A [C]2-Deoxyglucose analysis of the functional neural pathways of the limbic forebrain in the rat. III. The hippocampal formation

The regions metabolically activated in the rat brain following focal electrical stimulation of various components of the hippocampal formation were identified with the use of [¹⁴C]2-deoxyglucose (2-DG) autoradiography. The results of these experiments, conducted in the rat, showed that in the absence of elicited afterdischarge activity, stimulation of either the CA1 or CA3 field of the dorsal hippocampus resulted in bilateral metabolic activation of only the dorsal hippocampus as well as of a relatively restricted region within the dorsomedial aspect of the lateral septal nucleus, bilaterally. In contrast, stimulation of either the CA1 or CA3 field of the ventral hippocampus resulted in bilateral activation of the ventral hippocampus and no region of the dorsal hippocampus. Following such stimulation, the lateral septal nucleus was also labeled bilaterally, but the activated regions were situated in a position ventrolateral to those resulting from stimulation at dorsal levels. Stimulation of the subicular cortex, in contrast, resulted in only ipsilateral activation of the hippocampal formation and lateral septal nucleus. Further rostral levels of the lateral septal nucleus were noted to be activated following stimulation of subicular cortex as compared to stimulation of the cornu Ammonis.The hypothalamus was directly activated by two pathways, the postcommissural fornix and the medial corticohypothalamic tract. Following stimulation at dorsal and posterior levels of CA1 and the subiculum, the mammillary bodies were demonstrably labeled by input from the postcommissural fornix. Regions of the medial hypothalamus were activated via the medial corticohypothalamic tract following stimulation of the ventral subiculum.The amygdala, stria terminalis and its bed nucleus were also shown to be demonstrably activated following stimulation of the ventral subiculum, ventral CAl field and posterior prosubiculum. This pathway may represent an additional route by which hippocampal modulation may indirectly modulate hypothalamic function.The presence of elicited afterdischarges resulted in more extensive patterns of metabolic labeling within the hippocampal formation and lateral septal nuclei as compared to experiments in which afterdischarges were not elicited. The extent of the demonstrable labeling, both within, and extrinsic to the hippocampal formation appeared to be a function of the duration and severity of the elicited seizure discharge. Additional structures which were demonstrably labeled following the elicitation of seizure activity include the entorhinal cortex-prepyriform area, amygdala, substantia innominata, putamen, substantia nigra, olfactory and prefrontal cortices and medial thalamic nuclei.     

A [14C]2-deoxyglucose analysis of the functional neural pathways of the limbic forebrain in the rat. V. The septal area

The [14C]2-deoxyglucose (2-DG) metabolic mapping technique has been used to identify the regions responding with an augmented rate of metabolism following focal electrical stimulation of various sites within the lateral septal nucleus and medial septal nucleus/diagonal band (MSN/DB) complex in the rat. Since 2-DG uptake has been correlated with rates of functional activity, it was the intention of this study to suggest the anatomical substrates underlying various physiological and behavioral responses elicited by stimulation of the septal area. The results show that stimulation of any region within the lateral septal nucleus produced a profound bilateral activation of both the lateral septal nucleus, as well as the hippocampal formation. While stimulation of a number of different fiber systems associated with the lateral septum could contribute to the observed pattern of labeling, the data suggest that, functionally, a major consequence of such stimulation is the antidromic activation of CA3----lateral septum fibers to axonal branch points, beyond which, orthodromic propagation of the impulse produces activation in CA3 target regions, including subfields CA1 and CA3, as well as the lateral septal nucleus, bilaterally. In addition, regions typically manifesting metabolic activation following stimulation of the lateral septal nucleus included the ipsilateral diagonal band of Broca, nucleus accumbens, lateral preoptic area and lateral hypothalamus, posteriorly, and the prelimbic cortex, anteriorly. Occasionally, target regions of the postcommissural fornix, including the medial mammillary nucleus and anterior thalamic nuclei were also activated following stimulation of the lateral septal nucleus. In contrast to the widespread pattern of activation resulting from stimulation of the lateral septal nucleus, stimulation of the MSN/DB complex produced activation which was largely confined to the medial forebrain bundle. In a final phase of the experiment, afterdischarge activity was elicited by sodium penicillin injection into the lateral septal nucleus. Such treatment produced more widespread 2-DG uptake, including more extensive activation within the lateral septal nucleus, hippocampal formation, amygdala, and thalamus. Additionally, the prefrontal cortex and temporal neocortex were activated.     

