Presence of a cholinergic projection from ventral striatum to amygdala that is not immunoreactive for NGF receptor

The p75 neurotrophin receptor has nonapoptotic antineurotrophic actions in the basal forebrain

Because of controversy about the role of the p75 neurotrophin receptor (p75(NTR) ) in the cholinergic basal forebrain (CBF), we investigated this region in p75(NTR) third exon knockout mice that were congenic with 129/Sv controls. They express a shortened intracellular form of p75(NTR) , permitting detection of p75(NTR) -expressing cells. We performed separate counts of choline acetyltransferase (ChAT)-expressing and p75(NTR) -expressing neurons. In agreement with past reports, the number of ChAT-immunoreactive neurons in knockout mice was greater than in wild-type mice, and this was evident in each of the main anatomical divisions of the CBF. In contrast, the number of p75(NTR) -immunoreactive neurons did not differ between genotypes. The biggest increase in ChAT neurons (27%) was in the horizontal limb of the diagonal band of Broca (HDB), in which region the number of p75(NTR) -positive neurons was unchanged. Double staining revealed that some neurons in wild-type mice expressed p75(NTR) but not ChAT. In the knockout mice, all p75(NTR) -expressing neurons expressed ChAT. The increase in cholinergic neurons, therefore, was at least partially attributable to a higher proportion of ChAT immunoreactivity within the population of p75(NTR) -expressing neurons. Cholinergic neurons were also larger in knockout mice than in controls. In the hippocampal CA1 region, knockout mice had a greater number of cholinergic fibers. There was a 77% increase in hippocampal ChAT activity in knockout mice and a 38% increase in heterozygotes. The data do not support an apoptotic role but indicate a broad antineurotrophic role of p75(NTR) in the cholinergic basal forebrain.

Zinc-containing afferent projections to the rat corticomedial amygdaloid complex: a retrograde tracing study

The mammalian amygdaloid complex is densely innervated by zinc-containing neurons. The distribution of the terminals throughout the region has been described, but the origins of these zinc-containing fibers have not. The present work describes the origins of one major component of the zinc-containing innervation of the amygdaloid complex, namely, the component that innervates the corticomedial complex. Selective labeling of zinc-containing axons was accomplished by intracerebral microinfusion of selenium anions (SeO3(2-)), a procedure that produces a ZnSe precipitate in zinc-containing axonal boutons with subsequent retrograde transport to the neurons of origin. After infusions of SeO3(2-) into combinations of cortical, medial, or amygdalohippocampal regions, retrogradely labeled zinc-containing somata were found in all amygdaloid nuclei except for the medial and central nuclei, the bed nucleus of the accessory olfactory tract, the nucleus of the lateral olfactory tract, and the anterior amygdaloid area. Extrinsic zinc-containing projections to the same amygdaloid terminal fields were found to originate from the infralimbic, cingulate, piriform, perirhinal and entorhinal cortices, and from the prosubiculum and CA1. Commissural zinc-containing projections were found to originate from the posterolateral and posteromedial cortical nuclei and from the posterior part of the basomedial nucleus. Zinc-containing neurons have been implicated in the pathophysiology of epilepsy, in cell death after seizure or stroke, and in Alzheimer's disease, all clinical conditions that involve the amygdaloid complex. Identification of the zinc-containing pathways is a prerequisite to the elucidation of zinc's role in these disorders.

