields of the hippocampus, dentate gyrus, basolateral amygdaloid nucleus, piriform cortex, claustrum, tenia tecta, arcuate hypothalamic nucleus, dorsomedial hypothalamic nucleus, suprachiasmatic nucleus, tuberal magnocellular nucleus and supramammillary nucleus. In these regions, the signals of IL-1R2 mRNA were observed on likely neuronal cells. Around the mediodorsal thalamic nucleus and the paraventricular thalamic nucleus, dispersed intense signals were observed on the non-neuronal cells. In addition, the expression of the mRNA on the venules was observed at 12 h. The strength of signals significantly decreased by 48 h after the injection. These findings revealed the spatiotemporal induction of IL-1R2 mRNA in the rat brain following the systemic administration of kainic acid, which has shown to cause neuronal degeneration, suggesting the pathological roles of IL-1R2 in the brain.

Discussion

We present a new model for the generation of theta rhythm of the hippocampus. We propose that theta at CA1 involves extracellular current fluxes produced by alternating depolarizing and hyperpolarizing membrane potential fluctuations of large populations of hippocampal pyramidal cells. Pyramidal cells are, in turn, controlled by rhythmically bursting cholinergic and GABAergic cells of the medial septum/vertical limb of the diagonal band. We postulate that septal cholinergic and GABAergic rhythmically bursting cells fire in relative synchrony; their coordinated burst discharge (burst mode) drives the positive-going phase of intracellular theta and associated firing of pyramidal cells; their synchronized pauses (interburst mode) give rise to the negative-going phase of intracellular theta and an inhibition of pyramidal cells. We further demonstrate that the theta rhythm is controlled by a network of cells extending from the brainstem to the septum/hippocampus. During theta, tonically discharging cells of the nucleus reticularis pontis oralis activate neurons of the supramammillary nucleus; the supramammillary nucleus, in turn, converts this steady barrage into a rhythmical pattern of discharge which is relayed to GABAergic/ cholinergic rhythmically bursting cells of the medial septum. The septal rhythmically bursting cells modulate subsets of hippocampal interneurons and principal cells in the generation of the theta rhythm. We review evidence showing that the serotonin-containing neurons of the median raphe nucleus desynchronize the hippocampal electroencephalogram, presumably by disrupting the rhythmical discharge of septal cholinergic and GABAergic neurons. Finally, we summarize recent work indicating that the theta rhythm is critically involved in memory functions of the hippocampus and that its disruption (electroencephalographic desynchronization) may block or temporarily suspend mnemonic processes of the hippocampus.

The medial supramammillary nucleus, spatial learning and the frequency of hippocampal theta activity

Previous studies have shown that the presence of hippocampal theta activity (theta) is important for learning and that the medial supramammillary nucleus (SuM) is involved in the control of the frequency of theta. In the present experiments, a single-day version (20 trials) of the Morris water maze was used to investigate the effects of drug injections into SuM on hippocampal theta frequency and spatial learning. Two groups of rats received an injection of chlordiazepoxide (CDP, 0.5 μl, 40 μg/ μl) or saline (0.5 μl) into SuM 10 min before training in the Morris water maze. Two other groups of rats received an i.p. injection of 5 mg/kg CDP or saline, and two further groups received short (10 min) or long (15 min) immersion in cool water (22°C) before training. The results showed: (1) in all groups theta frequency was an inverse logarithmic function of training time; (2) systemic CDP or long cool water exposure decreased theta frequency to a greater extent (by 1 Hz), and also impaired learning to a greater extent, than the other treatments; (3) that SuM-CDP produced a modest decrease in theta frequency (0.35–0.5 Hz) and a modest impairment of spatial learning. These data suggest that theta frequency per se may be important for spatial learning and that total abolition of theta is not necessary for dysfunction; and that while a lesser part of the effect of i.p. CDP on spatial learning appears to be mediated by SuM the greater part appears to involve other nuclei as well.

Distribution and co-localization of nitric oxide synthase and argininosuccinate synthetase in the cat hypothalamus.