A [C]2-deoxyglucose analysis of the functional neural pathways of the limbic forebrain in the rat. IV. A pathway from the prefrontal cortical-medial thalamic system to the hypothalamus

The present study utilized the [¹⁴C]2-deoxyglucose (2-DG) cell labeling procedure to characterize a functional pathway from the prefrontal cortex (Pfc) and mediodorsal thalamic nucleus (MD) to the hypothalamus. Rats were injected with 2-DG prior to a 45 min experimental paradigm consisting of alternating 30 s on-off periods of electrical brain stimulation. Standard procedures were utilized for the removal and processing of brain tissue for X-ray autoradiography. In the first phase of this study, stimulation applied to the prefrontal cortex generally yielded a pattern of 2-DG distribution consistent with the findings of classical anatomical studies. Stimulation of the dorsomedial and ventromedial prefrontal cortex or the infralimbic cortex produced the most effective activation of the diencephalon. This activation was primarily limited to MD, with no involvement of any region of the hypothalamus. In the second phase of this study, brain regions activated following stimulation of sites along the rostro-caudal axis of MD were examined. Stimulation of MD resulted in the activation of the nucleus reuniens and other midline and non-specific thalamic nuclei. Stimulation of this nucleus also activated the ventromedial thalamic nucleus, medial aspects of the nucleus accumbens and the medial and sulcal prefrontal cortices. Again, in each of these cases, labeling within any region of the hypothalamus could not be detected. Since MD stimulation activated the midline thalamus, and the nucleus reuniens in particular, the last phase of this experiment involved stimulation of the nucleus reuniens in order to determine the source of medial thalamic inputs to the hypothalamus. Stimulation of the nucleus reuniens activated fibers which were distributed to both the medial and lateral hypothalamus. In addition, stimulation also activated the descending periventricular system, which could be followed to the level of the midbrain central gray and such limbic structures as the hippocampal formation, septal area, amygdala and prefrontal cortex. These findings indicate that Pfc-MD activation of the hypothalamus is achieved indirectly via interneurons within the nucleus reuniens.     

Radioautographic analysis of [C]2-deoxyglucose uptake in hippocampal formation of the rat during enforced locomotor activity-induced theta

The [¹⁴C]2-deoxyglucose ([¹⁴C]2-DG) uptake in the hippocampal formation of the rat was studied following enforced locomotor activity-induced theta (Mθ). Mθ was found to be essentially associated with an increase in 2-DG uptake in the stratum oriens of the hippocampal CA1-CA2 areas. These data contrast with our previous findings that physostigmine-induced theta (Iθ) is specifically associated with a decrease in 2-DG uptake in the stratum lacunosum moleculare of hippocampal CA1-CA2 areas. When both of our sets of radioautographic data are considered together, Mθ and Iθ appear to have a distinct neurophysiological basis.     

