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PubMed1975

Discrimination of odors in olfactory bulb, pyriform-amygdaloid areas, and orbitofrontal cortex of the monkey.

In the orbitofrontal olfactory area (LPOF) which was delineated in a previous paper, the capacity for odor discrimination was studied and compared with that in the anterior pyriform cortex (AP), the medial portion of the amygdala (MA), and the olfactory bulb (OB). Unanesthetized monkeys were used and eight odors were applied. 1. In the OB, 12.5% of the cells responded to only one odor, and the cells which responded to five odors were most numerous (25%). The total of the cells which responded to two, three, and four odors was 52%, which was less than the total of the cells responding to three, four, and five odors (67.5%). A small number oc cells responded to all eight odors (2.5%). The responses were classified as an increase (+type), a decrease (-type), or no change (no-type) in the rate of spike discharge. 2. In the AP and MA, no difference in the response patterns was found. The cells which responded to only one odor were 12.3% of the total, and the cells which responded to three different kinds of odors were most numerous (34.3%). The total of the cells responding to two, three, and four odors was 80%, much more than that in the OB. In addition, no cell responded to all eight odors. Concerning the response types, an increase followed by a decrease, or vice versa, in the rate of spike discharges (mixed-type) was observed which did not appear in the OB. Thus, an advance was found in the processing of olfactory information when compared with the OB. 3. A most striking finding in the LPOF was that 50% of the cells responded to only one odor. The cells which responded to two, three, and four odors decreased in this order, and no cell responded to more than five odors. These cells never responded to light or sound. 4. Using three very similar odors and five very different odors, it was apparent that the ability to discriminate odors of the same category is far more advanced in the LPOF than in the lower olfactory areas; and, in contrast, the lower olfactory areas also play a significant role in the discrimination of odors which belong to different categories. 5. It was concluded that the capacity for odor discrimination definitely improves along the olfactory nervous system from the lower to the higher areas. It is highly probable that a fine and sepcific discrimination of odors is performed in the LPOF.

Amygdala↗
PubMed1975

Olfactory bulb projections in the bullfrog Rana catesbeiana.

The projections of the accessory and main olfactory bulbs of the bullfrog are described as part of a long term analysis of the morphological differences in amphibian and reptilian telancephalons. Unilateral aspiration of the accessory olfactory bulb results in an ipsilateral projection to the pars lateralis of the amygdala via the accessory olfactory tract. Degenerating fibers from the accessory olfactory bulb are tracable into the cell-free zone between the dorsal striatum and the lateral pallium, and projections to these neural populations may also exist. Unilateral lesions of the main olfactory bulb reveal two major secondary pathways: an ipsilateral medial olfactory tract that projects to the rostral ventromedial portion of the medial pallium, the postolfactory eminence and the rostal, lateral and medial septal nuclei; and an ipsilateral lateral olfactory tract that projects to the dorsal striatum, the lateral pallium and the ventral half of the dorsal pallium. Two crossed secondary olfactory pathways to the contralateral telencephalon decussate via the habenular commissure after entering the ipsilateral stria medullaris. A crossed lateral pathway terminates in the dorsal striatum, the caudal, lateral pallium and the ventral portion of the dorsal pallium. A crossed medial pathway terminates in the internal granule layer of the main olfactory bulb.

Amygdala↗
PubMed2000

Comparison of odor receptive field plasticity in the rat olfactory bulb and anterior piriform cortex.

Recent work in the anterior piriform cortex (aPCX) has demonstrated that cortical odor receptive fields are highly dynamic, showing rapid changes of both firing rate and temporal patterning within relatively few inhalations of an odor, despite relatively maintained, patterned input from olfactory bulb mitral/tufted cells. The present experiment examined the precision (odor-specificity) of this receptive field plasticity and compared it with the primary cortical afferent, olfactory bulb mitral/tufted cells. Adult Long-Evans hooded rats, urethan anesthetized and freely breathing, were used for single-unit recording from mitral/tufted and aPCX layer II/III neurons. Partial mapping of receptive fields to alkane odors (pentane, heptane, and nonane) was performed before and immediately after habituation (50-s exposure) to one of the alkanes. The results demonstrated that odor habituation of aPCX responses was odor specific, with minimal cross-habituation between alkanes differing by as few as two carbons. Mitral/tufted cells, however, showed strong cross-habituation within the odor set with the most profound cross effects to carbon chains shorter than the habituating stimulus. The results suggest that although mitral/tufted cells and aPCX neurons have roughly similar odor receptive fields, aPCX neurons have significantly better odor discrimination within their receptive field. The results have important implications for understanding the underlying bases of receptive fields in olfactory system neurons and the mechanisms of odor discrimination and memory.