Argininosuccinate synthetase (ASS) and nitric oxide synthase (NOS) comprise part of the cyclic metabolic pathway to produce nitric oxide (NO). ASS is one of the arginine synthesis enzymes which synthesizes argininosuccinate from aspartate and citrulline, and NOS forms NO and citrulline from arginine. This study examines the localization of ASS and NOS in the cat hypothalamus using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and immunohistochemistry against ASS and NOS. NADPH-d positive and/or ASS-immunoreactive neurons were localized in the following areas: the anterior hypothalamic area, the anterior hypothalamic nucleus, the supraoptic nucleus, the suprachiasmatic nucleus, the periventricular complex, the paraventricular nucleus, the parvocellular nucleus, the lateral hypothalamic area, the dorsomedial hypothalamic nucleus, the dorsal hypothalamic area, the posterior hypothalamic area, and the supramammillary nucleus. NOS and ASS double-labeled neurons were found in the anterior hypothalamic area, the supraoptic nucleus, the central part of the paraventricular nucleus of the hypothalamus, the lateral hypothalamic area, ventral part of the parvocellular hypothalamic nucleus, the posterior hypothalamic area, and the supramammillary nucleus. Double-labeled neurons in the hypothalamus comprised 20.7-32.0% of ASS-immunoreactive neurons and 10.2-26.3% of NOS-immunoreactive neurons. The results suggest the existence of the 'NO cycle' in situ and the physiological importance of NO and argininosuccinate in several regions of the cat hypothalamus.

Supramammillary neural discharge patterns and hippocampal EEG.

Rhythmic multiunit activity, leading the negative peak of concurrently recorded dentate rhythmical slow-wave activity (RSA, theta) by a constant degree over a range of RSA frequencies, was observed in the supramammillary nucleus (SuM) after carbachol infusion (5%, 0.25-0.5 microliter) into the nucleus pontis oralis (RPO). As the rhythmic SuM activity survived bilateral transection anterior to SuM, its occurrence is not dependent on descending influences from the septum or hippocampus. Infusion of additional carbachol into the RPO resulted in epileptiform "sharp-waves" in the hippocampal EEG, and correlated nonrhythmic cell discharge in the SuM. Bilateral transection rostral to SuM abolished the sharp-wave related SuM activity (and restored SuM rhythmical activity). Thus, in contrast to RSA related rhythmical SuM discharge, sharp-wave related SuM discharge seems dependent on descending projections from the hippocampus.

122 Different distribution of L- and N-type Ca 2+ channel in rat neocortical neurons

Melanin-concentrating hormone (MCH) and neuropeptide glutamic acid-isoleucine (NEI) are expressed in neurons that are located mainly in the hypothalamus and project widely throughout the rat central nervous system. One of the main targets of melanin-concentrating hormone is the hippocampal formation, although the exact origin of the projections is unknown. By using injections of the retrograde tracer True Blue into the hippocampus, together with immunohistochemical analysis, we observed retrogradely labeled melanin-concentrating hormone-containing neurons in the lateral hypothalamic area, incerto-hypothalamic area, perifornical area, the periventricular nucleus of the hypothalamus, and in the internuclear area (between the dorsomedial and ventromedial nuclei of the hypothalamus), as well as a few retrogradely labeled and melanin-concentrating hormone-immunoreactive cells in the supramammillary nucleus. The afferents from the lateral hypothalamic area were confirmed using injection of the anterograde tracer biotinylated dextran amine, which enabled us to use histochemical analysis in order to visualize fibers and terminals in the hippocampal formation. In the medial septal nucleus, we found cholinergic neurons that are also putatively innervated by melanin-concentrating hormone immunoreactive fibers and project to the hippocampal formation. Finally, using two different protocols for immunoperoxidase, we were able to show GABAergic basket cells presumably innervated by melanin-concentrating hormone-immunoreactive fibers in the hippocampal formation. On the basis of the data collected herein, we hypothesize that the MCH/NEI projections from hypothalamic nuclei participate in spatial memory and learning through direct and indirect pathways. These pathways would enable the animal to organize its exploratory behavior during foraging.