An analysis of the efferent connections of the septal area in the cat

The neuroanatomical organization of the efferent connections of the septal area in the cat was analyzed by the use of anterograde ([3H]leucine radioautography) and retrograde (horseradish peroxidase histochemistry) tracing techniques. The results indicate that the lateral septal nucleus projects to the nuclei of the diagonal band, preoptic area, lateral hypothalamus, and supramammillary region. The projections of the septofimbrial nucleus supply the nuclei of the diagonal band and the medial habenular nucleus. Projection targets of the vertical limb of the diagonal band are widespread and include the preoptic area, lateral hypothalamus, anterior limbic cortex, amygdala, medial habenular nucleus, interpeduncular nucleus and hippocampal formation. The projection from the vertical limb to the hippocampal formation is organized in a topographical manner in such a fashion that cells positioned near the midline project to the dorsal hippocampus and adjoining subicular cortex while fibers originating from cells situated more laterally project to more ventral parts of the hippocampal formation. In general, the projections from the horizontal limb were similar to those from the vertical limb, but several differences were noted. Fibers arising from the horizontal limb are distributed to the ventral tegmental area and interpeduncular nucleus but this region seems to lack a projection to either the habenular complex or to the ventral aspect of the hippocampal formation. Fibers arising from the bed nucleus of the anterior commissure are distributed to the preoptic region, lateral hypothalamus, supramammillary region, posterior aspect of the medial mammillary nucleus and lateral habenular nucleus.     

A 14C-2-deoxyglucose analysis of the neural pathways of the limbic forebrain in the rat: II. The hypothalamus

An attempt was made to characterize the nature of the functional organization of the hypothalamus by observing the patterns of uptake of 14C-2-deoxyglucose (2DG) following electrical stimulation of different regions within the preoptico-hypothalamus in the rat. The experimental paradigm consisted of electrical brain stimulation delivered continuously for periods of 30 sec on and 30 sec off for 45 minutes following injection of 2DG. Brains were removed and processed for autoradiography. Activation of the medial forebrain bundle was noted following stimulation of the nucleus accumbens and lateral preoptico-hypothalamus. Activated fibers could be followed only in a caudal direction through the medial forebrain bundle and into the ventral tegmental area as a result of nucleus accumbens stimulation. Stimulation of the lateral preoptic region or of the anterior half of lateral hypothalamus produced activation of the lateral septal nucleus, lateral habenular nucleus, perifornical region, midline thalamus and ventral tegmental area. Since stimulation of the perifornical hypothalamus significantly activated the rostro-caudal extent of the midbrain cental gray, it is suggested that impulses from the lateral hypothalamus reach the lower brainstem via its connections with the perifornical hypothalamus. Ventromedial hypothalamic stimulation activated only the lateral septal nucleus, cortico-medial amygdala and medial preoptico-hypothalamus, while medial preoptico-hypothalamic stimulation resulted in increased 2DG uptake in the midbrain central gray, thus suggesting that medial hypothalamic impulses reach the brainstem by first ascending to the level of the preoptico-hypothalamus. Mammillary body stimulation orthodromically activated fibers in the mammillothalamic and mammillotegmental tracts and antidromically fibers in the fornix for a short distance.     

Metabolic mapping of the rat brain involved in thermoregulatory responses using the [C]2-deoxyglucose technique

The central nervous structures involved in thermoregulatory responses to thermal stimulation of the preoptic/anterior hypothalamic region were investigated in conscious, unrestrained rats by means of the 2-deoxy-d-[¹⁴C]glucose autoradiographic technique. Significant activation in metabolic activity was observed in the medial preoptic area, medial forebrain bundle, anterior part of ventromedial hypothalamus, anteroventral thalamus, dorsomedial thalamus, basal ganglia, pars compacta of substantia nigra, red nucleus and the reticular formation.     

A C-2-Deoxyglucose analysis of the neural pathways of the limbic forebrain in the rat: II. The hypothalamus

