Afferent Connections of Cytoarchitectural Area 6M and Surrounding Cortex in the Marmoset: Putative Homologues of the Supplementary and Pre-supplementary Motor Areas

Cortical projections to the caudomedial frontal cortex were studied using retrograde tracers in marmosets. We tested the hypothesis that cytoarchitectural area 6M includes homologues of the supplementary and pre-supplementary motor areas (SMA and pre-SMA) of other primates. We found that, irrespective of the injection sites' location within 6M, over half of the labeled neurons were located in motor and premotor areas. Other connections originated in prefrontal area 8b, ventral anterior and posterior cingulate areas, somatosensory areas (3a and 1-2), and areas on the rostral aspect of the dorsal posterior parietal cortex. Although the origin of afferents was similar, injections in rostral 6M received higher percentages of prefrontal afferents, and fewer somatosensory afferents, compared to caudal injections, compatible with differentiation into SMA and pre-SMA. Injections rostral to 6M (area 8b) revealed a very different set of connections, with increased emphasis on prefrontal and posterior cingulate afferents, and fewer parietal afferents. The connections of 6M were also quantitatively different from those of the primary motor cortex, dorsal premotor areas, and cingulate motor area 24d. These results show that the cortical motor control circuit is conserved in simian primates, indicating that marmosets can be valuable models for studying movement planning and control.

Claustral Input to the Macaque Medial Posterior Parietal Cortex (Superior Parietal Lobule and Adjacent Areas)

The projections from the claustrum to cortical areas within and adjacent to the superior parietal lobule were studied in 10 macaque monkeys, using retrograde tracers, computerized reconstructions, and quantitative methods. In contrast with the classical view that posterior parietal areas receive afferents primarily from the dorsal and posterior regions of the claustrum, we found that these areas receive more extensive projections, including substantial afferents from the anterior and ventral regions of the claustrum. Moreover, our findings uncover a previously unsuspected variability in the precise regions of the claustrum that originate the projections, according to the target areas. For example, areas dominated by somatosensory inputs for control of body movements tend to receive most afferents from the dorsal-posterior claustrum, whereas those which also receive significant visual inputs tend to receive more afferents from the ventral claustrum. In addition, different areas within these broadly defined groups differ in terms of quantitative emphasis in the origin of projections. Overall, these results argue against a simple model whereby adjacency in the cortex determines adjacency in the sectors of claustral origin of projections and indicate that subnetworks defined by commonality of function may be an important factor in defining claustrocortical topography.

Thalamic afferents emphasize the different functions of macaque precuneate areas

We studied the thalamic afferents to cortical areas in the precuneus using injections of retrograde fluorescent neuronal tracers in four male macaques (Macaca fascicularis). Six injections were within the limits of cytoarchitectural area PGm, one in area 31 and one in area PEci. Precuneate areas shared strong input from the posterior thalamus (lateral posterior nucleus and pulvinar complex) and moderate input from the medial, lateral, and intralaminar thalamic regions. Area PGm received strong connections from the subdivisions of the pulvinar linked to association and visual function (the medial and lateral nuclei), whereas areas 31 and PEci received afferents from the oral division of the pulvinar. All three cytoarchitectural areas also received input from subdivisions of the lateral thalamus linked to motor function (ventral lateral and ventral anterior nuclei), with area PEci receiving additional input from a subdivision linked to somatosensory function (ventral posterior lateral nucleus). Finally, only PGm received substantial limbic association afferents, mainly via the lateral dorsal nucleus. These results indicate that area PGm integrates information from visual association, motor and limbic regions of the thalamus, in line with a hypothesized role in spatial cognition, including navigation. By comparison, dorsal precuneate areas (31 and PEci) are more involved in sensorimotor functions, being akin to adjacent areas of the dorsal parietal cortex.

