Amygdaloid projections to subcortical structures within the basal forebrain and brainstem in the rat and cat

Abstract

The efferent fiber connections of the nuclei of the amygdaloid complex with subcortical structures in the basal telencephalon, hypothalamus, midbrain, and pons have been studied in the rat and cat, using the autoradiographic method for tracing axonal connections. The cortical and thalamic projections of these nuclei have been described in previous papers (Krettek and Price, '77b,c). Although the subcortical connections of the amygdaloid nuclei are widespread within the basal forebrain and brain stem, the projections of each nucleus have been found to be well defined, and distinct from those of the other amygdaloid nuclei.The basolateral amygdaloid nucleus projects heavily to the lateral division of the bed nucleus of the stria terminalis (BNST), to the caudal part of the substantia innominata, and to the ventral part of the corpus striatum (nucleus accumbens and ventral putamen) and the olfactory tubercle; it projects more lightly to the lateral hypothalamus. The central nucleus also projects to the lateral division of the BNST and the lateral hypothalamus, but in addition it sends fibers to the lateral part of the substantia nigra and the marginal nucleus of the brachium conjunctivum. The basomedial nucleus has projections to the ventral striatum and olfactory tubercle which are similar to those of the basolateral nucleus, but it also projects to the core of the ventromedial hypothalamic nucleus and the premammillary nucleus, and to a central zone of the BNST which overlaps the medial and lateral divisions. The medial nucleus also projects to the core of the ventromedial nucleus and the premammillary nucleus, but sends fibers to the medial division of the BNST and does not project to the ventral striatum. The posterior cortical nucleus projects to the premammillary nucleus and to the medial division of the BNST, but a projection from this nucleus to the ventromedial nucleus has not been demonstrated. Projections to the "shell" of the ventromedial nucleus have been found only from the ventral part of the subiculum and from a structure at the junction of the amygdala and the hippocampal formation, which has been termed the amygdalo-hippocampal area (AHA). The AHA also sends fibers to the medial part of the BNST and the premammillary nucleus.Virtually no subcortical projections outside the amygdala itself have been demonstrated from the lateral nucleus, or from the olfactory cortical areas around the amygdala (the anterior cortical nucleus, the periamygdaloid cortex, and the posterior prepiriform cortex). However, portions of the endopiriform nucleus deep to the prepiriform cortex project to the ventral putamen, and to the lateral hypothalamus.

Transneuronal Labeling of a Nociceptive Pathway, the Spino-(Trigemino-)Parabrachio-Amygdaloid, in the Rat

“…Finally, for all cases of injection in the parabrachial complex, retrograde labeling was present in the amygdala, confirming the reciprocal projections that have been described previously (Krettek and Price, 1978). In the ipsilateral amygdala, at survivals of 72 hr and less, PRV labeling was found in the Ce, with sparse to moderate labeling in the amygdalostriatal transition area (Fig.…”

Bilateral behavioral and regional cerebral blood flow changes during painful peripheral mononeuropathy in the rat

“…Bernard and colleagues (1989Bernard and colleagues ( ,1990Bernard and colleagues ( ,1996 have demonstrated a spino(trigemino)pontoamygdaloid pathway that may be involved with the affective-motivational dimension of pain. Conversely, anatomical and electrophysiological studies indicate the existence of an efferent pathway originating in the amygdala, synapsing within the periaquaductal gray and continuing on to the spinal cord dorsal horn that modulates pain (Hopkins and Holstege 1978;Krettek and Price 1978;Beitz 1982;Watson et al, 1983;Zhang et al, 1991;Bernard et al, 1996;Manning 1998). In addition, the basal ganglia receives nociceptive information through several sources including the amygdala, cingulate cortex, prefrontal cortex and the habenula (Ma and Han, 1991;Cenci et al, 1992;Ma et al, 1992;Chudler and Dong, 1995).…”

NMDA-dependent facilitation of corticostriatal plasticity by the amygdala

“…Yet, manipulations that increase NMDA currents (e.g., removal of extracellular Mg 2ϩ or postsynaptic depolarization) can facilitate LTP induction (26). Thus, the present study tested whether amygdalostriatal axons (33,34) can facilitate plasticity at cortical inputs to projection cells of the striatum (35), the medium spiny neurons (MSNs). We show that BLA synapses can facilitate induction of corticostriatal LTP, in part because they have a high NMDA-to-A MPA (␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) ratio.…”