An attempt was made to characterize the nature of the functional organization of the hypothalamus by observing the patterns of uptake of ¹⁴C-2-deoxyglucose (2DG) following electrical stimulation of different regions within the preoptico-hypothalamus in the rat. The experimental paradigm consisted of electrical brain stimulation delivered continuously for periods of 30 sec on and 30 sec off for 45 minutes following injection of 2DG. Brains were removed and processed for autoradiography. Activation of the medial forebrain bundle was noted following stimulation of the nucleus accumbens and lateral preoptico-hypothalamus. Activated fibers could be followed only in a caudal direction through the medial forebrain bundle and into the ventral tegmental area as a result of nucleus accumbens stimulation. Stimulation of the lateral preoptic region or of the anterior half of lateral hypothalamus produced activation of the lateral septal nucleus, lateral habenular nucleus, perifornical region, midline thalamus and ventral tegmental area. Since stimulation of the perifornical hypothalamus significantly activated the rostro-caudal extent of the midbrain central gray, it is suggested that impulses from the lateral hypothalamus reach the lower brainstem via its connections with the perifornical hypothalamus. Ventromedial hypothalamic stimulation activated only the lateral septal nucleus, cortico-medial amygdala and medial preoptico-hypothalamus, while medial preoptico-hypothalamic stimulation resulted in increased 2DG uptake in the midbrain central gray, thus suggesting that medial hypothalamic impulses reach the brainstem by first ascending to the level of the preoptico-hypothalamus. Mammillary body stimulation orthodromically activated fibers in the mammillothalamic and mammillotegmental tracts and antidromically fibers in the fornix for a short distance.     

Localization of synaptic responses in the in vitro turtle olfactory bulb using the [C]2-deoxyglucose method

Studies were carried out on the in vitro turtle olfactory bulb preparation with a modification of the [¹⁴C]2-deoxyglucose (2-DG) technique. Electrical stimulation of either the dorsal or ventral division of the olfactory nerve produced broad bands of activity, spreading across laminae, in the corresponding half of the olfactory bulb. Pretreatment of the isolated preparation in a low calcium bath eliminated focal 2-DG uptake induced by electrical stimulation of the nerve. In contrast, pretreatment with the GABAergic antagonist, bicuculline, produced a notable increase in 2-DG accumulation. These findings are discussed in the light of the topographical innervation of the olfactory bulb by the olfactory nerve as well as the known synaptic organization of the olfactory bulb and the putative neurotransmitters operative in local circuits.     

Bilateral [14C]2-deoxyglucose uptake by motor pathways after unilateral neonatal cortex lesions in the rat

The left sensorimotor (SM) cortex was removed in 1-day-old and 30-day-old rats. At 90 days of age [14C]2-deoxyglucose (2DG) was injected and the right motor (MI) cortex was electrically stimulated to produce predominantly left vibrissae movements. Animals were sacrificed and their brains autoradiographed. Right motor cortex (MI) stimulation activated subcortical structures bilaterally in 3 of 5 neonatally lesioned rats. Right MI stimulation activated most subcortical structures unilaterally in 30-day lesioned rats. This implies that a critical period for SM cortex injury may occur between 1 and 30 days of age. We suggest that removal of left SM cortex at 1 day of age occurs before or during the critical period and this induces right MI cortex to form bilateral subcortical connections. The bilateral 2DG uptake increases imply the bilateral connections are functional. The unilateral subcortical activation in 2 of 5 neonatally lesioned animals may have been due to differences in size of the lesion, parameters of stimulation, or perhaps due to the time of the lesion being near the critical period. We also suggest that removal of left SM cortex at 30 days of age occurs after the critical period, but that this does not affect the predominantly ipsilateral subcortical connections from MI cortex which have previously formed during normal development.     

Localization of synaptic responses in the in vitro turtle olfactory bulb using the [14C]2-deoxyglucose method

Studies were carried out on the in vitro turtle olfactory bulb preparation with a modification of the [14C]-2-deoxyglucose (2-DG) technique. Electrical stimulation of either the dorsal or ventral division of the olfactory nerve produced broad bands of activity, spreading across laminae, in the corresponding half of the olfactory bulb. Pretreatment of the isolated preparation in a low calcium bath eliminated focal 2-DG uptake induced by electrical stimulation of the nerve. In contrast, pretreatment with the GABAergic antagonist, bicuculline, produced a notable increase in 2-DG accumulation. These findings are discussed in the light of the topographical innervation of the olfactory bulb by the olfactory nerve as well as the known synaptic organization of the olfactory bulb and the putative neurotransmitters operative in local circuits.     