Amygdala dopamine levels are markedly elevated after self- but not passive-administration of cocaine

The influence of cocaine on rat brain monoaminergic neurotransmitters (dopamine, serotonin, noradrenaline) and their metabolites, and on binding of [3H]WIN 35,428 and [3H]GBR 12,935 to the dopamine transporter was measured after 4 weeks of cocaine exposure. Cocaine (mean daily dose 9.25 +/- 0.48 mg/kg) was self-administered (responders) or passively received (yoked) during sessions which lasted for 1 h per day. As compared with the controls, mean dopamine and serotonin levels were significantly elevated (+ 107% and + 47%, respectively) in amygdala of responders, but not of yoked rats, sacrificed 1 h after the last cocaine session. Dopamine and metabolite levels were normal in all other brain areas examined, including striatum, nucleus accumbens and medial prefrontal cortex, at both 1 h and 4 weeks withdrawal from cocaine. [3H]WIN 35,428 and [3H]GBR 12,935 binding were unaltered after cocaine exposure. These data provide additional support for the involvement of the amygdala in the acquisition of drug seeking behavior associated with cocaine self-administration.

Two types of cholinergic projections to the rat amygdala

The cholinergic innervation of the rat amygdala was studied immunohistochemically with antibodies against choline acetyltransferase and the low affinity p75 nerve growth factor receptor in normal rats and in rats lesioned with an immunotoxin, 192 IgG-saporin, directed against the p75 nerve growth factor receptor. The density of choline acetyltransferase-positive fibers was high in the nucleus of the lateral olfactory tract, the basolateral nucleus, and the amygdalohippocampal area; medium in the lateral nucleus, the cortical nucleus, the accessory basal nucleus, the periamygdaloid cortex, and the anterior amygdaloid area; and low in the medial and central nuclei. Nerve growth factor receptor-positive fibers were of medium density in the lateral nucleus, the accessory basal nucleus, the cortical nucleus, the anterior amygdaloid area, the periamygdaloid cortex, and the amygdalohippocampal area. The medial nucleus and the central nucleus displayed a low density of nerve growth factor receptor-positive fibers. The basolateral nucleus and the nucleus of the lateral olfactory tract also contained a low density of nerve growth factor receptor-positive fibers even though the two nuclei displayed the highest density of choline acetyltransferase-positive fibers in the amygdala. Injections of 192 IgG-saporin induced a complete loss of cholinergic nerve growth factor receptor-positive neurons in the basal forebrain but spared a subpopulation of nerve growth factor receptor-negative cholinergic neurons in the nucleus basalis-substantia innominata complex. Following 192 IgG-saporin injections, choline acetyltransferase-positive and acetylcholinesterase-positive fibers were essentially unchanged in the nucleus of the lateral olfactory tract and the basolateral nucleus and showed a partial reduction in the remaining nuclei of the amygdaloid complex. Cholinergic fibers emanating from cholinergic cell group 4 neurons reached the amygdala via the stria terminalis and the ventral amygdalofugal pathway. These observations indicate that two amygdaloid nuclei, the nucleus of the lateral olfactory tract and the basolateral nucleus, receive their cholinergic projections predominantly, if not exclusively, from nerve growth factor receptor-negative cholinergic neurons whereas all remaining amygdaloid regions receive fibers from nerve growth factor receptor-negative as well as nerve growth factor receptor-positive cholinergic neurons.

Cholinergic neurons in the ventral trapezoid nucleus project to the cochlear nuclei in the rat

A combination of retrograde axonal tract tracing and choline acetyltransferase immunocytochemistry was used to determine the cells of origin of the cholinergic innervation of the rat cochlear nucleus. The results showed that the cochlear nucleus receives a major cholinergic input from a group of small cells found in the ventral trapezoid nucleus. Experiments using an anterograde tracer confirmed the presence of a neuronal pathway from the ventral trapezoid nucleus to the cochlear nucleus and showed that this pathway travels via the trapezoid body.

A cholinergic propriospinal innervation of the rat spinal cord

Previous work has suggested the presence of a widespread, intrinsic cholinergic innervation of the spinal cord. A combination of retrograde axonal tract tracing and choline acetyltransferase immunocytochemistry was used to show that there is a propriospinal cholinergic innervation of the rat spinal cord that arises from short-range projections (spanning up to six spinal segments) of cholinergic neurons known as 'central canal' and 'partition' cells.