Distribution of pituitary adenylate cyclase activating polypeptide (PACAP) immunoreactivity in the hypothalamus and extended amygdala of the rat

Pituitary adenylate cyclase activating polypeptide (PACAP) is found in two forms of 27 and 38 amino acids (PACAP-27 and PACAP-38 respectively) in the mammalian central nervous system. Using antibodies to these two forms of PACAP, we examined the distribution of PACAP immunoreactivity in the rat hypothalamus and a number of extrahypothalamic areas. The patterns of immunostaining for PACAP-27 and PACAP-38 were similar: prominent terminal labelling was present in the retrochiasmatic area, median eminence, and posterior periventricular nucleus of the hypothalamus as well as the bed nucleus of the stria terminalis and amygdaloid complex. After colchicine treatment, immunopositive cell bodies were found in the preoptic region of the periventricular zone of the hypothalamus, the suprachiasmatic and paraventricular hypothalamic nuclei, neural structures adjacent to the median eminence (including the retrochiasmatic area, arcuate nucleus, ventromedial hypothalamus, and tuber cinereum), and the lateral mammillary and supramammillary nuclei. In all these areas, immunolabelling appeared specific since it was abolished by preabsorption of primary antisera with the appropriate PACAP peptide. However, the number of immunopositive cells in the suprachiasmatic nucleus was also reduced by preabsorption of PACAP-27/38 antisera with vasoactive intestinal polypeptide, suggesting that a subpopulation of cells in the suprachiasmatic nucleus express a peptide which has significant sequence homology with both PACAP-27/38 and vasoactive intestinal polypeptide. The distribution of PACAP immunoreactivity throughout the hypothalamus, bed nucleus of the stria terminalis, and amygdala suggests the involvement of PACAP in a number of processes including limbic, autonomic, and neuroendocrine functions as well as regulation of the circadian pacemaker. © 1996 Wiley-Liss, Inc.

Distribution of pituitary adenylate cyclase activating polypeptide (PACAP) immunoreactivity in the hypothalamus and extended amygdala of the rat.

Pituitary adenylate cyclase activating polypeptide (PACAP) is found in two forms of 27 and 38 amino acids (PACAP-27 and PACAP-38 respectively) in the mammalian central nervous system. Using antibodies to these two forms of PACAP, we examined the distribution of PACAP immunoreactivity in the rat hypothalamus and a number of extrahypothalamic areas. The patterns of immunostaining for PACAP-27 and PACAP-38 were similar: prominent terminal labelling was present in the retrochiasmatic area, median eminence, and posterior periventricular nucleus of the hypothalamus as well as the bed nucleus of the stria terminalis and amygdaloid complex. After colchicine treatment, immunopositive cell bodies were found in the preoptic region of the periventricular zone of the hypothalamus, the suprachiasmatic and paraventricular hypothalamic nuclei, neural structures adjacent to the median eminence (including the retrochiasmatic area, arcuate nucleus, ventromedial hypothalamus, and tuber cinereum), and the lateral mammillary and supramammillary nuclei. In all these areas, immunolabelling appeared specific since it was abolished by preabsorption of primary antisera with the appropriate PACAP peptide. However, the number of immunopositive cells in the suprachiasmatic nucleus was also reduced by preabsorption of PACAP-27/38 antisera with vasoactive intestinal polypeptide, suggesting that a subpopulation of cells in the suprachiasmatic nucleus express a peptide which has significant sequence homology with both PACAP-27/38 and vasoactive intestinal polypeptide. The distribution of PACAP immunoreactivity throughout the hypothalamus, bed nucleus of the stria terminalis, and amygdala suggests the involvement of PACAP in a number of processes including limbic, autonomic, and neuroendocrine functions as well as regulation of the circadian pacemaker.

Retrograde transport of brain-derived neurotrophic factor (BDNF) following infusion in neo- and limbic cortex in rat: relationship to BDNF mRNA expressing neurons.

Brain-derived neurotrophic factor (BDNF) was the second member of the nerve growth factor (NGF) family to be isolated. The ability of BDNF to be retrogradely transported following intraparenchymal infusion represents a unique neurobiological tool to determine the location of putative neuron-specific BDNF-responsive neuronal systems. In the present study, we infused recombinant human (rh) BDNF into the rodent neo- and limbic cortex and used a turkey anti-BDNF antibody to determine specific populations of neurons which retrogradely transport this neurotrophin. Frontal cortex infusion retrogradely labeled neurons within the ipsilateral and contralateral frontal cortex, basal forebrain, lateral hypothalamus, centrolateral, mediodorsal, ventrolateral, ventromedial, ventral posterior, rhomboid, reuniens, and medial geniculate thalamic nuclei, and locus coeruleus. Occipital cortex infusion retrogradely labeled neurons in the frontal, temporal, occipital, and perirhinal cortices as well as the claustrum, basal forebrain, thalamus, epithalamus, hypothalamus, and raphe nuclei. Dorsal hippocampal infusion retrogradely labeled neurons within the septal diagonal band, supramammillary nucleus, and entorhinal cortex and was also transported within various hippocampal subfields. Entorhinal cortex infusion retrogradely labeled neurons within the perirhinal cortex, endopiriform nucleus, piriform cortex, dentate gyrus, presubiculum, parasubiculum, CA1-CA4 fields, amygdaloid nuclei, basal forebrain, thalamus, hypothalamus, periaqueductal gray, raphe nuclei, and locus coeruleus. Amygdala infusion labeled neurons in the endopiriform nucleus, temporal cortex, piriform cortex, paralimbic cortex, hippocampus, subiculum, entorhinal cortex, amygdala, basal forebrain, thalamus, hypothalamus, substantia nigra, pars compacta, raphe, and pontine parabrachial nuclei. In situ hybridization experiments demonstrated that virtually all areas which retrogradely transport BDNF also express its message. Neuroanatomical distributional studies of BDNF will unravel specific central nervous system neurotrophic-responsive systems.