Effects of intraventricular norepinephrine on preoptic-anterior hypothalamic electrical activity in the freely-moving rat: modulation by ovarian steroid hormones

In freely-moving female rats the effects of intraventricular infusion of norepinephrine (NE) on multiunit activity (MUA) were examined in the Diagonal Band of Broca (DBB), medial preoptic area (MPOA) and anterior hypothalamic area (AHA), regions containing neurons producing luteinizing hormone-releasing hormone (LHRH). NE was infused at a dosage known to depress plasma LH levels in ovariectomized (OVX) rats and elevated plasma LH concentrations in OVX-estrogen-progesterone-primed (EBP) animals. It was found that in adult OVX rats MUA in the brain areas listed above was almost invariably inhibited by NE (20 of 23 cases or 87%; the other three cases showed no change in electrical activity). However, after priming with estrogen and progesterone only about one-third of the OVX-EBP rats gave an inhibitory response, with another one-third showing no change in MUA and the final one-third of the cases actually giving an excitatory MUA response to NE — the DBB neurons being the most positive in this regard. Thus it appears that responsiveness of LHRH and/or adjacent neurons to the modulatory action of NE may itself be modulated by the influence of gonadal steroids.     

The theta‐related firing activity of parvalbumin‐positive neurons in the medial septum‐diagonal band of broca complex and their response to 5‐HT1A Receptor stimulation in a rat model of Parkinson's disease

The parvalbumin (PV)‐positive neurons in the medial septum‐diagonal band of Broca complex (MS‐DB) play an important role in the generation of hippocampal theta rhythm involved in cognitive functions. These neurons in this region express a high density of 5‐HT_1A receptors which regulate the neuronal activity and consequently affect the theta rhythm. In this study, we examined changes in the theta‐related firing activity of PV‐positive neurons in the MS‐DB, their response to 5‐HT_1A receptor stimulation and the corresponding hippocampal theta rhythm, and the density of PV‐positive neurons and their co‐localization with 5‐HT_1A receptors in rats with 6‐hydroxydopamine lesions of the substantia nigra pars compacta (SNc). The lesion of the SNc decreased the rhythmically bursting activity of PV‐positive neurons and the peak frequency of hippocampal theta rhythm. Systemic administration of 5‐HT_1A receptor agonist 8‐OH‐DPAT (0.5–128 µg/kg, i.v.) inhibited the firing rate of PV‐positive neurons and disrupted rhythmically bursting activity of the neurons and the theta rhythm in sham‐operated and the lesioned rats, respectively. The cumulative doses producing inhibition and disruption in the lesioned rats were higher than that of sham‐operated rats. Furthermore, local application of 8‐OH‐DPAT (0.005 μg) in the MS‐DB also inhibited the firing rate of PV‐positive neurons and disrupted their rhythmically bursting activity in sham‐operated rats, while having no effect on PV‐positive neurons in the lesioned rats. The lesion of the SNc decreased the density of PV‐positive neurons in the MS‐DB, and percentage of PV‐positive neurons expressing 5‐HT_1A receptors. These results indicate that the lesion of the SNc leads to suppression of PV‐positive neurons in the MS‐DB and hippocampal theta rhythm. Furthermore, the lesion decreases the response of these neurons to 5‐HT_1A receptor stimulation, which attributes to dysfunction and/or down‐regulation of 5‐HT_1A receptor expression on these neurons. These changes may be involved in cognitive impairments of Parkinson's disease. © 2013 Wiley Periodicals, Inc.     