Action Potentials↗
PubMed1998

Effects of gestational methylmercury exposure on immunoreactivity of specific isoforms of PKC and enzyme activity during post-natal development of the rat brain.

Protein kinase C (PKC)-mediated phosphorylation has been implicated in neuronal growth and differentiation [R.S. Turner, R.L. Mazzei, G.J. Raynor, P.R. Girard, J.F. Kuo, Proc. Natl. Acad. Sci. U.S.A., 81 (1984) 3143-3147.]. We examined effects of gestational exposure to the neurotoxicant, methylmercury (CH3Hg), on the developmental profile of immunoreactivity (IR) for alpha, beta, gamma and epsilon PKC isoforms and cytosolic PKC activity. Long-Evans dams were dosed on gestational days (GD)6-15 (p.o.) with 0, 1, or 2 mg kg-1 day-1 CH3Hg dissolved in saline. Pups were sacrificed and perfused with buffered paraformaldehyde on post-natal days (PND) 1, 4, 10, 21, 45 and 85. The brains were sectioned sagittally, stained immunohistochemically, and examined throughout the medial to lateral extent. IR in neuronal cell bodies for PKC isoforms alpha, beta, gamma, and epsilon was densest in the olfactory bulb, hippocampus, shell of the inferior colliculus, pons, cerebral, piriform, and cerebellar cortex, whereas axonal staining was prominent in the brainstem, internal capsule, corpus callosum, anterior commissure, fornix and olfactory tract. In controls, the PKC alpha and epsilon IR was highest on PND1-4, decreased dramatically by PND10, and decreased further by PND21. In the neonate, the regional and cellular distributions of alpha and epsilon IR were similar. The PKC gamma IR was greater at post-weaning ages (PND21-85) with the greatest regional density apparent in the hippocampus, cortex, and cerebellum. Only the highest dose of CH3Hg (2 mg kg-1 day-1; GD6-15) produced a persistent decrease in regional alpha and epsilon, but not beta or gamma IR during the post-natal period. These regional and time-dependent changes in PKC isoforms were complemented by the examination of PKC activity in cortex, olfactory bulb, cerebellum and brainstem. Cytosolic PKC activity increased from PND1 to 10 in cortex, olfactory bulb, and cerebellum. On PND21, PKC activity decreased in the cortex and olfactory bulb, but remained high in the cerebellum. By contrast, PKC activity in the brainstem was highest on PND1 and 4 and decreased dramatically by PND21. CH3Hg (2 mg kg-1 day-1) significantly decreased PKC activity on PND1 and 4 in the cortex. The present results characterize the cellular and regional ontogeny of PKC isoenzymes alpha, beta, gamma and epsilon, and indicate that developmental exposure to CH3Hg can alter the ontogeny of specific isoforms and regional PKC activity.

Animals↗
PubMed1987

Reciprocal functional connections of the olfactory bulbs and other olfactory related areas with the prefrontal cortex.