Patterns of cortical input to the primary motor area in the marmoset monkey

In primates the primary motor cortex (M1) forms a topographic map of the body, whereby neurons in the medial part of this area control movements involving trunk and hindlimb muscles, those in the intermediate part control movements involving forelimb muscles, and those in the lateral part control movements of facial and other head muscles. This topography is accompanied by changes in cytoarchitectural characteristics, raising the question of whether the anatomical connections also vary between different parts of M1. To address this issue, we compared the patterns of cortical afferents revealed by retrograde tracer injections in different locations within M1 of marmoset monkeys. We found that the entire extent of this area is unified by projections from the dorsocaudal and medial subdivisions of premotor cortex (areas 6DC and 6M), from somatosensory areas 3a, 3b, 1/2, and S2, and from posterior parietal area PE. While cingulate areas projected to all subdivisions, they preferentially targeted the medial part of M1. Conversely, the ventral premotor areas were preferentially connected with the lateral part of M1. Smaller but consistent inputs originated in frontal area 6DR, ventral posterior parietal cortex, the retroinsular cortex, and area TPt. Connections with intraparietal, prefrontal, and temporal areas were very sparse, and variable. Our results demonstrate that M1 is unified by a consistent pattern of major connections, but also shows regional variations in terms of minor inputs. These differences likely reflect requirements for control of voluntary movement involving different body parts.

Patterns of afferent input to the caudal and rostral areas of the dorsal premotor cortex (6DC and 6DR) in the marmoset monkey

Corticocortical projections to the caudal and rostral areas of dorsal premotor cortex (6DC and 6DR, also known as F2 and F7) were studied in the marmoset monkey. Both areas received their main thalamic inputs from the ventral anterior and ventral lateral complexes, and received dense projections from the medial premotor cortex. However, there were marked differences in their connections with other cortical areas. While 6DR received consistent inputs from prefrontal cortex, area 6DC received few such connections. Conversely, 6DC, but not 6DR, received major projections from the primary motor and somatosensory areas. Projections from the anterior cingulate cortex preferentially targeted 6DC, while the posterior cingulate and adjacent medial wall areas preferentially targeted 6DR. Projections from the medial parietal area PE to 6DC were particularly dense, while intraparietal areas (especially the putative homolog of LIP) were more strongly labeled after 6DR injections. Finally, 6DC and 6DR were distinct in terms of inputs from the ventral parietal cortex: projections to 6DR originated preferentially from caudal areas (PG and OPt), while 6DC received input primarily from rostral areas (PF and PFG). Differences in connections suggest that area 6DR includes rostral and caudal subdivisions, with the former also involved in oculomotor control. These results suggest that area 6DC is more directly involved in the preparation and execution of motor acts, while area 6DR integrates sensory and internally driven inputs for the planning of goal-directed actions. They also provide strong evidence of a homologous organization of the dorsal premotor cortex in New and Old World monkeys.

Contrasting patterns of cortical input to architectural subdivisions of the area 8 complex: a retrograde tracing study in marmoset monkeys

Contemporary studies recognize 3 distinct cytoarchitectural and functional areas within the Brodmann area 8 complex, in the caudal prefrontal cortex: 8b, 8aD, and 8aV. Here, we report on the quantitative characteristics of the cortical projections to these areas, using injections of fluorescent tracers in marmoset monkeys. Area 8b was distinct from both 8aD and 8aV due to its connections with medial prefrontal, anterior cingulate, superior temporal polysensory, and ventral midline/retrosplenial areas. In contrast, areas 8aD and 8aV received the bulk of the projections from posterior parietal cortex and dorsal midline areas. In the frontal lobe, area 8aV received projections primarily from ventrolateral areas, while both 8aD and 8b received dense inputs from areas on the dorsolateral surface. Whereas area 8aD received the most significant auditory projections, these were relatively sparse, in comparison with those previously reported in macaques. Finally, area 8aV was distinct from both 8aD and 8b by virtue of its widespread input from the extrastriate visual areas. These results are compatible with a homologous organization of the prefrontal cortex in New and Old World monkeys, and suggest significant parallels between the present pathways, revealed by tract-tracing, and networks revealed by functional connectivity analysis in Old World monkeys and humans.

Cortical input to the frontal pole of the marmoset monkey

We used fluorescent tracers to map the pattern of cortical afferents to frontal area 10 in marmosets. Dense projections originated in several subdivisions of orbitofrontal cortex, in the medial frontal cortex (particularly areas 14 and 32), and in the dorsolateral frontal cortex (particularly areas 8Ad and 9). Major projections also stemmed, in variable proportions depending on location of the injection site, from both the inferior and superior temporal sensory association areas, suggesting a degree of audiovisual convergence. Other temporal projections included the superior temporal polysensory cortex, temporal pole, and parabelt auditory cortex. Medial area 10 received additional projections from retrosplenial, rostral calcarine, and parahippocampal areas, while lateral area 10 received small projections from the ventral somatosensory and premotor areas. There were no afferents from posterior parietal or occipital areas. Most frontal connections were balanced in terms of laminar origin, giving few indications of an anatomical hierarchy. The pattern of frontopolar afferents suggests an interface between high-order representations of the sensory world and internally generated states, including working memory, which may subserve ongoing evaluation of the consequences of decisions as well as other cognitive functions. The results also suggest the existence of functional differences between subregions of area 10.