Spatial distribution of [14C]2-deoxyglucose uptake in the glomerular layer of the rat olfactory bulb following early odor preference learning

Previous work has shown that odors induce focal uptake of [¹⁴C]2-deoxyglucose (2-DG) within the glomerular layer of the main olfactory bulb and that the amount of 2-DG accumulated in these foci increases after early odor learning. To determine if learning-associated changes in 2-DG uptake occur across the entire glomerular layer, we have mapped uptake throughout that layer at fixed angles in coronal sections through the bulb. Resulting arrays for individual bulbs were corrected for differing bulb size and averaged across experimental groups to address the spatial distribution of uptake. The average arrays revealed at least three discrete fields of uptake in naive, peppermint-exposed rats at postnatal day 19 that were not seen in air-exposed littermates. In agreement with previous studies, early preference training with peppermint odor given on postnatal days 1–18 increased 2-DG uptake at postnatal day 19 within odor-dependent patches of uptake in the posterior half of the midlateral bulb, whereas odor-dependent, ventrolateral patches of uptake did not increase to the same extent. In addition, early preference learning was associated with significantly increased 2-DG uptake averaged over the entire analyzed glomerular layer. These increases were smaller than those within odor-dependent foci and were distributed widely across the glomerular layer, showing low overlap between trained and control rats in anterior regions where peppermint odor did not stimulate 2-DG uptake. The widely distributed increases in 2-DG uptake after learning may reflect changed activity of centrifugal projections that diffusely innervate the glomerular layer. © 1996 Wiley-Liss, Inc.     

Behavioral and degeneration changes in the basal forebrain systems of aged rats: A quantitative study in the region of the basal forebrain after levo-acetyl-carnitine treatments assessed by Abercrombie estimation

One group of six male control rats [21 months old] and one group of six male rats of the same age, singularly stored in a cage, and treated with acetyl-l-carnitine-HCl (ALCAR: 60 mg/kg/day/p.o.) for six months were tested in the spatial learning/memory Morris maze-water task and for atrophy and cell loss in seven myelo- and cytostructurally defined basal forebrain (BF) cholinergic regions [Gritti et al., 1993 J Comp Neurol 329: 438–457]. Coronal sections 25 μm thick were cut through the BF regions and processed every 200 μm for choline acetyltransferase (ChAT) immunohistochemistry. The ALCAR-treated rats had significantly shorter exit times on the Morris maze-water task test than the control rats (ANOVA-enzyme: F_1,39 = 112.5, P = 0.0001; sessions: F_3,39 = 10.41, P = 0.0001; interaction: F_3,39 = 5.09, P = 0.0044). Degenerative morphological changes in the BF ChAT-positive cells were observed in the control rats, but not in the treated animals, in: the diagonal band of Broca, the magnocellular preoptic nucleus, the olfactory tubercle, the substantia innominata, and the globus pallidus (ANOVA-enzyme: F_1,2 = 14, P = 0,0003; structures: F_6,7 = 4, P = 0,0018; interaction: F_6,7 = 3, P = 0,0043). In the diagonal band of Broca (P < 0.0494) and in the magnocellular preoptic nucleus (P < 0.0117) there were significantly fewer ChAT-positive neurons in the aged control rats than in the ALCAR-treated rats. These results demonstrate that in rats aged from 15 to 21 months ALCAR treatment significantly attenuated spatial learning/memory impairment on the Morris maze-water task and also importantly reduced the degeneration in size and number of cholinergic cells in the BF.     

Acute administration of 1-N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a compound producing parkinsonism in humans, stimulates [2-C]deoxyglucose uptake in the regions of the catecholaminergic cell bodies in the rat and guinea pig brains

A modification of the [2-¹⁴C]deoxyglucose (2-DG) autoradiographic technique of Sokoloff et al.¹² was used to study the effects of acute administration of 1-N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (10 mg/kg, s.c.) in the rat and guinea pig brains. MPTP administration resulted in both species in a dramatic increase in the 2-DG uptake in the substantia nigra pars compacta, ventral tegmental area and locus ceruleus, brain areas containing the cell bodies of dopaminergic and noradrenergic neurons. Many other brain areas were not affected. In the rat the effects were time dependent, being maximal between 1 and 2 h after drug administration. The effects of MPTP on 2-DG uptake differ from those of other dopaminergic or catecholaminergic drugs and suggest a specificity of the action of this drug on catecholaminergic neurons.     