Reciprocal putative connections of the prefrontal cortex (PFC) (agranular insular, ventral and lateral orbital region) with the ipsi and contralateral main olfactory bulb (IOB; COB), the mediodorsal thalamic nucleus (MD), the basolateral amygdaloid nucleus (BLA) and the piriform cortex (PC) were investigated with electrophysiological techniques. Evoked field responses and orthodromic unit driving, generated in PFC following electrical stimulation of the above mentioned structures, were abolished following topical application of KCl, except for COB evoked mass potentials. Thus, locally generated activity was elicited in agranular insular cortex following IOB activation, the same region where recently, the taste cortex in the rat was localized. Since gustatory-visceral afferent information reaches insular cortex via 2-3 synaptic relays, autonomic, olfactory and gustatory inputs may interact at this level, and, as suggested previously for the mouse, play a key integrative role in flavor perception. Antidromically invaded neurons, 47% of which were identified by the collision-extinction technique, were also found in PFC areas which overlapped to a considerable extent with those from which orthodromic unit responses were obtained. In particular, closely spaced neurons in ventrolateral orbital (VLO) and lateral orbital (LO) regions were antidromically invaded following IOB and PC shocks; some neurons antidromically discharged by IOB were also transsynaptically activated following PC stimulation. These findings are in agreement with recent neuroanatomical studies which demonstrate axonal projections from PFC neurons to the IOB and COB in the rat and South American armadillo. In addition, stimulation of PFC regions dorsal to the rhinal fissure mostly inhibited spontaneous unit discharges recorded at the mitral cell layer of the IOB, suggesting that this effect may be partially mediated by excitatory inputs of prefrontal axons onto granule cells. The conduction properties, antidromic thresholds and activity-dependent variations in conduction velocity (CV) of bulbopetal neurons in prefrontal cortex were found to be similar to those exhibited by cells projecting to the IOB from olfactory peduncle regions, but not to those present in bulbopetal neurons of the horizontal limb of diagonal band, indicating that the OB may be subjected to centrifugal control by at least two cell groups differing in both histochemical and electrophysiological properties.

Afferent Pathways↗
PubMed1987

Quantitative autoradiography of brain binding sites for the vesicular acetylcholine transport blocker 2-(4-phenylpiperidino)cyclohexanol (AH5183).

2-(4-Phenylpiperidino)cyclohexanol (AH5183) is a noncompetitive and potent inhibitor of high-affinity acetylcholine transport into cholinergic vesicles. It is reported here that [3H]AH5183 binds specifically and saturably to slide-mounted sections of the rat forebrain (Kd = 1.1 to 2.2 X 10(-8) M; Bmax = 286 to 399 fmol/mg of protein). The association and dissociation rate constants for [3H]AH5183 binding are 8.6 X 10(6) M-1 X min-1 and 0.18 min-1, respectively. Bound [3H]AH5183 can be displaced by nonradioactive AH5183 and by the structural analog (2 alpha,3 beta,4A beta,8A alpha)-decahydro-3-(4-phenyl-1-piperidinyl)-2- naphthalenol but not by 10 microM concentrations of the cholinergic drugs acetylcholine, choline, atropine, hexamethonium, eserine, or hemicholinium-3 or by the structurally related compounds 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-phenylpyridine, (+/-)-N-allylnormetazocine (SKF 10,047), levoxadrol, or dexoxadrol. Quantitative autoradiography reveals that [3H]AH5183 binding sites are distributed heterogenously throughout the rat forebrain and are highly localized to cholinergic nerve terminal regions. At the level of the caudate nucleus-putamen, the highest concentrations of saturable [3H]AH5183 binding (713-751 fmol/mg of protein) are found in the vertical limb of the diagonal band and the olfactory tubercle, with lesser amounts (334-516 fmol/mg of protein) in the caudate-putamen, nucleus accumbens, superficial layers of the cerebral cortex, and the primary olfactory cortex. At day 7 after transsection of the left fimbria, [3H]AH5183 binding and choline acetyltransferase activity in the left hippocampus were reduced by 33 +/- 6% and 61 +/- 7%, respectively. These findings indicate that [3H]AH5183 binds to a unique recognition site in rat brain that is topographically associated with cholinergic nerve terminals.

Acetylcholine↗
PubMed1984

The neonatal cerebellum: the highest level of glucocorticoid receptors in the brain.

We investigated the postnatal development of glucocorticoid receptors (GR) in rat cerebral cortex, hippocampus, olfactory bulbs and cerebellum during a period when cell proliferation, including neurogenesis in the latter 3 brain parts, is intensive. The concentration of GR was determined as the specific binding of [3H]dexamethasone to the cytosol stabilized against the inactivation of unoccupied receptor molecules by sodium molybdate. Unoccupied GR levels were found to increase during the first week, most rapidly in the cerebellum, where it reached the maximum during the second week. Specific binding of [3H]dexamethasone to the cerebellar nuclear fraction has already been present at days 8 and 15. By the end of the second week the cytosolic unoccupied GR begin to decline in the cerebellum. Total receptor binding, however, estimated in adrenalectomized animals does not decline. On the other hand, at day 8 adrenalectomy did not reveal more receptors than obtained in intact animals. Large numbers of GR in the neonatal cerebellum may specifically mediate the adverse effects of glucocorticoids on the cerebellar development during the period when the intensive morphogenetic processes take place in this part of the brain.