Distribution of nerve growth factor-like immunoreactive neurons in the adult rat brain following colchicine treatment

Using immunohistochemical techniques, we have previously localized nerve growth factor (NGF)-like immunoreactivity in the normal adult rat central nervous system (CNS) exclusively in the hippocampal mossy fiber region and within basal forebrain cholinergic neurons--a cell population believed to be primary NGF consumers within the CNS. In the present investigation, we have attempted to identify potential producers of NGF by pretreating animals with colchicine. Such a treatment would be expected to block microtubule-assisted neuritic transport mechanisms, thus preventing the accumulation of antigens normally obtained by retrograde transport and forcing the accumulation of cell products normally exported anterogradely. Forty-eight hours after colchicine administration within their innervation territories, basal forebrain cholinergic neurons showed a marked loss of NGF-like immunoreactivity. Conversely, following colchicine treatment, many new populations of NGF-like immunoreactive cells were detected, several of which have been previously observed with in situ hybridization techniques for NGF mRNA. Many NGF-like immunoreactive populations, however, were not previously recognized by in situ hybridization methods, including cells of the striatum, reticular thalamic nucleus, paraventricular hypothalamic nucleus, supraoptic nucleus, lateral and medial septum, substantia innominata, and nucleus basalis. Furthermore, evidence is provided that colchicine-blocked, NGF-like immunoreactive neurons within the basal forebrain are not cholinergic, thus reinforcing the hypothesis that trophic support for these NGF-dependent neurons may be derived from distant and local sources. The distinctive distribution of NGF-like immunoreactive cells observed in this study strongly correlates with the reported distribution of NGF mRNA in CNS neurons, thus suggesting that our antibodies are uniquely recognizing NGF and not other related neurotrophins.

Further evidence for the absence of a descending cholinergic projection from the brainstem to the spinal cord in the rat

Serotonergic and catecholaminergic neurons are known to project from the brainstem to the spinal cord. However, evidence for a bulbo-spinal projection that is cholinergic is sparse despite immunocytochemical and physiological evidence for a cholinergic influence on the cord. In this study we examined the possibility of a direct cholinergic bulbo-spinal projection in the rat using a combination of retrograde axonal tracing techniques and choline acetyltransferase immunocytochemistry. Although many cells were found to project to the cord from the brainstem, none were identified as being cholinergic, confirming previous evidence that the cholinergic innervation of the cord is intrinsic.

Sprouting of cholinergic axons does not occur in the cerebral cortex after nucleus basalis lesions

Different doses of the excitotoxin quisqualate were used to make lesions in the caudal part of the ferret nucleus basalis, i.e. the part that projects to the visual cortex. The higher doses of the excitotoxin destroyed all nerve growth factor receptor-immunoreactive cells in the caudal nucleus basalis and gave rise to up to 75% loss of acetylcholinesterase-containing axons in the visual cortex. In sections stained for Nissl substance there was generalized tissue damage around the injection sites and extensive loss of all neuron types in areas surrounding the caudal nucleus basalis. Lower doses of the excitotoxin damaged only a proportion of the nerve growth factor receptor-immunoreactive neurons in the caudal nucleus basalis and produced a much lower depletion of acetylcholinesterase-positive fibres in the visual cortex. The only damage seen in sections stained for Nissl substance was a loss of magnocellular neurons in the vicinity of the injection sites. A quantitative morphological approach was used to show that either one week or three months after the lesions there was a linear correlation between the proportion of acetylcholinesterase-positive axons lost in the visual cortex and the proportion of nerve growth factor receptor-immunoreactive cells that had disappeared from the caudal nucleus basalis. Since the correlation lines for the short-term (one week) survival and the long-term (three months) survival experiments coincided, this indicated that no collateral sprouting of cholinergic axons had occurred in the visual cortex of the long-term survival animals regardless of size of the lesion in the nucleus basalis.