Connections of the marmoset rostrotemporal auditory area: express pathways for analysis of affective content in hearing

The current hierarchical model of primate auditory cortical processing proposes a core of 'primary-like' areas, which is surrounded by secondary (belt) and tertiary (parabelt) regions. The rostrotemporal auditory cortical area (RT) remains the least well characterized of the three proposed core areas, and its functional organization has only recently come under scrutiny. Here we used injections of anterograde and retrograde tracers in the common marmoset (Callithrix jacchus) to examine the connectivity of RT and its adjacent areas. As expected from the current model, RT exhibited dense core-like reciprocal connectivity with the ventral division of the medial geniculate body, the rostral core area and the auditory belt, but had weaker connections with the parabelt. However, RT also projected to the ipsilateral rostromedial prefrontal cortex (area 10), the dorsal temporal pole and the ventral caudate nucleus, as well as bilaterally to the lateral nucleus of the amygdala. Thus, RT has connectivity with limbic structures previously believed to connect only with higher-order auditory association cortices, and is probably functionally distinct from the other core areas. While this view is consistent with a proposed role of RT in temporal integration, our results also indicate that RT could provide an anatomical 'shortcut' for processing affective content in auditory information.

Development of non-phosphorylated neurofilament protein expression in neurones of the New World monkey dorsolateral frontal cortex

We studied developmental changes in the expression of non-phosphorylated neurofilament protein (NNF) (a marker of the structural maturation of pyramidal neurones) in the dorsolateral frontal cortex of marmoset monkeys, between embryonic day 130 and adulthood. Our focus was on cortical fields that send strong projections to extrastriate cortex, including the dorsal and ventral subdivisions of area 8A, area 46 and area 6d. For comparison, we also investigated the maturation of prefrontal area 9, which has few or no connections with visual areas. The timing of expression of NNF immunostaining in early life can be described as the result of the interaction of two developmental gradients. First, there is an anteroposterior gradient of maturation in the frontal lobe, whereby neurones in caudal areas express NNF earlier than those in rostral areas. Second, there is a laminar gradient, whereby the first NNF-immunoreactive neurones emerge in layer V, followed by those in progressively more superficial parts of layer III. Following a peak in density of NNF-immunopositive cell numbers in layer V at 2-3 months of age, there is a gradual decline towards adulthood. In contrast, the density of immunopositive cells in layer III continues to increase throughout the first postnatal year in area 6d and until late adolescence (> 1.5 years of age) in prefrontal areas. The present results support the view that the maturation of visual cognitive functions involves relatively late processes linked to structural changes in frontal cortical areas.

Cytoarchitectonic subdivisions of the dorsolateral frontal cortex of the marmoset monkey (Callithrix jacchus), and their projections to dorsal visual areas

We describe the organization of the dorsolateral frontal areas in marmoset monkeys using a combination of architectural methods (Nissl, cytochrome oxidase, and myelin stains) and injections of fluorescent tracers in extrastriate areas (the second visual area [V2], the dorsomedial and dorsoanterior areas [DM, DA], the middle temporal area and middle temporal crescent [MT, MTc], and the posterior parietal cortex [area 7]). Cytoarchitectural field 8 comprises three subdivisions: 8Av, 8Ad, and 8B. The ventrolateral subdivision, 8Av, forms the principal source of frontal projections to the "dorsal stream," having connections with each of the injected visual areas. The cytoarchitectural characteristics of 8Av suggest that this subdivision corresponds to the marmoset's frontal eye field. The intermediate subdivision of area 8 (8Ad) has efferent projections to area 7, while the dorsomedial subdivision (8B) has few or no connections with extrastriate cortex. Area 46, located rostrolateral to area 8Av, has substantial connections with the medial extrastriate areas (DM, DA, and area 7) and with MT, while the cortex lateral to 8Av (area 12/45) projects primarily to MT and to the MTc. The rostromedial prefrontal (area 9) and frontopolar (area 10) regions have very few extrastriate projections. Finally, cells in dorsal area 6 (6d) have sparse projections to DM, MT, and the MTc, as well as strong projections to DA and to area 7. These results illuminate aspects of the evolutionary development of the primate frontal cortex, and serve as a basis for further research into cognitive functions using a marmoset model.