Animals↗
PubMed2005

[Effects of Guanyu capsule on the behavior and cerebral cortex monoamine neurotransmitters in depressive model of olfactory bulb damage rats].

OBJECTIVE: To investigate the behavioral changes and the levels of monoamine neurotransmitters in the anterior cortex in the olfactory bulb damage rats after being treated with Guanyu capsules (GYC). METHOD: Open-field test and step-down passive avoidance test were used to observe the behavior in model rats. HPLC-ECD was used to analyze the influences of GYC on the levels of monoamine neurotransmitters. RESULT: In the model rats, there was a characteristic hyperactivity in the Open-field and learning deficits in step-down passive avoidance (P < 0.01). The contents of 5-HT reduced, and the rate of DOPAC/DA increased significantly (P < 0.01). GYC 1.2, 0.6 g x kg(-1) could correct behavioral changes increase the contents of 5-HT, and decrease DOPAC/DA level (P < 0.01). CONCLUSION: GYC can correct behavioral changes in rats model of olfactory bulb damage, and regulating 5-HT and DA metabolism in cortex is one of the antidepressive mechanisms of GYC.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2002

Characterization of cAMP degradation by phosphodiesterases in the accessory olfactory system.

To characterize the potential role of cAMP in pheromone transduction, we have examined the occurrence of cyclic nucleotide phosphodiesterases (PDEs) in the mouse vomeronasal organ (VNO). We show that the cAMP-specific isoforms PDE4A and PDE4D are found preferentially in the apical and basal layers, respectively, of the VNO neuroepithelium and in the rostral (PDE4A) and caudal (PDE4D) portions of the accessory olfactory bulb glomerular layer. Assays for cAMP hydrolysis showed that PDE activity in VNO homogenates was about half that measured in the cerebral cortex and olfactory epithelium, and the proportion of total activity inhibited by rolipram, a PDE4-specific inhibitor, was approximately 40%. Activity in the VNO was enhanced 60% by Ca(2+) and calmodulin (CaM), implicating the presence of Ca(2+)/CaM-dependent PDE1. Zaprinast, which is known to inhibit PDE1C isoforms, completely suppressed Ca(2+)/CaM-stimulated activity and, together, zaprinast and rolipram inhibited cAMP hydrolysis by approximately 70%. Our results suggest that PDE1 and PDE4 isoforms are the primary source of cAMP degradation in the VNO.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1993

Fiber connections of the amygdaloid formation of the lizard Podarcis hispanica.

The amygdaloid formation of the lizard Podarcis hispanica can be divided into three main groups of nuclei on the basis of their input from the main and accessory olfactory bulbs: the vomeronasal amygdala, the olfactory amygdala and the dorsal amygdaloid group, the latter group receiving afferents from neither the main (MOB) or the accessory olfactory bulb (AOB). The vomeronasal amygdala has a centrifugal projection to the AOB, an important commissural connection to the contralateral vomeronasal amygdala, a minor projection to nucleus accumbens, and a bilateral projection to the lateral cortex. The olfactory amygdala displays a bilateral afferents from the MOB, receives a contralateral afferent, and is reciprocally connected with the lateral cortex. Moreover, it receives an important input from the vomeronasal amygdala. The dorsal amygdaloid group receives projections from the other two amygdaloid groups, multimodal inputs from the anterior dorsal ventricular ridge and the dorsal cortex, and a putative cholinergic input from the basal telencephalon. Moreover, it is the site of origin of a prominent bilateral amygdalo-striatal projection that extends to the bed nucleus of the stria terminalis and the so-called amygdalo-striatal transition area, through which it may control both visceral and motor activities. The main extratelencephalic output of the amygdala courses through the stria terminalis and terminates in the ventromedial hypothalamic nucleus. The extratelencephalic afferents of the amygdala arise from several hypothalamic and anterior thalamic nuclei, from the mesencephalic and rhombencephalic aminergic cell groups, and from the rhombencephalic parabrachial nucleus.

Amygdala↗
PubMed2005

Expression and distribution of vanilloid receptor 1 (TRPV1) in the adult rat brain.