Neuronal Nicotinic Receptor a6 Subunit mRNA is Selectively Concentrated in Catecholaminergic Nuclei of the Rat Brain

Although the neuronal nicotinic receptor alpha 6 subunit was cloned several years ago, its functional significance remains to be investigated. Here we describe an in situ hybridization study of the mRNA for this subunit in the adult rat central nervous system using oligonucleotide probes. Specific alpha 6 mRNA labelling was restricted to a few nuclei throughout the brain; it was particularly high in several catecholaminergic nuclei [the locus coeruleus (A6), the ventral tegmental area (A10) and the substantia nigra (A9)] at levels significantly higher than those found for any other known nicotinic receptor subunit mRNA. Labelling for alpha 6 mRNA was also detected at lower levels in the reticular thalamic nucleus, the supramammillary nucleus and the mesencephalic V nucleus. Some cells of the medial habenula (medioventral part) and of the interpeduncular nucleus (central and lateral parts) were also labelled. The distribution of alpha 6 mRNA was compared with the distribution of the other known nicotinic acetylcholine receptor subunit mRNAs. In several nuclei, the expression of alpha 6 was complementary to those of other alpha subunits. Moreover, some of the cell groups (such as the substantia nigra, the ventral tegmental area and the locus coeruleus) previously thought to contain mainly alpha 3 mRNA in fact were found to contain high levels of alpha 6 mRNA. Finally, we found extensive colocalization of alpha 6 and beta 3, indicating the possible existence of nicotinic receptor hetero-oligomers containing both subunits. The present results show that alpha 6 is the major nicotinic acetylcholine receptor alpha subunit expressed in dopaminergic cell groups of the mesencephalon and noradrenergic cells of the locus coeruleus. This suggests the involvement of the alpha 6 subunit in some of the major functions of central nicotinic circuits, including the modulation of locomotor behaviour and reward.

Evidence for Differential Control of Posterior Hypothalamic, Supramammillary, and Medial Mammillary Theta-Related Cellular Discharge by Ascending and Descending Pathways

Single-unit discharge was recorded from cells in the posterior hypothalamic nucleus (PH), supramammillary nucleus (SuM), and medial mammillary nucleus (MM) during hippocampal theta (theta) elicited by stimulation of the reticular nucleus pontis oralis (RPO). In agreement with previously published work, theta-related cells in the PH (12 cells) were all classified as tonic theta-ON (increased tonic discharge rate during hippocampal theta), whereas those in the SuM (9 cells) and MM (15 cells) were all classified as phasic theta-ON (rhythmic discharge, in phase with ongoing theta). The effect of RPO stimulation on cell discharge was tested after hippocampal theta was abolished by infusion of procaine into the medial septum/vertical limb of the diagonal band. The RPO-elicited discharge patterns of all PH tonic theta-ON cells and all SuM phasic theta-ON cells survived septal procaine infusion. Further, the discharge rate of PH cells and the frequency of burst discharge of SuM cells during RPO stimulation both increased after the infusion. In contrast, septal procaine infusion abolished the RPO-elicited rhythmic discharge pattern in MM phasic theta-ON cells and attenuated their discharge rates. These results indicate that the PH and SuM form parts of an ascending system mediating hippocampal theta, whereas the MM receives (and perhaps relays to other parts of the limbic system) rhythmic input descending from the septo-hippocampal system. In addition, PH and SuM receive descending inputs that limit the discharge rates of their theta-related cells during hippocampal theta.