Cocaine- and amphetamine-regulated transcript in catecholamine and noncatecholamine presympathetic vasomotor neurons of rat rostral ventrolateral medulla

Presympathetic vasomotor adrenergic (C1) and nonadrenergic (non-C1) neurons in the rostral ventrolateral medulla (RVLM) provide the main excitatory drive to cardiovascular sympathetic preganglionic neurons in the spinal cord. C1 and non-C1 neurons contain cocaine- and amphetamine-regulated transcript (CART), suggesting that CART may be a common marker for RVLM presympathetic neurons. To test this hypothesis, we first used double-immunofluorescence staining for CART and tyrosine hydroxylase (TH) to quantify CART-immunoreactive (-IR) catecholamine and noncatecholamine neurons in the C1 region. Next, we quantified the proportion of CART-IR RVLM neurons that expressed Fos in response to a hypotensive stimulus, using peroxidase immunohistochemistry for Fos and dual immunofluorescence for CART and TH. Finally, we fluorescently detected CART immunoreactivity in electrophysiologically identified, juxtacellularly labeled RVLM presympathetic neurons. In the RVLM, 97% of TH-IR neurons were CART-IR, and 74% of CART-IR neurons were TH-IR. Nitroprusside infusion significantly increased the number of Fos-IR RVLM neurons compared with saline controls. In nitroprusside-treated rats, virtually all Fos/TH neurons in the RVLM were immunoreactive for CART (98% +/- 1.3%, SD; n = 7), whereas 29% +/- 8.3% of CART-positive, TH-negative neurons showed Fos immunoreactivity. Six fast (2.8-5.8 m/second, noncatecholamine)-, two intermediate (2.1 and 2.2 m/second)-, and five slow (<1 m/second, catecholamine)-conducting RVLM presympathetic vasomotor neurons were juxtacellularly labeled. After fluorescent detection of CART and biotinamide, all 13 neurons were found to be CART-IR. These results suggest that, in rat RVLM, all catecholamine and noncatecholamine presympathetic vasomotor neurons contain CART.

GABAB receptor subunits, R1 and R2, in brainstem catecholamine and serotonin neurons

GABA(B) receptors have been implicated in the GABAergic modulation of catecholaminergic and serotonergic pathways in the central nervous system. The GABA(B) receptor may require two subunits, GABA(B)R1 and GABA(B)R2, for functional activity. Using dual immunofluorescent labelling on adjacent cryostat sections, we investigated the presence of immunoreactivity for the GABA(B)R1 and GABA(B)R2 subunits in brainstem catecholamine (tyrosine hydroxylase-immunoreactive) and serotonin (tryptophan hydroxylase-immunoreactive) neurons. All neurons (>98%) examined in catecholamine groups A1, A2, A5, A6, C1, and serotonin groups B1-3 and B6-8 were immunoreactive for the GABA(B)R1 subunit. All A5 and A6 neurons (>97%) and at least 86% of A1, A2, C1, B2, B3, B7 and B8 neurons examined were GABA(B)R2-immunoreactive. The proportion of neurons with immunoreactivity for the GABA(B)R2 subunit varied between 0% and 99% for B1 neurons, and between 35% and 93% for B6 neurons. Statistical analysis showed that similar proportions of sampled neurons were immunoreactive for GABA(B)R1 and GABA(B)R2 in the A1, A5, A6, C1, B2 and B7 cell groups, whereas a smaller proportion of A2, B1, B3, B6 and B8 neurons were GABA(B)R2-immunoreactive than GABA(B)R1-immunoreactive. In general, our results suggest that GABA(B)R1 and GABA(B)R2 co-exist in the great majority of brainstem catecholamine and serotonin neurons. In the neurons that lack GABA(B)R2, the GABA(B)R1 subunit may act alone or with another protein.

Neurokinin-1 receptor immunoreactivity in hypotension sensitive sympathetic preganglionic neurons

Substance P activation of neurokinin-1 (NK1) receptors on spinal sympathetic preganglionic neurons (SPN) influences blood pressure. We identified SPN likely to subserve the baroreceptor reflex and established if these neurons showed NK1 receptor-immunoreactivity. Nitroprusside (NP) infusion or inferior vena cava (IVC) constriction activated similar numbers of SPN. Of these, about 40% were NK1 receptor-immunoreactive after NP infusion, but only about 20% were NK1 receptor-immunoreactive after IVC constriction. The distribution of Fos/NK1 receptor SPN suggested that substance P may preferentially target sympathoadrenal SPN.