The vanilloid receptor (TRPV1 or VR1) is a molecular integrator of various painful stimuli, including capsaicin, acid, and high temperature. It can also be activated by endogenous ligands, like the cannabinoid 1 receptor (CB1) agonist anandamide. TRPV1 is well characterized at the terminals of sensory nerves involved in the pain pathway. There is also evidence that TRPV1 is expressed in the brain but little is known about its function. Here, using commercially available specific antibodies to investigate the localization of TRPV1 in the brain of the rat, we report that TRPV1 was expressed in hippocampus, cortex, cerebellum, olfactory bulb, mesencephalon and hindbrain. Immunohistochemical analyses showed high expression in the cell bodies and dendrites of neurons in the hippocampus and in the cortex. To address the question of subcellular localization, immunoelectronmicroscopy was used. TRPV1-like staining was detected in the synapses (mostly, but not exclusively in post-synaptic dendritic spines), on the end feet of astrocytes and in pericytes. In summary, TRPV1 expression shows wide distribution in the brain of the rat, being found in astrocytes and pericytes as well as in neurons. Its localization is consistent with multiple functions within the central nervous system, including the regulation of brain vasculature.

Animals↗
PubMed2001

Long-lasting cholinergic modulation underlies rule learning in rats.

We studied the role of acetylcholine (ACh) in creating learning-related long-lasting modifications in the rat cortex. Rats were trained to discriminate positive and negative cues in pairs of odors, until they demonstrated rule learning and entered a mode of high capability for learning of additional odors. We have previously reported that pyramidal neurons in olfactory (piriform) cortex from trained rats had reduced spike afterhyperpolarization (AHP) for 3 d after rule learning. In the present study we examined the mechanism underlying this long-lasting modification. The cholinergic agonist carbachol reduced both slow AHP and firing adaptation in neurons from pseudotrained rats, but had no effect on neurons from trained rats, suggesting pre-existing cholinergic effect. Intracellular application of the calcium chelator BAPTA abolished the difference in slow AHP and in adaptation between groups, suggesting that the difference resulted from reduction in the ACh-sensitive, Ca(2+)-dependent potassium current, I(AHP). At the behavioral level, application of the muscarinic blocker scopolamine before each training session delayed rule learning but had no effect on further acquisition of odor memory. We suggest that intense ACh activity during rule learning enhances neuronal excitability in the piriform cortex by reducing I(AHP) and that the effect outlasts the stage of rule learning, so that ACh activity is not crucial for further odor learning.

Acetylcholine↗
PubMed2005

Ectopic galanin expression and normal galanin receptor 2 and galanin receptor 3 mRNA levels in the forebrain of galanin transgenic mice.

The functional interactions of the neuropeptide galanin (GAL) occur through its binding to three G protein-coupled receptor subtypes: galanin receptor (GALR) 1, GALR2 and GALR3. Previously, we demonstrated that GALR1 mRNA expression was increased in the CA1 region of the hippocampus and discrete hypothalamic nuclei in galanin transgenic (GAL-tg) mice. This observation suggested a compensatory adjustment in cognate receptors in the face of chronic GAL exposure. To evaluate the molecular alterations to GALR2 and GALR3 in the forebrain of GAL overexpressing mice, we performed complementary quantitative, real-time PCR (qPCR), in situ hybridization, and immunohistochemistry in select forebrain regions of GAL-tg mice to characterize the neuronal distribution and magnitude of GAL mRNA and peptide expression and the consequences of genetically manipulating the neuropeptide GAL on the expression of GALR2 and GALR3 receptors. We found that GAL-tg mice displayed dramatic increases in GAL mRNA and peptide in the frontal cortex, posterior cortex, hippocampus, septal diagonal band complex, amygdala, piriform cortex, and olfactory bulb. Moreover, there was evidence for ectopic neuronal GAL expression in forebrain limbic regions that mediate cognitive and affective behaviors, including the piriform and entorhinal cortex and amygdala. Interestingly, regional qPCR analysis failed to reveal any changes in GALR2 or GALR3 expression in the GAL-tg mice, suggesting that, contrary to GALR1, these receptor genes are not under ligand-mediated regulatory control. The GAL-tg mouse model may provide a useful tool for the investigation of GAL ligand-receptor relationships and their role in normal cognitive and affective functions as well as in the onset of neurological disease.

Animals↗
PubMed2001

Telencephalic cells take a tangent: non-radial migration in the mammalian forebrain.