Positron emission tomography analysis of [11C]KW-6002 binding to human and rat adenosine A2A receptors in the brain

Adenosine A(2A) receptors are found on striatal neurones projecting to the external pallidum. KW-6002 (istradefylline) is a potent and selective antagonist for the adenosine A(2A) receptors in the CNS and acts to inhibit the excessive activity of this pathway in the MPTP marmoset model of PD, thus relieving parkinsonism. The objectives of this study were to investigate the regional binding of the novel positron emission tomography tracer [(11)C]KW-6002 in the healthy human brain and the rat brain, along with receptor occupancy by cold KW-6002 at varying doses in human. The highest [(11)C]KW-6002 uptake in the rat brain was seen in striatum and lower levels in cortex and cerebellum. Brain [(11)C]KW-6002 uptake was well characterized in humans by a two-tissue compartmental model with a blood volume term, and the ED(50) of cold KW-6002 was 0.5 mg in the striatum. Over 90% receptor occupancy was achieved with daily oral doses of greater than 5 mg. In humans, blockable binding was present in all gray matter structures including the cerebellum, which has not been reported to express A(2A) receptors. MRS 1745, an A(2B) receptor selective antagonist, had no effect on the cerebellar binding of [(11)C]KW-6002 in rats, suggesting that this blockable signal is unlikely to result from an affinity for adenosine A(2B) receptors.     

Quantitative analysis of axon collaterals of single superficial pyramidal cells in layer IIb of the piriform cortex of the guinea pig

To understand the functional organization of the piriform cortex (PC), the axon collaterals of three pyramidal cells in layer IIb of the anterior PC and one pyramidal cell in layer IIb of the posterior PC were labeled and quantitatively analyzed by intracellular biocytin injection in the guinea pig. Single pyramidal cells in the anterior and posterior PCs have widely distributed axon collaterals, which exhibit little tendency for patchy concentrations inside as well as outside the PC. The total lengths of the axon collaterals of the three fully analyzed pyramidal cells ranged from 68 to 156 mm, more than 50% of which were distributed in the PC. The total number of boutons of the three cells ranged from 6000 to 14,000, 5000-7000 of which were distributed in the PC. It was estimated that individual pyramidal cells in layer IIb form synaptic contacts with 2200 to 3000 other pyramidal cells in the PC, indicating that single pyramidal cells in layer IIb receive input from a large number of other pyramidal cells. This high connectivity of the network of pyramidal cells in the PC can be regarded as the neural network operating parallel distributed processing, which may play an important role in experience-induced enhancement in odorant discrimination in the PC.     

Distinct patterns of neuronal inputs and outputs of the juxtaparaventricular and suprafornical regions of the lateral hypothalamic area in the male rat

We have analyzed at high resolution the neuroanatomical connections of the juxtaparaventricular region of the lateral hypothalamic area (LHAjp); as a control and in comparison to this, we also performed a preliminary analysis of a nearby LHA region that is dorsal to the fornix, namely the LHA suprafornical region (LHAs). The connections of these LHA regions were revealed with a coinjection tract-tracing technique involving a retrograde (cholera toxin B subunit) and anterograde (Phaseolus vulgaris leucoagglutinin) tracer. The LHAjp and LHAs together connect with almost every major division of the cerebrum and cerebrospinal trunk, but their connection profiles are markedly different and distinct. In simple terms, the connections of the LHAjp indicate a possible primary role in the modulation of defensive behavior; for the LHAs, a role in the modulation of ingestive behavior is suggested. However, the relation of the LHAjp and LHAs to potential modulation of these behaviors, as indicated by their neuroanatomical connections, appears to be highly integrative as it includes each of the major functional divisions of the nervous system that together determine behavior, i.e., cognitive, state, sensory, and motor. Furthermore, although a primary role is indicated for each region with respect to a particular mode of behavior, intermode modulation of behavior is also indicated. In summary, the extrinsic connections of the LHAjp and LHAs (so far as we have described them) suggest that these regions have a profoundly integrative role in which they may participate in the orchestrated modulation of elaborate behavioral repertoires.