Lymphokine-activated killer (LAK) cells discriminate between Epstein-Barr virus (EBV)-positive Burkitt's lymphoma cells

We have generated in vitro lymphokine-activated killer (LAK) cells from healthy donors by stimulating their mononuclear leukocytes with recombinant interleukin-2 (rIL-2) (100 U/ml). After 6 days in culture, the lytic properties of the LAK cells were analyzed in the 51Cr-release assay by utilizing a target panel of 6 paired lines consisting of an Epstein-Barr virus (EBV)-positive Burkitt's lymphoma (BL) cell line and an EBV-transformed lymphoblastoid cell line (LCL) from the same donor, the Raji BL line and the natural killer (NK) cell-sensitive K562 line. The patterns of lysis showed that the LAK cells discriminated between two categories of BL cell lines. Group I/II BL tumor cells which expressed the common acute lymphoblastic leukemia antigen (CALLA), the BL-associated glycolipid antigen (BLA) and phenotypically resembled biopsy cells were strongly lysed whereas group III BL cells which had assumed an LCL-like phenotype during culture and lacked the CALLA and BLA surface markers were only poorly lysed. The LCL targets were generally resistant to lysis but the K562 cell line was particularly sensitive. The outcome of cell depletion and monoclonal antibody (MAb) studies indicated that the LAK cell populations were phenotypically and functionally heterogeneous and consisted of at least 2 subpopulations of effector cells; a tumor-specific component and an NK-cell-mediated component.

Effects of constant infusion of gonadotrophin-releasing hormone in ovariectomized ewes with hypothalamo-pituitary disconnection: further evidence for differential control of LH and FSH secretion and the lack of a priming effect

Experiments were conducted in ovariectomized ewes after hypothalamo-pituitary disconnection (HPD) to examine LH and FSH secretion during constant infusion of gonadotrophin-releasing hormone (GnRH) or physiological saline and to determine whether or not a constant GnRH background enhances or diminishes pituitary responsiveness to GnRH pulses. Whereas pulsatile GnRH infusions maintained LH and FSH secretion, constant infusions (125 or 250 ng/h) led to the complete cessation of LH secretion and reduced FSH secretion. The rate of decline of plasma FSH concentrations was significantly (P less than 0.01) greater in animals receiving 250 ng GnRH/h than in saline-treated animals, whereas that in animals receiving 125 ng/h was not significantly different. When GnRH pulses were administered during constant GnRH infusion, the plasma LH pulse amplitudes were similar to those seen without the GnRH background. These data show that, in ovariectomized-HPD ewes FSH secretion does not require GnRH pulses and may merely reflect ongoing FSH synthesis and a constant low background of GnRH does not affect pituitary responsiveness to GnRH pulses.

Effects on plasma luteinizing hormone and follicle-stimulating hormone of varying the frequency and amplitude of gonadotropin-releasing hormone pulses in ovariectomized ewes with hypothalamo-pituitary disconnection

The effects on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion of various regimens of pulsatile gonadotropin-releasing hormone (GnRH) replacement were examined in ovariectomized (OVX) ewes after hypothalamo-pituitary disconnection (HPD). Hourly pulses of 500 ng GnRH restored gonadotropin secretion in OVX-HPD sheep. Replacement beginning 2 days after HPD gave consistent responses of LH and FSH within a week. Replacement beginning 61-96 days after HPD caused more gradual re-establishment of LH and FSH secretion with LH responses appearing immediately and FSH responses appearing 2 weeks later. When hourly GnRH pulses were increased in amplitudes from 250 to 500 ng the plasma LH baseline, peak values and pulse amplitudes were increased. There was no significant change in plasma FSH levels over 10 pulses at the higher dose. Decreases in GnRH pulse frequency led to increases in LH pulse amplitude and decreases in plasma LH baseline. In contrast, immediately after a change from a 2-hourly to an hourly mode, an increase in LH baseline occurred without an immediate reduction in LH pulse amplitude. Mean plasma FSH concentrations increased when the frequency was reduced from hourly to 2-hourly or 4-hourly. However, a change from 4-hourly to hourly pulses did not reduce FSH values within 7 days. It is concluded that changes in the pattern of LH secretion observed during the ovine estrous cycle could be accounted for, in part, by changes in GnRH pulse frequency.