During development of the mammalian telencephalon, cells migrate via diverse pathways to reach their final destinations. In the developing neocortex, projection neurons are generated from cells that migrate radially from the underlying ventricular zone. In contrast, subsets of cells that populate the ventral piriform cortex and olfactory bulb reach these sites by migrating long distances. Additionally, it has been recently established that cells migrate tangentially from the ventral ganglionic eminences to the developing cortex. These tangentially migrating cells are a significant source of cortical interneurons and possibly other cell types such as oligodendrocytes. Here we summarize the known routes of migration in the developing telencephalon, with a particular focus on tangential migration. We also review recent genetic and transplantation studies that have given greater insight into the understanding of these processes and the molecular cues that may guide these migrating cells.

Animals↗
PubMed1991

Human olfactory discrimination after unilateral frontal or temporal lobectomy.

Olfactory discrimination and detection was studied in 106 patients with unilateral cerebral excision in the right or left temporal lobe, right or left frontal lobe, left parietal lobe, or right frontal and temporal lobes, and in 20 normal control subjects. Detection thresholds for n-butyl alcohol, measured separately in each nostril, did not differ across subject groups or across nostrils, thus excluding any primary sensory loss. The discrimination task involved monorhinal presentation of repairs of unfamiliar odorants, which the subjects judged as same or different in quality. The results showed a significant deficit in discrimination confined to the nostril ipsilateral to the lesion in patients with temporal lobe removals. Patients with frontal lobe excisions were also impaired and, for patients with right frontal lesions including the orbital cortex, the impairment was found in both nostrils. Patients with left parietal lesions did not demonstrate any significant deficits. Normal subjects showed consistently better performance in the right than in the left nostril. The results are interpreted as reflecting the importance of the orbitofrontal cortex in olfactory discrimination. Temporal lobe lesions may disrupt the input to the orbitofrontal cortex, thereby producing poorer performance. The nostril difference in the normal subjects, together with the birhinal impairment in patients with right orbitofrontal damage, suggest a relative advantage of the right orbital region in olfactory processing.

Adult↗
PubMed1991

Development of paleocortical projections through the anterior commissure of hamsters adopts progressive, not regressive, strategies.

The perinatal development of anterior commissure projections was studied in hamsters by use of carbocyanine crystals implanted either into the commissure or into the ventrolateral prosencephalon. The earliest fascicles of growing commissural fibers had reached the midline on day 14 of gestation (E14). On E15, these fibers had entered the opposite hemisphere and reached the borders of their target regions. No waiting period was observed, since on E16 axons were already collateralizing into most targets. On P1, labelled cells were seen in all regions projecting through the anterior commissure in adults, namely, the anterior olfactory nucleus, olfactory tubercle, piriform cortex, nucleus of the lateral olfactory tract, bed nucleus of the stria terminalis, insular, perirhinal, entorhinal, and temporal cortices, as well as the amygdaloid complex. No evidence of topographical exuberance was detected. Counts of labelled neurons showed that the number of commissural cells increased gradually after birth. It is concluded that the development of paleocortical connections through the anterior commissure employs progressive strategies, lacking the regressive phenomena that are characteristic of the neocortical projections through the corpus callosum.

Aging↗
PubMed1981

Metabolic mapping of functional activity in the olfactory projections of the rat: ontogenetic study.

An ontogenetic study of the uptake of [14C]2-deoxy-D-glucose (2-DG) within the direct olfactory bulb projections and the tertiary olfactory projections was performed on rats of 1, 9 and 21 days old. Animals were exposed either to ethyl acetoacetate or to nest odor. In newborns, most of the direct olfactory bulb projections - anterior olfactory nucleus, anterior part of the olfactory tubercle, piriform cortex and nucleus of the lateral olfactory tract - appear labelled on films and therefore seem functional. No evidence of 2-DG uptake can be brought out in the cortical amygdala nucleus. AS regards the tertiary olfactory projections, there is no apparent functional activity, neither in the medio-dorsal and medio-ventral thalamic nuclei nor in the hypothalamic nuclei, e.g. the lateral preoptic area and the lateral hypothalamus. In 9-day-old pups, the direct olfactory bulb projections and the tertiary olfactory projections appear well-contrasted. Moreover, the patterns of labelling within the direct olfactory bulb projections are comparable to those observed in 21-day-old rats and in adult. These data are correlated with the postnatal development of the discriminating ability of the rat.

Aging↗