An autoradiographic examination of corticocortical and subcortical projections of the mediodorsal‐projection (prefrontal) cortex in the rat

Abstract

The efferent connections of the cortex projected upon by the mediodorsal thalamic nucleus (MD-projection cortex) have been re-examined autoradiographically in the rat following the microelectrophoretic injection of 3H-proline-leucine into different parts of the medial and sulcal MD-projection cortex. Contrary t o previous negative findings, the present experiments revealed a system of extensive corticocortical projections and indicated that different areas of the MD-projection cortex have distinctive patterns in both their corticocortical and subcortical projections. Thus, cells of Brodmann's area 32 send axons to the retrosplenial cortex, area 29d, the peri-and entorhinal cortices, and the presubiculum. Both supragenual and more posterior regions of area 24 project to the retrosplenial cortex and area 29d, but only the posterior portion projects additionally to the entorhinal area and presubiculum. The cortical targets of axons from the sulcal MD-projection cortex are mainly the anterior part of the piriform cortex and, for the posterolateral part of the sulcal cortex (insular area), the retrosplenial area, lateral entorhinal area, and presubiculum. While the medial and sulcal divisions of the MD-projection cortex project upon one another, the medial-to-sulcal projection is in general denser than its reciprocal.Earlier findings of projections to subcortical structures affiliated with the limbic system such as midline thalamic nuclei, hypothalamus, and paramedian mesencephalic tegmentum are confirmed, and appear to originate primarily in area 32 and the insular part of the sulcal cortex. The corticothalamic projection to MD in general terms reciprocates the organization seen in the thalamocortical projection from the various subnuclei within MD. Previously undocumented projections are demonstrated mainly from area 32 of the medial cortex and the insular part of the sulcal cortex to the lateral and basal amygdaloid nuclei, the medial part of the lateral septa1 nucleus, the nucleus accumbens, and the deep layers of the olfactory tubercle; the medial part of the lateral habenular nucleus receives a projection from areas 32 and 24. Projections to the pretectal area and superior colliculus appear to originate from all parts of the medial MD-projection cortex, but are markedly denser when the posterior part of area 24 is injected. The distribution of this corticotectal projection shows a highly characteristic configuration in which areas of high grain concentration surround areas of lower grain concentration.In the rat, as in all mammals, some cortical area near the frontal pole receives a projection from a prominent thalamic nucleus which is bounded by the internal medullary lamina and later corroborated by independent methods (Beckstead, '76; Krettek and Price, '77b1, the MD-projection cortex of the rat comprises the rostra1 one-quarter or so of the dorsal bank and the stria medullaris-the mediodorsal nu-'

Electrical Stimulation of Rat Medial Prefrontal Cortex Enhances Forebrain Serotonin Output Implications for Electroconvulsive Therapy and Transcranial Magnetic Stimulation in Depression

“…On the other hand, the areas around the rhinal sulcus, such as the lateral orbitofrontal cortex (LO) and the dorsal part of the agranular insular cortex (AID), constitute the lateral prefrontal cortex in rats, because they have reciprocal connections to the mediodorsal thalamic nucleus (Zilles and Wree 1995;Fuster 1997) which is a main anatomical criterion for belonging to the PFC. Although LO and AID have projection fibers to the dorsal raphe nucleus in rats (Peyron et al 1998;Beckstead 1979), these fibers, unlike those originating from mPFC, probably have no functional relevance for the serotonergic neurotransmission, because electrical stimulation of AID and LO did not alter hippocampal 5-HT output in the present study. There are two reasons for this functional difference between medial and lateral PFC: first, the medial PFC sends significantly more efferent fibers to the dorsal raphe nucleus than LO and AID; and second, only the medial PFC projects to the whole of the dorsal raphe nucleus (Peyron et al 1998).…”

“…Consistent with this hypothesis, it has been demonstrated that rat medial prefrontal cortex (prelimbic area) has dense efferent projections to both the dorsal and the median raphe nuclei (Aghajanian and Wang 1977;Beckstead 1979;Wyss and Sripanidkulchai 1984;Sesack et al 1989;Behzadi et al 1990;Peyron et al 1998). Thus, it is possible that PFC stimulation activates the raphe nuclei leading to increased -HT levels in terminal areas.…”

Rapid Synaptic Plasticity of Glutamatergic Synapses on Dopamine Neurons in the Ventral Tegmental Area in Response to Acute Amphetamine Injection

“…Addictive behaviors are thought to result from persistent molecular and cellular neuroadaptations in the mesocorticolimbic circuit that follow exposure to drugs of abuse. The mesocorticolimbic circuit includes dopamine (DA) neurons in the ventral tegmental area (VTA) that project to the nucleus accumbens (NAcc) and prefrontal cortex (Beckstead, 1979;Christie et al, 1985;Oades and Halliday, 1987;Carr and Sesack, 1996). Nearly all addictive drugs share the ability to cause DA release at nerve terminals in the NAcc (Di Chiara and Imperato, 1988), and this shared property of drugs with different molecular targets may be responsible for setting into motion maladaptive processes that underlie addiction (Koob, 1992;Nestler, 1992).…”

6-Hydroxydopamine lesion of the rat prefrontal cortex impairs motor initiation but not motor execution

“…The rat PFC receives cortical afferents which arise in secondary sensory areas, motor areas and paralimbic cortices (van Eden et al 1992), and it projects to various cortical and subcortical structures, e.g. midbrain, nucleus accumbens (ACC) and anteromedial striatum (Leonard 1969;Beckstead 1979;Sesack and Pickel 1992). Furthermore, the PFC receives a dopaminergic innervation from mesocortical dopamine (DA) cells (Bj6rklund and Lindvall 1984) and DAergic axon terminals exhibit synaptic contacts mainly with pyramidal neurons in deeper cortical layers (Verney et al 1990).…”